EMERGENCE, DISPERSAL AND REPRODUCTIVE
BIOLOGY OF CYDIA NIGRICANA (F. )
JEREMY CLIFFORD GRAHAM
B.Sc. (HONS) BRISTOL
A THESIS SUBMITTED FOR THE DEGREE
OF DOCTOR OF PHILOSOPHY OF THE
UNIVERSITY OF LONDON AND FOR THE
DIPLOMA OF IMPERIAL COLLEGE
DEPARTMENT OF PURE AND APPLIED BIOLOGY,
IMPERIAL COLLEGE,
SILWOOD PARK, ASCOT,
BERKSHIRE NOVEMBER 1984 To my Mother and Father Ill
ABSTRACT
A synthetic sex-attractant monitoring system, developed at Rothamsted Experimental Station, has been available to pea growers for detecting the immigration of male pea moth, Cydia nigricana (F. ), into pea crops, since 1976. Very little information was available as to how the trap catches of male moths related to the arrival of female moths, and whether those females were mated and ready for ovipos ition. This study involved extensive and intensive sampling of moth populations by aerial netting and by suction (D-Vac.), on commercial farms. Both the cereal emergence site, the pea crop and surrounding vegetation were sampled. Sex- attr act ant monitoring traps were positioned at both sites, and the population levels and fluctuations they indicated, were compared with the results from the sampling programme. The dispersion and dispersal of each sex was examined in relation to emergence, maturation and fecundity, mating status and physiological age (as revealed by dissection), as well as to the sex-attractant trap catches. The relation ship between larval infestation levels and plant phenology was recorded, and this in turn analysed with respect to immigration as indicated by sex-attractant traps and sampling results. In the laboratory, pea moth was cultured in a controlled environment (following the method developed at Rothamsted). Culture material was used to conduct exper iments on the effect of diet, host plant presence and phenology, on potential fecundity, actual fecundity and longevity in the laboratory. IV
TABLE OF CONTENTS Page
ABSTRACT ...... iii TABLE OF CONTENTS iv LIST OF TABLES vii LIST OF FIGURES ... ix LIST OF APPENDICES xix
1. INTRODUCTION ... 1 1.1. Introduction and Aims 1 1.2. Description of the Pest 3 1.3. The Control of the Pest 8 1.3.1. Earlier attempts with Control and Forecasting Pest Attack ...... 8 1.3.2. The Development of a Sex-attractant Monitoring System ...... 11
2. MATERIALS AND METHODS ...... 16 2.1. Field Studies ...... 16 2.1.1. Field Site Selection ...... 16 2.1.2. Field Site Description ...... 17 2.1.3. Crop Phenology ...... 21 2.1.4. Climatic Records ...... 21 2.1.5. Sample Units ...... 24 2.1.6. Sampling Programme ...... 30 2.1.7. Sampling Proceedure ... • ... 46 2.1.8. Sorting of Samples ...... 47 2.1.9. Dissection of Adult Moths ... 51 2.1.10.Infestation Levels ...... 56 2.1.11. Experimental Use of Sex-attractant 59 2.1.12. Calibration of the D-Vac. ... 60 2.2. Laboratory Studies ...... 63 2.2.1. Culturing C.nigricana ...... 63 2.2.2. Pea Growing ...... 65 2.2.3. The Effect of Diet ...... 66 2.2.4. Effect of Pea Plant Presence ... 67 2.2.5. Treatment of Field Data ...... 71 3. DISPERSION AND DISPERSAL ... 72 3.1. Introduction ...... 72 3.2. Dispersion ...... 75 V P a g e
3.2.1. Spatial Patterns of Dispersion in the Emergence Site ...... 75 3.2.2. Temporal Patterns of Dispersion in the Emergence Site ...... 88 3.2.3. Spatial Patterns of Dispersion in the Pea Field ...... 105 3.2.4. Temporal Patterns of Dispersion in the Pea Field ...... 117 3.3. Dispersal ...... 130 3.3.1. Spatial Patterns of Dispersal ... 130 3.3.2. Temporal Patterns of Dispersal 135 3.3.3. Differential Dispersal of the Two S exes ...... 137 3.4. Relationship Between Dispersion, Dispersal and Other Factors ...... 143 3.4.1. Relationship Between Sex-attractant Trap Catch and Dispersion/Dispersal 143 3.4.2. Relationship Between Dispersal and Plant Phenology ...... 169 3.4.3. Relationship Between Dispersal and Larval Infestation 178 3.5. Discussion ...... 2 00 MATING ...... 216 4.1. Introduction ...... 216 4.2. Site of Mating ... 218 4.3. Time of Mating ... 226 4.4. Frequency of Multiple Mating ... 229 4.5. Discussion ...... 231 MATURATION. LONGEVITY AND FECUNDITY ...... 238 5.1. Introduction ...... 238 5.2. Physiological Age Structure of Moth Populations ...... 243 5.3. Fecundity and Maturation in Relation to Dispersal and Mating ...... 255 5.4. The Effect of Diet on Longevity and F ecundity ...... 280 5.5. Longevity, Fecundity and Maturation in relation to Host Plant Phenology 2 85 5.6. Discussion ...... 294 VI
Page 6. DISCUSSION 302 7. S U M M A R Y __ 319 ACKNOWLEDGEMENTS 322
REFERENCES 323
APPENDICES -- 345 V l l
LIST OF TABLES Page f— ( i —1 • TABLE • Duration of various periods in the life cycle of C.niqricana according to different
authors ...... 5 growth stages of cereals ...... 22 TABLE 2.2. Explanation of the P.G.R.O. numerical code for the growth stages of peas ...... 23 CM CO TABLE • Description of the four fat body types of C.nigricana at various grades of abundance 53 1 CO - • • TABLE 1 Peak density of C.nigricana in vegetation surrounding emergence sites ...... 97 TABLE 3.2. Relationship between number of C.nigricana and distance to nearest pea field 134 TABLE 3.3. Sex ratios (males : females) of populations in various subdivisions of the environment 139 TABLE 3.4. Sex ratios (males : females) of aerial populations over various subdivisions of the environment, 1981 ...... 142 i— 1 TABLE • • Percentage of unmated and mated female C.nigricana in wheat field emergence sites 219 TABLE 4.2. Percentage of unmated and mated female C.nigricana in pea fields ...... 221 TABLE 4.3. Percentage of unmated and mated females confined in laboratory breeding chambers with males and plant material ...... 2 24 TABLE 5.1. Comparison of potential fecundity and mature egg load of mated and unmated female C.nigricana in crop regions of emergence sites ...... 276 TABLE 5.2. Comparison of potential fecundity and mature egg load of mated and unmated female C.nigricana of different age groups in crop regions of emergence sites 278 VI11 P a g e TABLE 5.3. Comparison of potential fecundity and mature egg load of mated and unmated female C.nigricana of different age groups in vegetation surrounding emergence sites ...... 279 TABLE 5.4. Fecundity and potential fecundity of female C.nigricana provided with different diets ...... 284 TABLE 5.5. Potential fecundity, fecundity and percentage of eggs laid on plant material, of female C.nigricana confined without and with plant material at different phenological stages ...... 291 TABLE 5.6. Preferred oviposition microsites on pea plant material ...... 293 IX LIST OF FIGURES Page Fig. 1.1. Life cycle of C.niqricana ...... 4 F ig . 2.1. Map showing geographical relationship between emergence sites at Childerley Hall and pea fields at Knapwell Wood Farm, Cambridgeshire, 1980 ...... 18 Fig. 2.2. Map showing geographical relationship between emergence sites and pea fields at Shimpling Park Farm, Suffolk, 1981 ... 19 Fig. 2.3. Map showing geographical relationship between emergence sites and pea fields at Shimpling Park Farm, Suffolk, 1982 ... 20 Fig. 2.4. Wheat field P, emergence site, Childerley Hall, Cambridgeshire, 1980: arrangement and numbering of sample units, and position of sex-attractant monitoring traps ... 25 Fig. 2.5. pea field J, Knapwell Wood Farm, Cambridge- shire, 1980: arrangement and numbering of sample units, and position of sex- attractant monitoring traps ...... 26 F i g . 2.6. Wheat field WAl, emergence site, Shimpling Park Farm, Suffolk, 1981: arrangement and numbering of sample units, and position of sex-attractant monitoring traps ... 27 Fig. 2.7. Pea field PAl, Shimpling Park Farm, Suffolk, 1981: arrangement and numbering of sample units, and position of sex- attractant monitoring traps ...... 28 Fig. 2.8. Wheat field WA2, emergence site, Shimpling Park Farm, Suffolk, 1982: arrangement and numbering of sample units, including transect sub-samples ...... 31 Fig. 2.9. Pea field PA2, Shimpling Park Farm, Suffolk, 1982: arrangement and numbering of sample units, including transect sub samples, and position of sex-attractant monitoring traps ...... 32 X Page Fig. 2.10. Pea field PB2, Shimpling Park Farm, Suffolk, 1982: arrangement and numbering of sample units, including transect sub samples, and position of sex-attractant monitoring traps ...... 33 Fig. 2.11. Emergence site WA2 and Pea fields PA2 & PB2, Shimpling Park Farm, Suffolk,1982: arrangement and numbering of transect sub-samples ...... 34 Fig. 2.12. D-Vac. sampling machine showing major components ...... 37 Fig. 2.13. Cutaway diagram of D-Vac. sampling head showing modifications associated with the use of the trolley attachment 38 Fig. 2.14. Modes of D-Vac. use with conventional sampling head ...... 40 Fig. 2.15. Components and design of trolley attach ment for use of D-Vac. in crops with tram-lines ...... 41 F ig. 2.16. Mode of tram-line sampling using D-Vac. and trolley attachment ...... 42 Fig. 2.17. Cutaway diagram of sex-attractant monitoring trap, showing parts and as s embly ...... 44 Fig. 2.18. Genitalia preparations of C.nigricana to show parts and diagnostic features 48 Fig. 2.19. External appearance of characters recognised as diagnostic from genitalia preparations ...... 50 F ig . 2.20. Diagrammatic illustration of the four fat body types of C.nigricana at various grades of abundance ...... 52 Fig. 2.21. Relationship of Physiological age (P.A.) to real age ...... 55 Fig. 2.22. Diagrammatic illustration of breeding chambers for C.nigricana showing main components and assembly ...... 64 - xi - 2.23. Effect of diet and pea plant presence on fecundity and longevity of C.nigricana 3.1. Relationship between log variance and log mean of populations of male C.niqricana, wheat field emergence site, 1981 . . . 77 3.2. Relationship between log variance and log mean of populations of male C.niqricana, wheat field emergence site, 1982 78 3.3. Relationship between log variance and log mean of populations of female C.nigricana, wheat field emergence site, 1981 ... 79 3.4. Relationship between log variance and log mean of populations of female C.niqricana, wheat field emergence site, 1982 80 3.5 . Relationship between log variance and log mean of populations of C.nigricana in wheat field emergence sites 1981 & 1982 81 3.6. Spatial distribution of populations of C.niqricana in the perimeter and centre of the crop in the emergence site, 1981 83 3.7. Spatial distribution of populations of C.niqricana in the perimeter and centre of the crop in the emergence site, 1982 84 3.8. Spatial distribution of aerial populations of C.niqricana over the perimeter and centre of the crop in the emergence site, 1981 ...... 87 3.9. Spatial distribution of populations of C.nigricana in and around the emergence site, 1981 ...... 89 3.10. Analysis of variance for density gradients of C.nigricana populations across the emergence site, 1981 ...... 91 3.11. Spatial distribution of populations of C.nigricana in and around the emergence site, 1982 92 X l l 3.12. Temporal distribution of C.nigricana in the crop at the emergence site, 1980 3.13. Temporal distribution of populations of C.nigricana in the crop at the emergence site, 1981 ...... 94 3.14. Temporal distribution of populations of C.nigricana in the crop at the emergence site, 1982 ...... 95 3.15. Density of C.nigricana in the emergence sites, 1981 & 1982 ...... 98 3.16. Temporal distribution of populations of male C.nigricana in and around the emergence site, 1981 ...... 101 3.17. Temporal distribution of populations of female c.nigricana in and around the emergence site, 1981 ...... 102 3.18. Temporal distribution of aerial populations of male C.nigricana over and around the emergence site, 1981 ... 103 3.19. Temporal distribution of aerial populations of female C.nigricana over and around the emergence site, 1981 ... 104 3.20. Temporal distribution of populations of male C.nigricana in and around the emergence site, 1982 ...... 106 3.21. Temporal distribution of populations of female C.nigricana in and around the emergence site, 1982 ...... 107 3.22. Relationship between log variance and log mean of populations of c.nigricana in vegetation surrounding the pea fields, 1981 Sc 1982 ...... 108 3.23. Relationship between log variance and log mean of populations of C.nigricana in and around pea fields, 1981 S c 1982 ...... 110 Xlll Page Fig. 3.24 . Spatial distribution of populations of C.nigricana in and around the pea field, 1981 ...... 111 Fig. 3.25. Spatial distribution of populations of C.nigricana in and around pea field PA2, 19 82 ...... 114 Fig. 3.26. Spatial distribution of populations of C.nigricana in and around pea field PB2, 19 8 2 ...... 116 Fig. 3.27. Temporal distribution of populations of male C.niqricana in and around the pea field, 1981 ...... 119 Fig. 3.28. Temporal distribution of populations of female c.nigricana in and around the pea field, 1981 ...... 120 Fig. 3.29. Temporal distribution of aerial populations of male C.niqricana over and around the pea field, 1981 ...... 123 Fig. 3.30. Temporal distribution of aerial populations of female C,niqricana over and around the pea field, 1981 ...... 124 Fig. 3.31. Temporal distribution of populations of male C.niqricana in and around pea field PA2, 1982 ...... 126 Fig. 3.32. Temporal distribution of populations of female C.niqricana in and around pea field PA2, 1982 ...... 127 Fig. 3.33. Temporal distribution of populations of male C.niqricana in and around pea field PB2, 1982 ...... 128 Fig. 3.34. Temporal distribution of populations of Female C.niqricana in and around pea field PB2/ 1982 ...... 129 XIV P a g e Fig. 3.35. Relationship between sex-attractant trap catch of male C.nigricana and density of males in the emergence site, 1981 ... 146 Fig. 3.36. Relationship between sex-attractant trap catch of male C.nigricana and density of females in the emergence site, 1981 ... 148 Fig. 3.37. Temporal distribution of catches of male C.nigricana in sex-attractant traps in the emergence site, 1980 ...... 150 Fig. 3.38. Temporal distribution of catches of male C.nigricana in sex-attractant traps in the emergence site WAl, 1981 ...... 152 Fig. 3.39. Temporal distribution of catches of male C.nigricana in sex-attractant traps in the emergence site WBl, 1981 ...... 152 Fig. 3.40, Relationship between sex-attractant trap catch of male C.nigricana and density of males in pea fields, 1981 & 1982 ... 157 Fig. 3.41. Relationship between sex-attractant trap catch of male C.nigricana and density of females in pea fields, 1981 & 1982 ... 159 Fig. 3.42. Temporal distribution of catches of male C.nigricana in sex-attractant traps in pea field J, 1980 ...... 162 Fig. 3.43. Temporal distribution of catches of male C.nigricana in sex-attractant traps in pea field K, 1980 ...... 162 Fig. 3.44. Temporal distribution of catches of male C.nigricana in sex-attractant traps in pea field PAl, 1981 ...... 165 Fig. 3.45. Temporal distribution of catches of male C.nigricana in sex-attractant traps in pea field PBl, 1981 ...... 165 Fig. 3.46. Temporal distribution of catches of male C.nigricans in sex-attractant traps in pea field P a 2, 1982 ...... 168 XV Page Fig. 3.47. Temporal distribution of catches of male C.nigricana in sex-attractant traps in pea field PB2, 1982 ...... 168 Fig. 3.48. Development of wheat crops in emergence sites, 1981 & 1982 ...... 170 Fig. 3.49. Development of wheat crops and build up of male and female populations of C.nigricana in emergence sites 1981 Sc 1982 ••• ••• ••• ••• • * • * • * 172 Fig. 3.50. Development of pea crops 1981 &1982 a) Vegetative growth ...... 174 b) Reproductive growth ...... 175 Fig. 3.51. Distribution of damage by larvae of C.nigricana, pea field J, 1980 ...... 183 Fig. 3.52. Distribution of larval instars of C.nigricana within truss levels of pea plants, and length of exposure of crops in pea field PAl, 1981 ...... 186 Fig. 3.53. Relationship between the number of larvae of C.nigricana and the number of pea pods at truss levels in unsprayed areas of pea field PAl, 1981 ...... 188 Fig. 3.54. Development of infestation by larvae of C.nigricana and final composition of larval population in pea pods, pea fields PA2 & PB2, 1982 ...... 190 Fig. 3.55. Percentage pod damage at each truss level in three areas of pea field Pa 2 , 1982 192 Fig. 3.56. Percentage seed damage at each truss level in three areas of pea field Pa 2, 1982 ...... ^ • . ... 194 Fig. 3.57. Percentage pod damage at each truss level in three areas of pea field PB2, 1982 196 Fig. 3.58. Percentage seed damage at each truss level in three areas of pea field PB2, 1932 ...... 198 XVI Page Fig. 4.1. Percentage of mated female C.nigricana in each vegetation category along a hypothetical transect ...... 223 Fig. 4.2. Weekly percentage of mated individuals in populations of female C. nigricana in and around emergence sites, 1981 & 1982 ... 227 Fig. 4.3. Mating frequency in field populations of female C.niqricana, 1981 & 1982 ...... 230 Fig. 5.1. Weekly distribution of physiological age structure of male C.niqricana populations in and around emergence site and pea field, 1981 ...... 244 Fig. 5.2. Weekly distribution of physiological age structure of female C.niqricana populations in and around emergence site and pea field, 1981 ...... 245 Fig. 5.3. Weekly distribution of physiological age structure of male C.niqricana populations in and around emergence site and pea fields, 1982 ...... 247 Fig. 5.4. Weekly distribution of physiological age structure of female C.niqricana populations in and around emergence site and pea fields, 1982 ...... 249 Fig. 5.5. Physiological age of male C.nigricana populations in and around pea fields and in sex-attractant traps in pea fields 1982 ...... >.. 253 Fig. 5.6. Potential fecundity of female C.niqricana in populations in crop regions of the emergence site, 1981 ...... 256 Fig. 5.7. Potential fecundity of female C.niqricana in populations in crop regions of the emergence site, 1982 ...... 257 Fig. 5.8. Potential fecundity of female C .nigricana in populations in vegetation around the emergence site, 1981 ...... 258 XVI1 Page Fig. 5.9. Potential fecundity of female C.nigricana in populations in vegetation around the emergence site, 1982 ...... 259 Fig. 5 10. Potential fecundity of female C.niqricana in populations in vegetation around the pea field, 1981 ...... 261 Fig. 5.11. Potential fecundity of female C.nigricana in populations in vegetation around the pea fields, 1982 ...... 262 Fig. 5.12. Potential fecundity of female C.nigricana in populations in crop regions of the pea field, 1981 ...... 264 Fig. 5.13. Potential fecundity of female C.nigricana in populations in crop regions of pea field PA2, 1982 ...... 265 Fig. 5.14. Potential fecundity of female C.nigricana in populations in crop regions of pea field PB2, 1982 ...... 266 Fig. 5.15. Mature egg load of female C.niqricana in populations in crop regions of emergence site, 1981 268 Fig. 5.16. Mature egg load of female C.nigricana in populations in crop regions of emergence site, 1982 268 Fig. 5.17. Mature egg load of female C.nigricana in populations in vegetation around the emergence site, 1981 ...... 270 Fig. 5.18. Mature egg load of female C.nigricana in populations in vegetation around the emergence site, 1982 ...... 270 Fig. 5.19. Mature egg load of female C.nigricana in populations in vegetation around the pea field, 1981 272 Fig. 5.20. Mature egg load of female C.nigricana in populations in vegetation around the pea fields, 1982 272 Fig. 5.21. Mature egg load of female c .nigricana in populations in crop regions of the pea field, 1981 ...... 273 Fig. 5.22. Mature egg load of female c.nigricana in populations in crop regions of pea field PA2, 1982 ...... 275 Fig. 5.23. Mature egg load of female C.nigricana in populations in crop regions of pea field PB2, 1982 ...... 275 LO CM Fig. • • The effect of diet on longevity of male and female C.nigricana ...... 2 82 Fig. 5.25. The effect of diet on physiological age at death of male and female C.nigricana 2 82 Fig. 5.26. Effect of plant presence and phenological stage on physiological age at death of male and female C.nigricana ...... 2 87 Fig. 5.27. Effect of plant presence and phenology on longevity of male and female C,nigricana 2 89 xix LIST OF APPENDICES ~ Page Appendix I. D-Vac. Calibration ...... 346 H 1 h • Appendix Lists of samples taken and numbers of male and female C.niqricana in those samples ...... 352 H H H Appendix • The effect of pea plant presence on the attractiveness of the natural pheromone of C.niqricana ...... 362 Appendix IV. Infestation levels in pea crops 364 .Appendix V. Analysis of percentage mating among female populations of C.nigricana ... 368 1. INTRODUCTION 1.1. Introduction and Aims The pea moth, Cydia nigricana (Fabricius), is a serious pest of peas in the main commercial pea growing areas of eastern England (Anon. 1977). The insect is also a pest in North America (Brittain, 1921; Fluke, 1921; Hanson Sc Webster, 1936; Baker, 1937), Japan (Kuwayama, 1937) and much of Europe (Langenbuch, 1941; Nolte, 1959; Franssen S c Kersen, 1960) and Scandinavia (Schwan, 1941; Inkila, 1948; Ekholm, 1963; Stenmark, 1971a; 1971b; 1972; 1974; Tuovinen, 1981). The taxonomy of the species has recently been reviewed, and the pest is correctly named Cydia rusticella (Clerck) (Robinson & Nielsen, 1983). However, this may be challenged because of familiarity and extensive usage in the literature, and the name C.nigricana is used throughout this thesis. The larvae of C.nigricana bore into the pea pods, damaging seeds and lowering the market value of the crop. The pest is difficult to control, mainly because of the accuracy required in the timing of insecticide sprays. The pea crop in this country can be divided into three groups (Bardner, 1978) : a) Dry-harvested peas, harvested after the plants have senesced. b) Vining peas (for freezing and canning), harvested when green. c) Green peas for market, where peas in pods are sold direct to the consumer. In England, damage caused by larvae of C.niqricana to dry harvested peas usually results in little weight loss and low percentages of peas damaged (often considerably less than 10%). However, damage levels can vary enormously (Bardner, 1978) and the 'cosmetic' effect on the consumer is very important. Consumers have come to expect a good quality product, and the processors demand a comparatively clean harvest of peas from the growers. Dried peas grown under contract to processors are subject to penalty clauses for 'waste and stain' damage and some crops may even be rejected. However, dried peas may be sold on the open 2 market, particularly when there are world shortages of pulse crops. Inevitably, the economic threshold for control measures varies. Vining peas are subject to even less damage, because they are exposed for a shorter period of time (Anon. 1977), but even less damage is tolerated by processors. Consequently insecticide applications tend to be prophylactic to prevent any damage. Green peas for market are also not heavily attacked; the consumer tolerates what damage there is, no doubt because it is not apparent until after purchase. Recently a new method of monitoring the arrival of C.niqricana into pea crops has been introduced (Macaulay, 1977), using a synthetic sex-attractant to detect the pre sence of adult male moths. This system has proved to be a successful improvement on previous, often labour intensive, systems, directed at providing growers with warnings of imminent pest attack. However, the system was launched with some untested assumptions and gaps in our knowledge of the pest have remained. This study was undertaken to: i) Overcome shortcomings in the sex-attractant monitoring system by examining basic features of the biology and ecology of C.nigricana, which could and should have been more thoroughly investigated at or near conception of the system. Of particular importance are aspects of female reproductive biology viz. time and place of mating and egg maturation, and the population dynamics of both sexes in different parts of the environment. ii) Explain more precisely, how and why the system is generally successful and thus vindicate its use, but at the same time identify those areas that require further illumination. 3 1.2. Description of the Pest The pea moth ,C.niqricana, has a Palaearctic distribution, extending from China and Japan through Europe (Bradley, Tremewan & Smith, 1979), and was introduced into North America in 1893 (Fluke, 1920a; Cameron, 1938). In Britain the species is described as widely distributed, as far north as Renfrewshire and Perthshire (Bradley et al, 1979). The adult moths are fully described by Bradley et ^1 (1979) , being grey brown with a golden sheen on the fore wings, and white strigulae on the outer costal margin; the hind wings are a lighter shade. The moths are about 6mm. long and have a wingspan of up to 16mm. Sexual dimorphism is apparent; the males are smaller, more slender and lighter in colour, in both the forewings and the abdomen. In the British Isles the moths emerge over a long period, variously reported as commencing from the end of May (Gould & Legowski, 1964; Macaulay, 1977) through June (Cameron, 1938; Wright & Geering, 1948; Lewis, Wall, Macaulay & Greenway, 1975) . Adult moths may be found well into August. The life-cycle is shown in fig. 1.1. The duration of the emergence period varies according to different workers; some of their results, together with other aspects of the life history are collated in Table 1.1. The moths are active during the afternoon or early evening (Fluke, 1920a; 1920b; Baker, 1937; Wright & Geering, 1948; Ekholm, 1963; Lewis et ad/ 1975), both at the emergence/overwintering site (i.e. a field under peas the previous season) and pea fields, if conditions are suitable. The sexes emerge together, and the sex ratio is recorded as 1:1 (Langenbuch, 1941; Stenmark, 1972). Different authors have reported adult longevity as ranging from seven up to 28 days (Table 1.1.), which suggests emergence may continue until late July. The variable duration of the preoviposition period as reported in the literature is shown in Table 1.1. The eggs can laid singly or in pairs (Fluke, 1920a; Brittain, 1921; Gould Sc Legowski, 1964), but also in groups of up to five (Gould & Legowski, 1964). They are not laid until 4 Fig. 1.1. Life cycle of C.nigricana 5 Table 1.1. Duration of various periods in the life cycle of C.nigricana according to different authors PERIOD DURATION CONDITIONS AUTHOR (days) ADULT 14 Field Fluke, 1920a EMERGENCE 19 Fi e l d Fluke, 1920b 27-34 F i e l d Brittain, 1921 54 Field Hanson &c Webster, 1936 29 Field Baker, 1937 30-56 F i e l d B a k e r S c Perron, 1944 35-57 F ield W r i g h t S c Geering, 1948 ADULT LI F E 21-28 Field Ekholm, 1963 7-14 17 *C 10 F i e l d Stenmark, 1972 16.5+1 (S.E. ) 23 'C L ewis S c Sturgeon, 1978 females culture 17.4+1.2 23 'C males culture 21.0+2.2 23 *C females diapausing cocoons PREOVIPOSITION 3 Field Fluke, 1921 4-7 Insectary Brittain, 1921 8 or less Field Baker, 1937 5-13, av.9 Field Langenbuch, 1941 4-8,av.5-6 Field Baker S c Perron, 1944 5-11,av.8 Insectary W r i g h t S c Geering, 1948 2-3 23 *C S c F i e l d Lewis S c Sturgeon, 1978 INCUBATION 14 F ield Fletcher, 1894 7-10 F ield Fluke, 1920a;1921 2-3 Insectary Brittain, 1921 8 F ield H a n s o n S c Webster, 1936 c.7 F ield Baker, 1937 7-8 F i e l d Cameron, 1938 6-8 F ield B a k e r S c Perron, 1944 6-11,av.7-8 Field W r i g h t S c Geering, 1948 9, 6, 3 15', 20*,25 'C 15,7,5 15*, 20*,2 5 ’C Lewis S c Sturgeon, 1978 LARVAL LIFE 16-26 Field Fluke, 1920a 10-27 F ield Fluke, 1921 17-20 Insectary Brittain, 1921 22 F ield Miles, 1926 17.5,65 20*,ll'C Ozols, 1933 19-28 Field H a n s o n S c Webster, 1936 c. 21 Field Baker, 1937 21-28 Field B a k e r S c Perron, 1944 6 the peas are in flower (Wright & Geering, 1948; Franssen, 1954) , and are then positioned at random on the upper half of the plant (Wright & Geering, 1948; Gould & Legowski, 1964; So, 1975). The eggs may be laid on all surfaces of the stems, leaflets, petioles, stipules, sepals and pods (Fluke, 1921; Baker, 1937; Cameron, 1938; Wright & Geering, 1948; Ekholm, 1963). The egg is flattened and oval in shape, and measures about 0.75mm. by 0.5mm. (Cameron, 1938; Wright & Geering, 1948). The incubation period has been variously recorded as anything from two to 15 days (Table 1.1.). Initially semi-translucent, the fertile eggs become whitish and more opaque as a pair of irregular red streaks develop. These disappear towards hatching, when the outline of the larva, especially the head capsule, can be seen through the chorion (Cameron, 1938; Wright & Geering, 1948). The neonate larvae, 1.2mm. in length, are very active and move over the plant surface for "a short time" (Cameron, 1938) or 24hrs. according to Wright and Geering (1948). The larvae bore into the pod, and the entrance hole heals with a small callus, which is largely un detectable externally (Fletcher, 1894; Brittain, 1921; Fluke, 1921; Cameron, 1938). The larvae are white with a dark brown sclerotised head capsule and prothoracic tergite, and pass through five instars (Cameron, 1938; So, 1975); the fifth stage has a lighter coloured head capsule and prothoracic shield. The duration of the larval period varies with temperature; different authors 1 records range from 10 to 28 days (Table 1.1.). When full grown, the larva cuts an oval hole in the pod wall (which by this stage may be dry and parchment like) , and drops to the ground. The larva enters the soil and spins a waterproof silken cocoon, incorporating soil particles, which gives some rigidity. Wright and Geering (1948) found 92.6% (sample size not stated) of cocoons were in the top 5cm. of the soil. The larva remains in this cocoon in diapause, and undergoes a certain amount of change, becoming a deeper yellow colour, and shorter and more distended (Cameron, 1938). The following May or June, pupation occurs; larvae deeper in the soil may leave their 7 cocoons and move towards the surface, to spin a fresh cocoon in which to pupate (Cameron, 1938). The duration of the pupal stage has been reported as 12 to 14 days (Cameron, 1938; Wright & Geering, 1948) and 21 to 28 days (Brittain, 1921; Fluke, 1921) . In his study of natural control agents of C.nigricans, Cameron(1938) thoroughly describes three hymenopterous parasites reared from English material, and cites a fourth from the continent. These are the braconid Ascoqaster quadridentata wesmael, and the ichneumonids Glypta haesitator Gravenhorst, Anqitia (Holmgren) spp. and Epiurus (Foerster) spp. (= Pimpla F.). Anqitia is now correctly recognised as Diadeqma Morley (Fitton, pers. comm.). Wright and Geering (1948) recorded the ichneumonid Hemiteles ridibundus Gravenhorst, although this was not a definite identification and is the only reference for C.nigricana; it is not a species of Hemiteles, as the genus is now understood, (Fitton, pers. comm.). In North America the braconids Macrocentrus ancylivorous Rohwer and Macrocentrus thoracicus Nees are listed as parasites of C.niqricana (Thompson, 1946). In this study very low levels of parasitism were encountered; two specimens of Diadeqma spp. and one G.haesitator (det. M.G.Fitton, British Museum (Natural History)), and four specimens of A.quadridentata (det. T .Huddleston, BM(NH)), emerged from material collected in August 1981. 8 1.3. The Control of the Pest 1.3.1. Earlier attempts with Control and Forecasting Pest Attack The first attempts to control C.niqricana in the early years of this century, were largely based on the use of arsenical sprays. Wright and Geering (1948) cite Fletcher (1901) using Paris Green (acetate and arsenite of copper), Miles (1926) and Kuwayama (1937) demonstrating decreased attack with lead arsenate, and Ozols (1933) achieving a 15% reduction in the number of damaged seeds, with calcium arsenate and lime dust. However, Brittain (1921) in Nova Scotia, conducted trials with various arsenate salts, and achieved lesser success, particularly on later sown crops. As early as 1920 in North America, where natural enemies of C.niqricana were lacking (Cameron, 1938) , Fluke (1920a), following little success with light traps, sprays and cultural practices, advocated the selection of early maturing varieties of peas, sown as early as possible. Fluke (1921) concluded that no practical control method existed; it was suggested that the lack of control with arsenical sprays may be due to the larvae of C.niqricana not eating the outer part of the pea pod. Cameron (1938) thoroughly reviewed the natural control agents, and concluded that biological control was the only method offering any hope of success. Wright and Geering (1948) cite Hey (1946) as first using D.D.T. against C.niqricana and also describe their own thorough investigations with the insecticide. They investigated the effects of concentration, application rate, formulation and time of application. They demon strated little or no difference in efficacy between concentrations, application rates and suspensions and emulsions, but showed significantly improved control with early sprays or two sprays, over a single late spray. The recommendation was made of one spray for crops harvested green, and two sprays for those harvested dry. They pointed out that the first spray should be applied before egg hatching had started, which for crops sown in late 9 April or May, was estimated as seven to 10 days after the first flowers appear. Three years later, Wright, Geering and Dunn (1951) demonstrated varietal differences in the susceptibility of peas to moth attack. These were largely due to differences in maturation rate, and hence duration of exposure to attack. Following the successful use of D.D.T. emulsions, Edwards (1954) used D.D.T. dust to equally good effect, thus removing the need for a local water supply. Wright and Geering (1948) had noted the importance of timing spray applications, and Gould and Legowski (1959) showed that although D.D.T. was more persistent than some of the other insecticides available at the time (e.g. Endrin), two sprays did not provide the control theoretic ally attainable. The importance of correct timing, thus avoiding the cost of unnecessary sprays, was highlighted by Legowski and Gould (1962), in their examination of the economics of control. They found that in years of low and average yields, the costs were not favourable, and even on fields with high yields, pod infestations of 25% (not a very common occurrence) were necessary to justify two applications. Indeed they stated that if a grower could rely on 50% control from a single spray at the correct time, but 70% control was all that could be expected with two sprays, then a single spray was more justified. How ever, this was based on one, short, season's results, and the proviso was added that if 50% control with one application was not a reliable level, two sprays were recommended for protection over longer periods. Since the level of profit was always likely to be minimal, the necessity of efficient spraying was emphasised, and the need was recognised for a forecasting system, or at the very least identification of the areas and conditions in which C.niqricana was a recurrent pest. A spray warning service was initiated in 1959 (Gould, Legowski & Atkins, 1962) in response to the need for information on the time of moth emergence and egg laying in the field. This service was run by the National Agricultural Advisory Service (N.A. A.S., now the Agricultural Development and Advisory Service, a .D.a .S.). 1 0 The warnings to growers were based on detection of eggs in certain pea crops, and issued through N.A.A.S. advisors, the press and local television, as well as the information being passed to the Pea Growers Research Organisation (P .G.R.O., now the Processors and Growers Research Organisation, P.G.R.O.), canning firms and spray contractors (Gould S c Legowski, 1962). The warnings were based on field observations of presence of moths in emergence sites, and subsequent sampling for moths and eggs in the current pea crops. How ever, the warnings were issued with the stipulation that they did not imply the need to spray, and were only a timing guide for those wishing to spray. Considering the economic aspects, a forecast of attack severity was explicitly required to allow more confident advice on whether or not spraying was necessary. Accordingly, correlation coefficients were calculated for egg numbers and the final level of pod infestation at harvest (Gould & Legowski, 1962). It was predicted that a pod infestation of 10% to 30% could be expected if the peak number of eggs found on a 10 plant sample was 10 (Gould & Legowski, 1962; 1964); this estimate of 10% to 3 0% was not accurate enough for economic calculations (Gould S c Legowski, 1964). In addition the method was expensive both in time and manpower, and only a few select fields could be sampled in areas where C.nigricana was a known recurrent serious pest. The pressure for accurately timed sprays was increased with the trend to replace the organochlorine pesticides, such as D.D.T. Trials were conducted over a number of years to find suitable alternatives (Gould Sc Legowski, 1968). The results, although encouraging, are confused by the poorly timed applications in some years; this coupled with variable persistence, gave variable control. In Canada, insecticide trials were still being conducted in 1975 and 1976 (Thompson S c Sanderson, 1977) ; a range of treatments gave 70 to 75% reduction in damage, but this was not sufficient to meet Canadian quality control standards for seed. The development of egg counting for monitoring and possibly forecasting, allowed spray warnings to be issued 1 1 to inform growers when to spray. The impracticality of sampling more than a few fields imposed the restriction of area warnings, and did not permit more exact information about individual farms or fields. 1.3.2. The Development of a Sex-attractant Monitoring System Despite the improvement offered by the egg-count warning system over the unreliable method of detecting moths in the field by netting, Lewis et al (1975) stated that even fields sprayed strictly according to predictions, up to 20% of peas were still being damaged. This poor control was ascribed to the inefficiency of the insecticides and their application, variable microclimate and to the limitations of the sampling method. They advocated the development of a more sensitive and convenient system, preferably for use at more sites, which would give more reliable warnings. This was to be achieved by the detection of moth arrival in the peas, instead of continuing with egg monitoring and refining the sampling (e.g. Wilson, 1959; Condrashoff, 1967; Jennings & Addy, 1968; Rice, Sadler, Hoffmann & Jones, 1976) . Lewis et ad (1975) noted that several tortricid species had been monitored with varying success with naturally emitted pheromones and synthetic sex-attractants, and preliminary field studies were made. One major difference between C.niqricana and the other tortricids previously investigated, is that the latter are pests of perennial fruit orchards. Consequently monitoring is aimed at detecting moth emergence in the resident population. In contrast, the monitoring of C.nigricana seeks to provide information about an immigrating population. Female C.niqricana produce an attractive sex pheromone (Lewis et al, 1975), and preliminary experiments with traps containing virgin females, gave larger catches than previously recorded for other tortricid species. Considerable progress was also made with the development of synthetic sex-attractants, and a sex-attractant monitoring system was deemed feasible. It was noted that since the traps catch only males, their detection was of 12 little use, unless it could be related to the arrival of females, the timing of oviposition and larval infestation. The latter would indicate whether spraying was necessary on economic grounds, and the former the timing of such sprays (Lewis et aJL, 1975). Electroantennographic (EA8) responses of male moths were investigated (Wall, Greenway & Burt, 1976) and although an incomplete series of compounds was studied, 12-carbon acetates emerged as strong candidate attractants. Field tests followed, and the compounds (E)-10-dodecen-l-yl acetate and (E, E)-8,10-dodecadien-l-yl acetate were found to be strong attractants. Lewis and Macaulay (1976) made extensive tests with various trap designs, using smoke emission to evaluate the odour plume shape, comparing trap shape, retentive properties of sticky materials and elevation. The most favourable design was the triangular tent shaped trap, made of aluminium with a removable polycarbonate insert coated with sticky material. Further trials (Macaulay S c Lewis, 1977) optimised the area of the sticky surface, and its position in the trap. Macaulay (1977) demonstrated that the traps indicated moth arrival earlier than egg counts, and a significant correlation was obtained between the first occasion when 10 moths were caught in either of a pair of traps, and the date of finding eggs. He found no advantage in siting traps at emergence sites. In order to investigate the relationship between male arrival' and the timing of spray application, Lewis and Sturgeon (1978) studied certain aspects of the female reproductive behaviour. Preoviposition period, fecundity and longevity were recorded, but more importantly the relationship between rate of egg development and temperature was defined. This enabled accurate prediction of hatching date (and hence spray date) to be made after 80% of development had occurred, based on local temperature means. The pheromone has now been identified as the diene (E, E)-8, lO-dodecadien-l-yl acetate (E, E8,10-12 : Ac) using a combination of analytical techniques, and confirmed by gas chromatographic and biological assay. Other related compounds, attractive to male G.nigricana in the field, 13 were not found in female extracts, and E, E8,10-12 : Ac could not be detected in male moths (Greenway, 1984) . Further work with sex-attractants was concerned with interactions between traps. Wall and Perry (1978) categorise the interactions as "interference", where the trapping zones from pairs or lines of traps arranged along the wind direction overlap, and "competition", where the trapping zones from traps arranged strictly across the wind overlap. In a series of experiments in 1977 and 1979, Wall and Perry (1978; 1980) demonstrated interactions at trap spacings of 25 - 200m. in lines of two, three or five traps arranged along the wind. In lines of two, the upwind trap caught more moths than the downwind trap; in lines of three the upwind trap caught more moths than the total catch of the other two, although in lines of five, the upwind and downwind traps caught more moths than the other three. It was concluded that the number of traps in a line had a greater effect on the distribution of moth capture, than the spacing. However, all these experiments 2 were conducted with 10 p.q. doses of the sex-attractant E, E8,10-12 : Ac which is a high dose. Further trials in 1979 (Wall & Perry, 1981) compared the effects of different doses of the two sex-attractants E, E8,10-12: Ac and (E)—10—dodecen—1—yl acetate (E10-12:Ac). It was found that with various doses of E10-12:Ac and lower doses of E, E8,10-12 : Ac, the upwind trap did not catch more than the other traps, although interactions were still occuring as shown by suppressed catches compared to an isolated reference trap. Wall, Sturgeon, Greenway and Perry (1981) 2 have also demonstrated that traps containing 10 jig. E, E8,10-12: Ac can contaminate the surrounding vegetation, which when traps are removed remains attractive for at least 60 minutes. In 1978 a commercial monitoring system, consisting of a pair of triangular tent traps, with sex-attractant lures and height adjustable stands, was marketed by Oecos Ltd.1, after discussion with Rothamsted Experimental Station (R.E.S.), A.D.A.S and P.G.R.O. This system is 1 Oecos Ltd., 130 High Street, Kimpton, Hertfordshire. 14 used by growers in their own fields, and adopted by A.D.A.S. to replace their egg count system and enables advice to be passed to growers who are not using the system. The sex-attractant used with the traps is the less attractive monene pheromone analogue E8,10-12:Ac, rather than the natural pheromone. This is because the latter is unstable and degrades to inhibitory compounds, so lures with this chemical were unsuitable for long term monitoring, due to the rapid decline in activity (Greenway S c Wall, 1980; 1981; 1982; Greenway, Wall S c Perry, 1982) . The photochemical breakdown of the natural pheromone can now be prevented by the antioxidant N-2-octyl-N1-phenyl -p-phenylene diamine (Greenway S c Wall, 1982), and so stable lures with the more attractive E, E8, 10-12:Ac are now available for detecting low density poulations at the start of the flight season for experimental purposes, or monitoring in vining pea crops. However, the natural pheromone is still unsuitable for long term monitoring of high density populations, because the larger numbers of male moths attracted and caught, can lead to saturation of the sticky surface after a few days. This would necessitate removal of trapped moths by the grower or frequent replacement of the sticky base plate. The system is used as follows. A pair of traps is erected, arranged at right angles to minimise wind direction effects, about 75 - 100m. apart on adjacent headlands in each pea field. The traps are installed towards the end of May before the moths emerge, and placed at about two thirds crop height (Lewis S c Macaulay, 1976) , the necessary readjustment being made to stand height as the plants grow. The traps are examined, and the number of moths recorded, every two days. The threshold is considered to have been reached when 10 or more moths are found in either trap on each of two consecutive two day periods. The grower then uses daily temperature means, either from the farm or from local meteorological stations, to calculate the percentage development of the eggs. When a total of 80% development is attained, the spray is applied two or three days later. A second application is usually recommended after a further 14 days. However, it was shown (Perry, Macaulay Sc Emmett, 15 1981) that the use of a few monitoring systems to provide warnings for a large area, in the same manner that the egg counts had been used, was unreliable. The value of the system in individual fields was stressed, and that this could be further improved by specialist interpretation. In 1980, A.D.A.S. and P.G.R.O. improved the system with the introduction of a telephone answering scheme for growers using the monitoring traps. This removed the pressure on the grower to record temperature data and calculate his own spray date. When his traps have attained the threshold level, the grower can telephone A.D.A.S. and listen to a pre-recorded message predicting a spray date. He is advised to call again a few days later to confirm the predicted spray date; the computer model is updated three times a week. Although most growers now make use of the monitoring system, and are strongly advised to do so, those few that don't can still receive limited advice from A.D.A.S. and P.G.R.O., because of the wealth of information received by telephone from cooperating farmers. It is made clear that good advice cannot be provided to growers who don't make use of the traps. 16 2. MATERIALS AND METHODS 2.1. Field Studies 2.1.1. Field Site Selection Selection of suitable field sites was made with respect to certain conditions i) Expected population level of adult moths ii) Size and physical character of the area iii) Convenience and accessability While the first was most important to this study, it was the most difficult to evaluate. Initially, a number of sites were considered by interviewing pea growers, from lists supplied by A.D.A.S. and P.G.R.O. An estimate of damage attributable to C.niqricana the previous year was obtained, and permission sought to erect traps containing sex-attractant for C.nigricana at the overwintering/ emergence site. A brief description of these sites and current pea crops was taken with respect to:- i) Crop ii) Area and shape iii) Presence and nature of tramlines iv) Condition and form of boundary vegetation Over a period of seven to 14 days, the traps were inspected and the moth catch removed and counted. It was assumed that those sites with both higher catches and high levels of C.niqricana damage the previous season, were likely to provide workable populations. The sampling techniques employed, required undrilled tramlines in both emergence site and pea crop. A cereal crop, preferably wheat, rather than for example potatoes was required at the emergence sites. Experience in 1980 showed that surrounding vegetation provided an important refuge, and sites were chosen to evaluate this by comparison between different types of vegetation. On these bases the following sites were selected. 1980: Emergence sites, Childerley Hall, Dry Drayton, Cambridgeshire. National Grid Reference (all figure) 53532628 Pea fields, Knapwell Wood Farm, lying about 3km. SW of emergence sites. Grid Reference 53332603 17 1981: Emergence site and adjacent pea field, Shimpling Park Farm, Shimpling Street, nr. Bury St. Edmunds, Suffolk. Grid Reference 58672522 1982: Emergence site and adjacent pea fields, Shimpling Park Farm, Shimpling, Suffolk. Grid Reference 58662522 The Suffolk site used in 1981 and 1982 was 18Km. SE (25Km. by road) of Broom*s Barn Experimental Station (Higham, nr. Bury St. Edmunds, Suffolk) which was used as a field base during these seasons. 2.1.2. Field Site Description 1980: The geographical relationship between emergence sites and pea crops is shown in fig. 2.1, together with other relevant information. All emergence site sampling was done in field P (estate nomenclature), being comparatively flat with a slight depression to the North, and bounded by hedge row, tall ( 5m.) in the East, West and Southwest and shorter (ca.2m.) in the North and Southeast. All pea crop sampling was done in field J; it was flat and bounded by hedgerow. 1981: Essential information and the geographical relation ship of emergence sites and pea crops is given in fig.2.2. Emergence site sampling was done in WA1 ("W" = Wheat, "A" = field A, "1" = 1981) a gently rolling field with a slight ridge manning East-West and dropping away in the North, South and West. Boundary vegetation included old hedgerows and understorey and herbaceous ditch banks that lack hedge. Pea field PAl ("P" = Peas, "A" = field A, "1" = 1981) despite its small size, was chosen because of its obvious suitability in other characters, not least its proximity to the emergence site. It was separated from the latter by hedgerows, while to the North it was bounded by a ditch bank and to the East abutted directly on Field Beans, with a little ruderal vegetation in between. 1982: The relationship between the fields is shown in fig.2.3. The emergence site comprised fields PAl and PBl and the field beans separating them in 1981. One change at the site was the removal of hedges in the South and West to clear drainage ditches. Two pea fields were sampled; PA2 an elongate field gently sloping from the North to a stream in the South, and PE2 a flatter field dipping away to the South. - 18 - Fig . 2.1. Map showing geographical relationship between emergence sites at Childerley Hall and pea fields at Knapwell Wood Farm, Cambridgeshire, 1980 N Field P 37.2 hectares Both wheat (cv Hobbit) in 1980 Field R 19.0 hectares on peas (cv Maro) 1979 Tramlines running SW/NE created by tractor wheels Field J 13.4 hectares Peas (cv Maro) 1980 Field K 41.7 hectares Peas (cv Maro) 1980 Tramlines running N/S created by tractor wheels 19 Fig. 2.2. Map showing geographical relationship between emergence sites and pea fields at Shimp ling Park Farm, Suffolk, 1981 N 1 km. »------i Field WAl 14.6 hectares Wheat 1981 on peas 1980 Field WB1 6.1 hectares Undrilled tramlines running E/W with two circumferential tramlines Field PAl 1.8 hectares (cv Maro) Field PBl 0.4 hectares (cv Maro) Undrilled tramlines running N/S with two circumferential t r uni ines 20 Fig. 2.3. Map showing qeographical relationship between emergence sites and pea fields at Shimpling Park Farm, Suffolk, 1982 N > ,.. , 1 km. . i Field WA2 3.2 hectares Wheat on peas (PAl and PBl) and beans Field WC2 20.2 hectares Wheat 1982 on peas (cv Maro) 1981 Undrilled tramlines (WA2) running N/S with two circumferential tramlines Field PA2 7.3 hectares (cv Maro) Field PB2 8.9 hectares (cv Maro) Undrilled tramlines running E/W with two circumferential tramlines 21 Hedgerow was present all round field PB2 and to the North of PA2, however this was inaccessible in the former because of a deep ditch, and sampling was discontinued in the latter when no moths were caught. The grassbank in the East of PA2 was distinguished by large areas of the vetches Vicia cracca L. and Lathyrus pratensis L. 2.1.3. Crop Phenology Emergence sites: All emergence sites were under wheat. Plant phenology was inadequately recorded in 1980, with only five values taken between the beginning of June and the beginning of August. In 1981 and 1982, weekly assessment was made by walking along tramlines and randomly selecting ten flag leaves or ears, with about ten paces between each selection. The decimal growth stage (Zadoks, Chang & Konzak, 1974; Tottman, Makepeace & Broad, 1979) (Table 2.1) of the oldest ear on the plant was recorded, with the number of nodes on its culm and the number of tillers on the plant. Pea fields: In 1980 only two records were taken at the beginning of the season, because work in the pea crop then stopped; the plants were scored on a scale provided by E.D.M.Macaulay at Rothamsted. In 1981 a weekly assessment was made, with ten random selections as described above. The vegetative and reproductive stages were recorded, using a numerical system produced by P.G.R.O. (Gane>Biddle & Knott, 1984) and summarised in Table 2.2. In 1982 the frequency of sampling was increased, with over 30 samples taken from the end of May to mid-July. 2.1.4. Climatic Records In 1981 and 1982 specific aspects of climate were continuously recorded throughout the season. Temperature was recorded at ground level, in a small clearing in the wheat field, with a bimetallic thermograph, shaded from direct solar radiation by a seed tray. Wind speed and direction were recorded with a Woelffle anemometer mounted at 1.3m. just above crop height. Further meteorological data, such as rainfall and sunshine hours are available from Broom's Barn Experimental Station, 18Km. NW of the 1981/ 1982 field siteu 4 BOOTING 7 MILK DEVELOPMENT i-3 H i PJ 40 70 h tr o h 41 Flag leaf sheath extending 71 Caryopsis (kernel) water ripe 3 0) 42 72 1-3 to 43 Boots just visibly swollen 73 Early milk o c+ h-1 44 74 $ 45 Boots swollen 75 Medium milk PJ 13 4 6 — 76 N to |w ft lx 47 Flag leaf sheath opening 77 Late milk PJ 73 3 iQ 48 78 PJ CD PJ X W 3 49 First awns visible 79 CD PJ 8 DOUGH DEVELOPMENT 73 O ft 5 INFLORESCENCE (EAR/PANICLE) EMERGENCE (D H i H- 80 PJ O 50 O n 35 51 First spikelet of inflorescence just visible 81 fl> CD H O 52 82 9? CD H i I PJ 53 £ of inflorescence emerged 83 Early dough td to h-1 ft to 54 84 h W o CD 55 j of inflorescence emerged 85 Soft dough oj I Cb P, 56 86 CD 87 Hard dough 0 57 * of inflorescence emerged H H- 5 5 88 VO 3 <1 PJ 59 Emergence of inflorescence completed 89 vo H 6 ANTHESIS (FLOWERING) 9 RIPENING O O 60 90 Cb 61 Beginning of anthesis 91 Caryopsis hard (difficult to divide) CD 62 92 Caryopsis hard (not dented by thumbnail) H i O 63 93 Caryopsis loosening m daytime H 64 94 Over-ripe, straw dead and collapsing 65 Anthesis half-way 95 Seed dormant s CD 66 67 H O 68 K 69 Anthesis complete 23 Table 2.2. Explanation of the P.G.R.O. numerical code for the growth stages of peas (From Gane, Biddle & Knott# 1984) DESCRIPTION OF GERMINATION STAGES Code Stage Description Gl Seed swell Seed fully swollen G2 Radicle present Radicle approximately 1cm. long G3 Plumule and Plumule approximately 1cm. long radicle present G4 Emergence Shoot above ground on 50% or more plants. Rows clearly visible DESCRIPTION OF VEGETATIVE STAGES Code Stage Description VI First node Fully expanded simple leaf, no tendril present V2 Second node Fully expanded simple leaf with simple tendril V3 Third node Fully expanded simple leaf with compound tendril th . Vn n node Any number of nodes on the main stem, with fully expanded leaves, according to cultivar. Compound leaves can be formed on later nodes DESCRIPTION OF REPRODUCTIVE STASES Code Stage Description Rl Detectable buds Small buds (approximately 6mm.) enclosed in terminal shoot R2 Visible buds Buds visible outside terminal shoot R3 1 open flower Open flower present on 50% of plants R4 Full flower Open flowers present on all plants R5 Flat pod Flat pods, approximately 50mm. long on the oldest podding truss (i.e. the lowest truss on the plant) P6 Pod swell Pods swollen, but with small immature seeds on the first podding truss R7 Pod fill Pods containing green seeds, which fill the pod cavity on the first podding truss R8 Green wrinkled Outer surface of pods wrinkled on the first pod podding truss, seeds becoming starchy R9 Yellow wrinkled Pods yellow and wrinkled on the first podding pod truss, seeds starchy RlO Dry seed Pods parchment-like and seeds within dry 24 2.1.5. Sample Units 1980: The emergence site (field P, fig.2.1.) was initially marked out in a grid with flags every 5 0m. When it became apparent that it was impractical to sample the whole field, the sample area was reduced, and only the western half was used (fig. 2.4.). Later in the season when a piece of equipment was constructed for use in tramlines, longer sample units were used, achieved by combining five central quadrats to give a 250m. sample. The pea crop (field J, fig. 2.1.) was also marked out in a 50m. grid, with no subsequent alterations (fig.2.5.). In each of the fields, three sampling categories were recognised; the numbered quadrats were assigned the letter prefix corresponding to the following:- H Hedgerow P Perimeter of crop C Centre of crop Marked in this way the central area of the wheat crop was twice the perimetal area, while the hedge was considered to be linear, although in reality quite dense. The central area of the pea crop was three-quarters of the perimetal area. The number of units available for sampling was follows:- Emergence site Pea field Hedgerow 23 28 Crop Perimeter 23 28 Crop Centre - early season 46 21 late season 8 21 1981: The emergence site (field WAl, fig.2.2.) and pea crop (field PAl, fig.2.2.) were marked out in a grid with flags every 50m., with the intention of using a 50m. length of vegetation as the sample unit. However calculations of time cost, derived from experience in 1980, lead to an increase in sample unit length to 150m. The boundary vegetation was readily assigned to 150m. lengths (figs. 2.6. Sc 2.7.). The crops were again subdivided into perimetal and central regions; the perimetal band width was 50m. at the emergence site WAl, and 25m. at the pea 25 Fiq. 2.4. Wheat field P, emergence site/ Childerley Hall, Cambridgeshire/ 1980: arrangement and numbering of sample units/ and position of sex-attractant monitoring traps N 26 Fig. 2.5. Pea field J, Knapwell Wood Farm, Cambridgeshire, 1980; arrangement and numbering of sample units, and position of sex-attractant monitoring traps N A » 100 m. » A SEX-ATTRACTANT TRAP Direction of arrow indicates long axis of trap 27 Fig. 2.6. Wheat field WAl, emergence site, Shimpling Park Farm, Shimp ling, Suffolk, 1981: arrangement and numbering of sample units, and position of sex- attractant monitoring traps 28 Fig, 2.7. Pea field PAl, Shimpling Park Farm, Shimplinq, Suffolk, 1981: arrangement and numbering of sample units, and position of sex-attractant monitoring traps S! & Pi S of arrow indicates long axis of trap < g « o H - H Eh -P o I Q) X 8 Ch - H m p a 29 field PAl. The 150m. unit in the crops was represented by a 75m. length of tramline, both sides being sampled (section 2.1.6.). Each sample unit was marked at its extremities with flags, allocated a number and assigned a letter prefix corresponding to the following:- H Hedgerow U Understorey of hedgerow G Grassbank without hedgerow, or with hedgerow inaccessible B Bean crop (field PAl only) P Perimeter of crop C Centre of crop V Vetch bank 1 The increased number of boundary vegetation categories over 1980 was due to the clear distinction of areas with and without hedges, and was partly the reason why the site was selected. The differing areas of fields WA1 and PAl gave the following number of sample units, such that within each field there was the same number of perimetal and central units:- Emergence site Pea field Hedgerow 6 2 Understorey 6 2 Grassbank 4 1 Beans - 1 Crop Perimeter 10 4 Crop Centre 10 4 Vetch bank1 — 1 1 The vetch bank was along the western margin of Field WBl (fig. 2.2.), part of which was under peas in 1980. It was expected both to harbour a resident population and provide further area of food plants (hence its inclusion under pea field) . Two vetch species were abundant, V.cracca and L.pratensis. 1982: 150m. sample units were marked out with flags at the emergence site WA2 and pea crops PA2 and PB2. Because of hedge clearance described in section 2.1.2., there were no hedge samples around the emergence site. The hedge 30 around field PB2 was inaccessible to sampling because of drainage ditches, and the two hedge sample units in the North of field PA2 were discontinued when access became difficult in mid-season, and no moths had been caught. The 150m. crop sample unit in emergence site WA2 was represented by a 75m. tramline length as in 1981 (fig.2.8.), however with the larger size of the pea fields and the time cost restriction on the number of samples, the 150m. unit was sampled in one length (figs.2.9. & 2.10.). The following number of units were available such that there was an equal number of units from the crop centre, crop perimeter and surrounding vegetation Emergence site Pea fields PA2 PB2 Hedgerow - 2 (discontinued) - Understorey - 2 - Grassbank 5 2 5 Vetch bank - 1 - Crop Perimeter 5 5 5 Crop Centre 5 5 5 The vetch bank to the East of field PA2 is the same bank studied in 1981. Following encouraging results in 1981, a number of transects were planned from centres of emergence to centres of pea crops, to fit regressions on the number of moths against distance. To minimise effort, the samples for the transects were taken from the main sample units. Since transect samples were only 50m. long, the longer sample units were subdivided accordingly. The positions of the transects and their association with the main sample units are given in fig.2.11. 2.1.6. Sampling Programme Aim: The main programme was designed to sample intensively in sites throughout the season, and so provide relative estimates of populations of the two sexes from an emergence site and pea crop, both within crops and in surrounding vegetation. These estimates were needed to determine the 31 Fig. 2.8. Wheat field WA2, emergence site, Shimpling Park Farm, Shimpling , Suffolk, 1982: arrangement and numbering of sample units, including transect sub-samples I i 32 Ficr. 2.9. Pea field PA2/ ShimplinqPark Farm, Sh imp ling, Suffolk/ 1982: arrangement and numbering of sample units, including -transect sub-samples, and position of sex-attractant monitoring traps 33 Fig. 2.10. Pea field PB2, Shimpling Park Farm, Shimplinq, Suffolk^ 1982: arrangement and numbering of sample units7 including transect sub-samples, and position of sex-attractant monitoring traps f c - * ------h / P j cn < £ •H QS o X Eh g rd g Eh rd p i £ <£ m O EH o i—l g < a cn a : o Q) Eh *H P & Eh P rd rd < o U g 1 0) •H p V g p W •(—1 £ p cn Q •H O - 4 Fig . 2.11. Emergence site WA2 and Pea fields PA2 & PB2, & PA2 fields Pea and WA2 site Emergence 2.11. . Fig Cbd samples hmln akFr, hmln, ufl, 1982: Suffolk, Shimpling, Farm, Park Shimpling ragmn, n ubrn o rnet sub transect of numbering and arrangement, \ \ \ \ \ \ \ \ \ \ \ i 34 i 35 distribution of the moths in relation to:- a) Dispersal - Comparison with indications from sex-attractant trap catches of male moths, to demonstrate overall population movements. - Calculation of sex ratios and, with the assumption of a 1:1 ratio, to assess the extent of differential dispersal of the two sexes. b) Timing and location of mating - An assessment of mating frequency as revealed by the presence of spermatophores in the bursa copulatrix of the female. c) Maturation - An assessment of the state of maturation of the ovaries, and physiological age of both sexes, based on predetermined characters. Design: Number of areas 1980 1 1981 1 1982 1 Number of s ites 1980 2 a) Wheat field P b) Pea field J 1981 2 a) Wheat Field WA1 b) Pea field PAl 1982 3 a) Wheat field WA2 b) Pea field PA2 c) Pea field PB2 Number of sample units 1980 169 1981 51 1982 47 Number of vegetation categories 1980 3 1981 7 1982 6 Number of samples per week 1980 65 over 3 days 1981 51 over 3 days 1982 47 over 3 days 36 Duration of sampling programme Last week of May to the first week of August (11 weeks) Sampling pattern 1980 Random 1981 Systematic 1982 Systematic Techniques: a) Suction: Description of the D-Vac. A suction sampler was assembled according to the design of Thornhill (1978), based on the "D-Vac." produced by Dietrick (Dietrick, Schlinger & Van Den Bosch, 1959; Dietrick, 1961). Thornhill refered to his machine as a motorised insect sampler (pers. comm.) and although the one used in this study was modified further, it will be referred to as a D-Vac. (fig. 2.12.). In previous models the linen sample bag has been held in position by overlapping the edge of the bag around the rim of the fibre-glass head, and held firm by the tightly fitting internal collar on the extension piece (j in fig. 2.12.). This method was used in the first part of the 1980 season. However the design and construction of a trolley-type attachment tested in 1980, necessitated a redesign of the fibre-glass sampling head. This allows the bag to be held in place by "Velcro" strips under an internal flange, fitted to divert material into the sample bag (fig. 2.13.); the sampling head can now be used with or without the extension piece. When the extension piece is used, a coarse mesh (ca. 1cm.) plastic netting filter screen is included (fig. 2.13.) to prevent larger fragments of plant material from entering the bag, impeding airflow and reducing efficiency as well as complicating the sorting of the sample. Care was still taken to remove plant material from the mesh during sampling, since airflow is reduced if it is allowed to accumulate. : Use of the D-Vac. The sampling head was not used in the vertical mode to sample a unit area, since it became apparent early in 1980 that the time and effort involved was too great and the technique was not appropriate for low density 37 Fig . 2.12. p-Vac, sampling machine showing major components The 2-stroke engine (a) and centrifugal fan unit (b) are mounted on a standard rucksac "H"-frame (c). The two metre length of 20cm. bore canvas flexible tubing (d), has internal wire strengthening and connects the fan inlet (e) to a fibre-glass head (f), which contains the linen sample bag. The flexible tubing is secured at both ends with jubilee clips (g), and is joined to the fibre-glass head via a flexible connecting piece (h) which allows for an expansion in the bore. The extension piece (j) is held in place by elastic straps (k). 38 Fig . 2.13. Cutaway diagram of D-Vac. sampling head showing modifications associated with the use of the trolley attachment a) Strengthened flexible canvas tubing, 20cm. bore b) Aluminium band c) Aluminium supports d) Wooden handles e) Flexible connecting section f) Plastic netting screen (ca. 1cm. mesh) to prevent fouling of fan blades g) Aluminium strengthening bands h) Fibre-glass head section j) Fibre-glass extension piece k) Elastic strap m) Linen sampling bag n) Velcro strip, attached around rim of sampling bag and just below internal flange (p) p) Internal flange of fibre-glass, fitted to divert material over velcro into sampling bag q) Plastic netting screen (ca. 1cm. mesh) to filter coarse material out 39 populations. The sampling head was used in horizontal mode (Richmond & Graham, 1969) like a sweep net (Dietrick, 1961). In 1980 no distinction was made between the hedge and understorey, and sampling was performed to cover the vegetation from ground level to about 2m. In 1981 and 1982 hedge sampling was at a constant level of about lm. (fig. 2.14a.), while understorey and grassbanks were sampled by dragging the head along (fig. 2.14b.). While it is possible to use the D-Vac. in the latter mode in crop tramlines, it is nevertheless awkward and the machine cumbersome to use. It was also found to be damaging to pea plants, and continued over several weeks would have been destructive to the sample units. Accordingly a trolley-type attachment was designed and produced specifically for use in crops with tramlines (preferably undrilled) (fig. 2.15.). The trolley attachment is attached to the D-Vac. head and the extension collar is not used. The vertical inlet in the box section is the same area as the round sampling head, and this opening draws air and insects from the left as it passes along the tramline. The wheel provides support and allows steering, while the offset acute-angled front serves to divide the crop and guide it past the trolley. A small deflector vane at the back of the opening prevents the crop from being drawn into the box and fouling. The trolley-attachment was used for all crop sampling in 1981 and 1982, including the beans adjacent to pea field PA1. The 150m. sample unit (in fields WAl,PAl and WA2) was taken as two 75m.lengths down each side of a tramline, since the sample is drawn from the left, the unit takes the form of an elongate loop, taken clockwise such that sampling is always from undisturbed vegetation (fig. 2.16.). Calibration samples were taken to compare modes of D-Vac. use and different attachments; these are described in section 2.1.12. b) Kite net: A standard kite net (Watkins & Doncaster1 ) was used in the afternoon or early evening, to sample the active moth population over the crops and surrounding 1 Watkins & Doncaster, Four Throws, Hawkhurst, Kent. 40 Fig. 2.14. Modes of D-Vac. use with conventional sampling head a) Sweeping hedgerows; Sampling head carried along at a slow walking pace, with inlet appressed to vegetation at a height of 1.0 - 1.5m. b) Sweeping herbaceous understorey and grassbanks: Sampling head dragged along at a slow walking pace, with inlet held at an acute angle to the ground. 41 Fig. 2.15. Components and design of trolley attachment for use of D-Vac. in crops with tram-lines a) Conventional fibre-glass D-Vac. head b) Handle on trolley attachment c) Elastic strap securing D-Vac. head to trolley down tube d) Trolley down tube e) Trolley front "box" section f) Deflecting vane at rear of inlet opening g) Plastic netting screen (ca. 1cm. mesh) to filter coarse material out h) Vertical inlet opening, of equal surface area to circular opening of conventional head j) front support wheel Arrows indicate direction of airflow. 42 Fig. 2.16. Mode of tramline sampling using D-Vac.and trolley attachment Sample is drawn from undisturbed vegetation on the left- hand side of trolley attachment, such that a sample may be taken from an elongate loop as indicated by the arrows. 43 vegetation. Samples were taken from the same sample units as for the D-Vac., and were made with rapid strokes to and fro just clear of the vegetation (in practice about 180 sweeps in 1.5 - 2.0 mins.). Since understorey units corresponded to hedgerow units, and for purposes of aerial sampling were one and the same, the sampling design was adjusted slightly with fewer numbers of samples. Kite netting was used only in 1981, with 30 and 13 samples at the emergence site WAl and pea field PAl respectively. Although the time available in the activity period was considerably less than for pre- or post- activity periods, netting was less time consuming than D-Vac. use hence the samples could be taken over only two days. c) Sex-attractant traps: At the beginning of the season, when several sites were being considered for final selection, the lure employed was (E,E)-8, 10-dodecadien-l-yl acetate (E,E8,10-12: Ac), the more potent natural pheromone (Greenway, 1984); it is more effective at lower moth densities and as a close range attractant (Wall & Perry, 1981a). For long term monitoring during the season, the analogue attractant (E)-10-dodecen-l-yl acetate (El0-12:Ac) (Wall et al, 1976) was used, supplied in a 3mg. dose. The traps (fig. 2.17.) wsre similar to the commercially available tent-shaped cardboard models, but were the more robust aluminium design (Lewis & Macaulay,1976; Macaulay & Lewis,1977). The clear perspex base plate was coated with the retentive material "Tangletrap"1. The natural rubber serum stoppers (1-f sleeve stoppers in W.87 Red2 ) impregnated with attractant were suspended on aluminium wire from the apex of the trap top. Growers use monitoring traps only in pea crops, because Macaulay (1977) showed little advantage in siting traps at emergence sites. In this study male moths were monitored both in the peas and in the emergence sites. In accordance with standard monitoring proceedure, pairs of traps were erected with their long axes at right angles, 1 Tanglefoot Corporation, Grand Rapids, Michegan, U.S.A. 2 West Pharmarubber Ltd, St. Austell, Cornwall, England. 44 Fig, 2.17. Cutaway diagram of sex-attractant monitoring trap, showing parts and assembly a) Aluminium tent-shaped trap top b) Elastic strap securing trap to stand c) Sex-attractant lure suspended from trap apex by- d) Aluminium wire e) Perspex insert f) Retentive surface g) Telescopic trap stand h) Securing screw for adjustable stand 45 75 - 100m. apart on adjacent headlands, even though there is now good evidence that certain sex-attractant doses cause traps to interact over these distances (Wall & Perry,1978; Perry, Wall & Greenway, 1980; Wall & Perry, 1981) (section 1.3.2.). For this reason monitoring traps were only placed in the pea fields in 1982, because of the close proximity of the emergence site. The traps were mounted on adjustable stands, and arranged at crop height in the wheat, and two thirds crop height in the peas, as recommended to growers (Lewis S c Macaulay, 1976) . When the pea crop was at earlier stages, the traps were supported on bricks to achieve the desired height, as the stands provided were too high. The trap catches were counted and removed on a daily basis whenever possible. The trapping efficiency may decline after a number of moths have been caught, because of the physical deterioration of the retentive surface due to moth scales (Riedl,1980). Efficiency was maintained by thoroughly stirring the sticky material when the moth catch was removed, or replacing the sticky plate when soiling became too great. Attractant traps were used not only to indicate dispersal of male C.nigricana, but additionally, provided evidence that males were active at any given time. During the 1982 season, samples of male moths were taken from the monitoring traps sited in the pea fields. These were dissected to assess the physiological age of moths caught in the traps. In 1982 experiments with sex-attractant traps were conducted in field WC2 (fig. 2.3.); these are described in section 2 .1 .1 1 . d) Direct observation: Observation of moths flying over the crop gave direct evidence of the activity period. When active moths are abundant they can be readily seen against the sky by crouching down at crop height; in 1980 and at certain times in 1981 and 1982 when moths were less abundant binoculars were used to look for moths against the dark back ground of a hedgerow. In 1982 both sexes were collected in the emergence site by walking along tramlines and searching for moths resting on flag leaves, where they were clearly visible; they were then removed to a small tube using a pooter. 46 2.1.7. Sampling Proceedure Whenever possible the attempt was made to mix the sampling sequence of units from different vegetation categories to minimise weather and time of day effects. In 1980 10 hedge, 10 crop perimetal and 15 crop central samples were randomly selected from the units available at the emergence site each week; for reasons explained above only 10 hadge samples were selected at the pea field. In 1981 the aim was to take all 51 samples over a period of three days. 12 of 36 emergence site units and five of 15 pea crop units were randomly selected for day 1 , with a further 12 and five from the remaining 24 and 10 for day two, leaving 12 and five for day three. Each daily group of 17 samples were then arranged in the most convenient order such that the five pea crop samples were both pre ceded and followed by six emergence site samples. In 1982 the aim was to sample all 47 units over three days; how ever with transects imposed on the programme, the number of samples was increased to 76. Although many of these samples were 50m. instead of 150m , the increased number meant considerable increase in time cost, because of the handling time for each sample. To keep overall sampling time to three days, since more than three dry days could not be relied upon, the sampling sequence was as the following example:- Day 1 Grassbank PA2 Crop perimeter WA2 Crop centre PB2 Day 2 Crop perimeter PA2 Crop centre WA2 Grassbank PB2 Day 3 Crop centre PA2 Grassbank WA2 Crop perimeter PB2 The groups of samples on days 1 and 2 were randomly selected. C.nigricana are known to be active during the after noon (Lewis et al, 1975) although the peak of activity, as indicated by sex-attractant trap catch and direct observation, may vary according to temperature. The D-Vac. was used to sample the inactive population of moths and its use was therefore restricted to the pre-activity period. In practice this meant sampling in the morning as soon as the vegetation was dry. Sampling may also be done in the post activity period in the late evening, and a note was made 47 of the period in which samples were taken. The contents of the D-Vac. sample bag were emptied into a labelled polythene bag and secured. After five or six samples had been taken they were placed in an expanded polystyrene cool box with frozen glycerine bags. The insects were cooled by this treatment and appeared moribund on returning to the laboratory all samples were frozen to kill and preserve the insects. Kite net samples were taken by the same selection proceedure as above, over a period of two days. The net catch was immediately inspected and all Microlepidoptera removed with a straight pooter, and transferred to labelled 2" x ■§•" tubes. These were subsequently placed in the cool box and thence to the deep freeze on return to the laboratory. 2.1.8, Sorting of Samples D-Vac: The samples were allowed to thaw and the contents emptied into a kitchen colander. They were sifted so that most of the insects and smaller pieces of debris fell through to a sheet of paper, larger insects were then sorted from the remaining coarse material which was dis carded. All the Microlepidoptera were removed, placed in a small labelled tube and retained. All other insects were also retained in a labelled tube and returned to the freezer. The Microlepidoptera were examined under a dissect ing microscope, and the specimens of C.nigricana sorted using external recognition features determined in 1980 (J.D.Bradley pers. comm.) from genitalia preparations (Robinson, 1976) (figs. 2.18. & 2.19.). The number of Microlepidoptera and the number of each sex of C.nigricana was recorded and the insects returned to the freezer. It is not known how damaging double freezing may be, but it was -unavoidable, as the time was not available to sort such a large number of samples. Kite net: The Microlepidoptera were counted, examined and recorded as above. 48 Fig . 2.18. Genitalia preparations of C.nigricana to show parts and diagnostic features: a) female *aa apophyses anteriores *ap apophyses posteriores *bc bursa copulatrix * diagnostic db ductus bursae features * ob ostium bursae used for * pa papillae anales identification sa sterigma lamella ante-vaginalis * si signum sp sterigma lamella post-vaginalis te tergite VIII pa ap aa sp ob sa te db be si BOO jr 49 Fig . 2.18. Genitalia preparations of C.niqricana to show parts and diagnostic features: b) male ae aedeagus *cl clavus CO costa * diagnostic * cr corona features * cu cucullus used for sa s acculus identification sc SdCCUS Tksp saccular process *un uncus *va valva vi vinculum vp valva process 50 fig. 2.19. External appearance of characters recognised as diagnostic from genitalia preparations a) Female ob ostium bursae pa papillae anales sa sterigma lamella ante-vaginalis sp sterigma lamella post-vaginalis b) Male cr corona sp saccular process va valva ooo n l------r i b] 51 2.1.9. Dissection of Adult Moths Females: All females caught in 1981 and 1982 were dissected to assess the state of their ovaries and fat body, although some moths caught with a kite net were too damaged for successful dissection. The bursa copulatrix (fig. 2.18a.) was opened to count spermatophores, each one indicating a single mating (in addition the shape of the bursa confirms identification). Moths were pinned through the thorax, dorsal side uppermost and the wings removed with bow spring scissors. Dissection was under 0.9% saline (Pantin, 1962). The abdomen was tensioned by pinning through the ovipositor and the tergites removed with fine forceps and fine bow-spring scissors. The ovaries were carefully teased apart and uncoiled; by gently pulling the terminal filament, individual ovarioles were displayed. The total number of eggs per ovariole was counted, together with the number of mature chorionated eggs (indicated by total opacicity due to yolk deposition). The fat body types were scored (fig. 2.20 & table 2.3.) and the bursa opened to assess mating. Dissected females were stored individually in 70% alcohol for further reference, should it be necessary. Males: In 1981 samples of males and in 1982 all males were dissected in the way described above. Initially to assess the possibility of aging males and continued because of the similarity of the fat body to that of females. The diameter of the pigmented testes and the length and breadth of the accessory glands were measured, as possible indicators of age, but no accurate relationships were found. Age scores assessed by dissection ranged from 3 to 14 on an ordinal scale. In an attempt to validate the use of sugar and yeast bait traps for timing spray applications against Cydia pomonella(L.), Nel (1940) dissected females and recognised three physiological age (P.A. ) categories as follows:- Physiological Age I Females fresh or fairly fresh, having laid few eggs or only a relatively small proportion of their egg- total, ovaries usually large, ovarioles long and stretch ing forward well beyond bursa copulatrix; fatbody large 52 Fig. 2.20. Diagrammatic illustration of the four fat body types of C.nigricana at various grades of abundance For explanation see text accompanying Table 2.3. Key S eut ha bursa copulatrix o ovaries Diffuse fat Grade Grade 2 3 4 53 Table 2.3. Description of the four fat body types of C.nigricana at various grades of abundance The five grades of the four fat body types are more or less eguivalent to each other, such that a grade of any one fat type will tend to be associated with the same grade of any of the other three types. After dissection each of the four fat types was scored according to grade. Diffuse, emulsion and plate fats were scored from 1 to 3, while globular fat was scored from 1 to 5. The four scores were summated to give a phsiological age (P.A.) score between 3 and 14. A P.A. of 3 is possible since teneral moths with short abdomens and uninflated wings were newly emerged, and emulsion and plate fat was scored as < 1 , since these types appeared more pronounced than the grade 1 description. The diagrams in Fig. 2.20. illustrate the fat bodies in the females abdomen, but the grades are equally applicable to males. 54 in amount, cells and cell-aggregates large; usually 1 spermatophore in bursa copulatrix, opaque white or translucent, usually not dented; abdomen more or less fully occupied by ovaries and fatbody, or with only a small vacant space present anteriorly. Phsiological Age II Females moderately fresh, having laid more or less half of their eggs; ovaries of medium size, ovarioles of medium length and distinctly shortened; fatbody intermediate in amount, cells of medium size; usually 1 or 2 spermatophores, spermatophores clear and glassy, and usually somewhat dented; abdomen with large,, well-defined vacant space anteriorly. Physiological Age III Females phsiologically old and more or less spent, most of, or all the eggs laid; ovaries small; 1 , 2 , 3 or more spermatophores -in bursa copulatrix, spermatophores usually clear, glassy and dented. Nel states that newly emerged or freshly copulated pre- oviposition C.pomonella females have large ovaries occupy ing more or less the whole of the anterior abdomen, and that there is usually a large amount of fat body present. Dissection of teneral moths and older pupae in this study, revealed undeveloped ovaries with little or no oocyte differentiation, although the rest of the reproductive system was formed. The fat body consisted of both the emulsion type with oil droplets and thick sub-cuticular plates, but there were few dicrete globules (cells and cell-aggregates of Nel) and these do not develop until later. Nel's scale therefore corresponds to the older P.A. stages in this study; the following relationship may apply Nel (194 0) This study P.A. I P.A. 10 - 11 P. A- II P.A. 12 - 13 P.A. III P.A. 14 relationship between P .A. and real age under field conditions is unknown, since development will only proceed above a threshold temperature, and rate of aging may then vary with prevailing temperature conditions. In a constant laboratory environment, it appears from the limited data, that the P.A. of female C.nigricana bears a non-linear relationship to real age (fig. 2.21.). The developmental temperature threshold has not been 55 Fig. 2.21. Relationship of Physiological Age (P.A. ) to Real Age. Median and 25% percentiles of female C.nigricana reared in a constant environment of 20’C and 18L:6D light cycle. n 4 4 3 REAL AGE (Hours) 56 established for all life cycle stages of C.niqricana, but Lewis and Sturgeon (1978) estimated the developmental zero for eggs at 9.4*C at constant temperature and 8.5 C at fluctuating temperature, and fully developed pupae kept at 10’C will not emerge (Wall, pers. comm.). Additionally the developmental threshold is 10*C for both C.pomonella and Cydia funebrana (Treitschke) (Charmillot, Vallier & Tagini-Rosset, 1979). Thus assuming a developmental threshold of 10*C for C.nigricana and a linear relationship between temperature and development (the latter is perhaps more likely to be non-linear), it is calculated that 20 - 30 day-degrees (DD = max. + min./2 - 10) are required for development to P .A. 11, given that it takes 48 - 72 hrs. at 20*C to reach this stage. In the field the time taken to accumulate 20DD ranged from 48 - 192 hrs. Nel (1940) demonstrated that bait traps were biased towards older females of C.pomonella. The use of a D-Vac. in this study should be unbiased with respect to age, provided that within each sex, differently aged moths do not behave so differently in a manner that would tend to affect their chance of capture. 2.1.10, Infestation Levels Aim: To sample pea pods and vetch pods, and examine the distribution of infestation both within and between fields. Design: 1980 (a) Two’ pea fields: J and K Five unsprayed plots: Field J: Perimeter adjacent to hedgerow Perimeter adjacent to grassbank Centre Field K: Perimeter adjacent to hedgerow Centre Plot size: 12m. x 12m. Number of plants per sample: 50 Number of replicates: 1 57 1980 (b) One pea field: J Three unsprayed plots: Perimeter adjacent to hedgerow Perimeter adjacent to grassbank Centre Plot size: 12m. x 12m. Number of plants per sample: 50 Number of replicates: 4 1981 One pea field: PAl One unsprayed tramline running NS, plus vetch bank Number of plots: 6 - 1 Perimeter adjacent to grassbank 4 Central 1 Perimeter adjacent to hedgerow Vetch bank Plot size: 12m. x 12m. Number of plants per sample: 50 Number of replicates: 4 perimetal plots i.e. 4 samples 1 central plots i.e. 4 samples 1 Vetch bank 1982 Two pea fields: PA2 and PB2 Three plots per field (sprayed) Perimeter nearest to emergence site Centre Perimeter furthest from emergence site Vetch bank Plot size: 50m. x 50m. Number of plants per sample: 50-75 Number of replicates: 1 Methods: In 1980 five preliminary samples were taken from unsprayed plots in the two pea fields (design (a) above), and these were followed by further replication from only one field (design (b) above). Fifty plants were randomly selected for each sample and taken to the laboratory for examination. In 1981 samples were taken at the end of the season, 14 - 21 days pre-harvest. The samples from the four 58 central plots were taken in sequence running North to South. Plants were randomly selected, tied together for each sample, and returned to the laboratory. In 1982, there were no unsprayed areas; samples were again collected at the end of the season 14 - 21 days pre harvest. It was desirable to keep the percentage standard error of seed damage below the 10% level to allow for critical comparison between truss levels and plots. The following formula gives the standard error (S.E.) S.E. = /p (1-P) y N where P is the proportion of seeds damaged N is the total number of seeds Pilot samples were used to estimate percentage seed damage, the number of seeds per pod, and the number of pods per plant; it was calculated that 5 0 to 75 plants were required. In 1982 three samples of pods were also taken during the course of the season when plant phenology was recorded; these were opened to record damage levels to pods. In 1981 and 1982 samples of V.cracca and L.pratensis were collected from the vetch bank, and 200 pods removed from each species. In the laboratory the pods were removed from the plants, with the pods from each truss level kept together. Truss levels were counted from the first fruiting node; some lower pods had gone, but their presence was revealed by the remains of the pedicel. Paired pods were kept intact by removing them close to the main axis, while single pods were simply picked off. Only pods on the main axis were kept; the few side shoots were discarded because they could not be related to the other pods. The pods were stored in a cool room (0 - 5*C) until examination, although they were opened as soon as possible after harvest so that the larval stage could be recorded (live larvae were also required for culturing purposes). For each truss level the number of pods was counted, with subtotals for single and paired pods. All pods were opened, the number and instar of all larvae recorded and whether the pod was single or paired; in the case of the latter note was taken 59 if the sister pod was infested. In 1982, although not in 1980 or 1981, the number of damaged seeds in each pod was counted, with the total number of seeds for each truss level. 2.1.11. Experimental Use of Sex-attractants Aim: To determine the effect of pea plant presence on the attractiveness of the natural pheromone of C.nigricana Design: Number of fields: 1 Number of stations within field: 2 Number of treatments: Expt. 1 2 Expt. 2 2 Experimental design: 2 x 2 Latin Square Replication: Continuous as permitted by the weather Materials: Emergence site: 20.2 hectare field of wheat on peas (field WC2 in fig. 2.3.) with tramlines running NW/SE. Two permanent stations 150 - 200m. in from the field margin and 300m. apart along a tramline in the centre of the field. Permanent equipment at each station: one telescopic sex- attractant trap stand, two inverted large white buckets with a selection of large jars to serve as vases for plant material. Expt. 1: Treatment A - one aluminium trap top, one sticky insert or water trap, one rubber retaining band, one attractant lure impregnated with (E, E)-8 ,1 0 -dodecadien-l-yl acetate and antioxidant, selection of fresh pea plunt material with all phenological stages, fresh water for jar vases. Treatment B - control,as above, but without any pea plant material. Expt. 2: Treatment A - as above but fresh pea plant material with old reproductive stages only (fully inflated pods) Treatment B - as above but fresh pea plant material with young reproductive stages only (flowers and newly set pods) . Methods: Each treatment remained at a station for one activity period, edch block of the latin square design 60 (Perry, Wall & Greenway, 1980) therefore took two days. On the first day the treatments were randomly allocated to the stations and all materials positioned during the pre activity period. The following morning, trap catches were counted and the treatments at the stations were reversed. Male moths in the traps were kept for dissection and assessment of physiological age. 2.1.12. Calibration of the D-Vac. The calibration of the different modes of D-vac. use is necessary to enable valid comparison between samples in this study and also with other studies. In 1981 samples were taken to compare the new trolley attachment with the conventional head used in the sweeping mode. The two attachments were used alternately to take 25m. samples along a premarked line. Samples were taken in wheat, peas and beans, to examine all categories in which the trolley was used during the sampling programme. In 1982 samples were taken to compare the use of the D-Vac. in the conventional vertical mode with the two other techniques used in this study. D-Vac. sweeping was examined by sampling from a grassbank, while the trolley attachment was used in a wheat crop. Conventional D-Vac. use was by far more time consuming than either of these alternative modes, and it was for this reason these latter techniques were employed. In these calibrations 5m. was sampled conventionally, for every 25m. sampled by sweeping or with the trolley;'the former took lOmins. while the latter took only lmin. or less, not including the time taken to remove the sample to a polythene bag, which was constant. In the laboratory the insects in each sample were sorted into various groups according to size and taxonomic similarity. For 1981 samples, 18 insect categories were recognised. Because only a few samples were made with each method in each crop the raw data was pooled before transformation (Log (x + 1) ) and analysis by paired - t calculation. In 1982 more samples enabled comparison of machine sampling efficiency for individual taxonomic groups. Since the D-Vac. samples taken in the conventional vertical 61 manner were only from 5m., each count was adjusted by multiplying by a factor of five, to bring it to the same sample length as the other samples. Data was then trans formed to Loge (x + 1) for comparison. However because of the similarity between treatments before the five-fold adjustment, comparison was also made with the transformed 5m. value. There was no significant difference between the two modes of D-Vac. use in crops with tramlines (Appendix lb). The data collected in crops with the trolley attachment can be compared with data collected by D-Vac. sweeping without any correction factor; the two techniques are interchangeable in the crops studied. Thus the development of the trolley to facilitate sampling in crops with tram lines has produced a technique readily integrated into D-Vac. sampling programmes where different habitats occur. The D-Vac. calibrations performed in 1982 were not a pre-requisite for data analysis in this study, however they do permit some level of comparison of data collected here with that collected by conventional D-Vac. use. Additionally, since an estimate of increased efficiency of one mode of use against the other can be made, antd given that the 5m. strips sampled quantitatively are equivalent to 1.5 sq.m., absolute population estimates can be made with respect to density. With two exceptions, the adjusted counts for conventional use were greater than those for sweeping, although only significantly so in less than half of the individual categories (Appendix Id). However, catches of all size classes of insects and of all insects were significantly greater with quantitative D-Vac. use (Appendix Id) . In a wheat crop, conventional quantitative D-Vac. use was generally more efficient than the trolley (Appendix If). AS in the grassbank, conventional use was more efficient over 5m. than the alternative method used over 25m. in sampling larger insects over 7mm. in length (although not significantly so in either case) (Appendices Id Sc If). In both Appendices Id and If, the efficiency 62 factor of quantitative use against sweeping and trolley use is given where sufficient data allows. This shows that with respect to sweeping, insects became easier to catch as they became progressively smaller,,which is what would logically be expected. The implications of these calibrations for this study are that conventional use would have been a more efficient extraction method for sampling C.nigricana, all other things being equal. However because conventional use is far more time consuming, taking up to ten times longer to make a sample, and is potentially more destruct ive, particularly in the pea crop, it is felt that the techniques used were the most appropriate for studying the large areas involved. 63 2.2. Laboratory Studies 2.2.1. Culturing C.niqricana C. niqricana was cultured in the laboratory to provide experimental material. The culturing system used was the same as that used successfully at Rothamsted Experimental Station. Eggs were laid by females on wax paper (siliconised baking parchment) lining breeding chambers (fig. 2 .2 2 .). The eggs were counted under a dissecting microscope and surface sterilised in a series of large evaporation dishes containing the following:- 0.1% Sodium Hypochlorite solution, sterilised distilled water, 10% Sodium Thio sulphate solution, sterilised distilled water. The egg papers were dried on sterile tissue and placed in sterile extraction thimbles (80mm. x 22mm.), which were plugged with sterile cottonwool wrapped in "clingfilm". These were moistened with a few mis. of sterilised distilled water, and placed in wide necked 3" tubes which were then sealed with "clingfilm". Eggs were incubated at 20*C in a controlled environment (C.E.) room. On hatching, seven days later, young larvae were introduced onto a pea seed in a pea pod, using a soft brush bristle mounted in a drawn glass tube. One larva was placed in each pod and placed in a sterile 3" x 1 " glass tube, closed with a sterile polythene cap provided with a small ventilation hole. The larvae were reared in a C.E. room at 20*C with a 18L:6D light regime. The long day is necessary to prevent late fifth instar larvae from entering diapause (Wall, pers. comm.). After 10 - 14 days, pods containing larvae were transformed to a fresh sterile 3" tube with a moist sterile mix of fine sand and sieved peat, in which to spin a cocoon and subsequently pupate. After a further seven days, the remains of the pod and seeds were removed and examined to verify the larva was gone, and the pupation mix carefully probed to confirm the presence of a cocoon. The tubes were examined in the morning and evening 64 Fig. 2.22. Diagrammatic illustration of breeding chambers for C.nigricana showing main components and assembly a Main body of chamber - glass cylinder 120mm. x 40mm. b Wax paper (siliconised baking parchment) lining, held in position with parafin wclx c Muslin kept damp by capillary action humidifies chamber d Elastic band securing muslin and providing easy access to contents of chamber e Side arm of chamber - 10mm. glass tube welded on f Dental wick in side arm of chamber provides drinking water g Galvanised wire supports h Distilled water in which both dental wick and muslin are held j Seed tray d bD o b£» O 65 and teneral moths removed and sexed. The adults were introduced into the breeding chambers, ideally with 10 to 15 of each sex per chamber, although moths emerging over a protracted period were not mixed. The chambers were changed two or three times a week when the eggs were counted, and dead moths removed and sexed. 2.2.2. Pea Growing Pea plants were grown under glass to provide pods for rearing cultured larvae. Ideally a continuous supply was required, but in practice this was difficult to achieve; it was occasionally possible to supplement the supply with shop bought pea and Mange tout pods, imported from abroad. Plants were grown in 4" pots on the floor of a temperate glasshouse under a 20L:4D light regime, with a fan heater circulating the air and preventing the formation of a vertical temperature gradient. Plants were supplied with pea sticks or tied to canes for support. Greater success was achieved in 1982 when the plants were grown in a tropical glasshouse, double glazed, well heated and with improved lighting. The plant pots were placed on capillary matting on benches, which facilitated watering. In the temperate glasshouse the variety JI 1050 yielded 0.884 (+ 0.067 S.E.) pods per plant in 10 to 12 weeks after sowing, when the plants were senescing. In the tropical glasshouse the yield was 1.425 (+ 0.206) pods per plant in 12 to 15 weeks. The variety Melton with similar yields in the temperate glasshouse (no data) produced 1.791 (+ 0.335) pods per plant under tropical conditions. Plants thus lived longer and produced up to twice as many pods in these conditions. The poor yield is attributed to pest and disease problems as well as growing plants out of season. Downy mildew appeared on the first grown plants; it was controlled with two applications of "Persulon" (12.5% w/v fluotrimazole, Bayer1) fungicide, 14 days apart and did not reappear. Pea aphids (a cyrthosiphon pisum Harris) were the most persistent and damaging pest. Although successfully 1 Bayer U.K. Ltd., Eastern Way, Bury St. Edmunds, Suffolk. 6 6 controlled with "Phosdrin" (99% w/w mevinphos, organophos phorous insecticide, Shellstar1) on two occasions; however this chemical is not recommended for use in glasshouses, and application was discontinued. Partial control was achieved with pyrethroid formulations, but the populations regularly recovered, especially under tropical conditions, and calendar spraying was adopted. The aphids were most abundant at the growing point and on the pedicels causing fatal wilting of the parts affected, hence the poor yield. However the regular need for pods suitable for culturing larvae imposed a restriction on spraying, both on frequency and formulation. The aphids were tended by ants and parasitised by a braconid, though it is not known how these influences affected the populations. Wood mice (Apodemus sylvaticus L.) took germinating seeds from seed trays, and stripped a considerable number of pods from plants, before their presence was realised. They can be controlled by trapping. 2.2.3. The Effect of Diet Aim: To determine the effect of diet on potential fecundity, fecundity, fertility and longevity of C.niqricana. Design: Number of treatments: 3 diets Number of replicates: 2 (limited by availability of material) Materials: All treatments - Breeding chamber lined with wax paper (baking parchment) as an oviposition substrate, dental wick in side arm to provide fresh drinking water, damp muslin to humidify atmosphere of chamber (fig. 2 .2 2 .). Diets provided from dental wicks (No. 2) inserted into 2 " x glass tubes containing nutrient solution i) distilled water ii) 10% w/v Analar sucrose solution iii) 10% w/v commercial "set" honey (low laevulose/ dextrose ratio) solution 1 Shellstar Ltd., Ince Marshes, Ince, Chester, CH2 4LB 67 Details of allocation of insect material to treatments are as follows:- Replicate 1 2 Treatment i) 2 dcf 6 55 1 dd 7 55 ii) 5 dd 5 55 id 3 55 iii) 6 dcf 8 55 2 dcf i 5 Methods: Moths of both sexes, emerging over a period of 48hrs. were confined together in a breeding chamber. No attempt was made to standardise the number of moths or the sex ratio in the chambers, because of the limited emergence from the culture. Multiple numbers of moths were used, since preliminary experiments with solitary females confined with one or two males gave no oviposition and no successful matings. Treatments were arranged as in fig. 2.23a. All treatments provided with fresh water from the dental wick in the side arm, with treatment i) containing additional water to control for conditions in treatments ii) and iii). All replicates were maintained at 20"C and 18L:6D light cycle, and examined daily after oviposition commenced. Dead moths were removed and frozen, and survivors transferred to a fresh breeding chamber. Eggs were counted and then incubated at 2 0*C to assess fertility. Fresh diet was provided every two days, care being taken to dry thoroughly the outside of'the glass tube, since moths were observed to adhere to these by surface tension. All moths were subsequently dissected to score P.A. and for females, ascertain the number of successful matings and count the remaining eggs, with a subtotal of chorionated eggs. 2.2.4. Effect of Pea Plant Presence Aim: To determine the effect of both presence and phenological stage of pea plants on the potential fecundity, fecundity and longevity of C.niqricana. 68 F iq. 2.23. Effect of diet and pea plant presence on Fecundity and Longevity of C.niqricana. a) Effect of Diet Experimental treatment consists of standard breeding chamber supported over a tray of distilled water, with the addition of a 2" x glass tube containing the test diet and a dental wick within the chamber. b) Effect of plant presence and phenology Experimental treatment consists of standard breeding chamber supported over a tray of distilled water, with a glass tube containing 10% honey solution diet as in fig. 2.23a. above. The experimental plant material was held in the side arm by the dental wick, such that the cut end of the plant was immersed in the distilled water in the seed tray, and so remained fresh. 69 s s ______- / Distilled Water 10°/o Sucrose Sol. L------RfiNJW 10X Honey Sol. Control \ \ Old Reproductive Peas - 70 - Design: Expt. 1 Number of treatments: 5 Number of replicates: 1 Expt. 2 Number of treatments: 4 Number of replicates: 2 - 6 * * Limited availability of moths resulted in variable numbers per replicate. Materials: All treatments - Breeding chamber lined with wax paper as an oviposition substrate, dental wick in side arm to provide fresh drinking water, damp muslin to humidify atmosphere of chamber, dental wick in 2" x glass tube containing 10% honey solution. Fresh plant material of various phenological stages, field collecLed or glasshouse grown for the following treatments:- Expt. 1 i) Control - no plant material ii) Wheat ear and flag leaf iii) Young vegetative pea plant material with no reproductive stages iv) Young reproductive pea plant material (cream buds, flowers and newly set pods) v) Old reproductive pea plant material (fully inflated pods with starchy seeds) 7 Methods: Moths for experiment 1 were field collected from the centre of emergence site WA2 over a period of one hour to reduce age variability to a minimum. It was assumed that these moths had not encountered pea plants previously Moths for experiment 2 were from the culture. Treatments were set up as in fig. 2.23b. to ensure the plant material remained fresh. Replicates were maintained at 20 *C and 18L:6D light cycle. Treatments were examined every two days, when dead moths were removed and frozen, and the survivors transferred to a new breeding chamber with fresh plant material of the appropriate age and fresh honey solution. The eggs on the wax paper and the plant material were counted and then incubated at 205C to assess fertility. Replicates of the same treatment were kept together in covered seed trays filled with distilled water Treatments were separated in this way to minimise the chance of exposure to possible odour from other treatments All moths were dissected to assess mating and count eggs as described in the previous sections. 2.2.5. Treatment of Field Data Due to inclement weather during the seasons the total sampling schedule was not completed. A list of samples taken together with the number of male and female C.nigricana caught, is given in Appendix II. In 1981 and 1982 totals for the different vegetation categories in weeks with incomplete data were calculated from the mean values of those samples taken. In certain cases missing values were interpolated from the data of the preceding and following weeks. These totals were required to allow calculation of weekly percentages used to build histograms in the presentation of results. All histograms are plotted over the same time period of 11 weeks, although not all the weeks were necessarily sampled in any one year (Appendix II). 72 3. DISPERSION AND DISPERSAL 3.1. Introduction Earlier reviewers (Williams, 1957; Kennedy, 1961; Schneider, 1962) drew a distinction between migration, which they regarded as active, persistent and adaptive, and dispersal, which was seen as a passive accidental process, and not directionally adaptive. More recently (Johnson, 1966; Stinner, Barfield, Stimac & Dohse, 1983), there has been no attempt to distinguish between the two terms, and in this study migration and dispersal are regarded as synonymous. Taylor (1961) has shown that spatial patterns of dispersion can be a characteristic of the species within a habitat. Thus, in this study, spatial patterns will be seen to form in the emergence site, then break down and reform in a different habitat, the pea field. Insects do disperse incidentally as they move around while seeking food or mates (Johnson, 1966); in a large field which is much more homogeneous than most natural habitats, such movements may be described by diffusion equations, i.e. random movement. Diffusion equations do not allow for a "migration-prone" phase (Stinner et ad, 1983). At exodus and during flight, orientation is adapted to let insects fly out of and beyond the birthplace or emergence site and onto another oviposition site. This can be achieved by one or more flights, and is not a reaction to adverse conditions (Johnson, 1960). However, the exodus population should move off, not as independent individuals, but as a group or "patch" (Stinner et ad, 1983). Males and females do not necessarily migrate similarly; migratory populations always contain females from the beginning to the end of migration, while males may be more intermittent (Johnson, 1966). it is, of course, females that redistribute populations. Dispersive flights may be within the boundary layer above the vegetation, in which case the insects can generally control the direction of travel, and maintain a more or less linear track for relatively long distances, against or across the wind (Johnson, 1966). Most pest species however, 73 are not boundary layer fliers (Stinner et ad, 1983) and are consequently difficult to observe in flight. These insects show positive phototaxis, and penetrate their boundary layer by climbing steeply after take-off. Their track is largely controlled by the wind (Johnson, 1966), since they are out of range of optomotor orienting effects of the ground pattern (Kennedy, 1961). In general the direction of orientation (either inherent or induced) is adapted for getting dispersants away from the birthplace, rather than towards a destination. Orientation for shorter dispersive flights ( cf. very long migrations) may be affected by odour cues. Up wind flight in response to odour is odour-conditioned positive anemotaxis (Kennedy, 1977), not chemotaxis. Gradients strong enough to permit true chemotactic orient ation to a source only occur very close to the source (i.e. a few cm.). If odour does not condition the direction of dispersal, termination of flight occurs when some specific stimulus signals a resting place (Kennedy, 1961) and over rides the tendency for continued flight. Pheromone traps are becoming increasingly widely used for "monitoring" populations of economically import ant lepidopterous pests. In reality the traps may do no more than detect the presence or absence of pests, though their use becomes more sophisticated when trap catches are used in conjunction with the summation of heat units to predict various temporal occurrences of life history features, and provide more effective timing of insecticide applications. Thus pheromone traps have been used to show moth emergence (e.g. Dean S c Roelofs, 1970; Batiste, Berlowitz, Olson, Detar Sc Joos, 1973; Hagley, 1973; Minks S c De Jong, 1975; Riedl, Croft Sc Howitt, 1976; Bailey, 1980; Baker, Card6 S c Croft, 1980; Glen Sc Brain, 1982) or predict peak flight (e.g. Madsen & Peters, 1976; Baker, Shelton Sc Andaloro, 1982; Potter S c Timmons, 1983) . In all but one of these cited studies, the species involved was a pest of perennial fruit orchards, consequently monitoring was aimed at detecting emergence in the resident population, with the possibility of compounding effects due to immigrants. There appear to have been fewer studies devoted to 74 monitoring pests of annual crops (e.g. Saario, Shorey & Gaston, 1970; Baker et al, 1982; Henneberry & Clayton, 1982), although since pheromone traps are used to detect only immigration, interpretation of the trap catch should in theory, be more simple. The majority of authors however, have used the traps with no indication as to how trap catches relate to the density of adult insects in the field, although they frequently relate them to other estimates (e.g. subsequent damage levels at harvest, larval counts, overwintering egg masses etc.). This failing was noted by Stinner et al_ (1983) "The major problems that were perceived early in the history of these devices still plague entomologists i.e. the relationship (s) between trap catch and either ambient or in field densities of insects present. Even though researchers still use these types of devices in an 'early warning' capacity for invading pest species, it is clear that trap to actual density conversions have not been the subject of sufficient experimentation. Since most crop protection researchers want to use these devices as indicators of an approaching pest problem, lack of ability to make these conversions remains a monumental problem." They subsequently concluded that the possibilities for developing predictive models of insect pest movements are bleak. This study is one of the first attempts to resolve these relationships, since density determinations by independent sampling techniques (suction and netting) allow critical examination of the accuracy with which sex- attractant traps reflect population density and quantitative change, both in the emergence site and the pea crop. One feature crucial to the accuracy of this particular predictive system is the relationship between trap catches of males and the spatial and temporal distribution of females. The chapter first describes the spatial and temporal patterns of dispersion in emergence sites and pea crops. Patterns of dispersal from emergence sites to pea crops are then described, followed by the relationship between these various patterns and other factors. 75 3.2. Dispersion 3.2.1. Spatial Patterns of Dispersion in the Emergence S ite The spatial pattern of adult moths in the emergence site could result both from emergence and from movement within and about the crop. Both sexes showed aggregation at high densities, and within the confines of the crop itself, aggregation may have been concentrated in the centre of the field. The numbers of males (n = 11) and females (n = 3) caught with a D-Vac. in the crop at the 1980 emergence site were low, and only 13 males and no females were caught over the crop with a kite net (Appendices IIa & lib). These low densities do not merit critical examination, and aggregation would not be expected at such population densities. When organisms are arranged randomly, the variance 2 _ (S ) and the mean (x) are interdependent and equal. The ratio of the variance to mean has been used as an indicator of distribution; where the variance is larger than the mean, the distribution is contagious or clumped (Southwood, 1978). When the variance and mean of a series of samples from a natural population are plotted, they tend to increase together, and the relationship has been shown by Taylor (1961) to obey the power law: S = ax (r) where 'a1 and *b1 are constants; the latter is an index of aggregation characteristic of the species. Since, from (i) Log S 2 = Log a + b , Log x _ then the parameter 'b1 is the slope of a line fitted 2 _ through a series of points of Logs against Log x . If the slope 'b1 is significantly different from 1, that being the slope of the line of equality given by the Poisson series 2 - where S = x, it can be concluded that the organisms are aggregated at certain densities, though not at lower 2 _ densities where the line Logs = Log a + b Logx approaches the line S 2 = x. - The departure of the individual dispersion indices (variance : mean ratios) from unity can be tested by: 76 x where "X.^ has (n - 1) degrees of freedom (Bliss & Fisher, 1953). When samples are taken from a grid however, as in this study (rather than randomly) this test is not sufficient to determine the randomness of the distribution (Usher, 1971), since high counts may be grouped together in adjacent samples. If a gradient of numbers exists across the field, this can be tested by analysis of variance, only if the spatial position of the samples is known, and could not be shown with a completely random sampling technique (Usher, 1969) . Although the value can indicate an aggregated distribution, it cannot show whether this is caused by one large aggregation somewhere in the field, or by many small aggregations (e.g. single sampling points) and therefore a reflection of variance. The Log variance/Log mean relationship was determined for three differently aged populations of males and females within the confines of the crop in the emergence sites of 1981 and 1982. The slope 'b' of the line fitted through the total male population in 1981 (fig.3.la.) was not significantly different from 1 (t = 1.675, NS, 5df) while that for 1982 was (fig.3.2a.) (t = 6.758, p<0.01, 5df). For females the slope was significant both in 1981 (fig.3.3a.) (t = 2.811, p < 0.05, 5df) and 1982 (fig.3.4a.) (t = 2.801, p<0.05, 4df) . When the variance/mean points were plotted for both seasons, the slope was significant for males (fig.3.5a.) (t = 3.809, p<0.01, 12df) and females (fig.3.5b.) (t = 4.185, p<0.01, lldf) • These results indicate that C.niqricana is aggregated at higher densities, but for the majority of the season when populations are at low densities, the distribution is random. It is a feature of low density populations that even with a large number of samples the distribution tends to conform to the Poisson series (S = x), rather than becoming regular (S x) . This is clearly shown by this data, where two thirds of the points plotted on figs.3.la. to 3.4a., lie along the line of equality. The position of the point for males, week 4 in 1981 (fig.3.1a.), shows that the distribution in this week was atypical for natural 77 Fig . 3.1. Relationship between log variance and log mean of populations of male C.nigricana, wheat field emergence site, Shimpling Park Farm, 1981 y axes: Log^Q S 2 where S 2 = variance x axes: Lo9go x where x = mean number of moths per sample a) Total male population b) Male population below physiological age (P.A.) 10 c) Male population below P.A. 7 Numbers by points refer to weeks in the 1981 season. Variance and mean calculated from weekly D-Vac. samples from perimeter and centre of wheat crop. a) L°gi0 b ) L°gi0 C ) L°gio 78 Fig . 3.2. Relationship between log variance and log mean of populations of male C.nigricdna, wheat field emergence site, Shimpling Park Farm, 1982 y axes: Log^ S 2 where S 2 = variance x axes: Log^ x where x = mean number of moths per sample a) Total male population b) Male population below physiological age (P.A. ) 10 c) Male population below P.A. 7 Numbers by points refer to weeks in the 1982 season. Variance and mean calculated from weekly D-Vac. samples from perimeter and centre of wheat crop. c) Logic 79 Fig. 3.3. Relationship between log variance and log mean of populations of female C.nigricana, wheat field emergence site, Shimpling Park Farm, 1981 y axes: Log^^ S 2 where S 2 = variance x axes: Log-^ * where x = mean number of moths per sample a) Total female population b) Female population below physiological age (P. A. ) 10 c) Female population below P.A. 7 Numbers by points refer to weeks in the 1981 season. Variance and mean calculated from weekly D-Vac. samples from perimeter and centre of wheat crop. 80 Fig. 3.4. Relationship between log variance ctnd log mean of populations of female C.nigricana, wheat field emergence site, Shimpling Park Farm, 1982 2 2 y axes: Lo9i0 s where S = variance x axes: Lo<0]_o * where x = mean number of moths per sample a) Total female population b) Female population below physiological age (P.A.) 10 c) Female population below P.A. 7 Numbers by points refer to weeks in the 1982 season. Variance and mean calculated from weekly D-Vac. samples from perimeter and centre of wheat crop. 4 a) L°gi0 b ) Logio c) L o g io L ° g 1 0 x 81 Fig. 3.5. Relationship between log variance and log mean of populations of C.nigricana in wheat field emergence sites, Shimpling Park Farm, 1981 & 1982 2 2 y a x e s : L o <3]_q s where S = variance x axes: Log^Q x where x = mean number of moths per sample a) Total male populations b) Total female populations Solid symbols ( •) 1981 weeks Open symbols ( o ) 1982 weeks Logio x 82 populations, with a comparatively high mean, but very low variance (c.f. week 7, 1981). Data analysis for 1982 utilised all ten of the sample points from the crop area of field WA2, although only seven of these were under peas the previous season. This was because field WA2 comprised the area of pea fields PAl, PBl and a crop of broad beans in 1981 (Section 2.1.2.). C.nigricana was not expected to emerge from the area that had been under beans, since these are reported to be un attacked (Bradley et al, 1979) although they may be util ised according to Niezgodzinski (1965). In week 9 however, one pupal exuvium and one partially emerged adult attached to its exuvium, were found at a sample point from within this area, some 25m. from the nearest area under peas. Only low numbers of moths were caught in the three sample points, excluding them from calculations raises the mean and the variance, but does not alter the significance of any test. Analysis of variance did not demonstrate any gradient at the highest density in the crop in week 6, 1981, when the data and spatial position of the samples were represented on a map of the field (fig.3.6.). An analysis is not possible with the 1982 data, because of the small number of sample points, however the data may still be represented on a field map (fig.3.7.). Only in one week in both 1981 and 1982 (though weeks 5 and 6 were not sampled in 1982) did the variance : mean ratio of females significantly depart from unity; week 6 i n 1 9 8 1 (')(2 = ‘88.73, p<0.001, 19df) and week 4 in 1982 ( ‘)^ 2'= 57.51, p<[0.01, 9df) . Thus in both years females were only at sufficiently high density in the crop to show aggregation for one week, whereas males attained higher densities and were aggregated for periods of three or four weeks. This reflects the higher number of males caught in the emergence site. In both years the slope ‘b 1 of the regression line decreased as the oldest male moths were successively removed from the calculations (figs. 3. la - c., 3.2 a - c.). This suggests that emergence itself follows a random distribution in space. For females the slope only decreased when the very oldest moths were excluded, but did not show 83 Fig. 3.6. Spatial distribution of populations of C.nigricana in the perimeter and centre of the crop in the emergence site, Shimpling Park Farm, 1981 Positions on field map show the centre of the 150m. (2 x 75m. tramlines) D-Vac. sample points, with the numbers of males (first) and females caught with a D-Vac., at the time of peak density in week 6. 200 m. L J 84 F iq . 3.7. spatial distribution of populations of C.niqricana in the perimeter and centre of the crop in the emergence site, Shimpling Park F a r m , 1 9 8 2 Positions on the field map show the centre of the 150m. (2 x 75m. tramlines) D-Vac. sample points with the numbers of males (first) and females caught with a D-Vac., in w e e k 4. A 100 m. L j 85 further decline (figs.3.3a - c., 3.4a - c.). However for both sexes in high density weeks, even the youngest moths appear to have been aggregated: W e e k 6 1 9 8 1 d d P . A . 7 X 2 = 83.79, p<0.001, 19df 99 p .a .7 y 2 = 64.41, p<0.001, 19df W e e k 4 1 9 8 2 dcf P . A . 7 X 2 = 29.88, p<0.00l, 9df 99 p . a . 7 X 2 = 32.40, p<0.001, 9df This suggests that C.nigricana may be aggregated at or very soon after emergence at high density. Aggregation exhibited by the young moths was probably due to adult movement subsequent to, and immediately after emergence. It is however, also possible that adults were aggregated on emergence, and that therefore the cocoons were contagiously distributed in late spring. This could arise both from aggregated oviposit ion by females the previous season, and by differential survival of overwintering larvae, inversely related to density. >\, 2 As discussed above a significant value of x does not distinguish between a number of small aggregations (e.g. single sample points with high catches) and one large aggregation (e.g. several sample points with high catches associated with each other). The spatial position of the sample points at high density weeks must be examined. In 1981, week 6, the largest catches of males and females occurred at the same sample positions, and these points appear to be associated together in the South and East of the field, but apparently not in the perimetal area (fig. 3.6.). Although a gradient across the field was not indicated by analysis of variance, the mean number of moths from central samples was consistently greater than that from the perimeter at higher densities. There is a significant F value for both males (F = 8.306, p<0.01, 1 Sc 18df) and females (F = 16.255, p <0.005, 1 & 18df) , when these two crop areas are compared for week 6, 1981. In 1982 the larger catches of both sexes also occurred at the same sample points in the West of the field (fig.3.7.). As in 1981 these larger catches did not occur in the perimetal area of the crop, although much of the eastern part of the field was not under peas in the previous season. 86 There is high variance in both the perimeter and the centre when this eastern area is included, and there is consequently a low variance ratio. Analysis of the variance of samples drawn from only the area under peas (in 1981) gives a significant ratio for males (F = 7.23, p<0.05, 1 & 5df) but not for females (F = 5.146). for variance ; mean ratios of males and females taken over the crop in 1981 with a kite net, gave a significant value for males in all three weeks, but not for females; this reflects the much higher density of males in the aerial population. However the high ratio was reflecting only the variance, and analysis of variance did not demonstrate any difference between the perimeter and centre, though there was some tendency for higher catches (= aggregation) in the South and East of the field in week 6 (f ig . 3 .8.) . When not active, both sexes at high densities, appear to be aggregated in the centre of the crop. Within the limits of the crop, there is no indication that moths accumulate on headlands prior to dispersing to pea fields. Data suggests that moths became aggregated soon after emergence, and this implies that both sexes are very active, moving around within the crop over relatively long distances (e.g. 200 - 300m.). Thus moths may be capable of leaving the crop soon after emergence also. The apparent aggreg ation in the field centre may have been due- to movement of moths to preferred resting sites in the surrounding veget ation, although the distribution still requires that some moths prefer to remain in the centre of the field. In 1981 the peak density in the surrounding vegetation was at the same time as in the crop (Section 3.2.2.) and this does imply rapid emigration. There may however be no justific ation for distinguishing between the perimeter of the crop and the thin strip of surrounding vegetation, in that the latter demarcates the edge of the headland. The relation ship between D-Vac. samples in hedgerows and those in other habitats is unknown, but those from the understorey and grassbank have been shown to be directly comparable to those in the crop (Section 2.1.12.). If the catches from the grassbank and understorey around field WAl in week 6 87 Fig . 3.8. Spatial distribution of aerial populations of C.nigricana over the perimeter and centra of the crop in the emergence site, Shimpling Park Farm, 1981 Positions on the field map show the centre of the 150m. (2 x 75m. tramlines) kite net sample points with the number of males (first) and females caught with a kite net. a) W e e k 5 b) W e e k 6 200 m. L J 88 are included as a further 10 replicates of perimeter (= head land) , analysis of variance no longer gives a significant F-value for either sex when the centre and perimeter are compared (males F =0.387, NS, 1 & 28df; females F = 3.708, NS, 1 & 28 df). Similarly in 1982 when the catches from the grassbank around WA2 in week 4 are included (although one sample point was unsampled) , the higher density in the centre is no longer indicated, because of the large variance in the grassbank samples. When the spatial position and catch size of the 1981 understorey and grassbank samples is included on a map of the 1981 emergence site (fig.3.9.), the highest densities are found in the eastern half of the field. Analysis of variance on four groups (fig.3.10a.) reveals a gradient of increasing density running from West to East, although other gradients, e.g. SW to NE (five groups) could not be demonstrated (fig.3.10b.). Although there are insufficient sample points to test for gradients across the 1982 emergence site, sample Gl on the northern headland consist ently showed much greater catches than any other grassbank sample. The adjacent perimeter sample P2 usually had the greatest catch from the perimeter (fig.3.11a.& b.). This indicates that moths may have had a directional aspect to their spatial distribution, tending to accumulate in the East in 1981 and strongly aggregated in the North in 1982. 3.2.2. Temporal Patterns of Pispersion in the Emergence S it e Both sexes of C.nigricana showed peak emergence and peak density at the same time in the middle of the season; protandrous emergence was exhibited. The low numbers caught with a D-Vac. and a kite net at the 1980 emergence site do not permit critical examina tion, but when the data was pooled, for males at least there were four weeks at similar densities, then increase to peak density in week 7, followed by rapid decline (fig.3.12a.). The data for temporal distributions in the crops of the 1981 and 1982 emergence sites are given in figs.3.13. and 3.14.; the data are incomplete because of problems during the sampling programme. Wet weather 89 F ig . 3.9. Spatial distribution of populations of C.nigricana in and around the emergence site, Shimpling Park Farm, 1981 Positions on the field map show the centre of the 150m. (2 x 75m. tramlines) D-Vac. sample points with the numbers of males (first) and females caught with a D-Vac., at the time of peak density in week 6. 11*2 i i 37*16 23*15 7 H 3 24*18 17*13 11*6 66 U 25 6*2 21* 7 1 5 *6 2 8 *5 200 m. L J 90 Fiq. 3.10. Analysis of variance for density qradients of C.niqricana populations across the emerqence site, Shimplinq Park Farm, 1981 • Calculations based on D-Vac. catches from Understorey, Grassbank, Perimeter a n d Centre of crop. a) W e s t to East qradient Males ANOVA S o u r c e SS d f M S V-ratio Tabulated F at p = 0.05 at G r o u p 2 0 9 3 . 6 5 9 3 6 9 7 . 8 8 6 4 . 4 6 3 3 & 2 6 d f . R e s i d u a l 4 0 6 5 . 7 0 8 2 6 1 5 6 . 3 7 3 2 . 9 7 5 T o t a l 6 1 5 9 . 3 6 7 2 9 F e m a l e s ANOVA S o u r c e SS d f M S V - r a t i o Tabulated F at p = 0.05 at G r o u p 4 0 4 . 3 8 4 3 1 3 4 . 7 9 5 3 . 7 4 2 3 Sc 2 6 d f . R e s i d u a l 9 3 6 . 5 8 3 2 6 3 6 . 0 2 2 2 . 9 7 5 T o t a l 1 3 4 0 . 9 6 7 2 9 b) Southwest to Northeast q r a d i e n t , t h a t i s towards the peas Males ANOVA S o u r c e SS d f MS V - r a t i o Tabulated F at p = 0.05 at G r o u p 1 6 7 3 . 5 7 6 4 4 1 8 . 3 9 4 2 . 3 3 2 4 & 25 d f . R e s i d u a l 4 4 8 5 . 7 9 1 2 5 1 7 9 . 4 3 2 2 . 7 5 9 T o t a l 6 1 5 9 . 3 6 7 2 9 F e m a l e s ,ANOVA S ou r c e SS d f MS V - r a t i o Tabulated F at p = 0.05 at G r o u p 3 8 0 . 5 5 1 4 9 5 . 1 3 8 2 . 4 7 7 4 & 2 5 d f . R e s i d u a l 9 6 0 . 4 1 6 25 3 8 . 4 1 7 2 . 7 5 9 T o t a l 1 3 4 0 . 9 6 7 91 > Z 92 Fiq . 3.11. spatial distribution of populations of C.niqricana in and around the emergence site, Shimplinq Park Farm, 1982 Positions on the field maps show the centre of the 150m. (2 x 75m. tramlines) D-Vac. sample points with the numbers of males (first) and females caught with a D-Vac. N a) W e e k 4 i i 3C *10 6 * 3 i 2 * 3 5 * 2 1 4 * 2 0 1 7 * 1 3 -- B e a n s — 1*0 2 * 1 1 0 * 4 (1981) ,| 5*4 1 0 * 5 2 * 3 11 b) W e e k 7 1,— V 2 7 * 1 3 4 *0 if ' 1 0 * 3 i! \ 0*2 0*0 •l 2 4 * 4 ■ B e a n s - -- “i i 1*0 2 * 1 5 * 4 1 1 * 3 ( 1 9 8 1 ) 3 * 2 3 * 0 \ 3 * 0 1*1 II) II s II 0*2 \ n ■ ^ L 100 m. L J 9 3 Fig . 3.12. Temporal distribution of C.niqricana in the crop at the emergence site, Childerley Estate, 1980. Histograms show weekly catch expressed as a percentage of the seasonal total. Data pooled for moths taken with a D V a c . and a kite net *///!!). .D- Weeks numbered through the season commencing Monday 26 t h M a y . a) M a l e s b) F e m a l e s a ) *1 £ O H b ) WEEK 94 Fig . 3.13. Temporal distribution of populations of C.niqricana in the crop at the emergence site, Shimpling Park Farm, 1981 Histograms show weekly catch expressed as a percentage of the seasonal total. Weeks numbered through the season commencing Monday 25 May. a) Males : Total population in the perimeter and centre of t h e c r o p b) Females : Total population in the perimeter and centre of the crop c) Males : Population below physiological age (P.A.) 10 in the crop d) Females : Population below P.A. 10 in the crop Percentage of weekly total below P.A. 10 e) Males : Population below P.A. 7 in the crop f) Females : Population below P.A. 7 in the crop Percentage of weekly total below P.A. 7 n = seasonal total of population, calculated from extrap olated and interpolated data, where sampling was incomplete. <1 H W u Ph WEEK 95 Fig. 3.14. Temporal distribution of populations of C.nigricana in the crop at the emergence site, Shimpling Park Farm, 1982 Histograms show weekly catch expressed as a percentage of the seasonal total (not including estimates for weeks 5 Sc 6) Weeks numbered through the season commencing Monday 2 4 ^ May a) Males : Total population in the perimeter and centre of t h e c r o p b) Females : Total population in the perimeter and centre of the crop c) Males : Population below physiological age (P. A. ) 10 in the crop d) Females : Population below P.A. 10 in the crop Percentage of weekly total below P.A. 10 e) Males : Population below P.A. 7 in the crop f) Females : Population below P.A. 7 in the crop Percentage of weekly total below P.A. 7 n = seasonal total of population, calculated from extrap olated and interpolated data (except in weeks 5 & 6), where sampling was incomplete. s $ £ o E -r x W WEEK 96 towards the end of the 1981 season, and at the middle of the 1982 season, caused compaction of damp soil on the wheel and underside of the D-Vac. tramline attachment, and prevented sampling in crops. Although use of a D-Vac. was not prevented in the surrounding vegetation (unless it was raining) efficiency was undoubtedly impaired, since insects became stuck in a water film inside the extension piece. The missing value for week 9 in 1981 was interpolated as described in Section 2.2.5., and used in calculations of the total for the season. The missing values for weeks 5 and 6 in 1982 are far more critical, and may account for up to 50% of the season's potential total catch. There were no a priori reasons for assuming the same temporal distribu tion as 1981, although the distributions in the surrounding vegetation, described later, do suggest this. Weekly percentages for 1982 were therefore calculated from the numbers caught and do not include any estimates for missing v a l u e s . In the wheat crop in 1981 both sexes showed a peak density in the middle of the season at week 6 (fig.3.13a. & b. ) . The peak mean numbers of moths per crop sample (= per unit area) in this field were : males 12.6 * 2.12 (S.E.); females 6.5 t. 1.23. This peak was preceded by a trend of increasing density and followed by a steady dec line (fig.3.13a. Sc b.). In the first four weeks of 1982, moth densities in the crop showed a steady increase; in weeks 7 - 9 densities decreased (fig. 3.14a. Sc b . ) . T h e s e trends in the *1982 emergence site indicate that a peak density was attained between weeks 4 and 6. Although no independent estimate is available, population densities per unit area may have been similar between 1981 and 1982. The peak mean density per sample in the vegetation surrounding the emergence sites in 1981 and 1982 was similar (Table 3.1.)• If this indicates that densities in the emergence sites were similar in the two years, and emergence of both sexes was earlier (fig. 3.15a. Sc b.), then peak population density in the 1982 crop would have been in week 4 or 5. This is supported by temperature data; higher daily mean temperatures during the early weeks of the 1982 season would have increased development rates of pupae, and 97 Table 3.1. Peak density of C.niqricana in vegetation surrounding emerqence sites, Shimplinq Park Farm, 1981 and 1982 Peak mean number of moths per sample* in vegetation surrounding emergence site. 1 9 8 1 1 9 8 2 N u m b e r o f M e a n N u m b e r o f M e a n S a m p l e s C t s . E . ) S am p l e s ( ± S . E . ) M a l e s 1 0 21.1 1 6.64 5 14.2 t 8 . 6 3 F e m a l e s 1 0 7 . 9 t 2 . 8 9 5 1 0 . 8 t 5 . 0 6 * Grassbank and Understorey samples only. 98 Fig . 3,15. Density of C.nigricana in the emergence sites, Shimpling Park Farm, 1981 and 1982 Mean and standard errors calculated from weekly samples of moths caught with a D-Vac. Number of samples is the number taken per week from the perimetal and central areas of wheat crops. Data points for 1982 calculated only from those sample points that were under peas in 1981. a) Male populations b) Female populations NUMBER 1981 0 10 10 20 5 20 17 cw SAMPLES 1982 7 7 7 7 0 0 WEEK 99 lead to earlier emergence. Peak density in mid-season could be caused by progressive population accumulation/ with low death and emigration rates, and by mass emergence over a short period. Since moths with a higher P.A. value are older (Section 2.1.9.), and may have been at the emergence site for one week or more, they are not a component of the newly emergent population. The peak densities of males and females in week 6 in 1981 are still evident when two sub-populations of physiologically older moths are excluded from calculations (figs.3.13c. -f.). Therefore not only does peak population density occur in week 6, but also peak emergence of both sexes. When physiologically older moths are excluded from 1982 populations, the profile of the seasonal histograms is not altered (figs.3.14c. - f.) indicating that peak emergence probably occurred at the same time as peak density. Additional evidence for earlier emergence in 1982 is provided by the lines plotted on figs.3.13c. - f. and 3.14c. - f., showing the weekly percentage of moths below a given P.A. level. Comparison of respective pairs of these figures shows an earlier decline in 1982, although the shape is essentially the same, at least for males. The displacement is one to two weeks for males and two to three weeks for females. Figs.3.13a. Sc b. suggest that the species has protandrous emergence, since although more males than females were caught at the emergence site, proportionately more of the male population were caught earlier in the season. In 1981, 35% (n = 229) of the seasonal male catch was taken before week 6, compared with 13% (n = 35) of the seasonal female population. This is confirmed clearly by moths below P.A. 7 (figs.3.13e. Sc f.), where 47% of the male population (n = 165) were caught in the first five weeks, compared with only 16% (n = 31) of the newly emergent female population. a s the season progressed, particularly after week 6, the proportion of young moths in the male population decreases more rapidly than in the female population (figs.3.13e. Sc f.). Thus at the end of the season in week 10, only 7% of males were below P.A-7, compared with 50% of the females, although moth numbers 1 0 0 were low by this time. Despite the incomplete series in 1982, protandry is still evident. In the first three weeks, 86% of males and 82% of females were below P.A. 7 and newly emerged, but more than four times as many males (n = 62) as females (n = 14) were caught, representing 59% and 2 7% respectively of the seasonal total. The peak population density of males at week 6 in the crop in 1981 was clear in both subdivisions of the crop, although densities differed (figs.3.16b. & c.). Female density peaked in week 6 in the centre (f ig.3.17b.) , but remained at peak density for weeks 6 and 7 in the perimeter (fig.3.17c.). In the vegetation around Field WAl both sexes were at peak density in week 6 (figs.3.16d. & 3.17a.) at the same time as in the crop. This peak was shown in all subdivisions of the habitat (figs.3.16e. Sc f . , 3 . 1 7 e . - g.), except for males in the hedgerow (f ig. 3.16g.), where a plateau of density was attained for weeks 5 to 7. There were some anomolous catches of females in the gras^- bank (fig.3.17e.) but these may have been artefacts of low density. Peak densities were preceded by gradual increase and followed by decline in density. Proportionately more of the male seasonal total (34.2%) than that for females (25.3%) was caught in weeks 2 to 5, although the difference is not as marked as in the crop. Kite net samples were taken only at the 1981 emergence site in weeks 5 to 7; before and-after this period the occurrence of fine weather during the activity period was variable and unpredictable. In the populations flying over the crop, the peak density in week 6 indicated by the D-Vac. samples was not apparent for either sex (figs.3.18a. Sc 3.19a.), or subdivisions of the crop (figs. 3.18b. Sc c., 3.19b. Sc c.), rather there was a con sistent trend of lower density in .week 6, compared to weeks 5 and 7. Male mean density per sample was not significantly different between the three weeks in the two areas of the crop, suggesting that the density of moths flying above the crop is independent of peak population density and peak emergence. Female mean density was not different between weeks over the whole crop, or over the centre, but density over the perimeter in week 7 was significantly 1 0 1 Fig. 3.16. Temporal distribution of populations of male C.nigricana in and around the emergence site, Shimpling Park Farm, 1981 Histograms show weekly catch expressed as a percentage of the seasonal total. Weeks numbered through the season commencing Monday 2 5 ^ May. a) Total crop population from perimetal and central regions b) Crop central population c) Crop perimetal population d) Total surrounding vegetation population e) Grassbank population f) Understorey population g) Hedgerow population n = seasonal total of population, calculated from extrap olated and interpolated data, where sampling was incomplete. WEEK 1 0 2 Fiq. 3.17. Temporal distribution of populations of female C .niqricana in and around the emergence site, Shimplinq Park Farm, 1981 Histograms show weekly catch expressed as a percentage of the seasonal total. Weeks numbered through the season commencing Monday 25 May a) Total crop population from perimetal and central regions b) Crop central population c) Crop perimetal population d) Total surrounding vegetation population e) Grassbank population f) Understorey population g) Hedgerow population n = seasonal total of population, calculated from extrap olated and interpolated data, where sampling was incomplete. d) n - 2 9 6 a d t u x WEEK 103 Fig . 3.18. Temporal distribution of aerial population of male C.niqricana over and around the emergence site, Shimpling Park Farm, 1981 Histograms show weekly catch expressed as a percentage of a three week total. n d Weeks numbered from week 5, commencing Monday 2 2 June. a) Total crop population over perimetal and central regions b) Crop central population c) Crop perimetal population d) Total surrounding vegetation population e) Grassbank population f) Understorey/Hedgerow population n = total population for weeks 5 to 7. WEEK 104 Fig . 3.19. Temporal distribution of aerial populations of female C.nigricana over and around the emergence site, Shimpling Park Farm, 1981 Histograms show weekly catch expressed as a percentage of a three week total. Weeks numbered ftom week 5, commencing Monday 22 June. a) Total crop population over perimetal and central regions b) Crop central population c) Crop perimetal population d) Total surrounding vegetation population e) Grassbank population f) Understorey/ Hedgerow population n = total population for weeks 5 to 7. 5 8 7 5 0 7 WEEK 105 higher than week 6 (t = 2.53, p<0.05, 12df) . In contrast, both the sexes showed a peak of density in week 6 over the surrounding vegetation (Figs.3.18d. & 3.19d.) although differences were not significant because of the high variance. This peak was attributable to populations in the area of the hedge/understorey (figs.3.18f. Sc 3 . 1 9 f . ) , since the populations over the grassbank showed similar densities in all three weeks, and the temporal distribu tions were more like those of the population over the crop (figs.3.18e. Sc 3 . 1 9 e . ) . D-Vac. catches in the vegetation surrounding field WA2 indicated that both sexes showed an increase in density with a peak in week 6 (Table 3.1.) which was followed by a more rapid decline (figs.3.20d. & 3-21d.). Peak density was thus one to two weeks later than the predicted time of peak density in the crop. In the laboratory, within a 24hr. period, more C.niqricana emerged overnight or in the early morning (2200 - 1000), than during the day, in a constant environment (dark period 2400 - 0600). Freshly emerged moths were found in the morning (0800), indicating that emergence may be around dawn. 3.2.3. Spatial Patterns of Dispersion in the Pea Field Since there is no resident population of C.niqricana in pea crops, spatial distribution in the surrounding vegetation will reflect the direction from which moths have migrated. If migration were unidirectional, the population would be aggregated over a whole range of d e n s i t i e s . In 1980 only 11 moths were caught in the hedgerow around the pea field; eight of these were caught in the southern half of the field. This suggests a directional immigration which will be further described in the section on dispersal (Section 3.3.) The slope 'b' of Taylor's Power Law was calculated for populations of males and females in the surrounding vegetation of the three pea fields PAl (1981), PA2 and PB2 (1982). For males the value of 'b' was not signific antly different from 1 (t = 1.53/ NS, 17df) (fig.3.22a.), largely because males were at lower densities, and as 106 Fig. 3.20. Temporal distribution of populations of male C.niqricana in and around the emergence site, Shimpling Park Farm, 1982 Histograms show weekly catch expressed as a percentage of the seasonal total (not including estimates for weeks 5 & 6 in crop regions). Weeks numbered through the season commencing Monday 2 4 ^ May. a) Total crop population from perimetal and central regions b) Crop central population c) Crop perimetal population d) Surrounding vegetation (i.e. Grassbank) population n = seasonal total of population, calculated from extrap olated and interpolated data (except weeks 5 & 6 in a - c), where sampling was incomplete. WEEK 107 Fig . 3.21. Temporal distribution of populations of female C.nigricana in and around the emergence site, Shimpling Park Farm, 1982 Histograms show weekly catch expressed as a percentage of the seasonal total (not including estimates for weeks 5 & 6 in crop regions. Weeks numbered through the season commencing Monday 24 t h May. a) Total crop population from perimetal and central regions b) Crop central population c) Crop perimetal population d) Surrounding vegetation (i.e. Grassbank) population n = seasonal total of population, calculated from extrap olated and interpolated data (except weeks 5 & 6 in a - c) , where sampling was incomplete. WEEK 108 Fig. 3.22. Relationship between log variance and log mean of populations of C.nigricana in vegetation surrounding the pea fields/ Shimpling Park Farm, 1981 and 1982 y axes: Log^ S 2 where S 2 = variance x axes: Lo9go * where x = mean number of moths per sample a) Male population in surrounding vegetation b) Female population in surrounding vegetation Numbers by points refer to weeks in the seasons, • Field PAl, 1981 ■ Field PA2, 1982 □ Field PB2, 1982. Variance and mean calculated from weekly D-Vac. samples from surrounding vegetation samples (Understorey, Grassbank and Adjacent Beans only) 109 discussed above (Section 3.2.1.) low density populations tend to follow a Poisson distribution. The intercept 'a' was significantly greater than zero (t = 2.66, p<0.05, 17df), indicating that males may have been aggregated at some densities. Although females were also at low densities for several weeks over the two seasons, the slope of the fitted line was significant (t = 3.42> p<0.01, 16df) (fig. 3.22b.) and the intercept was also significant (t = 3.25, p<0.01, 16df). This indicates that females were aggregated over a wider range of densities in the surrounding vegetation. When catches from the whole fields were included, both the slope and intercept gave t-values of higher significance for males (slope : t = 4.13, p < 0.001, 15df ; intercept : t = 8.31, p < 0.001, 15df) (fig.3.23a.) and females (slope : t = 5.69, p < 0.001, 16df ; intercept : t = 7.39, p <0.001, 16df) (fig.3.23b.). Thus although males did not achieve such high densities as females during weeks of peak density in pea fields, both sexes were aggregated in these fields. In 1981 the first moths were caught in weeks 3 and 4 along the South and West boundaries (fig.3.24a.), immediately adjacent to the emergence site WAl (fig.2.2.). In week 6 the highest densities of males were taken from the hedge in the West (18 moths), the grassbank in the North (14) and the beans in the East (13) (f ig. 3.24b.) . In contrast females showed the highest density in the grassbank (20) and beans (12), but low density in the hedgerows next to the emergence site (fig.3.24b.). At the time of peak density in this field (week 7), both sexes were strongly aggregated in the grassbank (fig.3.24c.). In the crop, males remained at low density throughout, but the largest catches were on the western and northern perimeters adjacent to the highest densities in the surrounding vegetation (fig.3.24c.). Females attained higher mean densities in the crop, but only in the perimetal area. The central area was characterised by low densities, except for sample point C14, part of which lay very near the northern headland, where the catch (21 moths) in week 7, exceeded that in all perimetal samples (fig.3.24c.). In the vegetation around field PA2, the largest 110 Fig . 3.23. Relationship between log variance and log mean of populations of C.nigricana in and around the Pea fields, Shimpling Park Farm, 1981 and 1982 2 2 y axes: Lo9]_o S where S = variance x a x e s : L o 9]_q x where x = mean number of moths per sample a) Male population in crop and surrounding vegetation b) Female population in crop and surrounding vegetation Numbers by points refer to weeks in the seasons, •Field PAl, 1981 ■ Field PA2, 1982 □ Field PB2, 1982 Variance and mean calculated from weekly D-Vac. samples from perimetal and central region of crop, and surrounding vegetation (Understorey, Grassbank and Adjacent beans). I l l Fiq . 3.24. spatial distribution of populations of C.niqricana in and around the pea field, Shimp ling Park Farm, 1981 Positions on the field map show the centre of the 150m. (2 x 75m. tramlines in crop regions) with the number of males (first) and females caught with a D-Vac. a) W e e k 4 b ) W e e k 6 c) W e e k 7 b) L 100 m. 3 4 *4 3 ^------r ‘ _ - < 7" i c) r— 3 .2 1 | 6 . H 2*2 • l »l2#17j10 *10 1* 2 4 H 1 4 U 3 1 1 2 accumulation of immigrant moths occurred along the grass- bank in the South (fig.3.25a. & b.) which was shared with the emergence site WA2 (fig.2.3.). In addition similar densities were attained along the vetchbank in the East (f ig. 3.25b.) , presumably due to the emergence of the resident population. Moths were not caught at other sample points in the surrounding vegetation before week 7, and thereafter only in very low numbers. Of four males and four females, only one was caught at a point on the other side of the crop furthest from the emergence site, the remainder being caught on the southern edge of the field adjacent to the grassbank sample with the highest densities. The highest density of either sex in the crop was along the perimeter adjacent to this grassbank (fig.3.25b.). Males remained aggregated along this soutnern boundary, but females were dispersed across the field at peak density in week 7 (fig.3.25b.) (males 3.7 ± 2.06; females 14.4 1 1.15). Both sexes showed a tendency for higher density in the perimeter as compared to the centre : Perimeter of crop Centre of crop M a l e s (x ± S.E.) 6.5 ± 3.91 1.0 ± 0. 4 5 Females (x i S.E.) 6.0 1 2.00 2.8 1 0.80 Since moths were not caught in the surrounding vegetation adjacent to the perimetal sample points furthest from the emergence site, moths probably accumulated on this perimeter after flying over the centre of the crop from the concentr ation in the South, and not by omnidirectional immigration. After week 7 the population level rapidly declined with higher densities remaining in the perimeter in week 8 ; Perimeter of crop Centre of crop M a l e s (x t S.E.) 1.8 t 0.97 0.4 t 0.25 Females (x t S.E.) 3.2 t 2 . 2 7 1 . 6 t 0. 6 0 and with the greatest proportion of the whole population remaining in the crop: weeks 8 and 9, males 74% (total n = 19), females 91% (n = 33). In the vegetation around field PB2 the initial accumulation of males was in the Southeast while for females it was in the Northwest (fig.3.26a.). At the time of peak density in week 7, males were at similar 113 Fig . 3.25. Spatial distribution of populations of C.niqricana in and around pea field PA2, Shimplinq Park Farm, 1982 Positions on the field map show the centre of the 150m. D-Vac. sampling points, with the number of males (first) and females. a) Week 3 : All sample points b) Week 4 : Grassbank and perimetal sample points c) Week 6 : Grassbank sample points d) Week 7 : All sample points N r A 4 1 1 115 Fiq. 3.26. Spatial distribution of populations of C.nigricana in and around pea field PB2, Shimplinq Park Farm, 1982 Positions on the field map show the centre of the 150m. D-Vac. sampling points, with the number of males (first) and females. a) Week 3 : All sample points b) Week 4 : All sample points c) Week 6 : Grassbank sample points d) Week 7 : All sample points I1-- - - . )'-----„ c) ir ) a) i i 0*3 I 11.4 1-0^_ N \1.1 \3»2 1*2 0*0 1*1 1*1 A 3» 11 \ / 0*0 0*0 0*0 // 0*0 I 0*0 I 0*1 I 0«1 0*0 /I I o o 0*3 ‘1( If 116 itii-- b) d) r ] I /} • 10 1*2n A 2* 0 5» 9 0*0 0« 0 ' 4*6 2-2 1*3 0*2 0*4 oo V \ xVv- I / 0*0 I 1*6 I /I 200 m. / 0*0 1*3 0*0 1»8 / I/ 0*0 1*2 o o I 0-0 0»0 0*0 / 1*2l 1*3 v r.i i/ 6*9 'll 117 densities in four of the five surrounding sample points (4.75 1 0.48 for four points), and females were also at similar, though higher, densities in the same points (8.50 1 0.87 for four points) (fig.3.26b.). In week 8 the fifth sample in the Southwest had the highest catches of males (6 moths) and females (4), while the other four points held low density populations (males : 1.00 1 0.58 females : 0). In week 9 moths were only caught in this southwestern sample. Although the ditches around the field were cleared during the previous winter, a few plants of V.cracca were found in the Southeast. If this was a relict of a larger patch, accumulation of males there early in the season, may have been attributable to the protandrous emergence of a resident population. At the time of peak density in week 7, males were at low density in the crop (0.90 t. 0.18) with similar densities in the perimeter (1.00 i 0.32) and centre (0.80 i 0.20) (fig.3.26b.). Females attained higher density in the crop (3.20 i 0.71), but with higher density in the centre (4.00 i 1.38), as compared to the perimeter (2.40 1 0.25) (f ig . 3 . 2 6 b . ) . Thus pea fields PAl (1981) and PA2 (1982) had similar spatial distributions of females with the highest density in the perimeter, whereas PB2 (1982) differed and showed the highest density in the centre. The causal movements of these distributions were different and will be described in Section 3.3. 3.2.4. Temporal Patterns of Dispersion in the Pea Field In 1980 only the hedgerow around the pea field was sampled. Only three male(two in week 3, one in week 9) and eight female (three in week 4, five in week 9) C.nigricana were caught with a D-Vac., although sampling was carried out from weeks 3 to 11. These will only be discussed with respect to dispersal in Section 3.3.2. C.nigricana can sustain flight to travel for several kilometres (females in flight-mill studies) but up ward dispersal flights were not detected by suction traps at 1.6m. or above (Lewis et ad, 1975), although very low numbers were detected in that study. Dispersing moths may therefore be low level fliers and those arriving at 118 pea fields would almost certainly first encounter veget ation surrounding the crops. The pea field in 1981 was atypically small with only two sample points from hedgerows and their corresponding understoreys, one each from a grassbank and adjacent broad beans, and only four each from perimetal and central areas of the crop (fig.2.7.). Due to this low number of sample points and incomplete sampling programmes in some weeks, discussion of distribution trends is tentative. Both sexes showed peak density in the vegetation around the peas in 1981 in week 7 (figs.3.27e. & 3.28e.) one week later than that at the emergence site. Within the different habitat types of this vegetation, the two sexes were distributed differently both temporally and spatially (Section 3.2.3.). In the hedgerows males showed a steady increase in population from week 3 to week 6, when the population density peaked (mean 9.50 i 8.50 (S.E.) moths per sample) (fig.3.27h.) and then declined. In contrast, the male density in the understorey in week 6 was lower (2.00 1 0) (fig.3.27g.) and followed three weeks of similar densities. Sampling was incomplete in both weeks 7 and 8, but four moths were taken in one of the samples in each week. In the grassbank sample the male catch increased from week 6 to peak at week 7 (33 moths) then rapidly declined (fig.3.27f.) . In the broad bean sample the peak catch of 13 moths occurred in week 6 at the same time as the peak in the hedge, but was not preceded by gradual build up (fig.3.27d.). This distrib ution suggests immigrant males may have first arrived at the pea field in the hedgerow and understorey. There was also a movement of males into the adjacent beans, before moving into the peas. In contrast, females showed the highest catches in the hedgerow in week 5, one week earlier than males (f ig. 3.28h.) , but at a similar density (8.00 t. 6 . 0 0 ) . The peak density in the understorey and grassbank (3 and 43 moths respectively) occurred in week 7 as with males (figs.3.28g. & f.). The peak catch of 21 moths in the broad bean sample was not attained until week 8 (fig.3.28d.), two weeks later than that for males. Thus females appear 119 Fig . 3.27. Temporal distribution of populations of male C.nigricana in and around the pea field/ Shimpling Park Farm, 1981 Histograms show weekly catch expressed as a percentage of the seasonal total. t h Weeks numbered through the season commencing Monday 25 May. a) Total crop population from perimetal and central regions b) Crop central population c) Crop perimetal population d) Adjacent bean crop population (surrounding vegetation) e) Total surrounding vegetation population f) Grassbank population g) Understorey population h) Hedgerow population n = seasonal total of population, calculated from extrap olated and interpolated data, where sampling was incomplete. WEEK 1 2 0 Fig. 3.28. Temporal distribution of populations of female C.niqricana in and around the pea field, Shimplinq Park Farm, 1981 Histograms show weekly catch expressed as a percentage of the seasonal total- Weeks numbered through the season commencing Monday 25t^1 May. a) Total crop population from perimetal and central regions b) Crop central population c) Crop perimetal population d) Adjacent bean crop population (surrounding vegetation) e) Total surrounding vegetation population f) Grassbank population g) Understorey population h) Hedgerow population n = seasonal total of population, calculated from extrap olated and interpolated data, where sampling was incomplete. WEEK 1 2 1 to have arrived at the pea field at the hedge level and did not move into the other habitat types until two to three weeks later. The temporal distribution of the two sexes in the pea crop is more similar, although densities differed with more than twice as many females as males (sex ratio 0.43 : 1). Very few moths were caught up to week 6, then in the following week there was a sharp increase in the number of moths (males 3.00 i 0.73; females 9.83 t. 3 . 2 9 ) ; this was followed by progressive decline to the end of the season (figs.3.27a. & 3.28a.). Both sexes showed peak density in the centre in week 7 (males 2.00 1 0.58; females 8 . 0 0 t. 6.51) (figs.3.27b. & 3.28b.) indicating that moths moved rapidly into this area. Peak density of females in the perimeter was also in week 7 (9.25 i 3.17) (fig.3.28c.) while for males it was one week later (5.00 i 2.00) (fig.3.27c.). This suggests that males may have been moving into the crop slightly later than femaJes. a feature which will be discussed when the value of the monitoring traps as indicators of female immigration is considered. However, there were no males caught in the centre in week 8 (two samples) and the peak in the perimeter may reflect a tendency for males to leave the crop. Peak female density in the centre in week 7 was much higher than the weeks before and after, and females may also exhibit this tendency. This suggestion is strengthened by the timing and higher level of peak female density in the grassbank (43 moths) in week 7, and by the peak female density of 21 moths in the beans in week 8. Females may therefore move into the crop for oviposition but return to surround ing vegetation which may offer more cover and/or food sources. These later peaks in the grassbank and beans could have been caused by newly immigrant females. Examination of the P.A. and state of the ovaries in Chapter 5 will resolve this; older spent females are predicted in these populations. The temporal distribution of densities in the aerial population (kite net sampled) around the 1981 pea field, differed from that within the vegetation. Although only weeks 5, 6 and 7 were sampled, there was no indication of the gradual build up of populations in the surrounding 1 2 2 vegetation/ but densities showed a large increase from week 6 to 7 (males 19.25 - 5.28; females 18.25 "t. 9.55) (figs.3.29d. & 3.30d.). There were only two hedge/ ■understorey sample points and one each of grassbank and beans, but both sexes show this feature in each of these habitats (figs.3.29e. - g. & 3.30e. - g.). The density of both sexes showed a fall in week 6 from week 5 (figs.3.29e. 6c 3.30e.) before attaining a high level in week 7. Over the crop, both sexes showed the same temporal distribution as was indicated by D-Vac. catches for the populations within the crop. There was a sharp rise in density (males 16.00 ± 4.59; females 6.50 + 0.68) in week 7 (figs.3.29a. Sc 3.30a.). This distribution trend was shown by both sexes in the perimeter (figs.3.29b. S c 3.30b.) and the centre (figs.3.29c. & 3.30c.). However the scale of density increase from weeks 6 to 7 was not so great as that shown in D-Vac. samples, and there was a tendency for a more gradual increase in density, rather than a sudden influx, this was particularly so in the perimeter (figs.3.29b. S c 3.30b.). The aerial populations over the crop and about the surrounding vegetation had very similar temporal distributions and densities, and may have been less discrete than has been supposed for the populations in the vegetation. Around the 1982 pea fields, no subdivision of surrounding vegetation into different habitat types was made, all samples were classed as grassbanks, although differences were recognised. Three of the five sample points around PA2, and four of five around PB2 had lengths of hedgerow; these were inaccessible to sampling because of drainage ditches. These hedgerows may have influenced moth distributions in the underlying grassbanks since the greater architectural diversity would provide more refuges and feeding sites. The eastern headland of P a 2 w a s bordered by the vetchbank (Section 2.1.2.; fig.2.9.). Although population density in the vetchbank was undoubtedly subject to immigration and emigration, this habitat had a resident emergent population (1981 pod infestation V.cracca 8.0%; L.pratensis 61.0%) and provided host plants. The sex ratio in the vetchbank was exactly 1:1, a n d b o t h 123 Fig. 3.29. Temporal distribution of aerial populations of male C.nigricana over and around the pea field, Shimpling Park Farm, 1981 Histograms show weekly catch expressed as a percentage of a three week total. n d Weeks numbered from week 5, commencing Monday 2 2 June. a) Total crop population over perimetal and central regions b) Crop central population c) Crop perimetal population d) Total surrounding vegetation population e) Grassbank population f) Under storey/Hedgerow population g) Adjacent bean crop population n = total population for weeks 5 to 7. WEEK 124 F iq. 3.30. Temporal distribution of aerial populations of female C.niqricana over and around the pea field, Shimplinq Park Farm, 1981 Histograms show weekly catch expressed as a percentage of a three week total. Weeks numbered from week 5, commencing Monday 22 nci June. a) Total crop population over perimetal and central regions b) Crop central population c) Crop perimetal population d) Total surrounding vegetation population e) Grassbank population f) Understorey/Hedgerow population g) Adjacent bean crop population n = total population for weeks 5 to 7. WEEK 125 sexes showed peak density in week 7 (males 10; females 7) (figs.3.31f. S c 3.32f.). Anomalously, the first female was caught at the end of May, four or five weeks (no sample in week 5, values interpolated) before the first males. The population of both sexes in all the vegetation around field P a 2 showed a trend of increase to peak density in week 7 (males 3.00 ± 1.79; females 2.60 ± 1.43) (figs.3.31d. S c 3.32d.), when peak density is also assumed to have occurred in the crop (figs.3.3la. S c 3 . 3 2 a . ) . However when catches from the vetchbank were excluded, there was no one week of peak density, unlike 1981, rather the density of both sexes remained at similar low levels throughout the season (figs.3.31e. S c 3.32e.). The temporal distribution of moth density in vegetation around field PB2 was more similar to the grassbank of 1981, with a pronounced peak density of both sexes in week 7 (males 4.00 ± 0.84; females 7.20 ± 1.46) (figs.3.33d. S c 3 . 3 4 d . ) . In the crops of both fields, peak density occurred in week 7 in both the perimeter (PA2 males 6.40 ± 3.90; females 6.00±2.00; PB2 males 1.00 ± 0.32; females 2.40 ± 0.25) (figs. 3.31c. S c 3.32c.) and the centre (PA2 males 1.00 ± 0.45; females 2.80 ± 0.80; PB2 males 0.80 ± 0.20; females 4.00 ± 1.38) (figs . 3.31b. S c 3.32b.). While all moth populations in the crops of 1982 fields showed rapid decline after week 7, so do the populations in the surrounding vegetation, which does not support the conclusion from 1981 distributions, that moths left the crop and returned to surrounding vegetation. 126 Fig. 3.31. Temporal distribution of populations of male C.nigricana in and around pea field PA2, Shimpling Park Farm, 1982 Histograms show weekly catch expressed as a percentage of the seasonal total (not including estimates for weeks 5 & 6 in crop regions). Weeks numbered through the season commencing Monday 2 4 ^ May. a) Total crop pouplation from perimetal and central regions b) Crop central population c) Crop perimetal population d) Total surrounding vegetation population e) Surrounding vegetation population excluding vetchbank f) Vetchbank population n = seasonal total of population, calculated from extrap olated and interpolated data (except weeks 5 & 6 in a - c), where sampling was incomplete. WEEK 127 Fig . 3.32. Temporal distribution of populations of female C.nigricana in and around pea field PA2, Shimp linq Park Farm, 1982 Histograms show weekly catch expressed as a percentage of the seasonal total (not including estimates for weeks 5 & 6 in crop regions). Weeks numbered through the season commencing Monday 24"^ May. a) Total crop population from perimetal and central regions b) Crop central population c) Crop perimetal population d) Total surrounding vegetation population e) Surrounding vegetation population excluding vetchbank f) Vetchbank population n = seasonal total of population, calculated from extrap olated and interpolated data (except weeks 5 & 6 in a - c) # where sampling was incomplete. WEEK 128 F ig . 3.33. Temporal distribution of populations of male C.nigricana in and around pea field PB2, Shimpling Park Farm, 1982 Histograms show weekly catch expressed as a percentage of the seasonal total (not including estimates for weeks 5 & 6 in crop regions. Weeks numbered through the season commencing. Monday 24 t h May. a) Total crop population from perimetal and central regions b) Crop central population c) Crop perimetal population d) Total surrounding vegetation population (i.e. grassbank) n = seasonal total of population, calculated from extrap olated and interpolated data ( except weeks 5 & 6 in a - c), where sampling was incomplete. WEEK 129 F ig. 3.34. Temporal distribution of populations of female C.nigricana in and around pea field PB2, S h impling Park Farm, 1982 Histograms show weekly catch expressed as a percentage of the seasonal total (not including estimates for weeks 5 & 6 in crop regions). Weeks numbered through the season commencing Monday 2 4 ^ M a y . a) Total crop population from perimetal and central regions b) Crop central population c) Crop perimetal population d) Total surrounding vegetation population n = seasonal total of population, calculated from extrap olated and interpolated data (except weeks 5 & 6 in a - c) , where sampling was incomplete. WEEK 130 3,3. Dispersal 3,3.1. Spatial Patterns of Dispersal In 1980 three of the four moths taken with a D-Vac. in the hedgerow around the emergence site were from the adjacent sample points H21 and H22 (fig. 2.4.), to the North. In addition five of the seven males caught with a kite net around the hedge were from samples H22 and H23. Thus there was the suggestion of a directional element in the spatial distribution and therefore in emigration from the field. Eleven moths were caught in the hedgerow around the 1980 pea field, which was 3Km. southwest of the emerg ence site (fig.2.1.). Eight of these moths were caught around the southern half of the field, which again suggests unidirectional migration. Although C.nigricana are capable of flying several Km. (Lewis et al, 1975) the two populations in these fields were probably different, with both dispersing from South to North. In 1981 the highest densities in the emergence site at the time of peak density were in the East of the field, where three times as many moths of either sex were taken as in the West. E A S T W E S T Number of Mean ( t S. E . ) Number of Mean ( t S.E. Sample points per S ample Sample points per Sample Males 15 2 3 . 3 ± 4 . 1 9 1 5 7 . 6 ± 1 . 7 6 Females ’ 15 1 0 . 6 ± 1 . 9 3 1 5 3 . 3 t 0 . 8 9 Although high densities were attained in the hedges and understoreys shared with pea field PAl in the Northeast (fig.2.2.), the highest densities of both sexes were achieved in the most easterly understorey, and male density in the grassbank to the South was also comparatively high. This suggests that there may have been considerable dispersal due East. There were pea fields lying about lKm. to the east in 1981 (e.g. field WC2, fig.2.3.), but damage levels were reported to be low (Sir John Richmond, pers. comm.) and lower male densities were indicated by pheromone (not sex-attractant analogue) trap catches during a series of experiments in the emergence site WC2. Thus 131 the occurrence of a migratory flight in this direction cannot be confirmed. At the 1981 pea field, male populations showed initial accumulation in the shared hedge along the western boundary. Greater numbers were taken in this hedge on the pea crop side, while in the understorey the population was larger on the wheat field side. D-Vac. efficiency in hedgerows is uncalibrated and direct comparison with samples from other habitats may not be appropriate. Never theless there is the suggestion that initial movements out of the wheat crop may be at the lower level of the under storey, whereas movement across or through the boundary is higher up in the hedge. The highest densities of either sex around the pea field were attained in the grassbank along the northern headland, and high catches were also recorded along the edge of the beans in the East. Both sample points were furthest from the 1981 emergence site, and attained these densities before moths had moved into the crop. These populations could have arisen by easterly dispersal of moths from the western part of the northern headland of the emergence site, however, densities were consistently low there and this explanation does not seem plausible. Moths could also have arrived in the Northeast of the 1981 pea field by dispersing from the alternative emergence site field WBl a few hundred metres to the Northeast (fig.2.2.). However, the spatial distribution in the 1982 pea field P a 2 (section 3.2.3.) indicates that moths may fly over the centre of a field and preferentially accumulate along the headlands (see below). Accumulation in the vegetation around the 1981 pea field may therefore have arisen after dispersive flight right over the field, which was certainly atypically small. In addition the sudden influx of moths into pea crops (section 3.3.2.) indicates a delayed immigration for some reason; for example if the phenology of the crop was unsuitable for oviposition, females might have remained in the surrounding vegetation if it offered more cover. Males seeking mates might remain with the females, as well as benefiting from the better cover. 132 Around the emergence site in 1982, the highest densities occurred on the northern headland adjacent to the 1982 pea field, P a 2, with the only other noticeable accumulation on the eastern headland, near to the other 1982 pea field, PB2. The highest density around PA2 was along this former headland shared with the emergence site, and apart from the resident population in the vetchbank, very few moths were caught elsewhere in surrounding veget ation; immigration into pea field PA2 was certainly 'from this focus in the South (section 3.2.3.). However, as described in section 3.2.3. and above, females at least showed accumulation along the headlands but not in the centre of the field. This distribution could have arisen by flight over the centre of the field, or by dispersal around the edge of the field with moths remaining close to the boundary vegetation. In contrast to field PA2, migrating moths arrived at pea field PB2 from the Northwest and possibly the South east, and thus dispersal in 1982 is unlikely to have been due to a simple response to wind direction. Wind direction at the time of main population movement varied from NNE through South to WNW and is unlikely to have caused aggregations either by dispersing insects downwind or through anemotaxis. Moths were evenly distributed (except in the Southwest, section 3.2.3.) in the surrounding veget ation, when the main movement into the crop occurred, and, unlike pea fields PAl and P a 2, the highest densities were found in the•centre of the field (section 3.2.3.). Although all three pea fields of 1981 and 1982 were consistent in the temporal distribution of moth movements, three different spatial outcomes were exhibited. Immigr ation into PAl was apparently along several headlands, with moths only moving into the edge of the field, despite its small size. Field PA2 was larger and showed a similar distribution, with moths confined to the edge of the crop along all headlands, but which arose by dispersal from a compact source, and not by immigration from the corresponding grassbank. Immigration into field PB2 was along several headlands like PAl, but moths accumulated in the centre. 133 In 1981 the spatial and temporal patterns of dispersal were examined by plotting the number of moths caught at the 1981 emergence site WAl against distance from the pea crop. The distance used was from the centre of the sample point to the nearest peas (either fields PAl or PBl) and was calculated from fig.2.6. For the majority of weeks the slope of the fitted line was negative (Table 3.2.) indicating that both sexes were more abundant nearer to the peas. The slope became successively more negative in the weeks in the first half of the season, and was most negative for both sexes during week 6, when moths were aggregated at the time of peak density. After this time the slope progressively increased towards zero, as the low density populations were more evenly distributed across the field. Although the amount of variance explained by regression was generally low, a significant correlation coefficient was obtained for a number of weeks, particul arly for female populations (Table 3.2.). Females were negatively correlated to distance for the greater part of the season, whilst males were distributed independently of proximity to pea fields. This reflects a strong directional element to female migration and suggests that females move to pea fields more than males. However the wind direction for most of week 6 and the first few days of week 7, i.e. at the time of main moth movement, was SW during the activity period and the windspeed consist ently moderate. Moths from a large area of the field could therefore have been blown towards pea fields PAl and PBl. If this were the case, it is not the females that were actively moving to pea fields, but males actively remaining in the emergence site, while the females were passively transported away. To further examine these relationships the sampling programme of 1982 was modified to incorporate the transects described in section 2.1.6. Unfortunately because of bad weather at the critical time in mid-season, and the lower catches (including many 'zeros') associated with a shorter sample unit, there is insufficient data to critic ally analyse. 134 T a b l e 3.2. Relationship between number of C.niqricana and d i s t a n c e t o n e a r e s t p e a f i e l d S l o p e *b 1 o f l i n e a r r e g r e s s i o n equation (fitted by least s q u a r e s ). n = n u m b e r o f s a m p l e p o i n t s . MALES Week n S l o p e R - s q u a r e d r Probability ( n - 2 d f ) 2 & 3 3 6 - 0 . 0 0 6 6 1 4 . 5 % 0 . 3 8 1 < 0 . 0 5 4 3 6 - 0 . 0 0 5 2 5 . 3 % 0 . 2 3 0 NS 6 3 6 - 0 . 0 3 7 5 9 . 1 % 0 . 3 0 2 N S 7 2 6 -0.0124 4.1% 0 . 2 0 3 NS 8 2 4 - 0 . 0 0 1 5 0 . 6 % 0 . 0 7 8 NS 1 0 32 - 0 . 0 0 3 7 2 0 . 0 % 0 . 4 4 7 < 0 . 0 5 FEMALES Week n S l o p e R - s q u a r e d r Probability ( n - 2 d f ) 2 & 3 3 6 - 0 . 0 0 0 3 0 . 3 % 0 . 0 5 5 N S 4 3 6 - 0 . 0 0 4 2 25.6% 0.506 <0.01 6 3 6 -0.0243 17.8% 0 . 4 2 2 < 0 . 0 1 7 2 6 - 0 . 0 1 5 2 3 9 . 5 % 0.629 <0.001 8 2 4 -0.0106 48. 0% 0 . 6 9 3 < 0 . 0 0 1 1 0 3 2 - 0 . 0 0 2 1 15.1% 0.389 - <0.05 135 3.3.2. Temporal Patterns of Dispersal In 1980, only three males and one female were caught with a D-Vac. in the hedgerow around the emergence site; two of these were caught in week 4, at the same time that moths were first recorded in the crop D-Vac. samples. (fig.3.12a.). Seven males were also netted in weeks 3, 4 and 5; four of these were caught in week 3, when three males were also netted flying over the crop (fig.3•12a.). This suggests rapid movement, for males at least, from the crop to the surrounding vegetation. Only the hedgerow around the 1980 pea field was sampled, and low population levels were indicated (sections 3.2-3. Sc 3.2.4.). Two males and three females were caught in weeks 3 and 4 respectively, followed by four or five weeks (no sample in week 6) of zero catch and then a further one male and five females in week 9. Although the relationship between the populations in the two study fields is not known, migration appears to have commenced as soon as moths emerged at the beginning of the season, and pea fields were soon found. Moth movement then appears to have been suppressed by the cool, wet weather of midsummer, and only at the end of the season when conditions improved did any further migr ation occur. For both males and females in 1981, peak population density in the wheat crop and the surrounding vegetation of the emergence site, occurred in week 6 (section 3.2.2.). As the seasonal profile of weekly catches in the surround ing vegetation (figs.3.16d. & 3.17d.) is the same as that for the crop (figs.3 16a. & 3.17a.), with no discernible time delay, a proportion of male and female population moved out of the crop less than one week after emergence. Densities of flying moths tended to be lower over the crop in week 6 (figs.3.18a. & 3.19a.), but higher about the surrounding vegetation (figs.3.18d. Sc 3.19d.), which suggests aerial populations over the crop may have been rapidly depleted at this time, as moths accumulated in the hedgerows. Both sexes showed gradual build up in the vegetation around the 1981 pea field, PAl, with peak density in week 7 (figs.3.27e. S c 3.28e.) but aerial popul ations showed sudden increase to this peak density 136 (figs.3.29d. & 3.30d.), one week later than that at the emergence site However in the two hedgerows which were shared with the emergence site, and therefore those habitats first encountered by dispersing moths, male density peaked in week 6 (fig.3.27h.) while females peaked in week 5 (f ig. 3.28h.) . The highest moth densities in the pea crop were in week 7 (figs.3.27a. & 3.28a.), indicating that migration from the emergence site to the pea crop at the time of peak population density, occurred over a period of approximately one week or less. However moths that emerged earlier in the season and dispersed to the pea field did not enter the crop immediately, but accumulated in the surrounding vegetation. Peak density of males in the perimeter of the pea crop was in week 8, one week later than that for females; it was suggested that males moved into the pea crop after females (section 3.2.4.) Some support for this is provided by the earlier accumul ation of females in the hedgerow, which indicate- females moved to the pea field before males. In 1982, peak population density of both sexes in vegetation around the emergence site occurred in week 6 (section 3.2.2.), and although unknown, peak density in the crop was predicted for weeks 4 or 5. There was thus a slight delay in the shift of the populations out of the wheat crop. There was little or no difference between weeks 4 and 5 in a number of features of the temperature regime (e.g. weekly mean; weekly mean between 1400 and 2 000 hrs.; weekly total number of hours above flight thresh- old between 1400 and 2000 hrs. ), which could affect activity Incidentally, temperature dependent development preceding emergence is also unlikely to have been affected, and provides support for the predicted peak emergence period. However, there was a decrease in the weekly total sunshine hours from week 4 (30hrs.) to week 5 (17.9hrs.), as well as increased rainfall between week 4 (5.6mm.) and week 5 (28.6mm.), 18Km. away at Broom's Barn. The flight period * This period is used as the potential period of activity; over 95% of moth activity occurs during this period (Lewis et al, 1975). 137 is not extended if it has been interrupted by rain showers (Lewis et al, 1975). The unfavourable conditions that prevented sampling in the crops, may have reduced moth activity, and emigration from the wheat to the surrounding vegetation could not occur as soon after emergence as in 1981 and possibly 1980. Both sexes did show a build up in the vegetation around the 1982 pea fields PA2 and PB2, similar to that around the 1981 pea field. Peak density was also in week 7 (figs.3.3Id. to 3.34d.) at the same time as the highest densities in the pea crops (figs.3.31a. to 3.34a.), and one week later than peak density around the emergence site. Rapid emigration from the wheat field to the pea crop is again shown. However all three pea fields were close to emergence sites, which may be atypical. Moth populations forced to fly greater distances to pea fields might not be expected to arrive at pea fields so soon after leaving the emergence site, however the early occurrence of moths around pea field J in 1980,- which was comparatively isolated, does suggest that this is a possib i l i t y . Immigration into the pea crops was sudden, and did not reflect the gradual population build up in the surround ing vegetation, unlike emigration from the wheat to the immediate vegetation, and from there to vegetation around pea fields. This was shown in 1981, when both sexes showed large increase in numbers from weeks 6 to 7 (figs. 3.27a. & 3.28a.), and implied in 1982, when large catches in the crops in week 7 (figs.3.31a. - 3.34a.) coincided with peak density in surrounding vegetation (figs.3.31d. - 3.34d.) (section 3.2.4.). 3.3.3. Differential Dispersal of the Two Sexes Different numbers of males and females were caught in emergence sites and pea fields, and within these fields there were differences in the various habitats and crop areas. To examine the various sex ratios, the overall sex ratio for C.nigricana populations in the whole environment must first be established. In this study an estimate can be calculated using D-Vac. catches, with the assumptions that males and females have an equal likelihood of being 138 caught, and that a D-Vac. is equally efficient in all habitats. Calculation must allow for the differing size and character of fields and equilibrate for the differing proportional area of samples in the various vegetation categories. Hence a highly biased ratio from a given number of sample points in one habitat will not greatly influence the overall sex ratio, if the ratio from the same number of samples in another habitat covering ten times the area, was nearer to unity. Using this method the best estimate for the 1981 population was 1.18 males : 1 female, while in 1982 it was 1.5 : 1, although the lack of samples at the time of peak density undoubtedly influences this value. A ratio of 1 : 1 was expected from culture results in the laboratory, and Lewis ejt al (1975) found a ratio of 1.07 : 1 (60 males, 56 females) in emergence traps in the field. With the sex ratio assumed to be unity, deviations shown by natural populations in various habitats and fields can be examined. Sex ratios for each vegetation type were readily estimated from the seasonal totals used to calculate weekly percentages. Moths below P.A. 7 in the emergence site are assumed to be newly emerged. The seasonal ratio of this age class in the crop was 1.8 s 1 in 1981 and 2 . 0 : 1 in 1982, indicating that females leave the emergence site very soon after emergence and before the males. Weekly sex ratios of the whole crop population in emergence sites shows a trend of increase in the latter part of the season, and remains male biased throughout. The high ratio at the beginning of the season reflects protandrous emergence, but a male bias at peak density and thereafter again indicates that females move out of the emergence site more readily than males and do so rapidly. The sex ratio, as estimated from seasonal totals, in different classes of the environment, approximating to a transect from an emergence site to a pea crop is given in Table 3.3. Although estimates for 1982 may be less accurate because of unsampled weeks, there is considerable agreement between the two seasons. The most important difference is that the sex ratio is male biased in the wheat crop, while in the pea crop it is female biased to a similar level. 139 Table 3.3. Sex ratios (males ; females) of populations in various subdivisions of the environment. S h i m p l i n o Park Farm, 1981 and 1 9 8 2 Sex ratios calculated from seasonal D - V a c . t o t a l s Emergence site W A l , 1 9 8 1 W A 2 , 1 9 8 2 C r o p t o t a l 2 . 3 6 : 1 2 . 1 7 : 1 Crop perimeter 2 . 7 2 : 1 2 . 5 0 : 1 Crop centre 2 . 1 7 : 1 2 . 0 4 : 1 Surrounding vegetation 2 . 7 4 : 1 1 . 8 7 : 1 H e d g e r o w 2 . 3 4 : 1 - Understorey 2 . 6 8 : 1 - - G r a s s b a n k 4 . 7 5 : 1 1 . 8 7 : 1 P e a f i e l d s P A l , 1 9 8 1 P A 2 , 1 9 8 2 P B 2 , 1 9 8 2 Surrounding vegetation 0 . 9 0 : 1 0 . 9 6 : 1 0 . 7 6 : 1 H e d g e r o w 1 . 8 0 • 1 - - • Understorey 1 . 7 6 • 1 - - G r a s s b a n k 0 . 6 6 • 1 0 . 9 6 : 1 0 . 7 6 : 1 B e a n c r o p 0 . 5 3 1 - - C r o p t o t a l 0 . 4 3 : 1 0 . 6 4 : 1 0 . 2 5 : 1 Crop perimeter 0 . 5 1 • 1 0 . 8 5 : 1 0 . 5 0 : 1 Crop centre 0 . 2 8 • 1 0.28 : 1 0.14 : 1 140 This feature of dispersal could have important consequences for the use of monitoring traps. The overall ratios in the wheat crops were similar in the two seasons, and in both fields the ratio was some what higher in the perimeter, suggesting that females move out of the crop more readily than males, which thus tend to remain in the crop. In 1981 the ratio in the surrounding vegetation was more male biased than in the crop, suggesting accumulation of males around the field, and that females not only leave the crop soon after emergence, but also leave the vicinity of the field. However further examin ation of the surrounding vegetation shows that the higher ratio was entirely due to higher catches of males in grass- banks to the South where females did not aggregate. The ratio in hedgerows and understorey was the same as the rest of the crop. In 1982 all the surrounding vegetation was classed as grassbank, and the sex ratio did not show an elevated male bias, rather it was similar to but slightly less than that for the crop. The ratio in the vegetation around pea fields PAl and PA2 was near to unity, and that for pea field PB2 nearer to unity than any emergence site ratio. Around PAl there were marked differences in the different vegetation categories. This was probably not a habitat effect, since the ratios were male biased in the hedge and understorey nearest to the emergence site, but female biased in the grassbank and beans furthest from the emergence site. The ratios in the grassbanks around PA2 and PB2 were more similar to the grassbank around PAl than the hedgerows, and samples nearest the emergence site WA2 did not show a greater male bias than other grassbank samples. The ratios in pea crops were consistently, though variably, female biased, markedly so in some areas. All fields were consistent in showing a lower ratio in the centre of the crop as compared to the perimeter. The degree of female bias in the centre of pea crops was much greater than the male bias in emergence sites. There was therefore a clear differential dispersal of the two sexes. Females left the emergence sites sooner after emergence and more readily than males. Similar 141 numbers of each sex may have reached the vegetation around the pea fields, but females were more widely dispersed. Lower numbers of males moved into the crop and of these the majority only reached the edge of the crop, even when the field was small. The sex ratios of the 1981 aerial populations differed markedly from those populations within the vegetation, at least for the emergence site (Table 3.4.). Over the wheat crop, far larger numbers of males were caught, although even at these extreme levels, the ratio was more male biased over the perimeter, possibly reflecting the suggestion that females leave the emergence site very readily. The ratio in the populations over the surrounding vegetation were similar to those over the crop, and there may be no distinction between the two areas. There was no suggestion of further male bias over the grassbanks indicated by D-Vac. catches. The higher densities of males in emergence site aerial populations are in accordance both with the findings of Lewis et al (1975) who recorded ratios up to 70 : 1 over wheat, and with findings in this study in 1982, when the upper levels of the wheat in field WA2 were hand searched for moths. Over a period of about two hours 35 females were collected for experimental purposes, over the same period it was estimated that about five times as many males could have been collected (only 35 were kept). The aerial samples around the pea field do appear to give similar indications to the vegetation samples. in samples nearest to the emergence site there was a strong male bias, while further away the aerial populations were female biased. This is unexpected, since even over the pea crop itself the aerial population was male biased. 142 Table 3.4. Sex ratios (males ; females) of aerial populations over various subdivisions of the enviroment, Shimpling Park Farm, 1981 Sex ratios calculated from kite net catches in weeks 5,6 & 7. Emergence Site WAl Crop total 13.33 : 1 Crop perimeter 14.76 : 1 Crop centre 12.58 : 1 Surrounding vegetation 10.38 : 1 Hedgerow / Understorey 10.11 : 1 Grassbank 11.39 : 1 Pea field PAl Surrounding vegetation 1.37 : 1 Hedgerow / Understorey 5.46 : 1 Grassbank 0.70 : 1 Bean crop 0.54 : 1 Crop total 2.55 : 1 Crop perimeter 2.23 : 1 Crop centre 2.85 : 1 143 3.4. Relationship Between Dispersion, Dispersal and Other F actors 3.4.1. Relationship Between Sex-attractant Trap Catch and Dispersion / Dispersal Sex-attractant monitoring traps were used both in emergence sites and pea crops. The degree to which trap catches reflect the dynamics of moth densities, as revealed by D-Vac. catches, can be ascertained for the fields studied. a) Emergence sites In emergence sites sex-attractant trap catch is insensitive to population density fluctuations as shown by regression analysis of moth density and sex-attractant trap catch, and also by comparison of seasonal patterns of trap catches and D-Vac. samples. Sex-attractant traps were used in the emergence sites of 1980 and 1981, with two traps per field, arranged as described in section 2.1.6. In 1980 traps were sited in field P (fig.2.4.) and in 1981 in fields WAl (fig.2.6.) and WBl. Expressing weekly catches, of both monitoring traps and D-Vac., as a percentage of the total season's catch, enables a comparison of trends between techniques and between years. The low population densities in 1980 were reflected by comparatively lower sex-attractant trap catches in the emergence site; the traps in emergence site WAl in 1981 caught nearly five times as many moths. The small number of moths caught with a D-Vac. and a kite net in the 1980 emergence site do not allow any correlation with weekly numbers of males in the sex-attractant traps. With the larger moth numbers in the 1981 emergence site, the relationship between sex-attractant trap catch of males and the density of moth populations (as shown by D-Vac. samples) can be examined. Weekly mean sex-attractant trap catch was not linearly related to weekly D-Vac. catches (Log transformed data) of males, when total and subpopulations drawn from different areas (crop only, crop and surrounding vegetation, crop within 250m. radius of traps, crop and surrounding vegetation within 250m. radius of traps) were considered 144 (figs.3.35a. - d.). It is clear that in the first half of the season, low sex-attractant trap catches were recorded over a range of moth densities. In the second half of the season (including week 6 at peak density) a higher but more consistent level of trap catch was made over a wider range of densities, extending beyond the range of densities in the first half of the season at both extremes (figs. 3.35a - d.). In the absence of competition between sex-attractant traps and females, trap catch of males should be independ ent of female moth density. Weekly mean trap catch was not related to weekly D-Vac. catches of females in popul ations drawn from the crop and surrounding vegetation, but was, surprisingly, correlated with subpopulations drawn from the crop region (fig.3.36a. - d.). This was probably an artefact caused by the coincidence of low density and low sex-attractant trap catch in the first half of the season. Positive correlation with female density is not expected, since the most likely influence of female moths would be supressed catches due to competition, and hence negative correlation. The consistency of sex-attractant trap catch over a wide range of moth density in the second half of the season is shown by the good fit to regression lines fitted through the points for weeks 6,7,8 and 10. The significant value of 'r1 in these instances does not indicate a relationship since the slope of the fitted lines is low (f igs . 3.35a.. - d. , 3.36a. - d.) . There is no data point on the graphs for week 9, since no D-Vac. samples were taken. Inclusion of a data point with an interpolated D-Vac. catch serves to depress the slope more (y = 0.238 + 2.126) although the goodness of fit is reduced (R-sguared 29%). Although the distribution of the data points for weeks 2 to 5 are poorly described by fitting a line, the slope is very similar to that for the latter part of the season, and again suggests that sex-attractant trap catch is consistent at a lower level independent of moth density. Seasonal histograms of moth populations sampled with a D-Vac. showed peak density and peak emergence occurred in the middle of the season (section 3.2.2.). 145 Fig. 3.35. Relationship between sex-attractant trap catch of male C.nigricana and density of males in the emergence site, Shimpling Park Farm, 1981 x - axis: Lo^io + D-Vac. catch of males (Male catch/ D-Vac. sample / Week) . y - axis: Log^ Sex-attractant trap catch of males (Male catch / Trap / Week) . Numbers by data points refer to weeks in the season, (Week 2 commencing Monday 1 s t June) . a) Weekly mean D-Vac, catch calculated from all sample points in the crop and surrounding vegetation (36 sample points). b) Weekly mean D-Vac. catch calculated from all crop sample points only (20 sample points). c) Weekly mean D-Vac catch calculated from crop and surround ing vegetation sample points within 250m. of the sex- attractant traps (15 sample points). d) Weekly mean D-Vac. catch calculated from crop sample points within 250m. of the sex-attractant traps (8 sample points). Log, „ Male Catch / Sex —attractant Trap /Week 1.5 1.6 1.8 2.5 2.0 2.1 2.3 2.4 1.7 1.7 2.2 2.3 2.4 1.9 2.0 2.1 1.9 2.5 2.2 2.4 1.5 1.6 2.1 2.2 2.5 1.8 1.5 2.0 2.3 1.7 1.8 1.9 1.6 2.0 1.8 1.9 2.1 2.2 1.6 1.7 1.5 2.3 2.4 2.5 o1 + aeCthDVc Sample/Week Catch/D-Vac. Male ^ + Log10 16 - 146 - Weeks Weeks Weeks Weeks Weeks Weeks Weeks Weeks Weeks ek -10 - 6 Weeks Weeks Weeks = y = y = y - 6 = r = r r 25.5% = r = y = y r - 2 = r = y = 76.7% r = y = y = r = r -10 1 - 2 r - 6 = r 76.0% = r -10 - 6 0.481NS = r r - 2 = r r = y = y - 2 =0.419NS = r - 2 r = y - 2 = r r = y = r 25.4% = r 0.396NS = r 15.7% = r -5 - 2 -10------0 1 - 2 2 2 2 2 2 2 2 2 2 2 2 2 74.6%= 21.1%= 13.9%= = 23.1%= 17.5%= 0.505NS 0.864NS .0x + 0.305x .4x + 0.547x 5 .7x 1.60 + 0.575x 10 0.428 NS n 0.459 NS 0.431x + 0.431x .8x + 0.284x 0.S76NS 5 0.465x + 0.465x 0.874NS 10 .3x+1.47 0.333x+ 0 1 0.346x+ 0.373NS 5 0.977p <0.05 0 1 0.588x+ .0x+ 2.070.400x+ il 1.47 +0.288x 0.504NS i— 0.516x+1.66 ------ CD ------en OJ ------— 2.12 1.30 2.13 1.65 1.35 2.13 1.65 147 Fig. 3.36. Relationship between sex-attractant trap catch of male C.niqricana and density of females in the emergence site, Shimpling Park Farm, 1981 x-axis: Log^^ (x + 1) D-Vac. catch of females (Female catch/D-Vac. sample / Week). y-axis: Log^^ Sex-attractant trap catch of males (Male catch / Trap / Week) . Numbers by data points refer to weeks in the season s t (Week 2 commencing Monday 1 June) . a) Weekly mean D-Vac. catch calculated from all sample points in the crop and surrounding vegetation (36 sample points). b) Weekly mean D-Vac. catch calculated from.all crop sample points only (20 sample points). c) Weekly mean D-Vac. catch calculated from crop and surround ing vegetation sample points within 250m. of the sex- attractant traps (15 sample points). d) Weekly mean D-Vac. catch calculated from crop sample points within 250m. of the sex-attractant traps (8 sample points). I I CD £ k h-1 1 | | 1 1 1 1 1 o n h-1 O X (3 cn n ___ + 4k cO 1 \— CD CD t o t o __ H ►u LHCD • ___ o j ___1 II O o CD CD 2 CDOJ hi CO 1 t o t o t o 2 2 (3 (3 cn X 2 1 ii XX - 4 O + • CD 0 3 O O CD H-* y l h ___ i to ro t o t o n o roto H-* a \ • h ___ __ II 1 2 O cn CD GJ • hi i- * CO ___ __ i 1— O 2 (3 C3 C3 DC cn CD ___ ii X + CD 4k to • O CD CD - a H * h-« II a h- CD • hi CD M CD 11 4k o t o o CO o o CD 1-1 •a A 1 1 1 1 1 1 1 1 o CD cn X (D X CO L n u i — 1 L _ ii + X (-■hJ h-1 o • CD o __ 1 4 ^ to CO j ___ n O cn h • $ 1___ CO t o t o h -* U) a CDGD o o cO ___ •a 0 A i___ r o r o __ M 2 (3 (3 * 5 1 CO I-* 11 II X + CD cO CD CD 4* a •• K co hi K co 0 CO ___ ii CD a i— • h CO o ___1 II cn 2 4k CD I-1 • O 1-1 ___ 1 >43 H* __ o f— (D cn X X CD CD h -* CD II + X to ro H* CD • o KJ a t—' CO II CO4* CD GJ • >1 ___ 1 CTi II a cO • o O h o CD o A - o __ ___ 1 CD i 1 u i 1 w h-> 1 1 1 1 1 CD CD X V) CO X h-> O __ i i X + L ■■ o CD • h-> O GJ h - 1 CD 4 ^ CO i i 4 * n a M • t o t o o j o c n CD h CD 4 k t o (3 2 X W 2 ___ 1 CO t o h—1 i 11 i i + X CO ___ H 1 O CD i—* •• CD CD y c n CO i II JO O h o h - 1 I - 1 • __ i i 1 h h - o CD • CD CO i— Log10 Male Catch / Sex-attractant Trap /week Trap Sex-attractant / Catch Male Log10 ___ o CD CD 1—* CD IV 0 0 — t II • X + t o - 4 o 4 * l h OJGJ 1— i H* CO II a cO • h | CD 0 % c d i i CD h o • 2 2 2 CD CO CD ___ 1 1 1 1 1 1 1 1 2 CD MW o CO h - X r o (—• LH LH ___l l ' i i X + cO • o CO CD CD * ►< 4 * t o CO II - 1 4 ^ n • c n OJ II - 1 - CD O 4 * O i n O r 0 A n M tO tO 2 CD (3 X" Cn CD 2 5 1___ n + •• cO GJ CD y 0 CD _____ t o n N ) M O M r o t o • ___1 n 4 k 2 - o o - a cn h h • h - cO i H- CD (I) X O cn CD s: 0 3 II + XX t o h -* GJ o CD CD h - I -O r o i i i n • 4 k U i < J\ ii CD • 2 CD o CD CO h L- .... 1___ H-* t— H * H * LH L°q10 (x + 1) Female Catch /D-Vac. Sample/Week 149 In neither the 1980 emergence site, field P, nor the 1981 emergence site, field WAl, was there a pronounced peak catch with sex-attractant traps (figs.3.37. & 3.38.), though there was a tendency for greater catches in week 9 towards the end of the season. Emergence site WBl in 1981 did show peak trap catch in week 7 (fig.3.39.), one week later than peak population density in emergence site WAl/ although the attractant traps caught only half as many moths as those in the latter field. Interpolation of trap catches in emergence site WBl is complicated because there is no independent indication of population fluctu ation; more importantly the sex-attractant traps were sited in close proximity to pea field PBl and the attract- ant traps sited there. Trap catches in field WBl were therefore not determined by male populations in this field alone, but likely to have been influenced both by popul ation changes in pea field PBl, and by interaction (Wall & Perry, 1978; 1980 & 1981a) with the other traps, to a degree that cannot be resolved. Although there was no peak of sex-attractant trap catch in emergence site WAl, at the time of peak emergence and population density of males, there was a marked four to five-fold increase in catch from week 5 to week 6 (fig.3.38.), followed by a plateau of catch level, followed by decline at the end of the season. This seasonal trap distribution differs from that in the 1980 emergence site, where a more consistent level was maintained through the season (f ig.,3 - 37.) . In the first four and five weeks of each season, 182 and 257 males respectively were caught with attractant traps in 1980, and 146 and 237 males respectively in 1981. These catches are not significantly different at p = 0.05 (*^ with Yates' correction = 0.816). Trap catch over this period was not likely to have been limited by any property of the traps (since higher catches were made later in the season). If moth movement was not greatly restricted by climatic conditions, the attractant traps clearly caught similar numbers of males at what were undoubtedly two different densities, even though it was only the beginning of the season (if weather conditions were important, catches in 1981 should have been higher, 150 Fiq. 3.37. Temporal distribution of catches of male C.niqricana in sex-attractant traps in the emergence site, Childerley Estate/ 1980 Histograms show weekly catch expressed as a percentage of the seasonal total. Weeks numbered through the season commencing Monday 26u May. a) Trap (i) SE corner, NE / SW orientation b) Trap (ii) S headland E/W orientation c) Total for two traps. n = seasonal total of trap catch. WEEK 151 Fig. 3.38. Temporal distributions of catches of male C.nigricana in sex-attractant traps in the emergence site WAl, Shimplinq Park Farm, 1981 Histograms show weekly catch expressed as a percentage of the seasonal total. th Weeks numbered through the season commencing Monday 25 May a) Trap (i) E headland/ N/ S orientation b) Trap (ii) N headland, E / W orientation c) Total for two traps n = seasonal total of trap catch. Fig. 3.39, Temporal distributions of catches of male C.nigricana in sex-attractant traps in the emergence site WBl, Shimpling Park Farm, 1981 Histograms show weekly catch expressed as a percentage of the seasonal total. th Weeks numbered through the season commencing Monday 25 May a) Trap (i) S headland, E / W orientation b) Trap (ii) W headland, N / S orientation c) Total for two traps n = seasonal total of trap catch. a) a) c) I TOTAL 152 K E E W b) b) 2 4 5 4 3 2 1 1 — 6 7 8 n - c - 9 )84 10 11 153 which was not the case). If trap catch was reflecting male population density, the catch in week 6 should have been followed by gradual decline, instead of a plateau followed by a slight increase in week 9. It appears that in week 6 trap catch was suppressed and/or thereafter elevated. The trap catch in week 6 not only coincides with peak male emergence and density, but also with an even more pronounced peak of female emergence and large increase in female population density (section 3.2.2.). Newly emergent females releasing pheromone could have been competing with the traps. Electroantennogram evidence shows that exposure to E ,E8,10-12:Ac (the pheromone) reduces the male response to E10-12:Ac (the analogue) (Wall, pers. comm.). This is to be expected since the analogue is much less active and not present in the natural pheromone (Greenway, 1984). Therefore, the increase in trap catch in week 6 was not likely to be the result of increased male response after exposure to the pheromone, rather the potential male catch in the absence of female competition may have been greater. Trap catch was not limited by saturation of the sticky surface, although the latter was deteriorating at this time, and was changed shortly afterwards. Catches during week 6 did not exceed 100 moths in any flight period, whereas catches of 120 were recorded in other traps during this study. It is the trend of sex-attractant trap catches after week 6 which shows most deviation from D-Vac. catches. Whilst female density declined rapidly after week 6, trap catches increased, possibly because of the reduced comp etitive effect. The higher trap catches may have still been below the full potential in the absence of females; similar numbers of males were caught in traps in week 8, when even fewer females were present. Finally the highest trap catches were recorded in week 9, when, although D-Vac. samples were not taken, the interpolated female density was about one eighth that of the peak level in week 6. The plateau of sex-attractant trap catch in the latter part of the season may therefore have been an artefact produced by a steady decrease in female competition. However, D-Vac. 154 catches of males suggested similar densities in weeks 5 and 7, yet numbers in sex-attractant traps were much higher in week 7, and as suggested above this may have been a suppressed level. Since the increased trap catch from week 5 to 6 showed the same proportional change as D-Vac. catch, sex-attractant trap catch in week 5 was evidently lower than expected (D-Vac. data in week 5 was based on fewer sample points, however the extrapolated density is likely to err towards an underestimate, which accentuates the discrepancy)• The poor trap catch in week 5 was almost certainly due to poor weather, which is also why only a limited number of D-Vac. samples could be taken. Temper ature at ground level did not exceed the 17*C flight threshold (Lewis et ad, 1975) for five continuous days during this week. Kite net samples taken on the two warmer days (22n<^ & 23r<^ June) showed an aerial population of males with the same high density as weeks 6 and 7 (section 3.2.2.). The trap catches in emergence site WAl, were, however, lower on these two warm days , than in other traps, including those in pea crops. Field Trap (i) NS orientation Trap(ii) EW orientation WAl 19, 7 12, 7 i—i 00 WBl o 31,32 PAl 33,33 39,36 ["• I—1 O] PBl 17,38 CO Prevailing wind directions during the activity of 22n<^ and 23 rd June were SSE and SW respectively. Consideration of geographical relationships of these four fields (fig.2.2.) and the position of the traps shows that, at least for the 23 rd , odour plumes from traps in emergence site WBl, and pea fields PAl and PBl probably passed over field WBl, while that from traps in WAl did not. The most unexpected and anomolous feature of trap catches is those high catches in weeks 7 to 9. An explan ation is required as to why older populations of males show an increased response to a pheromone analogue in the presence of (competing) females, and after exposure to the natural pheromone, over and above the response of similar sized, younger populations of naive males in the absence of females. 155 b) Pea fields The relationship between sex-attractant trap catch and population levels in pea fields is more important to ascertain, since it is this on which the use of the monitoring system as a predictive tool is based. Sex- attractant traps sited in pea crops were far more sensitive to changes in moth density than those sited at emergence sites. Trap catch reflected the density of both sexes within the crop, although the relationship was better in some fields than others. This is shown by regression analysis of weekly trap catch and weekly D-Vac. catch, arid by seasonal distributions of attractant trap and D-Vac. catches. Sex- attractant traps were used in two pea fields in 1980, 1981 and 1982. In 1980 there was no D-Vac. data for the pea crop itself and very low numbers were taken in the surrounding vegetation. In 1981 and 1982 the relation ship between sex-attractant trap catch and moth density in pea fields was more simple than that at the emergence site. In each of the three pea fields (PAl, PA2 & PB2) the weekly cumulative sex-attractant trap catch (two traps) was correlated with both cumulative male D-Vac. catch (PAl, r = 0.96; P a 2, r = 0.99; PB2, r = 0.97) and cumulative female D-Vac. catch (PAl, r = 0.98; PA2, r = 0.99; PB2, r = 0.92). Although correlation would be expected with two sets of cumulative data, these very high correlations do imply a good relationship between moth density and trap catch, with -increase in moth density being reflected by proportional increases in trap catch. Using all data from in and around the three pea fields for which D-Vac. data is available shows that Log. mean sex-attractant trap catch of male C nigricana per week is correlated with Log.(x+ 1) mean D-Vac. sample per week of both males (fig,3.40a. ) (r = 0.451, p<0.05, 19df) and females (fig.3.41a.) (r = 0.604, p<0.01, 19df). An improved fit is obtained if only those moth populations in the crop are considered. Log. trap catch of males was correlated with Log. D-Vac. catch of males (fig 3.40b.) (r = 0.652, p < 0 01, 17df) and females (fig.3.41b.) (r - 0.760, p<0.01, 17df) . Trap catches therefore reflect 156 Fig . 3.40. Relationship between sex-attractant -trap catch of male C.nigricana and density of males in pea fields/ Shimplinq Park Farm, 1981 and 1982 x-axis: Log-^ (x + 1) D-Vac. catch of males (Male catch/ D-Vac. sample / Week). y-axis: Log^^ Sex-attractant trap catch of males (Male catch / Trap / Week) . ■ ■ Pea field PAl, 1981 • • Pea field PA2, 1982 o o Pea field PB2, 1982 Numbers by data points refer to weeks in the season, commencing Monday 25^ May in 1981, and Monday 2 4 ^ May in 1982. a) Weekly mean D-Vac. catch calculated from all sample points (crop and surrounding vegetation). b) Weekly mean D-Vac. catch calculated from crop sample points only. Log, Male Catch / Sex-attractant Trap / Week 3 5 .c 0 . 1 9 . 0 8 . 0 7 . 0 O.fc .5 0 4 . 0 .3 0 2 . 0 1 . 0 0 . 0 I i i I I l I I I | i i i i I i <*0 ^ Male Catch/ D-Vac. Sample/Week e e W / e l p m a S . c a V - D / h c t a C e l a M ^ + o<=*10k s k e e W 5 - 2 s k e e W s k e e W 0.641 p 0.05 0 . 0 < p 1 4 6 . 0 = r 0.766x + 2.17 1 . 2 + x 6 6 7 . 0 = y -0.270x + 1.44 4 . 1 + x 0 7 2 . 0 - = y = % 1 . 1 4 = 2 r 6-11 S N 5 5 0 . 0 = r = % 3 . 0 = 2 r 1.740x + 7 6 . 1 + x 0 4 7 . 1 = y = 0.01 0 . 0 < p 2 5 6 . 0 = r = % 5 . 2 4 = 2 r 2-11 ------ 157 I I 158 Fig. 3.41. Relationship between sex-attractant trap catch of male C.niqricana and density of females in pea fields, Shimplinq Park Farm, 1981 and 1982 x - axis: Lo9]_o + ^ D-Vac. catch of females (Female catch/ D-Vac. sample / Week). y - axis: Log^ Sex-attractant trap catch of males (Male catch / Trap / Week) . ■ ■ Pea field PAl, 1981 • • Pea field PA2, 1982 o o pea field PB2, 1982 Numbers by data points refer to weeks in the season, commencing Monday 25^ May in 1981, and Monday 24^ May in 1982. a) Weekly mean D-Vac. catch calculated from all sample points (crop and surrounding vegetation). b) Weekly mean D-Vac. catch calculated from crop sample points only. Logln Male Catch / Sex-attractant Trap /Week - 5 . 0 1.0- 2 - 5 . 2 - 5 . 1 - 0 . 3 - 5 . 0 2 - 5 . 2 1.0- - 5 . 1 - 0 . 3 . . 0 0 - - 1 . 1 0 . 1 9 . 0 8 . 0 7 . 0 6 . 0 5 . 0 4 . 0 3 . 0 2 . 0 1 . 0 0 . 0 i i i i i i i i i i i i i i i i i Log10 + Female Catch/D-Vac Sample Sample /Week Catch/D-Vac Female + Log10 ek 6 • 6 Weeks ek 2 Weeks ek 2 Weeks y ; Y ; Y r ; r r : r r y r r 2 2 2 0.89% 9 8 . = 0 57.7% 7 . 7 = 5 < 5 0 . 0 < p 0 7 . 0 x 1 7 . 0 S N 9 0 . 0 ------5 1 4 . 1 + x 2 2 . 0 0.01 0 . 0 < p 0 6 7 . 0 11 3 5 . 1 + x 3 4 . 1 0.01 0 . 0 < p 4 0 6 . 0 11 1.54 5 . 1 + x 2 1 . 1 % 3 4 . 8 % 5 . 6 3 ------4 0 . 2 + 159 I I 160 within crop density of both sexes better than the density in and around the crop. This may be because there is a heavy weighting on the comparatively small area of surrounding vegetation, due to a disproportionate number of sample points (6 of 14 in 1981, 5 of 15 in 1982 fields). Male moth densities in particular were higher in surrounding vegetation than in the crop. Trap catch increases rapidly over a narrow range of male moth density within the crop (fig.3 .40b.),whereas female density within the crop increases over a wider range (fig.3.41b.). At higher moth densities the sex- attractant trap catch reaches an asymptote reminiscent of, and at a slightly higher level than that at higher moth densities in the emergence site. a s in the emergence site there appears to be a different relationship Jpetween trap catch and moth density in the two halves of the season. For male populations in the crop only, sex-attractant trap catches were correlated with mean D-Vac. sample catch in weeks 6 to 11 (r = 0.64, p<0.05, 9df), whereas in weeks 2 to 5 they were not at all correlated (r = 0.05) . Similarly females were correlated in weeks 6 to 11 (r = 0.70, p<0.05, 9df) but not at all in the first half of the season (r = 0.09). Thus in the first half of the season, that is at the most important time with respect to monitoring low densities and predicting immigration, there was, as in the emergence site, no relationship between trap catch and moth density. In contrast to data for the 1981 emergence site, the temporal distribution of trap catch in pea fields through the season did show considerable agreement with temporal distribution of moth populations in pea crops in some of the study fields. In 1980 sex-attractant traps were used in the study pea field (field J) and in a nearby pea field (field K in fig.2.1.). Trap catches showed a minor peak at the beginning of the season in week 3 (field J, fig.3.42.) and a major peak at the end of the season in weeks 9 and 10 (figs.3.42. & 3.43.). The only males caught around field J were in weeks 3 and 9, and although extremely limited, there is agreement between the two sets of data. Although a comparatively high trap catch was shown in lbl F iq. 3.42. Temporal distributions of catches of male C.nigricana in sex-attractant -traps in pea field J, Childerley Estate, 1980 Histograms show weekly catch expressed as a percentage of the seasonal total. Weeks numbered through the season commencing Monday 2 6 ^ May a) Trap (i) N headland, E / W orientation b) Trap (ii) E headland, N / S orientation c) Total for two traps n = seasonal total of trap catch. Fig. 3.43. Temporal distributions of catches of male C.nigricana in sex-attractant traps in pea field K, Childerley Estate, 1980 Histograms show weekly catch expressed as a percentage of the seasonal total. Weeks numbered through the season commencing Monday 2 6 ^ May a) Trap (i) W headland, N /S orientation b) Trap (ii) N headland, E / W orientation c) Total for two traps n = seasonal total of trap catch. % TOTAL 162 WEEK 163 field J in week 3, it was entirely due to one day's catch and a threshold was not attained. There was a possible peak in the female population in the surrounding vegetation in week 4, so an insecticide application may have been required. A threshold was not reached until late in the season on 23rd/ 24th July, in week 9, when the second peak of moths in the hedgerow was recorded with a D-Vac. Clearly the poor weather during the middle of the season that prevented, or at best impeded sampling, and when only low population levels were indicated, also prevented migration of the populations to the pea crops. In pea field PAl in 1981 moth densities in the crop were at low levels in weeks 4 to 6 with a large increase in population level in weeks 7 and 8. The sex-attractant traps sited in field PAl and the nearby pea field PBl, showed increasing catch from week 4 with a maximum attained in week 7. This was followed by a plateau of catch level and then decline (figs. 3.44. & 3.45.) similar to that in the nearby emergence site. The sex-attractant trap catches in field PAl therefore indicated the timing of peak population density in week 7, but not the magnitude. Since peak female density occurred in week 7, the lack of a more pronounced peak of trap catch is probably due to competition for males between females and traps. There were two alternative monitoring trap threshold dates for 1981, according to whether the grower was examining his traps on odd or even days, viz in the simplest case:- Day '(n + . . .) 1 2 3 4 5 6 7 8 Trap catch (either trap) 0 0 0 11 11 0 0 0 Case A - examination days / / // Case B - examination days / / / / Case a gives 11 moths on two consecutive two day period examinations (days 4 and 6) and therefore constitutes a threshold. Case B gives 22 moths at one inspection (day 5) but is preceded and followed by zero (or low) catches, and is therefore by definition not a threshold . A threshold in both fields was attained on the 2 4 ^ / 2 5 ^ June in week 5, and so anticipated the main immigration into the crop. This threshold was followed by five days of zero catch in all traps, and the alternative 164 Fig . 3.44. Temporal distributions of catches of male C.niqricana in sex-attractant traps in pea field PAl/ Shimplinq Park Farm, 1981 Histograms show weekly catch expressed as a percentage of the seasonal total. th Weeks numbered through the season commencing Monday 25 May a) Trap (i) N headland/ E / W orientation b) Trap (ii) W headland, N / S orientation c) Total for two traps n = seasonal total of trap catch. Fig. 3.45. Temporal distributions of catches of male C.nigricana in sex-attractant traps in pea field PBl, Shimplinq Park Farm, 1981 Histograms show weekly catch expressed as a percentage of the seasonal total. Weeks numbered through the season commencing Monday 2 5 ^ May a) Trap (i) W headland, N/S orientation b) Trap (ii) N headland, E / W orientation c) Total for two traps n = seasonal total of trap catch. l 30- el / TOTAL 20- 40- 10- 2 4 5 4 3 2 1 6 7 8 n = n 9 =22 10 165 546 11 WEEK 166 f—i threshold was then reached on 30 June / 1 July in week 6. Although the D-Vac. catch of males was low in week 6, the level of females was slightly higher, and if the progeny of these earliest immigrants significantly contributed to the damage of the crop, then the sex-attractant traps gave an accurate prediction (if trap inspection periods gave the second threshold). If early females are not important then the alternative threshold also gave a premature warning. The record of male moths in the traps apparently before they were present in the crop, may be due to the attraction of moths from the surrounding vegetation, or may indicate the insensitivity of the D-Vac. to low densities. The traps in pea field PAl were sited in the Northeast of the field (fig.2.7.) where initial immigration to the surrounding vegetation may have occurred (section 3.2.3.). The traps in pea field PBl were situated in the North, very close to the emergence site WBl (and the sex-attractant traps there), and moths may have been attracted directly from this source. In 1982 sex-attractant traps were used in both pea fields PA2 and PB2. Although the seasonal profiles from both fields are very similar (figs. 3.46. Sc 3.47.), they are quite distinct from the 1981 catch profiles. The population changes shown by the trap catch are much closer to the population trends in the crop as shown by D-Vac. catch, than any other sex-attractant trap results presented. Male populations in pea crops showed a slight build up in weeks 3 and 4 (although numbers were low in PB2), and a peak of numbers in week 7 followed by a rapid decline (figs 3.31a. Sc 3.33a. section 3.2.4.). The sex-attractant traps suggested a slight accumulation in weeks 2 and 3, with a peak in week 7 followed by a rapid decline, with no plateau of trap catch. A threshold, again depending on the timing of trap inspection, was attained on 9^ / ICj June in week 3 (field Pa 2 only). Females were in the crop at this time (fig.3.32a.) and an insecticide application may have been advisable. If trap catches in week 3 had not constituted a threshold (because of the two day inspection t h period) the alternative was not reached until 3(j June / s t 1 July in week 6. There is unfortunately no D-Vac. data from the pea crops for week 6, but a slight accumulation 167 Fig. 3.46. Temporal distributions of catches of male C. nigricana in sex-attractant traps in pea field PA2, Shimpling Park Farm, 1982 Histograms show weekly catch expressed as a percentage of the seasonal total. Weeks numbered through the season commencing Monday 24 th May. a) Trap (i) E headland, E / W orientation b) Trap (ii) S headland, N / S orientation c) Total for two traps n = seasonal total of trap catch. Fig. 3.47. Temporal distributions of catches of male C.nigricana in sex-attractant traps in pea field PB2, Shimpling Park Farm, 1982 Histograms show weekly catch expressed as a percentage of the seasonal total. Weeks numbered through the season commencing Monday 24^th May a) Trap (i) N headland, N/S orientation b) Trap (ii) W headland, E / W orientation c) Total for two traps n = seasonal total of trap catch. V. TOTAL 168 WEEK 169 could well have occurred before the main immigration in week 7, as in 1981. However, D-Vac. samples were not taken because of wet weather, and moth movement may also have been temporarily arrested. The suggestion made for 1981 data that sex—attractant traps in pea crops might attract males from surrounding vegetation or emergence sites in close proximity, is also plausible for 1982. The traps in field PA2 were sited in the Southeast (fig.2.9.) very close to the emergence site WA2, while those in field PB2 were sited in the North west (fig.2.10.) again close to the emergence site. Initial immigration and colonisation occurred in vegetation around these headlands, and would thus have provided a source of males, from which a considerable number could have been attracted to the sex-attractant traps, leading to premature thresholds. 3.4.2. Relationship Between Dispersal and Plant Phenology a) Emergence site The migration of the greatest number of either sex from the wheat crop to the surrounding vegetation and thence to the pea crop occurred in weeks 6 to 7 in both 1981 and 1982. At this time, development of the wheat was one week to 10 days more advanced in 1982 than 1981, as shown by the decimal growth stage (section 2.1.3.) (fig.3.4 8.). Emergence and population increase were also earlier in 1982 than in 1981 (section 3.2.2.). Prevailing temperature conditions might be expected to exert a similar influence on the rate of development of both the plants and the moths, leading to a synchronised relationship between certain phenological stages of the crop and moth emergence, population build up, emigration etc. Population increase of males (though not emergence) was initially a linear function of the date (weeks 2-6, 1981, y = 11.61 + 0.452x, r2 = 96.1%; weeks 1-4, 1982, 2 y = 0.23 + 0.449x, r = 99.5% while for females it was a curvilinear function (fig.3.49.). The development curves of crop growth and population build up of both sexes was clearly earlier in 1982 by a consistent period, which suggests synchronous development. If emigration from the 170 Fig. 3.48. Development of wheat crops in emergence sites, Shimpling Park Farm, 1981 and 1982 Data points show mean and standard error of decimal growth stage, based on weekly samples (number of plants - 10) . ■--- ■ Emergence site WAl, 1981 •---• Emergence site WA2, 1982 WEEK 171 Fig . 3.49. Development of wheat crops and build up of male and female populations of C.niqricana in emergence sites, Shimplinq Park Farm, 1981 and 1982 a) Decimal growth stage of wheat crops. Data points show means and standard error of weekly samples (number of plants = 10). ■ -■ emergence site WAl, 1981 • -• emergence site WA2, 1982 b) Build up of male populations of C.nigricana. Data points show mean and standard error of moths per D-Vac. sample from within the crop region. ■ -■ emergence site WAl, 1981 • -• emergence site WA2, 1982 c) Build up of female populations of C.nigricana. Data points show mean and standard error of moths per D-Vac. sample from within the crop region. ■ -■ emergence site WAl, 1981 • -• emergence site WA 2 , 1982 I I 172 P -j o _L L. i_n CTi _____ I o cr> ______i en Decimal Growth Stage _____ 1 o (_n ui Number of moths/Sample N u m b e r of mothsSample/ 1 9 8 1 W E E K : 173 emergence site is an intrinsic property of population biology, the decimal growth stage of the wheat crop, with some consideration of temperature, could be used to pre dict emigration from the emergence site. This in turn would inform the grower when to pay particular attention to his monitoring traps in pea crops, particularly in vigilantly examining the traps at regular 48hr. intervals. However, emigration appears to have occurred at weeks 6 to 7 in both years, despite the relatively advanced development of the population in 1982; in addition the 1982 weekly mean temperature was significantly higher in weeks 4 and 5, though not week 6 (week 4: t = 3.5 97, p<0.01; week 5: t = 2.877, p<0.05; week 6: t = 1.480, NS at 6df) which would thus enhance this bias. Migration from the emergence site was therefore delayed (relative to the build up of the population) in 1982 and appears not to be an inherent feature of popul ation growth and development. Some other factor must, therefore, have triggered migration; a likely candidate is an odour cue from the pea crop. b) Pea fields If pea crops provide an odour cue to initiate migration from the emergence sites to the pea fields, the phenological stage of the pea crop at the time of immigr ation is likely to be similar in different fields in different years. Crop development in both 1982 pea fields was more advanced than 1981 as shown by both vegetative and reprod uctive characters (see section 2.1.3.) (fig.3.50.). Veget ative growth in 1981 was determinate with no further growth past the 1 8 ^ node (growth stage Vl8), thereby limiting the number of fruiting nodes. Indeterminate vegetative growth in 1982 crops gave taller plants with a larger number of fruiting nodes, this indeterminate growth was more marked in field Pa 2 (fig.3.50b.). , The first possible threshold (as described in the previous section) in 1981 occurred when the plants were still in bud (R2)(fig.3.50b.), and the alternative threshold (B) just under a week later when the plants were in flower (R3 to R4) (f ig. 3 o 50b. ) . The first threshold date (a ) in 174 Fig. 3.50. Development of pea crops, Shimpling Park Farm, 1981 and 1982 a) Vegetative growth. Data points show means and standard errors of vegetative growth stage of peas (number of plants = 10). ■----■ pea field PAl, 1981 •----• pea field PA2, 1982 o----o pea field PB2, 1982 Weeks numbered through the season commencing Monday 25^1 May in 1981, and Monday 24*~ May in 1982. WEEK 175 Fig . 3.50. Development of pea crops, Shimpling Park Farm, 1981 and 1982 (continued) b) Reproductive growth. Data points show reproductive growth stage of pea crops determined from samples of 10 plants ■ ■ pea field PAl, 1981 • • pea fields PA2 and PB2, 1982 (both fields virtually identical) th Weeks numbered through the season commencing Monday 25u May in 1981, and Monday 24 May in 1982. Thresholds A and B are alternatives according to whether sex-attractant trap catches were recorded on even or odd days. The period of main immigration (week 7) in both years is also shown. WEEK 176 1982 (both fields) , although much earlier than 1981 thresh olds, also occurred with the crops in full flower (R4) (fig.3.50b.) and there is thus some agreement between fields. However, the alternative 1982 threshold, on exactly the same date as 1981 threshold B, was when the crops were at stage R7 to R8 (fig.3.50b.), with the oldest pods inflated with fully grown seeds, and the pod valves beginning to harden and wrinkle. Newly hatched larvae might be expected to have a lower level of successful establishment on such pods. Although the crops were described as R7 to R8 (since this was the oldest growth stage), the more detailed pheno- logical data collected in 1982 shows that 25% of the plants still had flowers during the first half of week 6, and about 50% of PB2 plants and 80% of PA2 plants had young uninflated pods at this time. Eggs laid at the time of these thresholds would not hatch until some days later. Calculation of hatching dates using Lewis and Sturgeon's (1978) weighted regression for egg development, gives the following predicted spray dates: threshold A, 1982:23 rd June (week 5); threshold A, 1981: lO^1 July (week 7); thresh old B, 1982:10^ July (week 7); threshold B, 1981; ll ^ July (week 7). The 1981 crop was at stage R5 in week 7, when the oldest reproductive stage was small flat pods. However the availability of young reproductive stages in week 7 1982 was considerably less; only 25% of plants in Pa 2 and 15% of plants in PB2 had young uninflated pods, and there was no flower. Furthermore the above discussion refers only to the phenological stages encountered by the progeny of the earliest female immigrants, although the contribution made to final damage levels by these larvae is unknown. The main immigration of females in both years did not occur until week 7; eggs laid at the beginning of this week are predicted to have hatched nine days later in either year. This hatching would have occurred between the spray date predicted from threshold B in both years and a recommended second application 14 days later. High damage levels were recorded, despite the low availability of young pods, particularly in 1982. The ability of young larvae to utilise old pods is in accordance with recent findings from A.D.A.S. field sites. 177 It was suggested that in 1981, populations of moths accumulated in surrounding vegetation, and delayed immigr ation, while the crop was at an early stage and possibly unsuitable for oviposition. In 1982 D-Vac. data was lacking from the critical period in mid-season, but some immigration occurred in weeks 3 and 4, but may then have been prevented by the inclement weather in weeks 5 and 6, but while pea plants continued to develop. The effect of pod age on larval success was not investigated in this study, although rd Wright and Geering (1948) claim that no larvae in 3 instar or younger survive after seed hardening (equivalent to stages R8, R9 S c RlO) . Larval infestation levels at different truss levels were recorded, and since pod age is revealed by setting dates recorded in phenology data, indications of levels of establishment in differently aged pods will be examined in the following section. Thus there is no suggestion of a 'preferred' growth stage stimulating immigration, although there is an extended period where several reproductive stages are represented. There was some tendency for threshold catches to coincide with flowering, such that larvae hatching 10 to 14 days later would encounter young pods. However, the accuracy of threshold catches in indicating immigration and for predicting hatching will be discussed in Chapter 6. There is evidence that pea plants are attractive to male C.niqricana, from experiments conducted to determine any interaction between the natural pheromone emitted from lures in sex-attractant traps and the presence of surrounding pea plants (Section 2.1.11.). In experiment 1, using sticky traps on the first six days and then water traps for four days, the treatment with pea plants arranged around the trap caught more males on every occasion (Appendix Ilia.). Using the Latin Square ANOVA plan of Perry et aT (1980) to remove the effect of day, site and day X site interaction, a significant treatment effect was shown (log transformed data, F = 10.117, p<0.05, 1 S c 4df) (Appendix Ilia.). In a further experiment (2 ) comparing older reproductive pea stages with young reproductive stages arranged around the traps (Section 2.1.11.), the young stages treatment caught more males on each of four occasions (Appendix Illb.). Analysis of variance using the same ANOVA plan indicated 178 above did not show a significant treatment effect (log trans formed data, F = 15.161, NS, 1 & ldf)(Appendix Illb.) because of the small number of degrees of freedom for error. Using an ANOVA plan to realise a cross-over design (Perry et al, 1980) provides one extra degree of freedom for error, and does give a significant treatment effect (log transformed data, F = 30.322, p<0.05, 1 S c 2df) (Appendix Illb.). This latter analysis is not strictly correct because the experi ment was designed for the more rigourous ANOVA plan, and furthermore this analysis includes the unsubstantiated assumption that there was no day X site statistical inter action. Although the response of male C.niqricana to the natural pheromone in sex-attractant traps cannot be justif iably extrapolated to the analogue used for monitoring, these results raise the possibility that the response of male C.nigricana to sex-attractant monitoring traps may be influenced by the aging and senescence of the pea crop, in addition to, and compounding other effects. 3.4.3. Relationship Between Dispersal and Larval Infestation a) Emergence site There was no positive relationship between larval infestation in one year, and the number of moths caught the following year; larval infestation was at the same level across the field in 1981, but there were high densities of moths in all age groups in the centre of the emergence site in 1982. Emergence and spatial distribution in emergence site WA2 (1982) were examined with respect to infestation levels in pea field PAl (1981). The unsprayed strip lying North/ South across PAl, which was sampled to assess infestation (Section 2.1.10.), approximately corresponds to the three D-Vac. samples P2, C8 and P6 in WA2 (fig.2.8.). The total number of moths in three age groups from these samples was compared with infestation levels (Appendix IVa.). Although no assessment of larval sex ratio was attempted, the two adult sexes were considered separately, since differential behaviour of the two sexes would influence spatial arrange- I.T— ments (sexing of mature 5^n instar larvae is possible when the pigmented testes of males are visible through the 179 cuticle). The percentage pod infestation was high in all three sampling areas (Appendix IVa.), with the infestation in the South significantly higher than in the centre (t = 4.039, p < 0.05, 3df). Pod infestation gives only a coarse indic ation of the potential adult distribution, because of the widespread occurrence of multiple infestations in pods at this site. Across the field 30% of infested pods had two or more larvae, and the maximum of five larvae per pod is unusual. The incidence of multiple infestation was greater in the South (Appendix IVa.) although not significantly different across the field. Consideration of this feature and the fact that plants in the North had fewer pods, shows that the number of larvae per plant was similar across the field (Appendix IVa.) with no significant differences. This index could be considered as an estimate of density per unit area, given that seed drilling rates were constant across the field, and if germination success was uniform. However, although no data is available to confirm this, the impression gained during the season, was that plants were more sparse at the top of the slope in the South, although they were not significantly smaller than elsewhere. Further more, this density index is calculated from the total number of larvae found in all instars. Young larvae that were still feeding in pods would have been killed or removed at harvest, which was shortly after the infestation samples were coll ected. Wright and Geering (1948) stated that 10 to 15% of the larval population are removed under normal conditions of harvesting, and that no larvae m the 3 instar, or younger, survive once further feeding is prevented by the hardening of the seeds. The number of larvae per plant in two age classes, including 5 th instars that have left the pods and dropped to the ground (as shown by damaged seeds, frass and exit holes), was not significantly different in the three areas (Appendix IVa.). The total number of adult moths of either sex, and in three age classes, caught in the centre of the field during the season, was consistently two to four times greater than the catch from either of the two perimetal regions, which were not significantly different from each other (Appendix IVa.). The central D-Vac. sample (C8) was taken along exactly the same strip left unsprayed 180 the previous year, whereas the two perimetal D-Vac. samples were perpendicular to this strip. Emergence from the area of the unsprayed strip was not expected to be higher than from the rest of the field, because despite spray applic ations, the whole crop was heavily infested. A sample of pods (n = 117) collected from another part of the field three weeks previous to the infestation samples had 25% pod damage, and end of season samples collected from the sprayed field, PB2, to introduce wild insects into the Rothamsted culture, were also heavily infested. The seed from pea fields PAl and PBl were sold soon after harvest because of "the severe damage" (Sir John Richmond, pers. comm.), whereas the harvest from other pea fields on the estate was stored. The high density of adult moths in the centre of the 1982 emergence site is not related to larval infestation in the previous year; even the number of moths younger than P . A. 7, which are considered to be comparatively newly emerged, was higher than in the corresponding perimetal population. If the uniform distribution of larvae in 1981 predicted uniform distribution of adult emergence, it is apparent that even moths of low P.A. did not reflect spatial patterns of emergence, and there must therefore be consider able movement of adult moths, soon after emergence. The alternative explanation is differential survival of over wintering larvae, such that the distribution’ of larvae in infested pods is unrelated to the distribution of larvae surviving diapause and/or successfully pupating. Possible causal mechanisms are heavier predation of larvae, cocoons, pupae or emerging adults, along headlands by carabids, game birds, corvids etc. Conventional wisdom suggests that highest larval densities and thus aggregated emergence the following season, would be concentrated along the headlands first encountered by immigrating female moths. There was clearly no suggestion of such an effect in this field, although it was atypically small• b) Pea fields In 1980 pod infestation in pea field J was at a low but variable level. Mean pod infestation was highest in 181 the perimetal area with a hedge (2.502%, n = 2971 pods), intermediate in the perimetal area without a hedge (1.442%, n = 2849) and lowest in the centre (0.864%, n = 2859). The highest and lowest were significantly different (arc-sin transformed, t = 2.744, p<0.05), but other comparisons were not. In both perimetal areas there was a tendency for higher percentage damage at truss levels 8 and 9, while in the centre this was not the case (fig.3.51.). In the perimeter with hedge area, there were nearly twice as many larvae as in the perimeter without hedge, and nearly three times the number in the centre. Although poorly recorded in 1980, crop phenology data in week 4 when a few females were caught in the surrounding vegetation, showed that there were newly set pods on truss levels 1 and 2, and flower on the third. While some damage in these lower truss levels may be attributable to larvae from these first females, (although not all since some larvae in these pods were in young instars), most larvae were probably the progeny of the later arriving females in week 9, one month before the infestation samples were harvested. This is borne out by the number of larvae in each instar, since at the time of harvest 46% of the larvae were below instar 5. In the 1981 pea field the level of pod damage was much higher, with the levels shown in Appendix IVa. Within each of the three areas, analysis of variance showed significant differences in percentage pod damage between truss levels in both the North and centre, but not the South (Appendix IVb.). There was also a significant differ ence between sub-samples in the centre, probably because the four sub-samples were collected from four different areas on a line running North to South; such that the two central sub-samples nearest the headlands had damage levels at just over 50%, while the other two nearer the centre had just over 40% pod damage. Exclusion of counts from the upper truss levels with low, variable numbers of pods and damage levels, and reanalysing (e.g. truss levels 1 to 8, 1 to 6), shows that there were no differences between truss levels and that a more or less constant percentage of pods were damaged (Appendix IVb.). 1 8 2 Fig. 3.51. Distribution of damage by larvae of C.niqricana Pea field J, Childerley Estate, 1980 Histograms show percentage pod damage (arc-sin transformed) with standard errors, based on five samples of 50 unsprayed plants. Percentage pod damage, number of pods and number of larvae shown for each truss level, in three areas of the field. Truss level 1 is the oldest at the bottom of the plant. a) Perimeter of field without hedgerow b) Perimeter of field with hedgerow c) Centre of field 183 NUMBER OF PODS 128 180 235 273 305 267 220 249 250 23 5 1 9 6 145 102 49 15 NUMBER OF LARVAE 2 1 1 4 2 2 2 8 5 8 2 3 2 0 0 n 1 1 NUMBER OF PODS 145 235 262 283 320 286 273 262 2 5 8 232 1 7 3 121 71 t NUMBER OF LARVAE 1 3 5 4 11 6 7 9 12 11 3 1 4 0 0 NUMBER OF PODS 1 0 9 2 2 8 274 305 297 303 282 28 4 241 193 1 7 3 99 51 17 3 NUMBER OF LARVAE 1 0 3 1 2 4 5 1 3 1 1 1 C 1 184 However, as indicated in the description of the relationship between larval infestation and adult density the following season, the number of larvae is more import ant than the percentage damage. Similar numbers of larvae were taken from each of the three areas as shown by a non significant variance ratio for areas in a three-level ANOVA (Appendix IVc.). There was a significant F-value for truss level, but there was no significant interaction between area and truss level (Appendix IVc.). As expected there were significant differences in the number of larvae in different instars, as well as a significant variance ratio for larval instar X truss level interaction, reflecting a preponderance of older instars in the oldest truss levels. There was also a significant interaction between larval instar and area, due to greater numbers of younger larvae (instars 1 to 4), and less older larvae (instar 5) in the South (Appendix IVc.). This can be seen from the composition of the larval population at the time of sample harvaest (fig.3.52.). When the total number of larvae at a truss level was high (levels 1 to 6) the percentage of larvae in each instar was comparatively constant, e.g. ca. 1% for lst instar, 2-5% for 2n<^ instar, 7 - 12% for 3r<^ instar etc. Examination of plant phenology records shows that truss level 1 had open buds and flower 51 days prior to the harvest date, and that a new truss level was exposed every three to four days until the youngest levels (fig.3.52d.). Depending on the two alternative threshold dates and the immigration of female C.nigricana in weeks 6 and 7 shown by D-Vac. catches, plants were exposed to moths for a maximum of 37 to 44 days (fig.3.52d.). Thus the oldest truss levels (1 to 3 or 5) were exposed for a similar time while the younger truss levels were only exposed from the time they appeared. In each of the three areas, the number of larvae in each truss level was correlated with length of exposure, either after the beginning of week 6 or the beginning of week 7 (Appendix IVd.). There was a better fit with data of exposure after week 6, suggesting that early immigrant females do have a strong influence on the final number and distribution of larvae, a feature which has strong implica- 185 Fig. 3.52. Distribution of larval instars ot C.niqricana within truss levels of pea plants and length of exposure of crops in Pea field PAl/ Shimpling Park Farm, 1981 figs. a. - c. show percentage of larvae at each of five instars and those in the fifth instar which have vacated the pods, at each truss level. a) Unsprayed area in the North of the field. b) Unsprayed strip in the centre of the field. c) Unsprayed area in the South of the field. d) Length of exposure in days of truss levels of pea crops to oviposition by female C.nigricana after-two altern ative dates of moth immigration. Truss levels numbered up the plant, where level 1 is the oldest and lowest. 186 234567 89 10 Truss Level 1 2 3456789 10 Truss Level Truss Level 187 tions for the accuracy with which the threshold timing reflects female immigration. Notwithstanding this relation ship a better fit and more significant correlation was obtained with the number of larvae and number of pods at each truss level in the three areas (Appendix IVd. & fig.3.53.). This suggests that a constant proportion of pods in a truss level were damaged and was inferred pre viously in this section, when analysis of variance failed to show significant differences in percentage damage at different truss levels. There was no difference in the chance of damage to single or paired pods, and damage to one of a pair was not associated with increased likelihood of damage to the other. Thus the distribution of damage in the 1981 pea field was not related to either spatial or temporal patterns of dispersal of adult female moths. However, it is not known how the sampling methods used to evaluate these patt erns relate to the ovipositional activity of females. A range of differently aged pods were equally susceptible to larval damage, although the extent to which final larval distribution reflects oviposition patterns is also unknown. In the 1982 pea fields, percentage damage to pods showed a linear increase for 24 days up to over 40% damage at the time the samples were harvested (f ig. 3.54a.) . Changes in larval composition over this period were similar in both fields (figs.3.54b. & c.), although more older larvae appeared earlier in field PB2; this was probably due to earlier initiation of oviposition. Within each field, three areas were sampled. There were significant differ ences in both percentage pod damage and percentage seed damage between areas in all but one case, and in percentage seed damage between fields in all but two instances (Appendix IVe.). The percentage damage of both pods and seeds at the various truss levels within one sample area was different from 1981, with a trend of increasing damage with decreasing age in both fields (figs.3.55. to 3.58.). This was unlike 1981 where there was more uniformity of damage at most levels. As with 1981 plants, damage levels in the upper trusses were less meaningful because of the low number of pods involved. During week 4 when there was some immigration of 188 Fig. 3.53. Relationship between the number of larvae of C.niqricana and the number of pods at truss levels in unsprayed areas of pea field PAl/ Shimplinq Park Farm, 1981 Data from 200 plants in each of three areas o NUMBER OF PODS 3VAHVT JO ajQWflN 189 Fig. 3.54. Development of infestation by larvae of C.niqiicana and final composition of larval population in pea pods, Pea fields PA2 and PB2, Shimpling Park Farm, 1982 a) Development of infestation as shown by percentage pod damage in pea fields Pa 2 (•---- •) and PB2 (o---- o) . b) Percentage of larvae at each of five instars and those in the fifth instar which have vacated the pods, at four sample dates during the season in pea field PA2, together with composition of larval population at harvest in pea field PAl, 1981. c) Percentage of larvae at each of five instars and those in the fifth instar which have vacated the pods, at four sample dates during the season in pea field PB2, together with composition of larval population at harvest in pea field PAl, 1981. 190 40 - Percentage 30 - Pod Damage 20 - 10 - 0 -■ 8 10 12 14 16 18 20 22 24 26 28 30 2 JULY AUG. WEEKi 7 | 8 | 9 | 10 | 8 10 12 14 16 18 20 22 24 26 28 30 JULY AUG. WEEK: 7 8 9 10 J ^2 Fig. 3.55. Percentage pod damage at each truss level in three areas of Pea field PA2, Shimpling Park Farm, 1982 Graphs show percentage pod damage and standard errors. Standard errors calculated from normal approximation to binomial distribution with large numbers; error bars dashed where n < 30. a) Area of pea field nearest to emergence site. b) Centre of pea field. c) Area of pea field furthest from emergence site. 192 TRUSS LEVEL 193 Fig. 3.56. Percentage seed damage at each -truss level in three areas of Pea field PA2, Shimpling Park Farm, 1982 Graphs show percentage seed damage and standard errors. Standard errors calculated from normal approximation to binomial distribution with large numbers; error bars dashed where n < 30. a) Area of pea field nearest to emergence site. b) Centre of pea field. c) Area of pea field furthest from emergence site. 194 i i i i---- 1---- 1---- 1---- 1---- 1---- 1---- 1---- 1---- 1 1 2 3 4 5 6 7 8 9 10 11 12 13 TRUSS LEVEL Fiq. 3.57. Percentage pod damage at each truss level in three areas of Pea field PB2, Shimplinq Park Farm, 1982 Graphs show percentage pod damage and standard errors. Standard errors calculated from normal approximation to binomial distribution with large numbers; error bars dashed where n<30. a) Area of pea field nearest to emergence site. b) Centre of pea field. c) Area of pea field furthest from emergence site. 196 NUMBER OF PODS 90 85 76 54 46 31 8 3 3 100' a) 90- 80' 70' 60- PERCENTAGE 50' POD DAMAGE 40- 30- 20- 10- NUMBER OF PODS 63 86 71 41 37 20 16 8 3 3 1 100- b) 90- 80- 70- 60- PERCENTAGE 50- POD DAMAGE 40- 30- 2 0 - 10- NUMBER OF PODS 46 71 89 72 65 54 32 20 11 9 6 3 2 100“ c) 90- 80- 70- 60- PERCENTAGE 50- POD DAMAGE 40- 30- 2 0 - 10- -- 1---1-- -- 1---1-- -- 1---1-- 1 2 3 4 5 6 9 10 11 12 13 TRUSS LEVEL i :>i Fig . 3.58. Percentage seed damage at each truss level m three areas of Pea field PB2, Shimpling Park Farm, 1982 Graphs show percentage seed damage and standard errors. Standard errors calculated from normal approximation to binomial distribution with large numbers; error bars dashed where n < 30. a) Area of pea field nearest to emergence site. b) Centre of pea field. c) Area of pea field furthest from emergence site. 198 NUMBER OF SEEDS 275 357 395 345 210 185 121 28 7 9 100 a) 90- 80- 70- 60- PERCENT ASE 50- SEED DAM AS E 40“ 30 - 20 - 10 - NUMBER OF SEEDS 211 357 330 162 133 84 50 15 8 6 3 100 b) 90- 80- 70- 6 0 PERCENTASE 5°~^ SEED DAMASE 40_ 30- 20- 10- NUMBER OF SEEDS 108 245 334 306 263 245 153 66 28 16 11 13 4 100-1 c) 90- 80- i 70- i 60- PERCENT A3E 50- SEED DAM AS E 40- 3 0 20- lO t--- 1----1----1----1----1----1----1----1----1--- r 1 2 3 4 5 6 7 8 9 10 11 12 TRUSS LEVEL 199 females in pea field PA2 there were at least two flowering trusses on every plant and about five truss levels with flowers or fruits. There was little or no indication of any female immigration into pea field PB2, where the phenol ogy of the crop was the same as field PA2. Percentage damage to the first truss levels in field PB2 (figs.3.57 & 3.58.) was the same or slightly greater than that in field PA2 (figs.3.55. & 3.56.). This suggests that the early immigrant females in field PA2 did not greatly contrib ute to final damage levels, or alternatively that female immigration into PB2 at this time, did occur but was not detected by D-Vac. sampling. During week 7 the time of the main immigration into both fields about 95% of pods were fully inflated and the oldest truss levels carried dry pods with starchy seeds (stage R9, fig.3.50b.). These lower truss levels were clearly preferred less for oviposition and/or unsuitable for larval development as shown by less percentage damage compared to mid- and upper levels (figs.3.55. to 3.58.). 1982 plants were exposed to C.niqricana for a maximum of 29 days (assuming immigration from the beginning of week 7), compared to 37 to 44 days for 1981. The larval instar composition at harvest was the same in the two years (fig. 3.54.), since in 1982 this was achieved over a shorter period of time, the oviposition period during this latter season was shorter. This was undoubtedly enforced by the advanced development of the crop and its unsuitability. As in 1981 the similarity of damage levels in different areas of the fields and between fields, does not reflect adult spatial distributions. There was also no relationship to adult temporal distributions, because a wide range of differently aged pods may be attacked. 200 3.5. Discussion In the field C.nigricana larvae pupate in the Spring after protracted diapause and emerge two to three weeks later. Wheatley and Dunn (1962), studying the influence of diapause on time of emergence of C.niqricana, stated that the beginning of emergence may vary from year to year by three weeks or more; in this three year study, emergence in 1982 was two weeks earlier than 1980. They suggested that the variation in temperature requirements for post-diapause development leading to emergence, may be due to C.niqricana cocoons not responding immediately to increasing soil temp erature in the Spring. Temperatures from 4* to 11eC were most suitable for diapause development and a minimum of ten weeks exposure to the optimum of 5.6* to 7.8*C was needed. Wheatley and Dunn concluded that to predict the time of moth emergence, account must be taken of prevailing tempcj.atu.ras from about the end of August, although the developmental relationship was insufficiently known. This method differs from many currently suggested for other Lepidoptera, which generally assess heat accumulation only after January 1 (e.g. Sanders, 1975; Labanowski, 1981; Glen Sc Brain, 1982; Potter Sc Timmons, 1983; Richmond, Thomas Sc Bhattacharyya, 1983 . ) . Although Taylor (1981) reviews "physiological time" and concludes it is dependent on the temperature regime that the developing insect experiences, Philogene (1982) stresses that physiological time should be regarded as a function of both temperature and photophase/scotophase. Thus increasing day length might also be a mediating influence on the emergence °f C.niqricana, although cocoons are buried in the soil. In Choristoneura fumiferana(Clemens), Sanders (1975) found that emergence time on any given day depended on temperature, but was independent of photoperiod. Volney, Waters, Akers & Liebhold(1983) suggested that variation in times of emergence in Choristoneura spp. may be due to physiological morphs not recognised by appearance or host origin. Cydia molesta (Busck)emerged earlier from the South side of trees than from the North (Baker et al,1980) indicating the importance of radiant energy in influencing spatial patterns of emergence. Emergence of C.niqricana from areas lying to the North of tall hedgerows might therefore be delayed, although in this 201 study probably only the Southwest of the 1981 emergence site could have been influenced. Moisture may also be an important criterion for emerg ence, Pectinophora gossypiella(S aunders) show better emergence from moist soil than dry soil (Watson, Lindsey & Slosser, 1973; Clayton & Henneberry,1982), and Baker and Perron(1944) found that precipitation tended to assist emergence of C.niqricana. Periods of rain may have assisted moth emerg ence in the sites studied here, but since wet weather tends to be associated with cooler temperatures, there may have been some accumulation of moths very near to emergence. These would appear as soon as the temperature became favour able again, and might explain why Baker and Perron"also noted that bright warm spells usually preceeded maximum emergence. C.niqricana are able to emerge from depths of up to 30cm., and at 60cm., 75% of diapausing larvae successfully move to the surface before pupating (Wright & Geering,1948). This is in contrast to many species, e.g. P .qossypiella buried under 2.5cm. showed more than 95% failure to emerge (Henneberry Sc Clayton,1979). Notwithstanding current practice of minimum disturbance and direct drilling, cultural control of C.niqricana by ploughing to depths of 60cm. or more, would not be practical. Data from the laboratory culture suggested that emerg ence of C.niqricana may be around dawn, or over a short period as in other species (e.g. Callahan,1958; Banerjee & Decker, 1966a). Emergence at this time would give adults time to inflate and dry their wings before the afternoon activity period. Freshly emerged moths were caught in wheat with the D-Vac., occasionally with unexpanded wings, but always with short, contracted abdomens; the physiological age of these moths was 3, i.e. the very youngest. Emergence of Cydia ptychora (Meyrick), which flies at night or early morning (0700 - 1000) was mainly at night (Taylor, 1965) . Wheatley and Dunn (1962) examined emergence of C.niqricana at a number of controlled temperatures and concluded that the emergence curve was basically linear. Peak emergence of C.niqricana in the middle of the season, with the number of emerging moths tailing off before and after, is typical of other Lepidoptera studied, which show clear peaks even in multivoltine species with overlapping 2 02 generations. The time between first emergence and peak emergence of C.niqricana was about six weeks in this study, four to five weeks for Wright and Geering (1948), and ranged from two to over six weeks from 1937 to 1941, according to Baker and Perron (1944). Six weeks seems to be a typical period and is thus similar to other univoltine species such as Podesesia syringiae(Harris) (Potter & Timmons, 1983) , rather than multivoltine species which seem to show peak emergence in Spring generations after about three weeks (Baker et al, 1980; Baker et al, 1982; Glen & Brain, 1982). However in these studies, emergence patterns are shown by catches in emergence traps or inferred from pheromone-trap catches. The use of the D-Vac. in this study is to be preferred, since for moths to be recorded in most if not all designs of emergence trap, they have to be active. There may indeed be a "hidden dependency" (Baker et al, 1980) between emergence traps and pheromone traps as both are a measure of activity, and not necessarily emergence. Most day fliers develop into flight mature adults at a lower temperature than the flight thresh old; a cold period allows adults to emerge and even mature, but they do not take off until it becomes warmer, and then do so en masse (Johnson,1966)• D-Vac. samples can yield newly emerged moths and also exuviae, indicating that the sample is drawn from down to ground level and will reflect emergence. Although both sexes showed peak emergence within the same week, evidence was given to suggest that males emerged earlier than females. Wiklund and Solbreck(1982) state that protandry can be either incidental or adaptive. Earlier emergence of males would occur incidentally if male pupae were smaller, as in C.nigricana, since they should have shorter post-diapause development times. Protandry is an optimal reproductive strategy for both males and females, and is thus adaptive. Wiklund and Fagerstrom(1977) showed that with certain restrictions (including female monogamy), if all males have equal competitive ability, males emerging before the females, will on average, mate with more females than those emerging later. A3 life expectancy of males in creases, males should emerge earlier than females and maxi mise their reproductive fitness. They later showed 203 (Fagerstrom & Wiklund,1982) that protandry is a mating strategy for females as well, who are selected to minimise their time between emerging and mating, and therefore the chance of pre-reproductive death. In C.nigricana separate peaks of emergence for the sexes could not be resolved; because the species may not satisfy all the requirements of Wiklund and Fagerstrom's model. Protandry in C.nigricana is probably of the incidental type. The variance in eclosion times is assumed to be maintained by the environmental variability (Fagerstrom S c Wiklund, 1982), but there could also be genotypic differences. Truman (1973) showed that the time of activity of male An therea pernyi(G.M.) was influenced by adult developmental temperatures; females showed corresp onding shifts in the time of pheromone release. Thus in the field adults emerging earlier may be temporally i-'.dated within individual activity periods, as well as between them. Pheromone or sex-attractant traps are undoubtedly more sensitive survey tools for detecting moths than other systems, e.g. bait traps for C.molesta (Bailey, 1980), bait traps for Argyrotaenia velutinana(Walker) (Dean & Roelcfs, 1970), blacklight traps for Heliothis virescens(F.) (although not Heliothis zea( Boddie)) (Hendricks, Graham, Guerra S c Perez, 1973). They are now used for many species (Klassen, Ridgway Sc Inscoe, 1982; Wall, 1984). In this study sex-attractant trap catches of male C.nigricana over the whole season were linearly related to indices of adult male C.nigricana population density in pea fields, but not in emergence sites. Sex-attractant trap catch of males was also linearly related to indices of female C.nigricana population density in pea fields and certain subpopulations in emergence sites. Other workers investigating different species have had variable success in demonstrating relationships. With P.gossypiella, the number of male, female or total emergences on individual days were poorly correlated with male moth catches in gossyplure- baited traps (r = 0.38, 0.27, 0.28 respectively). However mean male, female and total moth emergences per cage per week over a period of one month were significantly correlated with trap catch (r = 0.83, 0.79, 0.82 respectively) (Henneberry Sc Clayton, 1982). For spring emergence of C.molesta, pheromone trap catch of males was well correlated 204 with male emergence in two years (r = 0.93, 0.96) and with female emergence in one year (r = 0.98) (Baker et al, 1980). Glen and Brain (1982) also found no significant difference in emergence curves of male and female C.pomonella, and these in turn were not significantly different from the curve of pheromone trap catch. Both groups of workers note that there was no protandry shown. Bailey (1980) found that the date of 5% catch of C.molesta in pheromone traps corres ponds with dates of 5% emergence of adults from pupae in corrugated card trunk bands, but does not say whether this was recorded by counting active moths in the emergence trap or searching for exuviae. However, the above are examples where both pheromone trap catch and emergence trap catch are dependent on favourable temperatures. More recently, Rothschild, Vickers and Morton(1984) were unable to demon strate any consistent correspondence between the daily pattern of adult C.molesta from corrugated card trap bands, and captures in pheromone traps or bait p ails. Mony species for which pheromone traps are u tilised are orchard pests, or otherwise resident pests. In emergence sites of C.nigricana the population is depleted by emigration. Furthermore the aerial moth population, as shewn by albeit lim ited kite net catches, on which sex-attractant traps may be presumed to act (although non-fliers may also be stimulated to fly ), does not bear any relationship with moth density or emergence. Although few if any workers have related pheromone trap catches to independent estimates of adult density, relationships have been demonstrated for some species with other life cycle stages or density indices. For C.pomonella it was possible to indicate the density response of pheromone traps by correlating seasonal trap catches of males with absolute infestation levels at harvest (Riedl & Croft, 1974). Sex pheromone traps for Archips arqyrospilus(Walker) caught numbers which reflected population levels estimated by other sample methods such as larval counts, harvest samples and overwintering egg masses (Madsen & Peters, 1976) . M aclellan (1978) obtained significant correlations between Spring larval counts and captures of males in Summer, when populations of four orchard tortricids were at moderate to high density. For one of these species, Spilonota ocellana(Schifferm uller) there was also correlation between captures of males in 205 Summer, and subsequent fru it damage. Johnson(1983) found a direct relationship between the number of H.virescens in pheromone traps and egg counts in the field . This class of relationship is that into which Macaulay's (1977) correlations fa ll, that of trap catch of male C.nigricana with final damage, and date of catch of 10 moths in a trap with date of first egg 12 days later. It is relationships such as these which enable traps to be used as detection and predictive t o o l s . With Plutella xylostellaf L .1 Baker et al(l982) did show that day-degree accumulations predicted the peak flights shown by pheromone catches, and that these could then be correlated with offset larval population levels. However, other workers have used sex-attractant or pheromone traps quantitatively with no other estimate of moth density. Thus Alford and Hammond (1 9 8 2 ) surveyed four species in the Plusiinae using only one synthetic pheromone and compared the densities. Ayre, Tumock and Struble (1982) concluded that the variability in inter-trap catches of Euxoa messoria (H arris)indicated that moths were not evenly distributed throughout the test area, however, since traps were spaced 2 at 1.6km. intervals to form a grid covering 64km ., this seems to have been a reasonable hypothesis. With P.xylostella Baker et al(1982) found significant correlation between pheromone catches of adults on the border and centre of 67% of their experimental fields, and correctly concluded that this was more likely indicative of sim ilar activity patterns, and not necessarily due to uniform distribution within the f i e l d . There are no a priori reasons for assuming that pheromone trap catches reflect male moth density. With trap catches of C.pomonella and infestation at harvest described above (Riedl & Croft, 1974), the trap catch response was non linear and the traps were not indicative at high infestation levels. The trap catch anticipated emergence of Spring flight adults from corrugated card trunk bands (an a rtificia l pupation site) in emergence traps, by up to eight days, indicating great efficiency at low moth densities. Trapping efficiency then declined towards the end of the Spring generation (Riedl et al, 1976). The maximum male catch of O strinia n u b ilalis(Hubner) in pheromone traps occurred after 2 06 the maximum male and female catches in lig ht traps (and also after most egg masses had been deposited), when moderate to large populations of moths were present (Oloumi- Sadeghi, showers & Reed, 1975). The number of male O .nubilalis flying under 3m. was not synchronised with the number of males captured in traps baited with pheromone or virgin females (DeRozari, Showers & Shaw, 1977)• In Madsen and Peters' (1976) study on Archips spp., although A. argyrospilus trap catches reflected the population levels estimated from other methods discussed earlier, traps for Arch ip s rosana (L.) caught high numbers of males but did not correlate with other population estimates. It was suggested that this was because males were attracted from sources outside the orchard, and in this respect may be sim ilar to C.nigricana. Thus there are as many examples demonstrating a lack of relationship between trap catches and density indices. Additionally, environmental factors such as temp erature or wind parameters may be sub-optimal for trap use during activity periods. Unrepresentative catches of C.pomonella in pheromone traps and U.V. lig ht traps were attributed to upper and lower temperature thresholds (Batiste, Olson & Berlow itz, 1973a; 1973b) . In the present study, it is suggested that the poor performance of sex-attractant traps in reflecting male density in emergence sites is attributable to competition from females, although a suitable explanation- of the mech anism cannot be provided. In most cases of poor trap perform ance, such as those mentioned above, female competition is mentioned or inferred, particularly at high densities, e.g. for H.virescens and H.zea (Hendricks et al, 1 9 7 3 ; Roach, 1 9 7 5 ) , C.pomonella (Howell, 1 9 7 4 ) , O.nubilalis (Oloumi- Sadeghi et al, 1 9 7 5 ) . However the patterns of trap catch of C.niqricana are not those that would be predicted under female competition. In Rhyacionia frustrana (Comstock), a protandrous species, high catches of males were made with female abdominal-tip homogenate, when emerging males were more abundant than females, but there was a sudden decrease when female emergence exceeded males (seasonal sex ratio was unity) (Berisford & Brady, 1 9 7 2 ) . With C.niqricana catches of males were lower in the absence of females in the first half of the season, followed by higher catches 207 in the presence of females, and furthermore these high catches are suggested to be below the potential. The fact that the sex-attractant is the less attractive pheromone analogue may be of importance. However, unless the laboratory evidence from EA2 recordings that exposure to the natural pheromone reduces the response to the analogue is not applicable to the field situation, the performance of the traps is difficult to explain. Although feral female competition with pheromone traps may jeopardize the development of monitoring systems Although not detection systems), the reverse, that of competition from pheromone with calling wild females, can be exploited. Dis ruption of mating was nearly 100% in Eucosma sonomana Kearfott (Overhulser, Daterman, Sower, Sartwell & Koerber, 1 9 8 0 ) , and mating disruption of P. gossypiella gav^ control that was as effective and cheap as conventional insecticide (Gaston, Kaae, Shorey & Sellers, 1 9 7 7 ) . However, attempts to disrupt mating of H.zea were most effective at lower moth population densities (Carpenter, Sparks S c Gueldner, 1 9 8 2 ) , which suggests that wild females compete well. Similarly "Disparlure" was used to disrupt mating of low density populations of Lymantria dispar(L-) (Beroza, Hood, Trefrey, Leonard, Knipling & Klassen, 1 9 7 5 ) . The correlation between sex-attractant trap catch of male C.nigricana with D-Vac. catches of adults, particularly females is an important finding. However, retrospective relationships using data for the whole season are of no pre dictive value, and it is therefore unfortunate that the relationship between trap catch and moth density in pea fields in the first half of the season, which leads up to and includes the sudden immigration of the pest, is very poor. The extent to which findings in this study can be used to refine the monitoring system for C.nigricana will be discussed in more detail in Chapter 6. Many species have diel periodicity of male sex attraction and female release, modified by temperature (e.g. Sower, Shorey S c Gaston, 1970; 1971; Comeau, Carde Sc Roelofs, 1 9 7 6 ; Webb S c Berisford, 1 9 7 8 ; Landolt & Curtis, 1982). In C.nigricana, female calling, as shown by period icity of male catch at female lure traps, may reach a peak between 1600 - 1800hr. (Lewis et al, 1975). However, the 208 period of male response may be longer; in Dioryc-tria ab ietella(Schifferm iiller) , the duration of male respons iveness to pheromone was about twice as long as the period of female release in 12L : 12D photoperiods (Fatzinger, 1973), Hence males might be caught in sex-attractant traps outside the female calling period. As each daily activity period progresses, the sex ratio in the aerial population of C.nigricana may become increasingly male biased. Male biased kite net catches were observed in this study, and Lewis et al (1975) recorded sex ratios of 3:1 to 9:1 up to 1400hr (although in relatively small catches) which pro gressively increased to an inbalance of 70:1 at the time of peak density. Banerjee and Decker (1966a) found that the periods of sexual calling in crambids were characterised by a great preponderance of actively flying male moths, and Taylor (1965) found a male biased catch of C.ptychora in light traps, when the population sex ratio was known to be unity. Male and female C.nigricana may disperse within or out of the emergence site at the beginning of the activity period, when flight is not for mating, sim ilar to the situation for O .nubilalis (Showers, Reed, Robinson & DeRozari, 1976). Thereafter active females are present in low numbers and males show increased activity as they search for calling females (Lewis et _aT, 1975), flights not being dispersive, but movements a mixture of random and oriented. Lewis e£ al_ (1975) could not demonstrate a significant difference between mean flight times of male and female C.nigricana, although females were slightly earlier. If calling females were rapidly found’ by males, and then stopped releasing pheromone while copulating (attracted males disperse once one has succeeded in copulating (Lewis et al, 1975)) this would remove much of the competition with sex-attractant traps aAd active sexually frustrated males would then be caught. Doane (1968) found that after mating, female L. dispar did not call and avoided males attempting to copulate, but they were active and searched for oviposition sites. However, small quantities of pheromone are very attractive (Wall ert al, 1 9 8 1 ) , and contaminated vegetation in the vicinity of a female that had been calling could remain attractive (Lewis et al, 1975; Wall et al, 1 9 8 1 ), especially if ohe pheromone gland was smeared onto the plant surface (Birch, 1 9 7 0 ) . 209 After mating females may fly again, dipersing to the surround ing vegetation as suggested by Lewis et al(1975) and which could also explain why mean flig h t times of the sexes were not different. Although this system might suggest bimodality in the daily distribution of flying females, this could be masked by variability between females, e.g. onset of calling time, duration of mating. In C.molesta there was no differ ence in the time of male activity at synthetic pheromone or live virgin female sources (Rothschild & Minks, 1974), how ever in this study the synthetic attractant was not the pheromone, but a less attractive analogue. Individual male C .nigricana may show different and variable response thresh olds under the influence of both internal and biotic and abiotic external factors (Wall & Perry, 1982). The main dispersive role is generally shown by the female, since it is her function to lay eggs in a new habitat (Johnson, 1966). Males are required to fertilise the female (Chapter 4) but this could occur at any time or anywhere. The timing of dispersal is often ensured by sexual immaturity of females at exodus (Chapter 5) . The migratory performance of C.nigricana puts them in Type 1 of Johnson's (1966) classification, defined as short lived adults that emigrate and die within a season, without returning to the eclosion site. The exodus flight of many insects is often vertical or at a steep angle, and often spiralling as the insects escape their boundary layer (e.g. Adkin, 1925; Blais, 1953; Common, 1954; Green & Pointing, 1962)-. This type of flig ht has been observed in C.nigricana (Lewis et al, 1975) although only by a rtificia lly released insects, and could not be confirmed by catches from suction traps at 1.0 to 7.4m. Such flights in other insects are typically up to 7.0 to 14.0m. and may thus be out of range of these traps. Up ward flights were not noticed during periods of observation in emergence sites in this study. This does not preclude the possibility that a certain proportion of the population could be wind dispersed above the boundary layer over greater distances than those achieved by actively dispersing individ uals, controlling their direction of flight just above the vegetation. In Rhyacionia buoliana(Schifferm uller), there seem to be two kinds of gravid female; some, more active than others, rise to 15m. and become wind dispersed (Green, 1962; 210 Green & Pointing, 1962). C.fumiferana is also transported both outside the boundary layer and low over the forest canopy (Henson, 1951; Greenbank, 1957). Prelim inary aggreg ation of dispersing insects may occur high in the air, synchronised as a consequence of mass emergence (Johnson, 1966), and this is therefore a possibility for C.nigricana. Dispersion of a "patch" ( cf . individuals) w ill then occur in a single direction, and settle together conforming to the rules given by Stinner et al_(1983), as an alternative to random diffusion (Brownian movement). With most day-flying insects, temperature controls the start of take-off in the morning (when light is already permissive) and light cuts off flight in the evening when temperature is still permissive (Lewis & Taylor, 1 9 6 5 ) . Flight periods of C.niqricana may be of this type, but Lewis et ad (1975) found that peak activity was noL necessarily associated with increases or decreases in temperature, and almost a ll moths are caught over the same period each day. In the closely related species C.pomonella, flight is circa dian and entrained to the daily photoperiod (Batiste et al, 1 9 7 3 b ). In addition the threshold temperature is usually two or three degrees higher than that needed to keep insects flying, so that a drop in temperature does not necessarily cause insects to alight (Johnson, 1 9 6 6 ) . This feature is an important consideration when seeking correlation between activity (e.g. as recorded in sex-attractant traps) and temperature regimes. Furthermore the threshold temperature for a species is a mean value, with the departure values for individuals distributed symmetrically around the mean up to two to three degrees (Taylor, 1 9 6 3 ) . Consequently as the temperature rises through this range, the number of individ uals taking off per unit time increases, until the mean temp erature and then decreases. If all the insects taking off remain airborne, the total number increases sigmoidally, so that the relationship of total numbers flying at anytime to temperature is not linear within a day (Johnson, 1 9 6 6 ) . This has been shown for C.nigricana using segregating suction traps (Lewis et ad, 1 9 7 5 ) and implies that the aerial popul ation is not depleted by emigrating insects. Aerial densities can change very rapidly from hour to hour and simulate the effects of individual responses (Johnson, 1 9 6 6 ) . For a single 211 species at an emergence site, the numbers remaining and available for take-off changes as accumulations that develop when the temperature fa lls, disperse when it rises, depleting the local population and affecting the daily flight curve (Johnson & Taylor, 1957). Rapid changes in aerial numbers should not be regarded as reflections of immediate flight responses (Johnson, 1966). Some of these influences may be responsible for the anomolous feature of aerial C.nigricana populations, that of very sim ilar densities between weeks, and high variance within activity periods. Lewis and Macaulay(1976) found that the vertical distribution pattern of C.nigricana between ground level and ca. 80cm. varied enormously and depended on the wind. Wright and Geering (1948), sweeping for C.niqricana over potatoes (emergence site) caught variable numbers due to the effect of environ mental conditions, or the changing activity of the moths (Wright et al, 1951) . Although male c.nigricana orientation to sex-attractant traps is undoubtedly anemotactic (odour modulated positive anemotaxis/anemomenotaxis), wind direction was not necessarily important in the directional aspect of population movement in this study. In 1980 dispersing moths appeared to migrate from South to North, and for 1981 it was suggested that moths could have been dispersed from the emergence site WAl by prevailing SW winds towards the pea field s. However this would imply that moths were carried by the turbulent air above the crop (and above the boundary layer) . If this were so, comparatively large catches would be predicted in the pea crop perimeter in the SW, since moths would accum ulate in the lee of the hedges separating the emergence site WAl and pea field PAl, as they were sucked down by eddies (Lewis, 1969). This was not the case, and Lewis et §1 (1975) caught significantly fewer moths in suction traps on the edge and 3m. into a field , than those 12m. and 24m. from the edge, although they suggested this itse lf could have been caused by disturbing eddies. Ekholm(1963) suggested C.nigricana fly upwind to pea fields if odour cues are present, but otherwise fly around in different directions and reach pea fields by chance. He cites a personal communication from an observer of a migration of C.nigricana through a forest. Hundreds of C.nigricana flying at a height of about 212 30cm. flew from the NE to a pea field, when wind direction during the relevant period of the Summer was principally from the SW; peas were already in flower. It was suggested in the dispersion sections that moths may leave the emergence site and enter surrounding vegetation at a low level. Moths therefore seem to disperse by active flight within the boundary layer, dropping into the vegetation when windspeed exceeds moth airspeed (Lewis et al, 1975), and flying upwind when suitable olfactory cues are encountered, but otherwise not influenced by wind direction. Other pest species behave sim ilarly, P.gossyp iella dispersed in all directions from a single release point (Flint S c Merkle, 1981) (although it may be an unjustified assumption that a rtificia lly released insects simulate natural populations (Johnson, 1966)). Amyelois transitella(Walker)dispersed approximately equal proportions of their progeny in all directions when wind direction varied, although anemotaxis was evident when wind was predominantly unidirectional (Andrews, Barnes S c Josserand, 1980) . Moths may not disperse great distances if suitable settling cues are presented to override the tendency for dispersive flight. White, Hutt and Butt(1 9 7 3 ) found that 90% of infestation resulting from an accidental release of C.pomonella in a pest free orchard, was within about 300m . Thus although C.nigricana adults have the capability to migrate a few thousand metres (Ekholm, 1963), dispersal may be terminated with an appetitive phase when a suitable habitat is located. In many monophagous species in natural habitats, there are two distinct aspects to host plant finding, first the host locality and secondly the host plant (Douwes, 1968). This is not necessarily so for a pest species in monoculture crops, although within the crop there w ill be preferred oviposition sites and/or phenological stages (Chapter 5). C.nigricana appears to delay entry into the crop and remain in surrounding vegetation, however it was suggested there may be a greater diversity or availability of resting and feeding sites there. Since the population in the vegetation around the peas (for 1981 at least) showed a gradual rather than sudden decline after the peak, females may have made oviposition sorties into the crop, and then returned to the surrounding vegetation. It seems feasible that immigrant 213 moths might confirm the presence of a pea crop, or determine suitability using olfactory or visual cues, before alighting in hedgerows. Franssen (1954) indicates that adult C .niqricana tended to keep to the borders of the field , and Wright and Geering (1948) found that moths were more common in dense rather than in sparse vegetation. Pea varieties with dense or bushy growth, showed most damage (Nicolaisen, 1928) and there was a strong correlation between larval density and plant cover (Wright et al, 1951), All this suggests that cover is an important factor in determining the distribution of resting adult moths. It provides an explanation of why emigration from emergence sites is so rapid, and for the distribution of adults in and around the pea crops in this study. In pea field PAl, moths were only found in the dense surrounding vegetation or crop perimeter close to this. In pea field PA2 moths were found in highest densities at the point source where the ditch bank vegetation was dense, and the pea crop also appeared more lush as well as containing large amounts of charlock providing more cover. Females did not appear to u tilise the hedgerows to the North, and this was probably because it was unsuitable. The western half of this northern hedgerow had little or none understorey and very twiggy, sparse shrub layer, while the eastern half was set back from the crop by a wide track. Although this hedge was only about seven to eight metres from the sown area of the field, the track may have precluded its use as a resting site near the crop. Sim ilar tracks on three sides in the North of pea field PB2 did not prevent the use of nearby hedgerows, but higher densities of females were found in the centre of the field, than in the perimeter. In general (the Southeast of pea field P a 2 being an exception) the plants on the out side of the crops appeared to be of a lower quality than in the centre, due to for example, shading, nutrient deficiency, wood-pigeon attack or other interference. If the cover offered by surrounding vegetation was also suboptimal the use of the dense crop in the centre is understandable. However resting positions do not reflect aerial distributions. In this study, kite netting did not show large differences between the perimeter and centre of the 214 field , and Wright and Geering(1948) found sweeping showed that there was no marked tendency for moths to be concent rated in or near hedgerows. Indeed since the moths are very mobile, the aerial distribution may tend to regular. Ovip- os ition by these regularly distributed females would lead to the more uniform patterns of damage and infestation found with no headland effect. There may s till be some minor in fluence on the distribution of damage, hence the South of p e a f i e l d P a I with the large hedge and dense understorey, as well as proximity to emergence site, had slightly greater damage. In pea field P a 2 damage was greater in the South where the crop was strong and weedy, intermediate in the centre where the crop was dense, and least in the North (furthest from the emergence site) where the crop was more sparse. In contrast the highest damage in pea field PB2 was furthest from the emergence site, but this was also the only area of the crop with ta ll dense hedgerow abutting the field. Even with low levels of damage in pea field J, 1980, the highest infestation was in the perimeter of the field sub tended by hedgerow. The close proximity of pea crops to emergence sites in this study is less typical than on other estates and is an ill-advised cultural practice known for a long time. In this instance pea crops would be found very soon during dispersal, but accumulation on headlands furthest from the emergence site could s t ill arise from populations flying over the crop, particularly when the field is small, as in 1981. However the lim ited data from an isolated pea field in 1980, did suggest that the period of dispersal can be very short. In this study the possibility of moths immigrating into pea fields from sources other than the emergence sites studied cannot be excluded. Although highly probable in 1980, the close proximity of emergence sites and pea fields in 1981 and 1982, would suggest that moths in pea field populations (or at least a high percentage of them) had come from these emergence site s. The highest damage levels in this study were found in the small fields of 1981. Legowski and Gould(1960) found that average pod attack was higher in fields of small area (less than four hectares), although this was not significantly different from other field size categories, and there was no correlation between size of field and degree of attack 215 (Gould et al, 1962). Legowski and Gould(1960) estimated that the mean damage caused by one larva was 1.7 seeds, this agrees well with the calculated values of 1.65 and 1.68 for the two 1982 field s, although the number of seeds per pod was slightly less in the present study. The incidence of multiple numbers of larvae in a pod was sim ilar in this study to that previously recorded. Ekholm(1963) found 5.55% (n = 5873 pods) with more than one larva, while Langenbuch(1941) recorded 11.0%. In 1980 no pods (n = 8640) had more than one larva, in 1981, 15.73% of pods (n = 4646), in 1982, 4.39% and 6.25% (n = 2029, 1361). The consistent percentage of infested pods at different truss levels in 1981 is in agreement with Ekholm(1963) who found about 40% pod damage on the first four truss levels, on plants with only six truss levels. The infestation levels in 1982 were high even though the plants were well matured. Selection and cultivation of early maturing varieties as suggested by Wright et ad (1951) might therefore not be a realistic cultural practice, and the early maturing varieties tested by these authors s till had 25 - 35% pod damage at dry harvest. 216 4 . MATING 4,1. Introduction In the previous chapter it was stated that, with respect to dispersal, mating can take place anywhere (Johnson, 1966). It does not matter where or at what time it occurs, although it is presumably advantageous if it has been effected by the time the female reaches a suitable ovi- position site. In specialist insects with a narrow niche, reproduction is highly host dependent. In some insects mating stimulates or induces vitellogenesis, but if mating and oviposition are not linked, energy used in vitellogenesis may then lim it the exploratory capability of a mated female and reduce the reproductive capacity (Labeyrie, 1978) . This can be circumvented by using the host plant as a sexual rendezvous; either both sexes may be attracted and meet there, or one of the sexes is attracted, which then releases pheromone and attracts the other sex. If mating is independent of oviposition or host plant, females would be expected to mate soon after emergence. Failure to do so would increase the risk of pre-reproductive death and negate the advantages to both sexes conferred by protandry. Possibly if suitable oviposition sites were not encountered by females for some time, the advantage of early mating would be lessened, particularly in a species where females only mate once. M ultiple mating has been found in most lepidopterous species studied, although the reasons and possible adaptive significance are not always provided. Byers (1978) suggests a number of possible explanations of the benefit of m ultiple matings, including the enhancement of genetic diversity, to remedy inadequate in itia l mating and to provide a paternal nutritional investment. The courtship and mating behaviour of C.nigricana was described by Lewis et al(1975); it is a succession of stereotyped behavioural steps, as commonly described for other species e.g. Trichoplusia n i(Hubner)(Shorey, 1964b), D. abietella (Fatzinger, 1973), Plodia interpunctella (Hubner) and Ephestia cautella(W alker) (Grant & Brady, 1975) P.gossyp iella (Colwell, Shorey, Gaston & Van Vorphis Key, 1978), C.molesta (Baker Sc Carde, 1979) and Adoxophyes orana 217 (Fischer von Roslerstamm) (Den Otter S c Klijnstra, 1980) . The successive steps are typically antennal elevation, activation (including flig h t), upwind orientation and copulation move ments (Bartell Sc Shorey, 1969a). The in itia l response has the lowest threshold of pheromone concentration and each successive step then has a higher threshold than the preceeding ( B a r t e l l Sc Shorey, 1969b; Fatzinger, 1973; Den Otter Sc Klijnstra, 1980),although different steps in the behavioural sequence might be evoked by different compounds in those species with multi-component pheromone (Den Otter S c K l i j n s t r a , 1980). Copulatory behaviour, which in C.niqricana commences with "fanning" by the male after he has alighted next to the female (Lewis et al, 1975) may also be dependent on a visual cue (Shorey S c Gaston, 1970) . The mean length of time that G.nigricana remains paired is unknown; it is likely to be a few hours, but possibly with a wide range. P.gossyp iella had a mean copul ation time of 2hrs. 14mins. with a range of 3mins.to 26hrs. 5 0mins. (Ouye, Graham, Richmond Sc Martin, 1964) and C.fumiferana a mean duration of 4hrs. with a range of 2hrs. 30mins to 8hrs. 15mins. (Outram, 1971). This chapter describes the spatial and temporal occurrence of mating in C.niqricana, and then relates this to other features of population development, viz. emergence and dispersal. The frequency of mating is described and then the costs, benefits and reasons of supernumerary matings are described. 218 4.2. Site of Mating C.niqricana mated first in or around the emergence site ; more than 90% of females were mated when they arrived in the vegetation surrounding the pea crops. More than 40% of females mated while still in the crop region of the emergence sites, and a further 30 to 40% mated in the surrounding vegetation of emergence sites (Table 4 .1.). In the field female C.niqricana were found in emergence sites resting on wheat flag leaves held horizont ally. Although not abundant, they were nevertheless very prominant to the human eye, and could be recognised from several metres away. A few mating pairs were also found under these circumstances, and when disturbed these dropped to the ground (single females flew off), where they became hard to find; those rediscovered were still paired. in each of the two emergence sites (1981 and 1982) there was no difference in the percentage of unmated females in the perimetal and central areas of the crop. This was shown by analysis of variance of the weekly number of un mated females expressed as a percentage (arc-sin trans formed data) of the weekly female total in each of the two crop regions (Appendix V a.). This analysis also showed that variance between weeks was low in both years, indicating that the percentage of unmated females did not show sig nif icant variation through the season. This analysis justifies pooling data from the perimeter and centre both within weeks and over the whole season, to give a single value for the wheat crop in.each year. This enables a comparison to be made between 1981 and 1982, since a straight comparison between weeks in the two years is not appropriate because of the differences in the temporal occurrence of features in population development. The percentage of unmated females in the wheat crops of 1981 and 1982 were not sig nif icantly different, when the proportions were tested using the normal approximation on binomial distributions with large numbers (Appendix Vb.). Analysis of the percentage of unmated females in each week through the season between the three vegetation categor ies around the 1981 emergence site, was limited by missing values due to both lack of samples and lack of females. 219 Table 4.1. Percentage of unmated and mated female C.niqricana in wheat field emergence sites, Shim pling Park Farm, 1981 and 1982 Data pooled for whole season of D-Vac. collected individuals. EMERGENCE SITE NUMBER OF NUMBER OF MATINGS TOTAL MATED FEMALES 01234 FEMALES WAl, 1981 Crop Centre 157 55.4 44.0 00.0 00.6 00.0 44.6 Crop Perimeter 67 56.7 41.8 1.5 00.0 00.0 43.3 Crop Total 224 55.8 43.3 0.5 0.5 00.0 44.2 Surrounding Vegetation 219 28.8 69.9 0.9 00.0 0.5 71.2 Overall Total 443 42.4 56.4 0.7 0.2 0.2 57.6 WA2, 1982 o Crop Centre 70 55.7 44.3 00.0 o o 00.0 44.3 Crop Perimeter 26 65.4 34.6 00.0 00.0 00.0 34.6 Crop Total 96 58.3 41.7 00.0 00.0 00.0 41.7 Surrounding Vegetation 127 17.3 77.2 5.5 00.0 00.0 82.7 Overall Total 223 35.0 61.9 3.1 00.0 00.0 65.0 220 However analysis of variance did not give a significant variance ratio when hedgerows and understorey were examined (data for six weeks, Appendix vc.)/ or when hedgerows, under storey and grassbank were examined (data for four weeks, Appendix Vc. ) . As with the crop area of the emergence sites there was no significant variance ratio for the weeks through the season. This analysis justifies pooling the data from the three vegetation categories around the 1981 emergence site as described above for the crop region. A comparison was then made between the percentage of unmated females in vegetation around the 1981 emergence site, and that in the vegetation around the 1982 emergence site, all of which was classed as grassbank. Using the normal approximation of a binomial distribution as above, to compare the surrounding vegetation, a significant difference between years was shown. The percentage of unmated females in the 1982 grass- bank was significantly less than that in all the vegetation around the 1981 field (d = 2.40, p<0.05) (Appendix vd.). Furthermore the probability of a significant difference was increased when only the populations in the 1981 understorey and grassbank (d = 2.82, p<0.01) and 1981 grassbank alone (d = 2.83, p<0.01) (Appendix Vd.) were considered, despite the more appropriate nature of these comparisons because of the obvious structural differences of the hedgerow. Within each of the two years the percentage of unmated females in the crop was significantly greater than that in the surround ing vegetation, as shown by .analysis of variance (Appendix V e .) . In and around the three pea fields (1981 and 1982), only low numbers of females were unmated (Table 4.2.), and no mating pairs were encountered in pea crops in the field. In the 198 1 pea crop and both of the 1982 crops, analysis of variance showed no differences in the percentage of un mated females between the perimetal and central regions with in each field (Appendix vf.). The percentage of unmated females from the crop area (data from perimeter and centre pooled) was not significantly different from that in the surrounding vegetation in any of the three fields (Appendix Vg.). For the two 1982 fields analysis of variance did not show any differences between the two crops or between the surrounding vegetation of the two fields (Appendix Vh.). 221 T a b le 4.2. Percentage of unmated and mated female C.nigricana in pea fields, Shimplinq Park Farm, 1981 and 1982 Data pooled for whole season of D-Vac. collected individuals. PEA FIELD NUMBER OF NUMBER OF MATINGS TOTAL MATED FEMALES 0 1 2 3 4 5 6 FEMALES PAl, 1981 Crop Centre 34 00.0 70.6 26.5 00.0 2.9 00.0 00.0 100.0 Crop Perimeter 61 4.9 75.4 14.8 2.3 1.6 00.0 00.0 95.1 Crop Total 95 3.2 73.7 19.0 2.1 2.1 00.0 00.0 96.8 Surrounding Veg . 168 8.9 69.1 19.1 3.0 00.0 00.0 00.0 91.1 Overall Total 263 6.8 70.7 19.0 2.7 0.8 00.0 00.0 93.2 PA2, 1982 Crop Centre 32 00.0 53.1 37.5 3.1 3.1 00.0 3.1 100.0 Crop Perimeter 53 9.4 41.5 30.2 18.9 00.0 00.0 00.0 90.6 Crop Total 85 5.9 45.9 32.9 12.9 1.2 00.0 1.2 94.1 Surrounding Veg 36 16.9 61.1 11.1 8 3 2.8 00.0 00.0 83.3 Overall Total 121 9.1 50.4 26.5 11.6 1.7 00.0 0.8 90.9 PB2, 1982 Crop centre 43 2.3 46.5 25.6 20.9 4.7 00.0 00.0 97.7 Crop Perimeter 18 22.2 44.4 22.2 11.1 00.0 00.0 00.0 77.8 Crop Total 61 8.2 45.9 24.6 18.0 3.3 00.0 00.0 91.8 Surrounding Veg 69 1.5 78.3 14.5 4.4 1.5 00.0 00.0 98.5 Overall Total 130 4.6 63.1 19.2 10.8 2.3 00.0 00.0 95.4 222 Comparisons between 1981 and 1982 using pooled data showed no differences in the proportion of unmated females in pea crops, or in surrounding vegetation (Appendix V j.). Since analysis of variance has shown that the two emergence sites were sim ilar between years, and the three pea crops* were sim ilar, both within and between years, data from the two emergence sites and the three pea fields may be pooled Thus f ig .4.1. shows the percentage of mated females along a hypothetical transect from the centre of an emergence site to the centre of a pea crop. This shows that 75% of females have mated when they leave the area around the emerg ence site, and 90 to 100% have mated when they enter the pea crop. The sim ilarity between the percentage mating in the surrounding vegetation and the crop perimeter of the pea field, is due to anomolous values in the crop perimeter of pea field PB2 in 1982, where four of 18 females were unmated. These were from three (of five) sample units, and are thus not readily explained; in addition there was only one unmated female in the vegetation surrounding this field . However, since the mating levels in the pea crop and surrounding veget ation were not significantly different in the other two pea fields, while the scale of difference is altered, the signif icance is not. This figure (fig.4.1.) describes the distr ibution of mating over a whole season; individual weeks show some variation. Earlier in the season within one year, there is a tendency for sm aller percentages of mated females throu ghout the environment, while later in the season the reverse is true. This aspect is more fully examined in Section 4.3. Laboratory experiments designed to examine the effect of the presence of pea plants on mating (Section 2.2.4.) showed there was a tendency towards increased mating in the presence of younger pea plant material (Table 4 .3 .). The highest percentage mating occurred in the presence of young vegetative or young reproductive pea material, although these were not significantly different from any other treat ment. In addition multiple mating only occurred in the pre sence of these two treatments. Since females arriving in pea crops in the field were usually mated, the presence of young pea plants was not expected to have been an important stimulus for mating, as these results may suggest. However it is possible that moths might perceive the odour from 223 F i g , 4.1. Percentage of mated female C.nigricana in each vegetation category along a hypothetical transect Hypothetical transect running from the centre of a wheat field emergence site to the centre of a pea field. Percentages calculated from pooled seasonal D-Vac. data of two emergence sites and three pea field s, Shimpling Park Farm, 1981 and 1982. N um ber o f F e m a le s 227 93 346 273 132 109 100-, 90- 8 0 - 7 0 - 6 0 - P e r c e n t a g e of females 50- m a ted 4 0 - 3 0 - 20 - 1 0 - s : O :> t ) 0 05 0 05 *d t ) t ) Q gj CD n r CD H i g H i g CD CD CD CD CD g CD b b b P b O g 0J rt QJ H- M b b H - f t f t b f t 3 3 0 CD o o 3 0 b CD CD CD g 0) g b CD b CD o o f t H g g 0 f t 0 b 0 b CD iQ a 0 a CD p 0 H i CD £ o b H- b H* b H i t ) g g 0 g o O \Q p iQ o H i CD H i < < 05 CD CD H- iQ iQ f t CD CD CD f t ft OJ P f t ft H- H- O 0 g g Vegetation Category 224 T a b l e 4.3. Percentage of unmated and mated females confined in laboratory breeding chambers with males and plant material TREATMENT NUMBER OF NUMBER OF TOTAL MATED FEMALES MATINGS FEMALES 0 1 2 Control - no plant 21 47.6 52.4 00.0 52.4 m a t e r i a l Wheat - Ripe ear 7 71.4 28.6 00.0 28.6 and flag leaf Peas - Vegetative 21 28.6 61.9 9.5 71.4 p a r t s o n ly Peas - Young 38 42.1 47.4 10.5 57.9 reproductive stages P e a s - O ld 15 60.0 40.0 00.0 40.0 reproductive stages A ll replicates provided with fresh 10% honey solution and fresh plant m aterial (except control) every two days. All replicates held at 20*C, 18 : 6 l i g h t : d a r k c y c l e . 225 nearby pea fields, while they are s till in or around emerg ence sites. Pea plant odour is noticeable to humans and was very strong on occasions during this study particularly when the plants were crushed by tractor operations during spraying. However, pea odour may be a strong mating stimulus to virgin females entering pea crops, inducing them to release phero mone and thus providing a mechanism to ensure mating. In addition, examination of the number of matings in pea crops ( S e c t io n 4.4.) shows that a mated female entering the crop had nearly a 5 0% chance of a further mating. 226 4.3. Time of Mating Mating occurs soon after emergence of the females and not at any one period of time in the season. Since females reaching the vegetation surrounding pea crops had, almost invariably mated at least once, the time of first mating is best studied at emergence sites. Emergence in 1982 was earlier than in 1981 and pooling weekly data from the two years is not appropriate. Analysis of variance showed no significant differences between the weekly percentage of unmated (and therefore also of mated) females in the crop perimeter and that in the crop centre (Section 4.2., A p p e n d ix V a.) in both emergence sites. The crop may thus be treated as one homogeneous area. Analysis of variance did not show a significant variance ratio between weeks, but there was a lot of variation and fluctu ation in the percentage of mated females in the crop (fig.4.2a.). This fluctuation was more pronounced in the 1981 emergence site than in that of 1982. The weekly number of females at the beginning and the end of the seasons was low, and therefore the percentage mated has a large standard error. Notwithstanding this lim itation, the high percentage of mated females in the crop at the beginning of both seasons (week 3, 1981; week 2, 1982) probably reflects protandry. The sex ratio in the crop was highly male biased (6:1 i n week 3, 1981; 4.6:1 in week 2, 1982), and hence newly emergent females would not be competing for males. At the time of peak population density in the middle of the season in 1981 (weeks 6 and 7, 1981; no data in 1982), the standard error of the percentage of mated females is sm all. Although the percentage of females mated in week 7 was not significantly less than that in week 6 at p = 0.05, the decline seen in week 7 was likely to have been a real feature and not an artifact of low numbers. This was because freshly emerged females outnumbered freshly emerged males (crop sex ratio of moths <” P.A. 7, 0.55:1, number of males = 18); competition for mates between calling females might then be expected. There were s till older males in the crop population (total crop population sex ratio in week 7, 1.52:1, number of males = 76), but although they may be able to mate several times (Section 4.4.), there may be a restr- 227 F ig - 4.2. weekly percentage of mated individuals in populations of female C.niqricana in and around emergence sites, Shimpling Park Farm, 1981 & 1982 a) Crop population; weekly data from perimetal and central areas pooled for all points sampled with a kite net in 1981, and with a D-Vac. in 1981 and 1982. b) Surrounding vegetation population; weekly data from Hedgerows, Understoreys and Grassbanks pooled for all points sampled with a kite net in 1981, and with a D-Vac. in 1981 and 1982. a) NUMBER OF FEMALES D-Vac. caught,1981 - 0 5 13 3 130 50 17 - 6 - »- Kite net, 1981 -- -- 17 15 14 - - -- o- D-Vac. caught,1982 1 5 11 56 - - 19 4 0 - - PERCENTAGE OF FEMALES MATED NUMBER OF FEMALES b) D-Vac. caught,1981 - 5 4 16 22 123 23 23 3 - Kite net, 1981 ---- 11 26 5 - - -- D-Vac. Cciught,1982 0 0 13 15 23 54 16 4 2 -- PERCENTAGE OF FEMALES MATED WEEK 228 iction to the rate of spermatophore production. Males capable of successfully mating (i.e. fertilising) would then be at a premium. Examination of the incidence of mating amongst a younger female population «P.A. 7) showed that the weekly percentage of females mated was only slig h tly less than that for the total population, and the shape of the seasonal curve was unaltered; 3 9 % of the young females caught in the crop were mated. This indicates that females can mate soon after emergence, and that many of those which mated in the emergence crop did so. In the surrounding vegetation of both emergence sites there was a steady increase in the percentage of mated females through the season (fig.4.2b.); the slightly higher values for the 1982 site were probably due to the earlier emergence in that year. In the second half of the season most females in the surrounding vegetation of both sites were mated. Kite net samples were taken in three weeks in the middle of the 1981 season (weeks 5, 6 and 7). The percentage of mated females in the aerial population over the crop was higher than that in the D-Vac. sampled population within the c r o p (fig.4.2a.), although not significantly (ANOVA, F = 6.92 NS, l,2df.). The peak of percentage mated in week 6 was s till clearly shown and was followed by a decline in week 7, sim ilar to that seen in the within crop population. The higher percentage of mated females (up to 75%) in these aerial populations may indicate that flying females tend to be mated, dispersing individuals. The weekly percentage of mated females in the aerial population sampled over the surrounding vegetation was much more like that within the vegetation (F = 0.18, NS, l,2 d f.). This would be expected if both populations were comprised of individuals with the same history, viz. mated and dispersing. 229 4.4. Frequency of M ultiple Mating The maximum number of matings by a single female, recorded in this study of 1423 field collected (D-Vac. and Kite net) females, was six; this was only in one individual and the next highest was four (in eight females). M o st individual females (62%) had mated only once, and 25% of females collected were unmated (fig.4.3a.). At emergence sites there was a mean of 1.03 m a t in g s per mated female (n = 455), although only 60% of females in or around emergence sites were mated (fig.4.3b.). A t p e a field s, where 93% of a ll females had mated (fig.4.3c.), t h e r e was a mean of 1.37 matings per mated female (n = 621). S in c e no females remained unmated in or around the pea fields by the end of the season, the best estimate of mating frequency in naturally dying females, may be calculated from those females caught in or around pea field s. Towards the end of the season the mean number of matings per female in pea fields in week 8 was 1.81 (n = 111) and in week 9 was 2.24 (n = 17). This is undoubtedly an over estimate since many females must have died before these later weeks; it seems probable that the modal number of matings is one, and that about 60% of females only mate once. 230 F i q. 4.3. Mating frequency in field populations of female C .niqricana, Shimplinq Park Farm, 1981 and 1982 Data pooled from within and between seasons for all females caught with a D-Vac. or a kite net. a) Total population from all vegetation categories sampled at emergence sites and pea fields. b) Population from all vegetation categories in and around emergence sites. c) Population from all vegetation categories in and around pea fields. a ) FREQUENCY (PERCENTAGE OF FEMALES) b) FREQUENCY (PERCENTAGE OF FEMALES) c) FREQUENCY (PERCENTAGE OF FEMALES) NUMBER OF MATINGS 231 4.5. D i s c u s s i o n C.niqricana first mated in or around the emergence site, so that most females had mated when they reached the vegetation around pea crops. Although females were only seen on the uppermost wheat leaves in the emergence sites, their vertical distribution was likely to have been influenced by prevailing wind velocity as in P.gossypiella (Kaae & Shorey, 1973). When wind velocity exceeds moth airspeed, flight is within the crop canopy (Lewis et ad, 1975). Since this applies to both sexes, females may alight within the canopy after a short flight within the canopy, responding males may then fly within the canopy at a similar height to the calling females. Since mating follows calling by the females, the timing of mating within an activity period, will be determined by the endogenous rhythm (Ono, 1 9 7 7 ) and modified by climatic factors. Since many females mate at the emergence site, mating is probably not dependent on any cues from pea plants (al though pea plant odour or presence may be a strong mating stimulus to females that reach pea crops unmated), and mating may even be a prerequisite for dispersal. Female R.buoliana do not normally migrate until fertilised soon after emergence (G re e n , 1962). Dispersing females therefore carry the extra weight of a spermatophore, and this could shorten the potential distance females could fly, through increased energy expend iture. There is however the possibility that’nutrient contr ibution from the spermatophore could provide females with energy without recourse to feeding, which would cause delay or otherwise expose moths to predation. In a specialist monophagous/oligophagous insect any hinderance to host plant finding w ill ultim ately reduce the reproductive capability of an individual. C.nigricana populations outside the main pea growing areas u tilise both perennial native hosts (e.g. V.cracca) and annuals (e.g. Vicia sativa L.); o n ly w it h annual hosts is there perhaps any difficulty in host finding, since emergence is always likely to be in the immediate vicinity of host plants. Nonetheless moths may still dis perse from native plants when densities become high; the large number of pods on clumps of V.cracca in this study, would not appear to have been a lim iting food source, but 232 the factors determining suitability are unknown. In the laboratory experiments there was a suggestion of increased mating in the presence of young pea plants. In wild popul ations (not agricultural) dispersing males may respond to host plants and female pheromone. Further evidence for this comes from the consistently higher catch of males in phero mone traps when these were surrounded by pea plant material (Section 3 .4 2 . ) . The high percentage of mated females in the young age category indicates that not only does mating occur in the e m e rg en ce sites, but soon after emergence. Lewis and Sturgeon (1978) found that most females kept in the presence of males, laid fertile eggs two to three days after emergence both in the laboratory at 23#C and in field cages where daily mean temperatures ranged from 10.5*C to 20.5’C. This indicates that moths mated within one to two days of emergence. Most moth species, examined in connection with pheromone studies, appear to mate within a few days of emergence (Shorey, 1964b; Taylor, 1967; Shorey, McFarland S c G a s t o n , 1968) . Some m ate very soon after emergence within the first activity period (Cheem a, 1956; Ouye, Garcia, Graham Sc M a r t in , 1965; B a n e r je e Sc D e c k e r , 1966a; K i r i t a n i S c Kanoh, 1984) , and others may be capable of this, e.g. C.pomone11a can mate within 12hrs. of emergence in the laboratory (Gehring Sc M a d se n , 1963) and in Diparopsis castanea Hampson there was no difference in the ab ilities of newly emerged males and males up to four days old, to mate with newly emerged to four day old females (M a rk s, 1976). Female moths would not be expected to mate immediately after emergence, since a paired moth could be prevented from successfully expanding the wings. In A.orana there was no pheromone production from female pupae or from pharate adults (N a g a ta , Tamaki, N o g u c h i S c Y u s h im a , 1971), but pheromone activity increased rapidly from the midnight after emergence u n til mating the following day. If female attractivity gives some indication of the time of mating, several species also appear to mate two to three days after emergence rather than within 24hrs. Female D.castanea were maximally attractive three nights after emergence (Marks, 1976), while in Diatraea saccharalis (F.), ultrastructure of the female pheromone gland suggested that there was no pheromone production for the first two 233 hours following emergence with a peak after 48hrs. (White, Amborski, Hammond & Amborski, 1973). In Ephestia kuhniella Zeller, Traynier (1970) found that three day old females gave the most potent pheromone extract. There was no difference in potency during the calling period in the diel cycle, but the male response was greatest when females first emitted. The duration between emergence and mating can also be determined by male responsiveness. Hence Outram(1971) found that male C. fumiferana were least responsive to females just after emergence (< 0.5 days old) and most responsive at two to four days old. Sim ilarly male A. or an a were not maxim ally responsive until at least four days after emergence (Den Otter Sc Klijnstra, 1980) . At the time of peak emergence of C.nigricana such a response would result in a large proportion of the male population being maximally responsive to a large number of emerging females within one to two days of female emergence, due to incidental protandry. If a period of peak attractivity occurs, this implies that there is a decline in attractivity. This has been demon strated in D . saccharalis (Perez S c Long, 1964) and C, fumiferana (Outram, 1971), but with Acrolepia assectella( Zeller), Rahn (1972) found that female age had no effect on female attract iveness, and the criterion used was successful mating, rather than simply attraction. There may also be a decline in female attractivity after mating; virgin female A.fasciata retained their maximum pheromone titre for up' to 10 days, but there was a 120 fold decrease after mating (Nagata et al, 1971). Mating also caused a decrease in attractiveness in C. pomonella (Gehring S c Madsen, 1963; Howell S c Thorp, 1972), A. orana (Minks Sc N o o rd in k , 1971), C. fum iferana (Outram, 1971), D. saccharalis (Perez Sc L o n g , 1964), Diatraea grandiosella (Dyar) (Langille Sc K e a s t e r , 1973) and A. assectella (Thibout, 1975). However, in other species, such as Noctuids where m ultiple mating is more prevalent (e.g. Byers, 1978), t h e r e may be no such effect (Shorey et, ad, 1968) . In H.virescens the time of mating of previously mated females was one hour later than the peak mating time of virgins (Raulston, Snow, G rah am S c L in g r e n , 1975). Although multiple matings are recorded from most of those species which show a decline in female attractivity, the modal number of matings is usually one, with more than 234 50% of all females typically mating only the once. This is shown in these and other species e.g. p .qossypiella (Lukefahr & Griffin, 1957; Ouye et ad, 1964), C.molesta (Dunstan, 1964), D , s accharalis (Perez S c Long, 1964), Agrotis orthogonia Morrison (Jacobson, 1965), A. or an a (Minks S c Noordink, 1971), C.fumiferana (Sanders, 1975), P.interpunctella and E.cautella (Arbogast, 1981). within one activity period the frequency of mating is often limited apparently by male ability. Banerjee and Decker(1966a) found that male Crambids could mate more than once but usually not on the same night. In H.virescens neither sex normally mates more than once in a night (Flint S c Kressin, 1968) . Male C.molesta could mate up to seven times but seldom mated more than once in 24hrs. both in cages and in orchards (Dunstan, 1964). Outram(1971) found that C.fumiferana males mated only once in 24hrs., and although Sanders(1975) found that males readily mated a second time within a few hours, the duration of the second mating was abnormally long. In a male biased field population this restriction could occur if mated females became less attrac tive. However, mated females may not necessarily become less attractive or possibly only so for a short period. In p.qossyp iella males mated successfully only once during the first 24hrs. as adults, but m ultiple mating occurred among females of the same age (Ouye et a l, 1965). In a fe m a le biased population of Q .nubilalis, the proportion of females mating was decreased (Ellio t, 1977). In Spodoptera litu ra (F.) the number of mated females tended to increase as male density increased, but the mating rate of males did not vary regularly with sex ratio or density (Otake S c Oyama, 1973). There may be a restriction on the rate of spermatophore pro duction, hence the prolonged second mating in C.fum iferana. In C.molesta the first mating results in the transfer of a large spermatophore, but subsequently these become sm aller and eventually no spermatophore is produced (George Sc H ow ard , 1968). Sim ilarly spermatophores became progressively sm aller in successive matings by C.fumiferana (Outram, 1971). Thibout and Rahn(1972) found that the volume of the f ir s t spermatophore in A. assectella was much larger than that of the following ones; this depended on emission rank rather than the time between two copulations. They ascribed this 235 phenomenon to a change in reproductive activity rather than the result of exhaustion. However, although each spermato- phore in the bursa copulatrix of the female represents a separate mating (Dunstan, 1964; Ouye et a l, 1965) t h e p r e sence of spermatophores does not necessarily indicate a successful (i.e. fertile) mating (Outram, 1971). A l t e r n a t ively mating may occur without the transfer of a spermato- phore, particularly when duration of copulation is short (Ouye et_al, 1965). In some species insemination is not achieved without spermatophore transfer, e.g. C.fumiferana (O u tram , 1971), while in others the reverse is possible. George & Howard (1968) found that, contrary to Dunstan (1964) some young male C.molesta mated with two females within 24hrs. and whether or not a spermatophore was transferred the number of fe rtile eggs was normal. Infertile matings are apparently not uncommon in the Lepidoptera (Campbell, 1961; Pointing, 1961; Taylor, 1967), and the most likely explanation for multiple mating in the many species mentioned where most females mate only once, is to remedy an inadequate first mating (Byers, 1978). Taylor*s (1 9 6 7 ) detailed study of mating in Atteva punctella (Cramer) suggested a correlation between infertility and multiple mating, since a significantly greater number of infertile females mated a second time, following a recovery of receptivity. The ineffectiveness of matings was due to male deficiences, but males may recover their- potency with age, and be successful in fertilising females on subsequent occasions. The criterion which led to second matings was an inadequate quantity of viable sperm. Thus although mating of single A.punctella males with different females resulted in the production and transfer of progressively smaller spermatophores, as in C.molesta and C.fumiferana described above,if an adequate quantity of viable sperm was transferred, females did not mate a second time. The factors controlling female receptivity following mating may be qualitative or quantitative. In pea fields about 30% of the female C.nigricana population showed supernumerary mating; this level is the same as that recorded for R.buoliana (Pointing, 1961), Choristoneura spp. (Campbell, 1961) and A.punctella (Taylor, 1967). M ultiple mating in C.nigricana may be to ensure that 236 females are fertile. The small number of females indulging in three, four or more matings may be due to failure of these individuals to cease being attractive or receptive. The increase in mating in old individuals at the end of the season may be due to a similar failure, or possibly if females had utilised all the sperm in the spermatheca. Multiple mating could enhance genetic diversity; increased phenotypic variation and tolerance would be of advantage to the species, especially in specialist insects where polymorphism is a survival strategy (Labeyrie, 1978). However in the system described above for C.nigricana, multi ple mating does not result in multiple male parentage in the females' progeny, because most females only mate once, and with two matings only the second may be fertile. The female genetic investment is the same regardless of the paternal genome. There may be a possible advantage to males indulging in multiple mating, since in many Lepidoptera, a system of sperm precedence operates, whereby the sperm used for fert ilising eggs is from the ultimate mating (e.g. Labine, 1966; Taylor, 1967; Flint & Kressin, 1968; Snow, Young & Jones, 1970; Brower, 1975). To be effective and allow the male's genes to the next generation, the second (or more) mating should presumably occur before the female has had the opport unity for oviposition. Lewis and Sturgeon(1978) found that 21 field caged female C.nigricana laid their eggs over a period of 22 days, with 50% of the pooled total laid in the first six days, thus allowing the opportunity for mating during the oviposition period. This system would also require females to remain attractive or recover receptivity after successful matings, thus while some male C.nigricana may appear to adopt this strategy by flying to pea fields, it is difficult to explain why only 30% of females became mated more than once. One consequence of transferring comparatively large proteinaceous spermatophores is a possible paternal nutrit ional investment in egg production (Boggs & Gilbert, 1979). This nutrient could be used directly in vitellogenesis and save female fat body, if mating occurred pre-vitellogenesis, or be used for somatic maintainance of the female during oviposition; in either case it should contribute to female longevity and thus maximise realised fecundity. Presumably 237 multiple mating should enhance this benefit, although in C.nigricana the spermatophore breaks down slowly if at all, and it was noted that a full bursa copulatrix could occupy a large volume of the abdomen. This therefore restricted the size of the other abdominal organs, notably the ovaries. In extreme cases of four and six matings the distended bursa copulatrix occupied most of the abdomen. In D.castanea, Marks (1976) found that multiple mating influenced egg fertility rather than fecundity, and female P.gossypiella that had mated only once, laid as many eggs as those that had mated more than once (Henneberry & Leal, 1979). Ensuring fertility seems to be the main objective in many species. Thus apart from whatever other functions multiple copulations may serve, the main reason is to ensure adequate fertilisation (Labine, 1966). In C.nigricana this is achieved with one mating for about 70% of females, and inadequacy rectified by further mating in the remainder. The reason why some males migrate to pea fields, despite the fact that mating is primarily a pre-dispersal phenomenon is now apparent. Although they are unlikely to mate with females successfully fertilised in or around the emergence site, there may be an opportunity to mate with unfertilised (but mated) females, and thus pass on genes. If competition between males in the emergence site is high, even in males that may have already mated, dispersing and seeking these females will be a cost effective strategy. In this study, laboratory experiments were: designed to examine the effects of single versus multiple matings on fertility and fecundity. Unfortunately because of the difficulty in rearing sufficient numbers of adults over and above that required to maintain a culture, coupled with a total lack of mating from more than 40 isolated pairs, these did not come to fruition. The mechanisms described above for C.nigricana mating frequency therefore remain conjectural. 238 5. MATURATION, LONGEVITY AND FECUNDITY 5.1. Introduction This chapter aims to answer questions about the fecundity and maturation of female C.niqricana. The import ance of these aspects in the optimisation of the sex-attract- ant monitoring system was recognised early on in the design stages (Lewis et al, 1975). Lewis and Sturgeon (1978) suggested that a period of three days should elapse after the threshold trap catch was attained and before commencing summation of temperature dependent egg development increments. This was to allow for a pre-oviposition period (POP) because the matur ation state of females newly arrived in pea crops was unknown. The use of changes in internal anatomical indicators such as fat body and organs to physiologically age adult insects, seems to have received far less attention in Lepidop- tera, compared to the Diptera where many different families have been investigated (e.g. Harlow, 1956; Rygg/ 1966; Adams & Nelson, 1969; Rosay, 1969; Tyndale-Biscoe & Hughes, 1969; Hawke, 1975; Begon, 1976; Magnarelli, 1976; Andreadis Sc Hall, 1980; Spradbery Sc Sands, 1981) . The feature of cyclical ovary maturation in the Diptera, complicated by autogenous and anautogenous individuals within and between many of the species studied, does not allow the use of these systems for Lepidoptera, or permit critical comparison between the two orders. Physiological age indicators have been used in C.pomonella (Nel, 1940; Hamstead Sc Gould, 1950; Geier, 1960; Section 2.1.9.) and C.molesta (Rothschild et al, 1984). With C.nigricana, given sufficient laboratory replication under varying temperature regimes, it should be possible to define the relationship between physiological age and real age. Field collected moths could then be aged by taking account of the temperature conditions over the days or weeks prior to moth capture. This level of sophistication is not yet available for C.nigricana, although the physiological age of field populations can now be shown. Fecundity depends primarily both on the number of primary oocyte cells that a female may produce, and the nutrient reserves available for egg production (Chew Sc Robbins, 1984). The fecundity of lepidopterous species shows a 239 tremendous variety, ranging from 11 to 5,000+ in the table given by Hinton(1981). Hinton gives fecundity data of six tortricid species as follows: A.rosanus 124 - 173, Pandemis cerasanaCHubner)284 - 359, S . ocellana 150 - 210 (Minder, 1959) , firnomoriia formosana (Scopoli) 14 - 84 (Dirimanov Sc Sengalevich 1962), Herpystis cuscutae Bradley 142 (Baloch, Mohyuddin Sc Ghani, 1962), Pammene fasciana (L.) 336 (Muller, 1957). The fecundity of female Lepidoptera may be affected by many factors. Larger or heavier females generally lay more eggs e.g. Ephestia elutella (Hubner) (Waloff, Norris Sc Broadhead, 1948), Tinea pellionella(L.) (Cheema, 1956), Qncopera intricata Walker (Martyn, 1965), Prionoxystus robiniae(Peck) (Solomon, 1967), Crambus harpipterus Dyar (Crawford, 1971). Since heavier females come from heavier pupae, the fecundity of the adult may also be directly related to the weight of the pupa or pharate adult, e.g. A. orthogonia (Jacobson Sc Blakeley, 1960) , Ennomos sub- signarius (Hubner) (Drooz, 1965), Acleris variana (Fern.) (Schmiege, 1965), Choristoneura conflictana (Walker) (Beckwith, 1970). Pupal weight may in turn be affected by quantity and quality of larval diet e.g. C.fumiferana (Blais, 1952; Miller, 1957), A. orthoqonia (Jacobson Sc Blakeley, 1960), H. zea, H. virescens and Alabama argill ace a (Hubner) (Lukefahr Sc Martin, 1964), Epiphyas postvittana (Walker) (Danthanaryana, 1975) , Anticarsia gemmatilis Hubner (Moscardi, Barfield Sc Allen, 1981); developmental temperature of larvae e.g. P. xylostella (Atwal, 1955) , T.ni (Shorey, Andres Sc Hale, 1962), E .postvittana (Danthanaryana, 1975); and larval density e.g. P.xylostella (Atwal, 1955), Tortrix viridana(L.) (Schutte, 1957), Pieris brassicae (L.) and Autograph a gamma (L.) (Long Sc Zaher, 1958; Zaher Sc Long, 1959), S . litura (Zaher Sc Moussa, 1961; Hodjat, 1970), E,postvittana (Danthanaryana, 1975), since all these affect larval size. However these relationships may be complicated by interaction or may not hold at all. When larvae of P.gossypiella fed on various artificial diets averaged 14, 12.9 and 25.6 days, the respect ive pupal weights were 21.3, 19.8 and 13.7mg. (Adkisson, Bull Sc Allison, 1960). In Panolis flammeafSchiffermuller) the number of eggs laid increased with pupal weight, but in comparisons between different localities, neither the 240 number of eggs for a given pupal weight, nor the rate of increase with weight was the same (Hagemann-Meurer & Thalenhorst, 1964). In L.dispar the fecundity of adults was reduced when development of the larvae was prolonged (Likventov, 1960). When the female is physiologically ready to lay, egg- laying, like other behaviour, is triggered by a particular combination of external stimuli (Hinton, 1 9 8 1 ). Oviposition patterns are dependent on both reproductive effort (number and size of eggs) (Chew & Robbins, 1984) and temporal and spatial egg distribution (onset of oviposition, oviposition rate, cluster size) (Labine, 1 9 6 8 ). Oviposition is affected by a number of biotic and abiotic factors acting on the female. It is possible for mating to stimulate oviposition, (Miskimen, 1966; Taylor, 1967), egg maturation, or both. Apart from direct effects, in many species, physical, chemo- sensory or visual contact with other individuals has a stim ulating effect upon the rate of oviposition and total number of eggs laid (Hinton, 1981). Some species have optimal temp eratures for oviposition e.g. 27 *C for C.pomonella (Isley, 1938), within a broad or narrow range, while others may lay similar numbers of eggs at quite different temperatures (Hinton, 1981). When exposed to unfavourable, but sublethal, temperature extremes, there is often a reduction in fertility before there is any decrease in fecundity. This may be due to both damage of oocytes, usually the more mature oocytes first, or damage to stored sperm in the spermatheca (Hinton, 1981). Oviposition may be entrained to a circadian rhythm e.g. Crambus trisectus Walker (Banerjee Sc Decker, 1966b) Crambus lopiarius Zeller (Crawford, 1967), or may be arhyth- mic in the absence of light cues e.g. Crambus teterrellus (Zincken) (Crawford, 1966). Oviposition may be affected by previous attack on the plant, and is deterred in O.nubilalis (Schurr Sc Holdaway, 1970), P.brassicae (Rothschild Sc Schoonhoven, 1977) and T.ni (Renwick Sc Radke, 1980) but increased in Paramyelois transitella (walker) (Curtis Sc Barnes, 1977). Oviposition is influenced by colour and texture of the oviposition sub strate e.g. in P.xylostella (Gupta Sc Thorsteinson, 1960) and Phthorimaea operculella (Zeller) (Traynier, 1975) or presence 241 and phenology of host plant e.g. for Scrobipalpa ocellatella (Boyd) (Robert, 1971) and P.transitella (Curtis Sc Barnes, 1977)). The selection of oviposition substrate by specialist phytophagous insects is generally determined by similar tarsal receptors to those involved with feeding acceptance and rejection; the ovipositor is assumed to play a secondary or negligible role (Jermy Sc Szentesi, 1978). Although high fecundities may be realised the success of the progeny may be severely reduced due to poor precision of egg-laying on the foodplant (Dethier, 1959). When conditions are unsuitable many species reabsorb their eggs; others may retain them and subsequently become less particular where acid when eggs are laid as they become older (Hinton, 1981). Oosorption is achieved by hydrolysing oocytes; the energy expended to release the proteins, fats and carbohydrates being much less than that supplied by the metabolites that are mobilized. Oocytes may undergo more or less normal development up to or beyond yolk deposition and then be reabsorbed. This ability confers considerable benefits since it permits the female to tolerate lack of food, oviposition sites and active spermatozoa, or other, abiotic, stresses. When the hazards are removed, oocytes may continue to develop normally, thus although the potential fecundity is irreversibly reduced, the female survives to lay some eggs (Hinton, 1 9 8 1 ). In P. interpunctella, E.cautella, E.kuhniella and Sitotroqa cerealella (Olivier) mature oocytes are degenerated in the bulla seminalis (Lum, 1 979). The chorions are weakened and ruptured by muscular contractions; this process may be a faster means of releas ing nutrients than digestion of the chorion. The specialisation of larvae for feeding and growth enables them to accumulate limiting nutrients which may be used for egg production (Chew Sc Robbins, 1984). Herbiv orous insects often assimilate nitrogen preferentially (in the form of amino acids and proteins) and excrete excess carbohydrate. The correlation between adult size and fecundity described above, suggests that it is larval nutrition that determines the reserves required for oogen esis. Nevertheless adult insects may also feed and this could enhance fecundity or longevity. Several authors 242 have investigated the effect of different diet solutions on adult Lepidoptera. As well as water and sucrose solutions (usually 5% or 10% w/v) 10% honey solution is also offered. Unlike pure sucrose, honey contains small quantities of many substances which may make it a more balanced diet for insects . As well as up to 80% reducing and non-reducing sugars (Crane, 1975), honey contains gums, tannins, dextrins, essential oils, esters, mineral salts, acids, yeasts and traces of vitamins (viz. Thiamin (B^)/ Riboflavin (^2 ^' Pyridoxine (B^) , Ascorbic acid (C) , Pantothenic acid and Nicotinic acid) both in solution and associated with pollen grains (David & Gardiner, 1961). Protein content is variable but generally low, e.g. 0.2% (Butler, 1974) or 0.04% nitrogen (range 0.00 to 0.133) (Crane, 1975). This chapter first describes the physiological age composition of C.nigricana populations in the various sub divisions of the environment, and continues with a descrip tion of the maturation state and potential fecundity of field populations of females. This is followed by results from the laboratory studies investigating, firstly, the effect of diet, and secondly the effect of host plant presence, on fecundity and longevity of female C.nigricana. The findings from the field and laboratory are then discussed in relation to dispersal and other features of the moth's biology. 243 5.2. Physiological Age Structure of Moth Populations The physiological age (P.A.) of male and female C.niqricana adults was determined by summation of fat body scores, after dissection (Section 2.1.9.). The P.A. structure of various populations of moths was studied by grouping sequential pairs of scores together, to give six age groups on an ordinal scale from 3 & 4 to 13 Sc 14 inclusive. The percentage of the moth population in each age group was calculated for each week in different vegetation categories, and represented on a series of histograms (figs.5.1. - 5.4.). In the first half of the season in 1981 and 1982, populations of both sexes within the crop region of the emerg ence sites were composed predominantly of physiologically younger moths (figs.5.la. - 5.4a.). This is to be expected since large numbers of moths were emerging over this period. At the time of peak emergence and peak density in week 6 in 1981, the crop populations of both sexes showed very similar P.A. distributions with 60 - 1 0 % of individuals in the two youngest age groups (figs.5.la. Sc 5.2a.). In week 7 males were older, with similar numbers over a wide range of P.A. , but with P.A. 11 & 12 as the mode (fig.5.1a.). In contrast the modal P.A. group of females in week 7 was still 3 & 4, the youngest group, and none were over P.A.10 (fig.5.2a.). This tendency for males to be older was shown in each week in the second half of the season. In week 10, although moth densities were low, the modal group for females was 5 Sc 6 , and for males was 9 & 10. Similar patterns of P.A. distribution were seen in the crop of the 1982 emergence site, where peak emergence and density occurred at, or soon after, week 4 (Chapter 3). The P.A. distribution of the two sexes in week 4 (figs.5.3a. Sc 5.4a.) was very similar to week 6 in 1981 (figs.5.la. Sc 5.2a.). In weeks 7 to 9 in the crop of the 1982 emergence site, male populations were comp osed of physiologically older individuals, and the modal group was 11 Sc 12 (fig.5.3a.); female populations were younger with the modal' group being 7 Sc 8 (fig.5.4a.). These P.A. distributions, particularly in the second half of the season may be due, in part, to the incidental protandrous emergence of males, with few males emerging 244 Fig. 5.1. weekly distribution of physiological age structure of male C.nigricana populations in and around emergence site and pea field, Shimpling Park Farm, 1981 Physiological age calculated by summation of four fat body scores. s t Weeks numbered through the season commencing Monday 1 June. a) Crop populations in emergence site b) Surrounding vegetation populations at emergence site c) Surrounding vegetation populations at pea field d) Crop populations in pea field Number on each histogram is the number of moths dissected, a dash indicates that no samples were taken in that week. (C) (d) WEEK 0 2&3 & 14 21 FREQUENCY (PERCENTAGE OF POPULATION IN EACH AGE GROUP) 10 11 PHYSIOLOGICAL, AGE GROUP 245 Fig . 5.2. Weekly distribution of physiological age structure of female C.nigricana populations in and around emergence site and pea field/ Shimpling Park Farm/ 1981 Physiological age calculated by summation of four fat body scores. s t Weeks numbered through the season commencing Monday 1 June a) Crop populations in emergence site b) Surrounding vegetation populations at emergence site c) Surrounding vegetation populations at pea field d) Crop populations in pea feild Number on each histogram is the number of moths dissected, a dash indicates that no samples were taken in that week. (c) (d) WEEK “ I 1 2& 3 6 4 17 5 6 FREQUENCY (PERCENTAGE OF 7 POPULATION IN EACH AGE GROUP) 8 9 9 "Mr i-1-1-1—i 2 10 0 11 4 If 8 Ioi214 Tlf"8lor2l4 PHYSIOLOGICAL AGE GROUP 246 Fig. 5.3. Weekly distribution of physioloqical age structure of male C.niqricana populations in and around emergence site and pea fields, Shimplinq Park Farm, 1982 Physiological age calculated by summation of four fat body scores. Weeks numbered through the season commencing Monday 2 4 ^ May. a) Crop populations in emergence site, WA2. b) Surrounding vegetation populations at emergence site, WA2. c) Surrounding vegetation populations at pea field PA2. d) Crop populations in pea field P a 2 . e) Surrounding vegetation populations at pea field PB2. f) Crop populations in pea field PB2. g) Surrounding vegetation populations pooled for pea fields PA2 and PB2 . h) Crop populations pooled for pea fields P a 2 and PB2. Number on each histogram is the number of moths dissected, a dash indicates that no samples were taken in that week. (b) (h) WEEK 1 2 4=}- 24 3 f h - r h 12 4 54 I 5 247 - l ------1------1 i------1------1------1------1------1------1 r- i - -|------1------1------1------1 i— i------1------1------1------1------1 i------i------1------r------r - 15 I 6 ...... ] £ k r — t i I i i T-1-1-1-I t—• i—ri—i—i—i—i—i—i 37 20 9 35 7 i-1-1-1-i-1-1 '— i-1-»-r- -,- rl.r~l i— i— i— i— r 11 10 13 8 I "I I I I »' — I 3 9 6 ar0^l4 4 T 8 l0i2rt 4 '6a4- l014l4 PHYS IOLOGICAL GROUP 24 8 Fig . 5.4. Weekly distribution of physiological age structure of female C.niqricana populations in and around emergence site and pea fields, Shimplinq Park Fanil, 1982 Physiological age calculated by summation of four fat body scores. Weeks numbered through the season commencing Monday 24 th May. a) Crop populations in emergence site, WA2. b) Surrounding vegetation populations at emergence site, WA2. c) Surrounding vegetation populations at pea field PA2. d) Crop populations in pea field P a 2. e) Surrounding vegetation populations at pea field PB2. f) Crop populationsin pea field PB2. g) Surrounding vegetation populations pooled for pea fields PA2 and PB2. h) Crop populations pooled for pea fields P a 2 and PB2. Number on each histogram is the number of moths dissected, a dash indicates that no samples were taken that week. (d) (a) (b) (c) (e) (f) (h ) WEEK 0 I—T--1---1-- 1-- 1-- 1 i-- <-- 1-- r 0 - i i------r r r — i— i---- 1— i ----- 1— i 13 8 14 , , rr-r -r-S r-r- i— i--- 1--- 1--- 1--- r 10 7 12 a e l . . . r I T i r — i---- 1----- 1---- 1---- 1---- » n - , r r 23 I 249 -i— i—i—r -i—i—i i i -i— i— i—i 53 ii 19 I ■1 7 ^ 3 . , i 1 1 1—i 1—I » 1 r -1 F 16 13 44 36 49 n r » a i— i--- 1--- 1--- r 31 7 I 13 1—r^T—T11 nr? i 5 3 J.' 9^13 1 8 -2-12—= 9- J- g iii 5'j! 6 10 1J 4 T 8Io12n 4 T 8r512rf 4T 8 K)1 2 l"4 PHYSIOLOGICAL AGE GROUP 250 after peak emergence had occurred. The distributions, nevertheless, clearly show that females leave the emergence site crop when they are physiologically young, and therefore soon after emergence. No females in the oldest P. A. group (13 & 14) were found in the crops of emergence sites, and indeed very few older than P.A. 9 or 10. In contrast some males clearly remained within the confines of the emergence site crop and undoubtedly died there. It should be noted that these discussions refer to physiological age and not real age. Populations of males would therefore tend to appear to be older than females if males were more active, since this would lead to increased respiration and metabolism of the fat reserves, on which the age scores are based. Aerial populations of moths over the emergence site were male biased, which shows that males were more active. The relatively sudden change in male P.A. structure between weeks 6 and 7 in the 1981 emergence site, might therefore be explained by exhaustion of male fat reserves as a result of active mate finding, at a time when very large densities of newly emergent females appeared. In the vegetation around the 1981 and 1982 emergence sites the P.A. distributions of both sexes shows that the modal age tended to get older as the season progressed (figs.5.lb. - 5.4b.). Populations of both sexes were slightly physiologically older than the corresponding population with in the crop, due to both real age differences and probably as a result of fat utilisation to disperse to the hedges. In both years-, at least in weeks of higher density, the modal P.A. of male populations in surrounding vegetation was greater than that for females in the same week. This suggests that not only did females leave the crop soon after emerg ence, but that they dispersed from the vicinity of the emerg ence site more readily and rapidly than males. Moth populations in pea crops and vegetation around pea fields were, for obvious reasons, physiologically older still (figs.5.1c. & d., 5.2c. Sc d., 5.3c. - h., 5.4c. - h.). Some moths, from both sexes, were still in the youngest P.A. groups both around and within the pea crops, and therefore dispersed from emergence sites to the pea fields extremely rapidly, possibly even within 24hrs. of emergence. 251 In 1981 the P.A. distribution of male moths in vegetation around the pea field was very similar to that in vegetation around the emergence site. This may be because half the vegetation around the peas was shared with the emergence site, and most males in samples from around the pea field were caught in this shared vegetation (Chapter 3) . The two sets of samples from the surrounding vegetation were probably drawn from the same population within these hedges. Female populations in vegetation around the 1981 pea field, and males and females in vegetation around the two 1982 pea fields, were generally physiologically older than the corres ponding populations around the emergence sites. This may be because stored fat was metabolised by actively dispersing moths which led to changes in the relationships between the different types of fat body. Although much of the vegetation around the 1981 pea field was very close to the emergence site, as described above, many more females than males were caught in the unshared vegetation along headlands furthest from the emergence site. If these females had originated in this emergence site, they had therefore flown further, however the possibility that these females could have come from elsewhere, cannot be excluded. Populations of both sexes within the pea crops were not or only slightly physiologically older than the corres ponding population around the crop. This could be explained if there was free exchange of individuals in ’and out of the crop, with females moving in for bouts of oviposition, and males still seeking mates, and both sexes returning to the surrounding vegetation for the greater diversity of resting sites offered. Samples of male moths were removed from the sticky plates in the sex-attractant traps sited in the two 1982 pea fields. Where possible these were dissected to assess P.A. (only those individuals that were adhered solely by their wings were suitable for dissection). The median P.A. of males caught in these traps was most similar to that of males caught with a D-Vac. in the pea crops of the two fields, rather than the population from the surrounding vegetation, or the overall population from the whole fields (fig.5.5.). If all males of different P.A. are equally 252 Fig . 5,5. Physiological age of male C.niqricana populations in and around pea fields and in sex-attractant traps in pea fields, Shimpling Park Farm ,1982 Points show median physiological age with 25% percentiles. A--- .A Male population caught in sex-attractant traps. ___ m Total male population from in and around pea fields PA2 and PB2. ____ Total male population from crop regions of pea fields PA2 and PB2. Total male population from surrounding vegetation of o------o pea fields P a 2 and PB2. 253 254 attracted to the sex-attractant traps, there is no evidence that males are attracted to the traps from outside the crop area. However the median P.A. of trap caught males was consistently greater than that of those individuals caught with a D-Vac., and a more narrow range of 12.3 to 13.5. The 25% and 75% percentiles of trap caught populations are closer to the median in most instances. Thus there is some suggestion that in pea crops, only males of older P.A. are caught in sex-attractant traps, throughout the season, and the P.A. of the catch is not representative of the popula tions in or around the pea field. These older individuals which are caught could be attracted from both within the crop and from surrounding vegetation. There is a further possible explanation for the older P.A. of males caught in the sex-attractant traps. Physiological aging could take place more rapidly as moths struggled on the sticky surface, and the traps may warm up as the * day progresses, which would also cause moths to physiologically age more rapidly; samples were not collected until near the end of activity periods. 255 5.3. Fecundity and Maturation in Relation to Dispersal and Mating Most female C.niqricana have 200 to 300 eggs in their ovaries at any time after emergence and before oviposition has commenced. The maximum potential fecundity recorded in this study was 400 eggs in one individual. The number of eggs per ovariole (potential fecundity) in females caught in the crops of emergence sites was about 25 to 30 in 1981 (fig.5.6.) and 30 to 35 in 1982 (fig.5.7.). This level was more or less constant for the whole season, with much of the variation attributable to low numbers of moths in certain weeks. The egg load of females caught with a kite net was the same or only slightly greater than in those caught with a D-Vac. The mean number of eggs per ovariole in females caught in vegetation around the emerg ence site was about 3 0 to 35 (figs. 5.8. Sc 5.9.) and therefore similar to that of females within the crop. There were no differences between egg load in different categories of surrounding vegetation in 198f and females caught with a kite net were the same as those individuals caught with a D-Vac. (fig.5.8a. - c.). There was a drop in potential fecundity in the grassbank population in week 6 (fig.5.8c.), although the lower densities associated with this habitat do not merit critical discussion. There is a suggestion of a (non-significant) decline in potential fecundity in the few females caught at the end of the season in vegetation around both emergence sites (figs.5.8d. Sc 5.9d.). Females still associated with emergence sites at this stage of the season are perhaps unlikely to be successful reproducers in pea crops, although native leguminous hosts might still be available. The lower potential fecundity of these few females, may have been due to reabsorption of eggs or a feature of biologically less fit individuals. The egg load of females around the pea fields was similar between the three fields in 1981 and 1982 (figs. 5.10. Sc 5.11.) and that at a similar level to females from the emergence sites. There were no differences between females from different vegetation categories of surrounding vegetation in 1981 (fig.5.10a. - d.), and females caught 256 Fig. 5.6. Potential fecundity of female C.niqricana in populations in crop regions of the emergence site, Shimplinq Park Farm, 1981 Mean number of eggs (-S.E.) per ovariole per female. •-- • Females caught with a D-Vac. o-- o Females caught with a kite net. Weeks numbered through the season commencing Monday 25 May. a) Crop central population b) Crop perimetal population c) Total crop population from perimetal and central regions NUMBER OF FEMALES KITE NET CAUGHT 13 12 8 3 3 5 D-VAC. CAUGHT 2 6 1 101 28 12 4 6 2 26 21 5 2 50 1 a) b) 40 - MEAN NUMBER OF EGGS 30 - PER OVARIOLE PER 20 - FEMALE (x is.E. ) 10 1— I i— i— i— i— i— i— i— i— i— i— i— i 1 2 3 4 5 6 7 8 9 10 11 1 2 3 4 5 6 7 8 9 10 11 WEEK NUMBER WEEK NUMBER 257 Fig. 5.7. potential fecundity of female C.nigricana in populations in crop reqions of the emergence site, Shimpling Park Farm, 1982 Mean number of eggs (-S.E.) per ovariole per female All females caught with a D-Vac. Weeks numbered through the season commencing Monday 24 May. a) Crop central population b) Crop perimetal population c) Total crop population from perimetal and central regions 1 1 3 14 5 1 b) 3 ' 4 ' 5 ‘ 6 e 1 9 ' io'ii 1 WEEK NUMBER 258 Fig . 5.8. Potential fecundity of female C.niqricana in populations in vegetation around the emergence site, Shimpling Park Farm, 1981 Mean number of eggs ( -S.E.) per ovariole per female. •-- • Females caught with a D-Vac. o-----o Females caught with a kite net. Weeks numbered through the season commencing Monday 25 th May. a) Hedgerow population b) Understorey population c) Grassbank population d) Total surrounding vegetation population NUMBER OF FEMALES KITE NET CAUGHT 5 18 5 18 D-VAC. CAUGHT 1 0 8 19 42 13 10 0 1 2 6 2 60 10 11 3 WEEK NUMBER 259 Fig . 5.9. Potential fecundity of female C.niqricana in populations in vegetation around the emergence site, Shimpling Park Farm, 1982 Mean number of eggs -S.E. per ovariole per female. All females caught with a D-Vac. Weeks numbered through the season commencing Monday 2 4 ^ May • NUMBER OF f e m a l e s D-VAC. CAUGHT 0 12 15 23 43 16 4 2 MEAN NUMBER OF EGGS PER OVARIOLE PER FEMALE (xts.E.) WEEK NUMBER 2 60 Fig. 5.10. Potential fecundity of female C.nigricana in populations in vegetation around the pea field Shimpling Park Farm, 1981 Mean number of eggs (-S.E.) per ovariole per female. •-- • Females caught with a D-Vac. o-----o Females caught with a kite net. Weeks numbered through the season commencing Monday 2 5 ^ May. a) Hedgerow populations b) Understorey populations c) Grassbank populations d) Adjacent bean crop populations e) Total surrounding vegetation populations 261 NUMBER OF FEMALES KITE NET CAUGHT 3 0 6 3 0 6 D-VAC. CAUGHT 0 4 13 5 1 6 1 0 1 0 1 4 3 2 0 0 4 on a) b) 3 0-j MEAN NUMBER 20- OF EGGS PER OVARIOLE PER 10 " FEMALE (x + S .E.) i — i— i— i— i— i— i— i— i— i— i i— i— i— i— i— i— i— i— i— i— i i NUMBER OF WEEK FEMALES KITE NET CAUGHT 1 0 19 0 2 41 D-VAC. CAUGHT 0 2 0 19 43 16 0 0 0 0 3 10 10 21 0 0 40n c ) d) MEAN 3 0 - NUMBER OF EGGS PER 20 - OVARIOLE PER FEMALE (icis.E.) 10 - — i— i— i— i— i— i— i— i— i— i— i i— i— i— i— i— i— i— i— i— i— i— i 12 3 45 67 89 10 11 12 3 45 67 89 10 11 WEEK NUMBER NUMBER OF KITE NET CAUGHT 4 2 66 FEMALES D-VAC. CAUGHT 1 6 17 38 57 45 1 0 MEAN NUMBER OF EGGS PER OVARIOLE PER FEMALE (x + S .E.) WEEK NUMBER 262 Fig. 5.11. Potential fecundity of female C.nigricana in populations in vegetation around the pea fields Shimpling Park Farm, 1982 Mean number of eggs (-S.E.) per ovariole per female. All females caught with a D-Vac. Weeks numbered through the season commencing Monday 2 4 ^ May. a) Total surrounding vegetation population, pea field PA2 b) Total surrounding vegetation population, pea Field PB2 WEEK NUMBER 263 with a kite net were the same as those caught with a D-Vac. (fig.5.10.). There was a decline in potential fecundity to wards the end of the season, particularly in the vegetation around the two 1982 pea fields. This may have been due to females moving back into the surrounding vegetation after laying eggs in the peas, or due to reabsorption of eggs by physiologically old females (Section 5.2.). Females only moved into the pea crops at about the time of peak density at the emergence site. The potential fecundity of the first females into the pea crops was about 30 to 35, the same as that of females in the surrounding vegetation at that time (fig.5.12. - 5.14.). Females pop ulations in the crop show a decline in fecundity as ovipos it ion takes place. The decline is comparatively gradual with about 5 eggs per ovariole less each week, or equivalent of about 40 eggs laid per week. The number of mature chorionated eggs held by females in different parts of the environment did show some slight differences. In emergence site crops females had 1 to 3 chorionated eggs per ovariole through the season (fig.5.15. Sc 5.16.). In the surrounding vegetation this level rose to 3 to 5 (figs.5.17. & 5.18.). This was also the level in the vegetation around pea fields (figs.5.19. Sc 5.20.). Within the pea crops the number of chorionated eggs per ovariole was more constant at about 5, indicating that a female could lay up to about 40 eggs at any one time (figs. 5.21. - 5.23.) . Since the potential fecundity of all females from the emergence site crops to the first individuals to enter the pea crops was more or less constant, this egg load must be achieved at or soon after emergence. The mean number of eggs per ovariole in females of P.A. 3 & 4 in the crop region of emergence sites was 18.58(- 0.77 S .E.) in 1981 and 25.48(-1.34) in 1982. For females of P.A. 5 & 6 it was 2 6.89 ( - 0.60) in 1981 and 31.11(-1.62) in 1982. In the crops of the emergence sites in both years mated females had significantly more eggs than unmated females (Table 5.1a.) and they also had significantly more chorionated eggs (Table 5.1b.). This feature could be an age effect since the youngest females which did have slightly less eggs, were 264 Fig . 5.12. Potential fecundity of female C.nigricana in populations in crop regions of the pea field, Shimpling Park Farm, 1981 Mean number of eggs (-S.E.) per ovariole per female. •-- • Females caught with a D-Vac. o-----o Females caught with a kite net. Weeks numbered through the season commencing Monday 2 5 ^ May. a) Crop central population b) Crop perimetal population c) Total crop population from perimetal and central regions NUMBER OF FEMALES KITE NET CAUGHT 1 4 29 1 10 18 D-VAC. CAUGHT 0 0 0 1 22 3 4 1 0 0 0 4 37 14 4 1 40-] a) b) MEAN 30- NUMBER CfF EGGS PER 20- OVARIOLE PER FEMALE (x + S . E .) 10- I I I I I I I I I I I I I I I I I I I I I I I 12 3 4 5 678 9 10 11 1 2 3 45 6789 10 11 WEEK NUMBER NUMBER OF KITE NET CAUGHT 2 14 47 FEMALES D-VAC. CAUGHT 0 0 0 5 59 17 8 2 MEAN NUMBER OF EGGS PER OVARIOLE PER FEMALE WEEK NUMBER 265 Fig, 5.13. Potential fecundity of female C.nigricana in populations in crop regions of pea field PA2, Shimplinq Park Farm, 1982 Mean number of eggs ( - S.E.) per ovariole per female. All females caught with a D-Vac. Weeks numbered through the season commencing Monday 24 ^ May. a) Crop central‘population b) Crop perimetal population c) Total crop population from perimetal and central regions NUMBER OF FEMALES D-VAC. CAUGHT 0 6 0 13 6 4 0 2 3 29 16 2 1 G) 4 0 - \ \ m ean 3 0 - \ NUMBER OF EGGS PER 20- OVARIOLE PER FEMALE 10- (x t S . E.) I l I I I--1--1--1--1--1--1 12 34 5 67 89 10 11 WEEK NUMBER 266 Fig . 5 .14. Potential fecundity of female C.nigricana in populations in crop regions of pea field PB2, Shimpling Park Farm, 1982 Mean number of eggs (-S.E.) per ovariole per female. All females caught with a D-Vac. Weeks numbered through the season commencing Monday 24 May. a) Crop central population b) Crop perimetal population c) Total crop population from perimetal'and central regions NUMBER OF FEMALES D-VAC. CAUGHT 0 1 0 20 12 8 40-1 a) m e a n 30- NUMBER OF EGGS PER 20- OVARIOLE PER FEMALE (xts.E.) 10- i i— i— i— i— i— i— i— i— i— i I I I I l I I (--1--1--1--1 1 2 3 4 5 6 7 8 9 10 11 1 2 3 4" 5 6 7 8 9 10 11 WEEK NUMBER 2b7 Fig. 5.15. Mature egg load of female C.niqricana in populations in crop regions of emergence site, Shimpling Park Farm, 1981 Mean number of chorionated eggs (iS.E.) per ovariole per female* • • Females caught with a D-Vac. o o Females caught with a kite net. Weeks numbered through the season commencing Monday 25t*1 May a) Crop central populations. b) Crop perimetal populations. c) Total crop populations from central and perimetal regions Fig. 5.16. Mature egg load of female C.nigricana in populations in crop regions of emergence site, Shimpling Park Farm, 1982 Mean number of chorionated eggs (-S.E.) per ovariole per female. All females caught with a D-Vac. Weeks numbered through the season commencing Monday 2 4 ^ May a) Crop central populations. b) Crop perimetal populations. c) Total crop populations from central and perimetal regions 268 NUMBER OF FEMALES KITE NET CAUGHT 13 12 9 4 3 5 D-VAC. CAUGHT 0 2 6 1 isiL28 12 4 0 0 6 2 26 21 5 2 MEAN NUMBER 10—, b) OF CHORIONATED EGGS PER 5- OVARIOLE PER FEMALE (x ± S . E .) 6 1 7 ' 8 1 9 ' 10'11‘ WEEK NUMBER NUMBER OF KITE NET CAUGHT 17 15 14 FEMALES D-VAC. CAUGHT 0 2 12 3 127 49 17 6 MEAN NUMBER OF CHORIONATED EGGS PER OVARIOLE PER FEMALE (x + S.E.) NUMBER OF FEMALES D-VAC. CAUGHT 0 4 8 42 13 3 0 1 1 3 14 5 1 0 MEAN NUMBER xq-, OF a) b) CHORION ATED EGGS PER 5 - OVARIOLE PER FEMALE (xls.E.) i r I I r*t — rW^'r:i— r 2 3 4 8 9 10 11 2 3 5 ' 6 ' 7 ' 8 ' 9 ' 10 'll' WEEK NUMBER NUMBER OF FEMALES D-VAC CAUGHT 1 5 11 56 18 4 0 MEAN NUMBER OF CHORIONATED EGGS PER OVARIOLE PER FEMALE (x. t S . E .) WEEK NUMBER Fig . 5.17. Mature egg load of female C.nigricana in Populations in vegetation around emergence site, Shimpling Park Farm, 1981 Mean number of chorionated eggs (-S.E.) per ovariole per female. •--- •Females caught with a D-Vac. o------o Females caught with a kite net. th Weeks numbered through the season commencing Monday 25 May a) Hedgerow populations. b) Understorey populations. c) Grassbank populations. d) Total surrounding vegetation populations. Fig . 5.18. Mature egg load of female C.nigricana in populations in vegetation around emergence site, Shimpling Park Farm, 1982 Mean number of chorionated eggs (-S.E.) per ovariole per female. All females caught with a D-Vac. Weeks numbered through the season commencing Monday 2 4 ^ May Total surrounding vegetation (i.e. grassbank) populations. 270 NUMBER OF FEMALES KITE NET CAUGHT 5 20 0 5 20 0 D-VAC. CAUGHT 1 0 8 19 43 13 10 0 1 2 6 2 63 10 11 3 MEAN NUMBER 10 —i OF a) b) CHORIONATED EGGS PER 5 - OVARIOLE PER FEMALE (x S .E.) t i i i i i i i i i i i l— i— — r-^n— i— i— i--1— i— i 12 3 45 67 8 9 10 11 1 2 3 4 5 6 7 8 9 1C 11 WEEK NUMBER NUMBER OF FEMALES KITE NET CAUGHT 6 4 5 11 24 5 D-VAC. CAUGHT 1 1 0 0 14 0 2 0 3 3 14 21 120 23 23 3 MEAN NUMBER d) OF CHORION ATED EGGS PER OVARIOLE PER FEMALE (x t S.E.) — i— i— i— i— i 1 1 ' 2 ' 3' 4 'T 7 8 9 10 11 WEEK NUMBER NUMBER OF FEMALES D-VAC CAUGHT 0 0 12 15 23 52 16 4 2 MEAN NUMBER OF CHORIONATED EGGS PER OVARIOLE PER FEMALE (x + S . E.) WEEK NUMBER 271 Fig . 5.19. Mature egg load of female C.nigricana in populations in vegetation around the pea field, Shimpling Park Farm, 1981 Mean number of chorionated eggs (-S.E.) per ovariole per female. •-- • Females caught with a D-Vac. o-- o Females caught with a kite net. Weeks numbered through the season commencing Monday 25th May. a) Hedgerow populations. b) Understorey populations. c) Grassbank populations. d) Adjacent bean crop populations. e) Total surrounding vegetation populations. Fig. 5,20, Mature egg load of female C.nigricana in populations in vegetation around the pea fields, Shimpling Park Farm, 1982 Mean number of chorionated eggs (-S.E.) per ovariole per female. All females caught with a D-Vac. Weeks numbered through the season commencing Monday 24th May. a) Total surrounding vegetation populations of pea field Pa 2. b) Total surrounding vegetation populations of pea field PB2. 272 NUMBER OF FEMALES KITE NET CAUGHT 3 0 6 3 0 6 D-VAC. CAUGHT 0 0 4 13 5 1 6 1 0 0 1 0 1 4 3 2 0 0 MEAN NUMBER 10~| OF a) b) CHORIONATED EGGS PER 5 - OVARIOLE PER FEMALE (x + S . E.) i i i i i i i i i i i r—T —!--1--1--1 12 34 56 78 9 10 11 ' 1 ' 2 ' 3 4 5 6 7 8 9 10 11 WEEK NUMBER NUMBER OF KITE NET CAUGHT 4 2 68 FEMALES D-VAC. CAUGHT 0 1 6 17 41 57 45 1 0 MEAN NUMBER OF CHORIONATED EGGS PER OVARIOLE PER FEMALE (icts.'E.) NUMBER OF FEMALES D-VAC. CAUGHT 0 7 5 6 12 3 0 2 7 7 11 36 4 2 MEAN NUMBER 10“| a) b) OF CHORION ATED EGGS PER 5 - OVARIOLE PER FEMALE (x± S .E.) — I— I— I— I— I— I— I— I— I— I— 1 1 2 3 4 5 6 7 8 9 10 11 WEEK NUMBER 273 Fig 5.21. Mature egg load of female C.nigricana in populations in crop regions of the pea field, Shimpling Park Farm, 1981 Mean number of chorionated eggs (-S.E.) per ovariole per female. •--•Females caught with a D-Vac. o-- o Females caught with a kite net, th Weeks numbered through the season commencing Monday 25 May. a) Crop central population b) Crop perimetal population c) Total crop population from central and perimetal regions NUMBER OF FEMALES KITE NET CAUGHT 1 4 31 1 10 18 D-VAC. CAUGHT 0 0 0 1 22 3 4 1 0 0 0 4 37 14 4 1 MEAN NUMBER 10—I OF a) b) CHORIONATED EGGS PER 5- OVARIOLE PER FEMALE (xts.E.) --1--1 I I ' I--1--1--1 2 3 4 ' 5 ' 6 ‘ 7 8 9 10 11 1 ' 2' 3' 4 5 6 7 8 9 10 11 WEEK NUMBER NUMBER OF KITE NET CAUGHT 2 14 49 FEMALES D-VAC. CAUGHT 0 0 0 5 59 17 8 2 MEAN NUMBER OF CHORIONATED EGGS PER OVARIOLE PER FEMALE (xts.E.) WEEK NUMBER 274 Fig. 5.22. Mature egg load of female C.niqricana in populations in crop regions of pea field1 PA2, Shimpling Park Farm, 1982 Mean number of chorionated eggs (-S.E.) per ovariole per female. All females caught with a D-Vac. th Weeks numbered through the season commencing Monday 24 May. a) Crop central populations. b) Crop perimetal populations. c) Total crop populations from central and perimetal regions. Fig. 5.23. Mature egg load of female C.niqricana in populations in crop regions of pea field PB2, Shimpling Park Farm, 1982 Mean number of chorionated eggs (-S.E.) per ovariole per female. All females caught with a D-Vac. Weeks numbered through the season commencing Monday 2 4 ^ May. a) Crop central populations. b) Crop perimetal populations. c) Total crop populations from central and perimetal regions. 275 0 2 3 29 16 2 WEEK NUMBER NUMBER OF FEMALES D-VAC CAUGHT 0 8 3 42 23 6 MEAN NUMBER OF CHORIONATED EGGS PER OVARIOLE PER FEMALE (x + S.E.) NUMBER OF FEMALES D-VAC. CAUGHT 0 1 0 20 12 8 0 1 0 11 4 1 MEAN NUMBER iq-| a) b) OF CHORIONATED EGGS PER 5- OVARIOLE PER FEMALE (x t S.E.) — i— i— i— i— i— ]— i— i— i— i— i I--1--1--1--1--1--1--1--1--1--1--1 1 2 3 4 5 b 7 8 9 10 11 1 2 3 4 5 6 7 8 9 10 11 WEEK NUMBER NUMBER OF FEMALES D-VAC CAUGHT 0 2 0 31 16 9 MEAN NUMBER OF CHORIONATED EGGS PER OVARIOLE PER FEMALE (xts . E.) WEEK NUMBER 276 Table 5.1. Comparison of potential fecundity and mature egg load of mated and unmated female C.niqricana in crop regions of emergence sites, Shimpling Park Farm, 1981 and 1982 a) Variance ratio, F, and tabulated F values from analysis of variance of potential fecundity (mean number of eggs per ovariole) of mated and unmated females. Female populations from crop region of emergence site pooled over whole season. Variance Tabulated F ll H o • o n Ratio F p = 0.05 t> 1981 214 75.201 3.842 6.635 l,oo df 1982 95 28.464 4.001 7.077 1,6 Odf b) Variance ratio, F, and tabulated F values from analysis of variance of mature egg load (mean number of chorionated eggs per ovariole) of mated and unmated females. Female populations from crop region of emergence site pooled over whole season. Variance Tabulated F n Ratio F p = 0.05 p = 0.01 1981 214 126.960 3.842 6.635 l,°o df 1982 95 ' 52.395 4.001 7.077 @ 1,6Odf 277 also less likely to have mated. Within more restricted age groups, there were still some significant differences between egg load of unmated and mated individuals (Table 5.2.). The possible explanation for increased egg load in mated females may be that mating stimulates egg production and chorionation of mature eggs, or that a nutrient contribution from the male allows more rapid egg production. Nutrient transferred from the male to the female in the spermatophore could be utilised for both egg production or somatic main- tainance, but could also lead to decreased utilisation of stored fat in the female. Thus mated females could be the same physiological age as unmated females, but be older in real time, and therefore had longer for egg production and maturation. In the vegetation surrounding the emergence sites, differences between unmated and mated females were not so marked, however some populations of mated females had signif icantly more eggs than their unmated counterparts of the same P.A. (Table 5.3.). It appears that in vegetation around emergence sites, mated females of a slightly older P.A. have more eggs, and particularly more mature eggs. Female C.nigricana produce all their eggs while still in or around the emergence site and soon after emergence. Egg production and maturation is enhanced in mated individ uals. All females have 250 to 300 eggs and up to 40 mature chorionated eggs in their ovaries, when they enter the pea crops. 278 Table 5,2. Comparison of potential fecundity and mature egg load of mated and unmated female C.nigricana of different age groups in crop regions of emerg ence sites, Shimpling Park Farm, 1981 and 1982 Variance ratio, F, and tabulated F values from analysis of variance of potential fecundity (mean number of eggs per ovariole) and mature egg load (mean number of chorionated eggs per ovariole) of mated and unmated females. Female populations of different physiological age groups from crop regions of emergence site pooled over whole season. Variance Tabulated F n Ratio F p = 0.05 p = 0.01 P.A. 3 Sc 4, 1981 Total eggs 81 4.400 4.001 7.077 1,6 Odf Mature eggs 81 43.255 4.001 7.077 1,60df P.A. 5 Sc 6, 1981 Total eggs 66 8.186 4.001 7.077 1, 6 Odf Mature eggs 66 7.571 4.001 7.077 1, 6Odf P.A. 7 & 8, 1981 Total eggs 47 2.369 4.085 1,4Odf Mature eggs 47 3.600 4.085 @ 1,4 Odf P.A. 9 Sc 10, 1981 Total eggs 18 1.610 4.414 1,18df Mature eggs 18 2.370 4.414 1, 18df P.A. 3 to 6, 1982 Total eggs 51 4.187 4.085 7.314 P.A. 7 to 10, 1982 Total eggs 34 0.454 4.171 (§> 1,30df Mature eggs 34 . 4.074 4.171 1, 3 Odf 279 Table 5.3. Comparison of potential fecundity and mature egg load of mated and unmated female C.niqricana of different age groups in vegetation surrounding emergence sites, Shimpling Park Farm, 1981 Sc 1982 Variance ratio, F, and tabulated F values from analysis of variance of potential fecundity (mean number of eggs per ovariole) and mature egg load (mean number of chorionated eggs per ovariole) of mated and unmated females. Female populations of different physiological age groups from vegetation around emergence sites pooled over whole season. Variance Tabulated F n Ratio F p = 0.05 p = 0.01 P.A. 5 Sc 6, 1981 Total eggs 36 0.975 4.171 © 1,30df Mature eggs 36 1.320 4.171 © 1,30df P. A. 7' Sc 8, 1981 Total eggs 67 0.334 4.001 © 1,60df Mature eggs 67 6.052 4.001 7.077 © 1,60df P.A. 9 Sc 10, 1981 Total eggs 47 1.039 4.085 © 1,40df Mature eggs 47 4.000 4.085 © 1,40df P.A. 5 Sc 6, 1982 Total eggs 28 12.441 4.225 7.721 © 1,26df Mature eggs 28 2.075 4.225 © 1,26df P.A. 7 to 10 ,. 1982 Total eggs 50 0.492 4.085 © 1,40df Mature eggs 50 7.229 4.085 7.314 © 1, 40df 280 5.4. The Effect of Diet on Longevity and Fecundity Feeding and drinking activity of adult C.nigricana was characterised by the extended proboscis being appressed to a moist surface for most of its length, anterior of the head. One individual was observed with the proboscis extended on the surface beneath the head and thorax, and another was observed with the proboscis inserted between the dental wick and glass tube in which the wick was contained. Feeding or drinking by adult C.nigricana was observed rarely in breeding chambers. With hourly inspection during the light phase over a period of 22 days, of 100 females and 146 males, drinking or feeding were observed on two occasions only. One male was drinking from the dental wick in the side arm of a breeding chamber at 1415hrs. and ceased- at 1505. One female was observed feeding from 10% honey solution on a dental wick at 1555 and ceased at 1600. Seven males and seven females of mixed age and history were observed at more frequent intervals over a period of 13 hours. One female was observed feeding from 10% sucrose solution from 1130 to 1340; a different moth was feeding at 2141, ceased at 2200, but recommenced at 2215 and continued until 2345. Regular observ ation of nine newly emerged males ( less than 48hrs. old) in a breeding chamber with 10% sucrose solution revealed no feeding activity from 0945 to 2345. The mean longevity of both male and female C.nigricana was not significantly different between the two replicates of each of three treatments with different diets (Section 2.2.3.)(fig.5.24.). Also mean longevity was not significantly different between treatments (fig.5.24.). The median P.A. of both males and females was very similar both within and between treatments, and between the sexes (fig.5.25.). Female fecundity was very variable, with the highest being a mean of 61.5 eggs per female attained by six females provided with water only. The lowest was zero oviposition from one female provided with 10% honey solution. The highest number of fertile eggs per fertile female was in the same water only treatment as above with 267 fertile eggs from four of the six females. There was no mating in one of the 10% sucrose replicates with three females, and in the honey replicate with zero oviposition, the female was mated 2 81 Fig . 5.24. The effect of diet on longevity of male and female C.nigricana Mean longevity in days (-S.E.) of moths in each of two replicates (solid symbols) and pooled value for whole treatment (open symbol). Fresh diets provided every two days. All replicates held at 20*C and under 18hr. photophase. a) Water only. b) 10% Sucrose solution. c) 10% Honey solution. F i g . 5.25. The effect of diet on physiological age at death of male and female C.nigricana Median physiological age with 25% percentiles of moths in each of two replicates (solid symbols) and pooled value for whole treatment (open symbol). Fresh diets provided every two days. All replicates held at 20*C and under 18hr. photophase. a) Water only. b) 10% Sucrose solution. c) 10% Honey solution. 2 82 n 2 6 8 6 6 12 5 1 6 5 3 8 5 2 7 8 1 9 25—1 a) b) c) 20- LONGEVITY (Days) x - S . E. T 1 1 i 1 r'i i 1 1 i 1 1 i i 1 1 i " 1 " r _ MALES FEMALES MALES FEMALES MALES FEMALES 5 1 6 5 3 8 5 2 7 8 1 9 7 7 10 12 10 12 12 12 12 12 12 12 13 13 13 13 13 13 13 13 13 13 b) c) □ <> ■ MALES FEMALES MALES FEMALES MALES FEMALES (Table 5.4.). Potential fecundity per female, calculated from the total number of eggs remaining in the females 1 ovaries added to those eggs laid, was variable between replicates, but similar between treatments when the data from the two repl icates was pooled (Table 5.4.). The pooled potential for chorionated eggs per female (chorionated eggs in ovaries plus eggs laid) was also very similar between treatments (Table 5.4.) as was the potential chorionated eggs from fertile females (chorionated eggs in fertile females' ovaries plus fertile eggs laid) (Table 5.4.). This potential fecundity data suggests that the potential for each female is not dependent on adult diet. The realised fecundity was very variable and cannot be critic ally examined. Realised fecundity could be increased with more nutrient rich diets, if this increased longevity, how ever in this limited experiment this did not occur. 2 84 Table 5.4. Fecundity and Potential fecundity of female C.niqricana provided with different diets Potential fecundities calculated from number of eggs laid plus number of eggs remaining in females 1 ovaries, averaged per female. Water 10% Sucrose 1 0 % H o n e y FECUNDITY S o l u t i o n S o l u t i o n Number of eggs per female Replicate (a)(no. of females) 61.50(6) 14.40 (5) 29.90(8) R e p l i c a t e (b) (no. of females) 5 . 8 3 (6) 1 . 3 3 (3) 0 . 0 0 (1) T r e a t m e n t t o t a l (no. of females) 3 3 . 6 7 (12) 9 . 5 0 (8) 2 6 . 5 6 (9) N u m b e r o f fertile eggs per fertile 0 Replicate (a) (no. of f e m a l e s ) 6 6 . 7 5 (4) 3 0 . 5 0 (2) 2 0 . 7 5 (4) R e p l i c a t e (b) (no. o f f e m a l e s ) 4 . 6 7 (3) 0 . 0 0 (0) 0 . 0 0 (1) T r e a t m e n t total (no. of females) 4 0 . 1 4 (7) 3 0 . 5 0 (2) 1 6 . 6 0 (5) Percentage fertility R e p l i c a t e (a) (no. o f e g g s ) 72.36 (369) 8 4 . 7 2 (72) 3 4 . 7 3 (239) R e p l i c a t e (b) (no. o f e g g s ) 4 0 . 0 0 ( 3 5 ) 0 . 0 0 (4) 0 . 0 0 (0) Treatment total (no. o f e g g s ) 69.56 (404) 8 0 . 2 6 (76) 3 4 . 7 3 (239) POTENTIALFECUNDITY Total potential per female Replicate (a) (no, of f e m a l e s ) 2 4 8 (6) 2 6 2 (5) 2 1 0 (8) Replicate (b) (no. of f e m a l e s ) 1 9 9 (6) 1 7 5 (3) 1 6 0 (1) T r e a t m e n t t o t a l (no. of females) 2 2 4 (12) 2 2 9 ( 8 ) 2 0 4 (9) Total potential chorionated eggs per 0 R e p l i c a t e (a) (no. of females) 9 8 ( 6 ) 62 (5) 82 (8) R e p l i c a t e (b) (no. of f e m a l e s ) 50 (6) 65 (3) 4 0 (1) Treatment total (no. of females) 74 (12) 63 (8) 77 (9) Potential chorionated eggs per fertile 0 Replicate (a) (no. of f e m a l e s ) 97 (4) 75 (2) 7 7 (4) Replicate (b) (no. of f e m a l e s ) 5 0 ( 3 ) 0(0) 4 0 ( 1 ) T r e a t m e n t t o t a l (no. of females) 77 (7) 75 (2) 7 0 ( 5 ) 2 85 5.5. Longevity, Fecundity and Maturation in relation to Host Plant Phenology The results of the experiments to determine the effect of plant presence were often variable between replicates within treatments. This may be due to the differing sources of moths: moths for experiment 1 (Section 2.2.4.) were field collected, while moths for experiment 2 (Section 2.2.4.) were cultured in C.E. rooms. The data from experiment 1 are presented as the first replicate in each treatment in all the following figures and tables. There was also variation between replicates within the treatments in exper iment 2, these replicates were set up at different times, with moths from different generations, some have differing numbers of moths and differing sex ratios. Since these may not be replicates sensu stricto, data are presented for individual replicates as well as treatment means. The median P.A. at death of both males and females was very similar for all five treatments (fig.5.26.), although there was some variation between replicates. The median P.A. of females was more constant between replicates than for males; males in some replicates died before they were physiologically old. The mean longevity of males and females was more variable both between replicates and between treatments (fig.5.27.). Replicates where the median P.A. was lowest were not necessarily those where moths lived for a shorter time, and replicates where moths achieved a high mean long evity were not characterised by a higher median P.A. at death. Analysis of variance did not give a significant variance ratio for treatments for males (F = 2.159, NS, 4,96df), but did for females (F = 2.897, p < 0.05, 4,96df). The mean longevity of females confined with wheat was significantly less than that of females confined with young reproductive pea parts (P.Y.R.) (t = 2.901, p<0.01, 43df) ; other treatments were not significantly different. The potential fecundity was also variable between replicates, and ranged from about 130 per female in one P.Y.R. replicate with five females, to almost 300 per female in one vegetative pea replicate with seven females. The highest mean potential fecundity was in females confined with wheat, followed by females with vegetative peas, the 2 86 Fig. 5.26. Effect of plant presence and phenological stage on physiological age at death of male and female C.nigricana Median physiological age and 25% percentiles of moths in each replicate (solid symbols) and pooled value for whole treatment (open symbol). All replicates provided with fresh 10% honey solution, and fresh plant material (no plant material in control) every two days. All replicates held at 20 *C and under 18hr. photophase. PHYSIOLOGICAL Range n 4 “ a 9 14 7 7 I 1 MALES 13 414 14 12 87 18 4 CONTROL 11 8 13 FEMALES 21 11 11 12 7 7 41 14 14 14 21 WHEAT 11 7 13 F M 11 13 7 31 13 14 13 9 7 7 7 AE FEMALES MALES 11 PEAS : VEGETATIVE 9 9 14 21 6 11 11 12 11 41 414 14 14 14 7 7 7 11 21 10 7 41 13 14 14 —i —i —i r i— i— i— i— i— i— 111 11 8 8 7 8 MALES 13 7 PEAS : YOUNG REPRODUCTIVES 4 12 9 9 13 5 13 a 3 177 7 41 14 210 12 8 14 14 12 31 13 13 13 EA E AE FEMALES MALES FEMALES t I t l 6 01 11 12 10 3 7 13 5 11 10 10 11 3 13 87 38 14 PEAS : OLD REPRO'S 14 " M t M ! " I —r i— 41 14 14 14 9 7 47 14 9 12 314 13 9 14 7 9 2 87 2 I I 288 Fiq. 5.27. Effect of plant presence and phenology on Iongevity of male and female C.niqricana Mean longevity in days (-S.E.) of moths in each replicate (solid symbols) and pooled value for whole treatment (open symbol). All replicates provided with fresh 10% honey solution, and fresh plant material (no plant material in control) every two days. All replicates held at 20*C and under 18hr. photophase. LONGEVITY (Dayc) n 7 7 4 18 7 7 7 21 W E T PEAS : VEGETATIVE 'WHEAT F AE FEMALES MALES F M 7 7 7 21 7 7 7 21 7 8 MALES 7 E S: Y UGRPOUTVSPEAS : OLD REPRO'S PEAS : YOUNG REPRODUCTIVES <► 4 5 \ 3 41 \ 7 7 ♦ I 6 1 EAE MLS FEMALES MALES FEMALES -- 7 1 -- 3 1 -- 5 1 -- 877 7 28 3 1 -- ( | -- I I | I I | I 1 47714 7 7 14 I I 289 290 control, P.Y.R., and the lowest from females with old reproductive pea parts (P.O.R.) (Table 5.5.). The potential number of chorionated eggs per female was however lowest in females confined with wheat (Table 5.5.) which may suggest that wheat does not stimulate egg maturation. Females with P.O.R. also had low numbers of mature eggs. The females confined with vegetative pea material had the highest number of mature eggs (Table 5.5.). The highest realised fecundity was also from females with vegetative material, with females in one replicate laying an average of 190 eggs each (Table 5.5.). The lowest realised fecundities were from females with wheat and P.O.R. , i.e. those with the lowest number of mature eggs in their ovaries. These two treatments also showed the lowest mean number of fertile eggs per fertile female, while the veget ative pea treatment with the highest realised mean fecundity also had the highest mean number of fertile eggs per fertile female, with fertile females in one replicate laying an average of 203 fertile eggs each (Table 5.5.). Therefore it appears that females confined with vegetative pea plant material were stimulated to lay more eggs than those in other treatments. They also laid more fertile eggs and a higher proportion of the females had mated (Table 5.5.). Females confined with P.Y.R. did not realise such high fecundities or lay as many eggs as control individuals, although a greater proportion of the females were mated in the former treatment. In treatments with plant material, females laid a variable percentage of their realised egg load on the plant tissue. The highest percentages were from females in one P.O.R. replicate, followed by those in some P.Y.R. replicates (Table 5.5.). The females confined with vegetative pea parts, which otherwise achieved the highest fecundities, laid the lowest percentages of their eggs on the plant sur face. However since these females laid such large numbers of eggs, the area of plant surface available may have been limiting, since these females did lay more eggs on plant material. Of eggs laid on pea plants, 60% were laid on stipules with 50% of the upper surface alone. The next most pre ferred sites were the upper surface of leaflets and the 291 Table 5.5. Potential fecundity, fecundity and percentage of eggs laid on plant material of female C.nigricana confined without and with plant material at different phenological stages Potential fecundities calculated from number of eggs laid plus number remaining in females 1 ovaries, averaged per female. Numbers in brackets following individual replicate values are number of females, either total or fertilised only, in the given replicate. Numbers in brackets following percentage oviposition on plant tissue are total number of eggs for the given replicate. * Since all females in this replicate were mated, this figure includes infertile eggs laid. "t Contents of one fertile female only, since no fertile eggs were laid. 292 VEGETATIVE YOUNG OLD CONTROL WHEAT PEAS REPRODUCTIVE REPRODUCTIVE POTENTIAL FECUNDITY PEAS PEAS Potential per female Replicate (a) 200.29(7) 242.10 (7) 165.33(7) 195.43 (7) 14 3 . 2 0 '7) Replicate (b) 2 31.43 (7) 298.71(7) 262.71 (7) 159.2? (7) Replicate (c) 241.29 (7) 247.29(7) 192.17 (6) Replicate (d) 224.14 (7) Replicate (e) 188.67(3) Replicate (f) 128.60 (5) Replicate (g) 135.33 (3) Treatment mean ( -S.E.) 224.34+ 12.36 242.1 237.00 +38.84 189.58 117.76 151.29 ± 8 00 Potential chorionated per $ Replicate (a) 62.00 (7) 76.00 (7) 97.14 (7) 77.71 (7) 69.29 (7) Replicate (b) 152.57 (7) 256.43 (7) 173.57 (7) 103.29(7) Replicate (c) 146.43 (7) 192.43(7) 109.50(6) Replicate (d) 132.70(7) Replicate (e) 68.67(3) Replicate (f) 71.40 (5) Replicate (g) 99.33 (3) Treatment mean ( - S.E.) 120.33 t 29.22 76.0 182.00 +46.28 104.70 +14.40 86.29 +17.0 Potential chorionated per fertile female Replicate (a) 150.00 (1) 88 0 (2) 116.67 (3) 81.40 (5) 72.00 '5) Replicate (b) 163.20 (5) *256.43 (7) *173.57(7) +120.00(1) Replicate (c) 181.20 (5) 235.40(5) 230.00(1) Replicate (d) 132.50 (2) Replicate (e) 58.00(1) Replicate (f) 62.25(4) Replicate (g) *99.33(3) Treatment mean (-S.E.) 164.80 19.04 88.00 202.83 143.51 119.58 ±24.01 96.00 ±24 0 FECUNDITY Number of eggs per female 13.29(7) Replicate (a) 17 .43 (7) 15.43 (7) 32.00 (7) 29.71(7) Replicate (b) 104.57 (7) 190.14(7) 108.43(7) 10.71(1) Replicate (c) 109 86(7) 155.86(7) 38.83(6) Replicate (d) 58.43 (7) Replicate (e) 28.67 (3) Replicate (f) 58.60(5) Replicate (g) 55.33 (3) Treatment mean ( ± S.E. ) 77.29 ± 29.97 15.43 126.00 + 48. 03 54.00+ 10.31 12.00 + 1.2 ■ Number of fertile eggs per fertile female Replicate (a) 102.00(1) 24.00 (2) 60.67 (3) 30.20(5) 12.00(5) Replicate (b) 116.80(5) 161.71(7) 67.00(7) 0.00 11) Replicate (c) 142.80(5) 203.40(5) 190.00(1) Replicate (d) 76.50(2) Replicate (e) 2.00(1) Replicate (f) 52.25 (4) Replicate (g) 1.33(4) Treatment meani ( ±S.E. ) 120.53+ 11.93 24.00 141.93 ± 42.38 59.90 ± 24.38 6.0 ± 6.0 Percentage fertility Replicate (a) 83.61 44.44 81.25 72.60 64.52 Replicate (b) 79.73 85.05 61 79 0.0 Replicate (c) >2.85 93.22 81.55 Replicate (d) 37.41 Replicate Percentage of eggs laid on plant tissue Replicate (a) 50.00(108) 36,.61(224) 62,.50(208) Replicate (b) 22.,01(1331) 44.,93(759) Replicate (c) 19. 98(1091) 4,,29(233) ReplIcate (d) 52.,81(409) Replicate (e) 53,,49(86) Replicate (f ) 12,.97(293) Replicate (g) 30 72(166) 293 sepals, with stems, petioles and other floral parts accounting for the remainder (Table 5.6.)- Table 5.6. Preferred oviposition microsites on pea plant material Percentage of eggs (n = 930) laid on different plant organs by female C.nigricana in laboratory experiments. Treatments held at 20 *C and under 18hr. photophase. Position on plant Percentage Stem 3.55 Leaflet - upper surface 9.03 - lower surface 0.65 Petiole / Tendril 1.29 Stipule - upper surface 50.00 - lower surface 10.32 Pedicel 0.65 Sepal 10.00 Petal 5.81 Pod 8.71 294 5.6. Discussion The ovaries and associated reproductive system of C.niqricana are virtually identical in shape and form to those of C.pomonella described in detail by Allman(1930). The fat body of C.niqricana differs somewhat from that of C.pomonella as described in Section 2.1.9. Despite the fact that different temperature conditions in the field could lead to similarly aged moths showing different P.A., the p . A. scale could be used to describe and distinguish between different sub-populations of both sexes of C.niqricana. Some individuals arrived at pea fields at a young P.A. and clearly reached the fields while still at a young real age. In general,moth populations became physiologically older both spatially and temporally. Many weekly sub-popul ations were characterised by moths of only one or two P.A. categories. Within weeks, moth populations of both sexes became physiologically older as they were found further away from the,crop of the emergence site. Moths in or around pea crops may have emerged more than a week previously and were therefore older in real time, and those that had dis persed within a week would have metabolised stored fat to provide the energy for dispersive flights, within any area 4 of the environment, moth populations tended to become physiologically older due to real aging of any residents and (at least after mid-season or when peak density was attained) lack of newly emerged immigrants; Clearly, this physiological aging through space and time is what would be predicted', the P.A. composition of these moth populations therefore conform to expectations, and the development and use of the aging scale is vindicated. The P.A. of moths again suggests different behaviour between the two sexes and this system has therefore provided good corroborative evidence for the differential dispersal of male and female C.nigricana previously described (Section 3.3.3.). Female populations in the crop regions of emerg ence sites were characterised by physiologically young individuals, which are undoubtedly newly emerged, throughout the season. They therefore differ from all populations of males and other populations of females which had a tendency to become physiologically older through the season , as 295 described above. Female C.nigricana therefore left the emergence site crop very soon after emergence. With C.pomonella, Nel (1940) and Geier(1960) found a full range of P.A. amongst females caught with bait traps and a light trap in an orchard, although the proportions of the different P.A. groups differed with the trap type. This result is to be expected since the C.pomonella populations comprised newly emergent and older residents, as well as immigrants. The apparent similarity in P.A. composition between female populations in vegetation around the pea field with female populations in pea crops may indeed suggest that there was a free exchange of individuals between the two areas, with females entering the crop for bouts of oviposition, then returning to the surrounding vegetation. However, it is possible that females in the crops were older in real time, but that this is not determinable with the resolution of the ordinal scale. The findings concerning the P. A. of male C.nigricana caught in sex-attractant traps are important and need further investigation and replication. If indeed trapped males are typically physiologically older than male populations in and around pea fields, this provides further support for the conjecture that performance of male C.nigricana in the field contradicts the behaviour predicted from the labor atory. Unfortunately, there is no information on the P.A. of males caught in sex-attractant traps sited in emergence sites. However, when the relationship between sex-attract- ant trap catch and indices of moth density were examined, no suitable explanation could be provided as to why what was presumed to be an older population of males showed increased response to the less attractive synthetic analogue used in the traps, after exposure to natural pheromone as female C.nigricana attained peak emergence. It is now clear that the male populations are physiologically older (and probably older in real age) and that furthermore it may be the oldest moths which respond to the traps. Clearly, these individuals have undoubtedly been exposed to the natural pheromone and there is a good chance that they have mated. 296 The potential fecundity of C.nigricana appears to be similar to fecundities recorded for other tortricids. Moths are clearly ready to lay eggs as soon as they enter the pea crops since they are carrying up to 40 mature eggs, and are also mated (Chapter 4). The incorporation of a three day pre-oviposition period (POP) for predicting spray date, as advocated by Lewis and Sturgeon(1978) is unnecessary, and would lead to an erroneous estimate of hatching date, since eggs could be laid at the time of threshold catch. In the event, the monitoring system has always been used without provision of a POP. The POP of two to three days after emergence, given by Lewis and Sturgeon (1978) is shorter but probably more accurate than that given by earlier workers, e.g. 4 - 7 days (Brittain, 1921), 4 - 8 days (Baker Sc Perron, 1944) , 5 - 11 days (Wright & Geering, 1948) . The POP of C.ptychora under natural conditions in an inseetary was 2.2 1 0.3 (S.E.) days (n = 25) (Taylor, 1965) and for C.pomonella at ca. 19.5*C was approximately one day (Gehring Sc Madsen, 1963). The decline in potential fecundity in pea crops sugg ested by the weekly samples was comparatively shallow. Although these are different populations of females, if this decline is related to the history of individuals, females apparently only lay about 40 eggs per week. it is however possible that further oocytes are developed from the germ- arium, or which if already present are beyond the resolution of the dissecting microscope. If females caught in pea crops towards the end of the season are representative of older, spent individuals (and not naturally less fecund moths), the number of eggs remaining (80 - 120) suggests that the realised fecundity in the field was about 150 eggs per female. The average fecundity of 21 field caged female C .nigricana was 91 - 57 (Lewis & Sturgeon, 1978). Reabsorption of oocytes in C.nigricana cannot be ruled out, and was also suggested to be a possibility in C.pomonella (Hamstead Sc Gould, 1950). The realised fecundity of female C.nigricana in laboratory experiments was highly variable, a feature also shown by C.pomonella in experimental treatments (Howell, 1981). This probably results from several uncontrolled factors, 297 such as sex ratio, adult density, quality and quantity of larval diet, disturbance etc. The maximum of about 200 eggs per female must approach the maximum for the species under optimal conditions, and exceeds the figure suggested above for realised fecundity in the field. It should be noted that the assumption that the number of eggs laid in the field is the same as the number laid in the laboratory has been shown to be false for C.fumiferana (Thomas, Borland S c Greenbank, 1980); only 70 to 86% of the laboratory potential was realised in the field. The fecundities recorded by Lewis and Sturgeon(1978) for female C.niqricana, of 70 - 41 in the laboratory (92 females)and 91 - 57 in the field (25 females), do not conform to this relationship. These fecundities are similar to treatment means in the middle of the range recorded in this study. The mean longevity of C.niqricana at 23 "C recorded by Lewis and Sturgeon(1978) was 16.5 - 1 (S.E.) for females and 17.4 - 1.2 for miles (ca. 500 moths), and is also similar to mean longevities recorded here. Both fecundity and/or longevity appear to exceed that for other species in the same genus e.g. C.molesta (Swingle, 1928), C.pomonella (Allman, 1930; Hamstead S c Gould, 195 0; Gehring S c Madsen, 1963; although not Howell, 1981), C.ptychora (Taylor, 1965; Akingbohungbe, Agbede Sc Olaifa, 1980). In this study there was no apparent difference in longevity or potential fecundity between diets of water, 10% sucrose solution and 10% honey solution; there was no treatment with starved moths. In C.pomonella the average longevity of moths in one experiment without and with water or with 5% sucrose were 4.7, 12.9 and 17.1 days respectively (26.7*C, 70% R.H., 16.5hr photophase) and significantly different (Howell, 1981). There were however no significant differences in fecundity (117, 130 and 139 eggs/female respectively) or fertility (71,70 and 75% respectively), since in this species oviposition is heaviest on the second or third day, and 90% complete on the fifth day, compared to 90% oviposition by female C.niqricana taking 15 days (pooled oviposition of 21 females) (Lewis S c Sturgeon, 1978). Isley(1938) and Gehring and Madsen (1963) also noted this short oviposition period in C.pomonella, the latter authors 298 describing females as reproductively old on day 6. In a further complex series of treatments to investigate the effect of different diets, Howell(1981) found considerable variation in longevity, fecundity and fertility within and between treatments. Starved moths and those with honey showed consistently reduced longevity. Howell does not state if the honey diet was changed after the replicate commenced, giving the impression that it was not. In this study, honey solutions were found to be fermenting after only a few days, and David and Gardiner (1961) found that the freshness of honey solutions influenced the feeding of P.brassicae; old stale honey solution was quite unsuitable. In conclusion Howell found only minor differences in C.pomonella fecundity due to diet, moths with water only were as fecund as those with other diets, and even s-carved moths were statistically equally fecund as mothsron other diets. All moths were fully fecund on the basis -of Hamstead S c Gould *s (1950) oocyte counts. In Cnephasia stephensiana(Doubleday) females supplied with 'btrong cane sugar solution" fed freely, suggesting that proboscis extrusion was a reflex action to sugars (Reid, 1941). compared to starved moths, the mean longevity of fed females was three times as great, with fecundity just under twice as great. In adult C.molesta, only one digestive enzyme, invertase, could be found in the gut (Swingle, 1928); eight other common enzymes -could not be detected. The presence of invertase, which hydrolyses sucrose to fructose and glucose, indicated that moths could be fed sucrose solutions. However the fecundity (69 eggs/ female) and longevity (9.8 days) of moths provided with 10% sucrose solution was no better than those provided with water only (65 eggs, 10.2 days), although both were better than starved moths (2.6 eggs, 7.5 days) (Swingle, 1928). In P.operculella, starved moths laid only slightly more eggs than the complement of mature eggs at emergence, availability of water doubled this, but 5% sucrose did not further increase fecundity. The longevity was increased with water, and further increased with sucrose (Fenemore, 1979) . It therefore appears that in these Miicrolepidoptera only free water is an essential adult requirement; this has 299 also been noted in 0.nubilalis (Kira, Guthrie Sc Huggans, 1969; DeRozari et al, 1977). Carbohydrate intake does not benefit longevity or fecundity, and Cydia spp. are probably unable to assimilate the protein available from honey sol ution. The only observed feeding by C.fumiferana was the occasional uptake of moisture; there was no strong tarsal response to sugar (Mitchell & Seabrook, 1974) found in more actively feeding Lepidoptera. Macrolepidoptera do benefit from carbohydrate uptake by the adults e.g. P.brassicae (David 6c Gardiner, 1961), Chorizagrotis auxiliaris (Grote) (Pruess, 1963), T.ni (Shorey, 1963), H.zea, H.virescens and A. arqillacea (Lukefahr S c Martin, 1964) and A. orthoqonia (Jacobson, 1965). Fecundity is also influenced by other factors during adult life. Oviposition rate increases with increasing temperature in C . pomone 11 a (Isley, 1938; Hamstead S c Gould, 1950; Howell, 1981). However Diaphania nitidalis(Stoll. ) had a fecundity of 300 - 400 at 21.1'C and 26.7*C, but only 83 at 32.2*C (Elsey, 1980) and more eggs were laid by H.virescens at 20 *C than at 25* or 30*C (Nadgauda S c Pitre, 1983); this is probably as a result of reduced longevity at higher temperatures. In diurnal species, light intensity during the activity or oviposition period can influence oviposition patterns. In Pieris rapae (l . ), solar radiation had both immediate and delayed effects, since few eggs were laid on overcast days, but more eggs than expected were laid on sunny days that followed overcast days (Gossard S c Jones, 1977). Mating and male presence are often a requirement for oviposition or egg maturation e.g. D.saccharalis (Miskimen, 1966) , P.xylostella (Hillyer S c Thorsteinson, 1971) and A.assectella (Thibout, 1974) although not in P .inter- punctella (Lum Sc Flaherty, 1970). Male presence is unlikely to be a requirement for oviposition by female C.nigricana in the field, since males do not move into pea crops in such large numbers as females (Chapter 3). In laboratory experiments C.nigricana demonstrated increased fecundity in some replicates with younger pea plant material, although performance of females in other replicates within the same treatment was poor and variable. Plant presence has been shown to stimulate oogenesis and 300 oviposition in other spercies e.g. P.xylostella (Gupta & Thorsteinson, 1960; Hillyer Sc Thorsteinson, 1971) , S .ocellatella (Robert, 1971), C.pomonella (Wearing, Connor S c Anbler, 1973; Wearing S c Hutchins, 1973), A. assectella (Thibout, 1974) and P.operculella (Fenemore, 1979). Plant presence is clearly not a prerequisite for the stimulation of oogenesis in C.nigricana because females are carrying mature eggs when they arrive at pea crops, and therefore, dis-counting long range air-borne stimuli, before they experience host plant effects. Preferred phenological stages or sites within plants have been shown for several species. a .gemmatalis showed reduced oviposition as host plants aged (Moscardi et al, 1981), T .ni laid eggs higher up cotton plants as plants aged (Wilson, Gutierrez S c Hogg, 1982), P. gossypiella laid more of their eggs on cotton bolls in preferance to veget ative parts, once the bolls became available (Brazzel S c Martin, 1957), and H.zea showed a preferance for peripheral shoots on peanut (Pencoe S c Lynch, 1982). In C.nigricana various authors have reported different preferred ovipos ition sites on peas. Brittain (1921), Baker (1937) and Cameron(1938) all state that sepals are the preferred oviposition site, while the more recent papers report that eggs are found on many parts of the plant with no special preference for flowers or pods (Wright S c Geering, 194 8; Gould S c Legowski, 1964). The preference for- stipules shown by ovipositing C.nigricana in the laboratory in this study is in partial agreement with Wright and Geering(1948) and Gould and Legowski (1964). Wright and Geering found 19.7% on stipules (with 15.2% on lower and 4.5% on upper surfaces) and 65.1% on leaflets (with 51.5% on the lower and 13.6% on upper surfaces). Gould and Legowski found 20.3% on the lower stipule, 29.0% on upper stipule, 24.5% on lower leaflet and 22.2% on upper leaflet surfaces. Wright and Geering also note that in the field, eggs were only found on pea plants and not found in fields before flowering, although eggs were found on non-flowering plants amidst crops that were in flower. Fluke(1920a) reported finding eggs on the stems and leaves of grasses and weeds growing in pea fields. The lower proportion of eggs found 301 on the lower surfaces of leaves and stipules in this study was probably due to the confinement within the experimental chambers, since the lower surfaces were often pressed against the chamber wall. Wright and Geering 1 s (1948) findings in the field with greater percentages on lower surfaces are in agreement with those in other species e.g. E.subsignarius (Drooz S c Solomon, 1964) and H.zea (Pencoe & Lynch, 1982) . Most diurnal insects prefer to lay in shade or only moderate light intensity (Hinton, 1981). C.nigricana differs from C .ptychora where the preferred oviposition site is the sepals or sepal remains on the pods (Olaifa S c Akingbohungbe, 1981) although this is also affected by mode of pod carriage; on erect pods, eggs were laid at the pod tip (Perrin, 1977). Surface texture can also determine oviposition micro sites; female C.pomonella did not oviposit near the leaf midvain where pubescence was heavy, and wax scales on the fruit surface also influenced the number of eggs laid (Hagley, Bronskill S c Ford, 1980) . Surface texture effects have also been noted in P.xylostella (Gupta S c Thorsteinson, I960), T.ni (Shorey, 1964a) and P. operculella (Traynier, 1975). The preferred oviposition site may only be available for a limited period; females ovipositing before or after this period may lay on other plant structures. Cydia prunifoliae Kozh lays singly on the lower surfaces of apple leaves at the end of June, and on the fruit early in July (Kolmakova, 1958). Towards the end of the season, after an unfavourable period, or as they get older, females may become less particular where they oviposit (Hinton, 1981). 302 6 . DISCUSSION As a result of the intensive sampling programme employed in this study, a large number of moths were collected and much more is now known about comparatively basic aspects of the biology and ecology of C.niqricana. Adults of C.niqricana emerge in late spring and summer after a protracted diapause as 5 ^ instar larvae. Emergence of both sexes showed a very marked peak in the middle of the pest's flight season, with the number of individuals emerging before and after, tailing off rapidly. Peak emergence in populations studied here was five to six weeks after first emergence, and compares favourably with Wright and Geering's (1948) estimate of four to five weeks. The shorter periods of two or three weeks, suggested by earlier workers (Fluke, 1920b; Baker & Perron, 1944) are probably inaccurate, although these workers were reporting the situation in the U.S.A. and Canada, where the period may be shorter. These shorter periods are more typical of multivoltine species such as C.molesta (Baker et. al, 1980) , C.pomonella (Glen S c Brain, 1982) and P.xylostella (Baker et al, 1982). Emergence of C.niqricana was undoubtedly protandrous, although the peaks of male and female emergence may have been separated by a few days only, and this could not be shown with weekly samples. Protandry has not been demonst rated or suggested before for this species, and is normally associated with Macrolepidoptera (Ford, 1972; Wiklund Sc Solbreck, 1982) and rarely mentioned in studies on Micro- lepidoptera, although Baker et al (1980) report no protandry in C.molesta. Protandry in C.niqricana may not be a result of selection but rather of the incidental form (Wiklund Sc Solbreck, 1982), being due to the shorter developmental time of the smaller male pupae. Nevertheless, protandry is the optimal reproductive strategy for both males and females (Wiklund Sc Fagerstrom, 1977; Fagerstrom S c Wiklund, 1982) when female monogamy is the normal situation, as has now been shown conclusively for C.niqricana for the first time. It seems reasonable to suggest that protandry will also be found in many other species where female monogamy is the 303 norm, if emergence is examined carefully. However, even when females mate successfully more than once, males that mate with virgin females are favoured, because females often lay a substantial proportion of their eggs in the first few days after fertilisation e.g. C.pomonella (Howell, 1981). This holds despite the fact that males mating with non-virgins generally gain sperm precedence and fertilise the remaining eggs (lLabine, 1966; Taylor, 1967; Flint S c Kressin, 1968; Snow et al, 1970; Brower, 1975). If egg production is high, a female is less likely to cease oviposition in favour of further mating (Marshall, 1982). In emergence sites following high infestation levels in peas, the spatial pattern of emergence was random. This reflected the uniform distribution of larval damage across the pea crop the previous season. At these densities, there was no suggestion of a 'headland effect' in the fi>al damage distribution, although this does not preclude the ^ossibility that infestations are initiated along headlands (Fi-nssen, 1954; Gould Sc Legowski, 1964) . It should be noted that infestation levels and therefore resultant moth densities were much higher than those expected under normal conditions of good husbandry. The uniformity of larval spatial distribution did not reflect the aggregated distributions of resting female C.nigricana in and around pea crops. Aerial populations of females were more uniform across the field however, and oviposition by these individuals would result in the larval distributions indicated. The aggregated distributions of resting females were not consistent between pea fields, between years or within years; they could be explained however in terms of the quality of resting sites offered. Support for this comes from Wright and Geering (1948) who found greater infestations when peas were mixed planted with oats and Wright et al (1951) who found that the greatest numbers of moths occurred where the crop was most dense. Hedgerow removal may therefore serve to drive moth populations into pea crops, while very weedy crops would be expected to harbour greater populations. Curiously, Nolte(1959) advocated mixed cropping of peas with oats or mustard as a prophylactic measure against attack by C.nigricana. It is not known, however, how these conditions of hedge removal and weedy crops affect the level or distribution of attack. In emergence sites both sexes became aggregated at high density and within a very short time after emergence, indicating moths were very active in and around the emergence site (again, note that such high densities are probably not achieved commonly, aggregation may therefore not be the norm). Aggregations of females within the emergence site were associated with the direction of the nearest pea fields, although this probably occurs only when pea fields are in close proximity to emergence sites, Ekholm (1963) suggested that C.nigricana fly around in different directions and reach pea fields by chance, when olfactory cues are absent. Aggregations of male C.nigricana were not associated with the proximity or the direction of pea crops in any w ay. Dispersal from in and around emergence sites to native vegetation and thence to pea fields, was very rapid, so that peak density in pea fields was at most one week later than peak density in emergence sites. The pea fields and emergence sites were atypically and ill-advisedly close together, although this did give some confidence about the origins of populations recorded in pea crops. However, this dispersal could still be very rapid when fields were more distantly spaced, since this distance is unlikely to be more than a few km., a distance that C.nigricana can readily fly on a flight mill (Lewis et al, 1975) . Thus migration from emergence sites to pea fields is too rapid to gain any in sight into potential pea field population density from a study of populations in emergence sites, a conclusion also reached by Macaulay(1977). There is a marked differential dispersal by the two sexes. The physiological aging technique showed clearly that females left the emergence site crop when stil physiol ogically young, i.e. soon after emergence. The sex ratio in emergence sites was male biased, while in pea fields the reverse was true. The overall sex ratio was 1:1, therefore many more females than males migrated to pea fields, while males remained behind in the emergence site crop, becoming old both physiologically and in real age, and many undoubtedly 305 died there. This rapid dispersal by females is expected because, although flight by newly emerged winged adult insects is not necessarily adaptive (Kennedy, 1961), migratory flight does not usually happen after insects have already spent part of their lives flying around in the emergence site (Johnson, 1960). Significant dispersal, when it starts, is usually an early, even the first main act (Johnson, 1966). Male C.nigricana do not show this rapid dispersal away from the emergence site however. This is because their main function is to fertilise females; if this is achieved in the emergence site, there is no reason for males to migrate. This study has shown that, although mated females had been found in emergence sites and pea crops (Wall, pers. comm.), mating generally occurs in or around the emergence site, and Lewis and Sturgeon(1978) found that females could mate within a day of emergence. Dispersal is therefore not the first main act of female C.nigricana, but the second. Some males do migrate however, and Macaulay (1977) stated that male C.niqricana moved into pea fields soon after emergence (although this was inferred from sex-attractant trap catch which may not be a valid way of showing this). Most females mate only the once, therefore most males probably mate only once (assuming that there are not large numbers of males dying as virgins), supernummerary matings probably occur to rectify infertile first matings. It is possible to speculate whether the males that do disperse to pea fields are virgins seeking mates. Males that have mated and transferred a large spermatophore probably have reduced survival potential (Shapiro, 1982) or reduced potency (Rutowski, 1979), and may no longer be capable of dispersing and then mating. These dispersing males may get the opportunity to mate with females that mated unsuccessfully (i.e. are infertile), since because the females leave the emergence site so rapidly, they may not become receptive again until well away from the emergence site. Males may therefore be distributed in an 'ideal free distribution' (Fretwell, 1972; Parker, 1970; 1974)with receptive females as the limiting resource. Steiner (1940) may have been reporting a similar occurrence in C.pomonella, when referring to a levelling off of the population between areas of heavy and light density, although both sexes were involved and the population was 306 probably resident. The potential fecundity of C. niqricana was 25 0 to 300 eggs per female and realised fecundity may have been 150 to 200 eggs. Females did not have a full compliment of eggs on emergence, but they were fully gravid when they reached the pea crops. Johnson (1966) states that insects of several different orders make the most lengthy and un distracted flights when females are sexually immature; after the ovaries are mature, flights are shorter and more local. The presence of a large egg load soon after emergence would probably preclude much pre-oviposition dispersal by females (Chew & Robbins, 1984). However, female C.niqricana normally migrate carrying the weight of a spermatophore; presumable the benefit in the form of nutrients offsets the disadvantages of increased wing loading. Immigration into pea crops is not determined by any growth stage, rather it probably occurs at flowering or anytime thereafter. Pods of a wide variety of age were susceptible to attack. Stamp (1980) details the advantages of laying eggs in clusters or singly. In C.nigricana the advantage of dispersed eggs, and therefore ensuing larvae, may serve to reduce the risk of sibling cannibalism, and single larvae are less likely to exhaust their food supply. Laying single eggs means that a female spends less time in one place, but may be conspicuous when moving about. Although not demonstrated, olfaction probably plays the major role in host plant location or at least the location of areas of host plants ( cf. individual plants) (Douwes, 1968) as in other Lepidoptera (Gara, Allan, Wilkins & Whitmore, 1973; Pliske, 1975) and other orders (Hans & Thorsteinson, 1961; Finch, 1978). It is likely that adult feeding, apart from a supply of free water, does not influence either fecundity or longevity in C.nigricana, and that adult moths do not need to feed on aphid honeydew or plant exudates. For males, their main function is to fertilise females; since this is achieved in or around the emergence site, there is no advantage in prolonging life. For males, mating may not be the first main act, since protandry means they may have been actively searching for receptive females throughout several activity periods. For females, prolonging adult 307 life could increase realised fecundity; since this is also a benefit to the paternal male, a nutrient contribution from the male to the female at mating is in the interest of both sexes. Marshall (1982) reviews the subject of male nutrient investment thoroughly, and states that the degree of investment should be determined by 1) degree of paternal certainty 2) the probability of obtaining future mates and 3) the effects of investment on reproductive gain as the result of that investment. In C.nigricans the degree of paternal certainty was about 0.7, since 70% of females only mated once, conversely since this probably means 70% of males only mated once, the probability of finding another receptive female was about 0.3; the third determinate is more difficult to ascertain. Males would be expected to invest in materials that limit the number of eggs a female can produce in a unit of time, since as a resource becomes more and more abundant, its effect on reproduction will become less and less (Marshall, 1982). Protein is the most obvious limiting material for egg production. After emergence protein is only available to adults in the form of amino acids in some nectars, and acquisition from this source is time consuming. For larvae, protein is accessible through eating plant material, and most protein for egg production is sequestered during larval feeding, especially for C.nigricana where the larval diet is seeds. Since larvae of both sexes accumulate protein, males can contribute a resource that is readily acceptable and can potentially increase egg production. Spermatophores are not solely proteinaceous, they also contain water and other things available to larvae, but not adults, such as hydrocarbons, lipids and cholesterol (Marshall, 1982). Eggs contain large quantities of water, but acquisition, like nectar feeding, is time consuming. Females would not be expected to indulge in feeding or drinking, if an alternative source of nutrient and water is available from males, the time saved would be better spent dispersing or possibly on oviposition. After emergence, adults have low levels of the hormone ecdysone, but this is required for hydrocarbon synthesis (Arnold & Regnier, 1975). By transferring ecdysone and hydrocarbons with the spermatophore, the male could decrease the pre-oviposition 308 period of the female. This benefit would be particularly available to protandrous species, since the male could synthesize ecdysone for a few days after emergence and transfer it to females, when females mate soon after emerg ence. Sufficient information now exists about the biology of C.nigricana to explain how and why the sex-attractant trap monitoring system has been successful in general. That it has been a successful improvement over the previous egg- count system is shown by the readiness with which it has been adopted by both the advisory services and growers alike. The findings reported here on the biology of the pest which are relevant to the monitoring system, are concerned primarily with the relationship between trap catch and density of both male and female moth populations, and also the reproductive state of those females. Sex-attracLant trap catch in pea crops was not quantitatively reTrted to density of males or females over the first part of the season up to and including the period of sudden immigration into the pea crop. The definition of this relationship is a pre-requisite if a system is to evolve from one of detect ion to one of monitoring sensu stricto, which demands that trap catch can be quantitatively related to a range of pest densities. Notwithstanding this failing, sex-attractant traps do catch male moths before the main immigration of females occurs. Indeed Macaulay's(1977) 10-moth threshold occurred 12 days before eggs could be detected in the crop. Further more eggs were sometimes found in the crop before adult moths were observed in sweep net catches (Gould & Legowski 1962). Threshold catches were attained one to five weeks before the main immigration of females occurred, when moth populations in the crop were at very low density, a feature implied by Gould and Legowski's (1962) findings and Macaulay's (1977) threshold. Gould and Legowski (1964) found that peak egg laying occurred three weeks after the first eggs were found, so since the contribution to final damage levels by the ensuing larvae from these first eggs is probably small, the threshold does give good advanced warning of 309 moth attack (main ovposition). Indeed calculation of spray dates based on threshold dates are likely to be well premature of egg hatch (Macaulay, Etheridge, Garthwaite, Greenway, Wall & Goodchild, 1985), although premature spraying is preferable to late applications. Since mating occurs before females enter the pea crop, very small numbers of males would be expected in the pea crop itself; this was verified by the D-Vac. catches. However, considerable numbers of males were caught in sex- attractant traps, which in itself shows how effective is the attractant. Because males were at low density within the pea crop, it is possible that traps attracted males from surrounding vegetation, since the traps were only about 25m. from the edge of the field, and can attract moths from over 50m. (Wall Sc Perry, 1981) . In this respect, all the traps erected in pea crops in 1981 and 1982 were within 100m. of emergence sites, thus males could even have been attracted from this source. It should be noted that traps were erected in positions where the grower was likely to have placed his commercial traps, i.e. for convenience of inspection or easiest access, either near farm tracks or gates into the field. This was borne out by this grower's own commercial traps positioned in other pea crops on the estate (however this grower did not use traps as instructed, often using only one trap in a field and even using attract ant lures purchased and retained from the previous season). On better managed estates sex-attractant traps in pea fields are unlikely to be attracting males from emergence sites, although they are likely to be attracting males from vegetation around the fields. It is perhaps relevant at this juncture to note that males caught in or around pea fields were not typical of the male population. Most males remained in the emergence sites, and those at pea fields may have been virgins and were also likely to have been physiologically old, as a result of active dispersal and mate searching. Older C.fumiferana and Halisodota argentata (Pack) showed changing activity patterns as they aged (Edwards, 1962). This response and the possibility that trap catch of males was influenced by the phenological stage of the crop surrounding the traps are factors which may lead to the poor quantitative relationship between trap 310 catch and male density. One of the most important findings is that females entering pea crops were mated and fully gravid and therefore ready to lay eggs, which was a fundamental assumption of the existing monitoring system. Thus the peak egg laying of Gould and Legowski (1964) probably corresponds to the main immigration of females, eggs found prior to this may have been laid by females making oviposition sorties into the crop (which might also explain why eggs could sometimes be found before moths). One reservation about Gould and Legowski's egg records is that all samples were taken from headlands; there is now no justification in assuming a headland effect (at the densities reported here). The build up of eggs should more properly be ascertained from samples drawn at random from the field. Although the main immigration of female C.nigricana into a pea crop was reflected by an increase in sex-attract ant trap catch of males, the timing is not predictable*, Threshold catches can be attained a considerable time before immigration, although in these instances delayed immigration is likely to be due to poor weather. Low temperatures will also prolong the incubation period of any eggs laid, and females that entered the crop at the time of threshold may well be dead. One of the weaknesses of the monitoring system highlighted, is the possibility of two alternative threshold dates in the same traps, often separated by several days or even weeks, as a result of inspection on odd or even days. It is unlikely that this weakness can be easily overcome, since the most obvious solution would be daily inspection of the traps, which necessitates a doubling of the grower's commitment. It might be possible to standardize the two-day inspection to either odd or even calendar dates, but it would perhaps not be surprising to find that traps are inspected on Mondays, Wednesdays and Fridays, and not strictly every two days. In order to guard against damage to crops of growers who achieve a threshold catch on the later alternative, a system with two day inspection periods will inevitably give premature spray warnings to growers who attain a threshold on the first possible date. 311 However, even the later alternative threshold can give premature warnings. This is not surprising since Macaulay1 s (1977) thresholds were attained 12 days (range 4 to 26 days) before the first eggs were found, not when they hatched, which on average would have occurred about 10 to 14 days later (although this assumes that eggs are found soon after being laid, this may not be justified as eggs may become more conspicuous as they develop) . Further more peak egg laying may occur three weeks after the first eggs were found; hatching of these would occur later still. It is therefore possible that a grower could follow the monitoring instructions to the letter, making his first insecticide application when 100% egg development after threshold was attained, and then a second application 14 days later, and achieve all this before main moth immigra tion has occurred. Clearly this is an extreme, the other extreme being when insecticide applications control the maximum number of newly hatched larvae (assuming threshold always precedes female immigration). In practice the situation in most fields probably falls somewhere along the continuum between the extremes, with growers achieving adequate but not optimum control; this is shown to a certain extent by the fact that damaged crops still occur. Indeed growers who operate the system correctly with two sprays do get good control (Wall, pers. comm.). Between 1979 and 1984, in 59 sites where spraying was done correctly (i.e. within -4 to +2 days of the predicted date from threshold), and at which damage in unsprayed plots exceeded 5% seed damage, 5 8 of the sites had less than 5% damage in the sprayed areas (Wall pers. comm, unpublished data). Nevertheless 5% damage may not be acceptable, since in years of plentiful supply crops sustaining 2-3% damage have been rejected for human consumption,and even better control (less than 1% damage) should be attainable Macaulay et al, 1985). Some improvement might perhaps occur, if the first spray was applied later after threshold than calculations suggested. Thus the introduction of an arbitrary period could be made, before percentage egg development increments were recorded. The period could possibly be fixed and not dependent on any climatic conditions or feature of moth biology. Such an approach would be 312 easier to introduce than, for example, changing the level of threshold, which is now familiar to trap users, even though ultimately it is trap catches that can be used to "fine-tune" the spray warning system. Perhaps the most likely type of improvement to the monitoring system that can be envisaged over the next few years is in trap positioning and spacing (density). Sex- attractant trap density is one factor which influences the magnitude of catch and, therefore, should be standardised in a monitoring programme (Riedl, 1980). The magnitude of trap catch is influenced because of trap interactions (Wall & Perry, 1978; 1980; 1981; Perry et al, 1980). This standardisation may be difficult to attain. With C.pomonella Charmillot (1979) found that a single trap was able to sample orchards up to lOha., while Riedl(1980) found that catch increased with area, but attained a plateau at densities of less than one per 7ha. These results are probably attributable to variability in the responding populations, with C.niqricana Macaulay(1977) found that some patterns of trap catch at sites about 1km. apart were similar, but Perry et al(1981) showed that reliable regional forecasts could not be provided using traps, because of the variability in populations. Perry and Wall (1984) have since shown that there can be a significant difference in populations at trapping stations less than 500m. apart in the same field (using natural pheromone attractant lures). Although they were unable to determine the optimum density for monitoring traps, Perry and Wall (1984) do suggest that in pea fields of greater than 50ha. , two pairs of traps should be erected in diagonally opposite corners, and the entire crop sprayed if either pair indicates a threshold catch. With the C.niqricana monitoring system, pairs of traps arranged at right angles were originally advocated to allow for changes in wind direction; these traps were suggested to be about 75m. apart (Macaulay, 1977)(latest instructions with the system advise 100m. apart). Experience shows that catches in these pairs of traps are frequently very similar, suggesting wind direction is not an important factor. Since these traps are interacting, 313 the continued use of paired traps is something of a paradox. Halving the number of traps to be inspected would undoubtedly be welcomed by growers, and could even be used as compensation or bargaining power, should daily trap inspection ever become a recommendation. Perry and Wall (1984) also recommend that specialist interpretation of data by A.D.A.S. should continue, to promote confidence in the system by growers. It is apparent that growers could help the system, by giving more thought to where they site their commercial traps. Instead of erecting traps close to farm tracks for convenience, they should site traps where, for instance, they were less likely to attract male moths from emergence sites. Although this might mean more time allocated to trap inspection, it should reduce the incidence of premature and "thus wasted insecticide application. m alternative to the introduction of an arbitrary delay period proposed above, might be the use of only one trap, and that trap sited in the centre of the field; this should delay threshold catch. Threshold catches are currently attained when moth populations are still at low density. The natural pheromone is a better close range attractant than the synthetic analogue currently supplied with the system (Wall & Perry, 1981) . There may therefore be some benefit in using stabilised natural pheromone in the commercial monitoring system, which would give much higher trap catches during the period when the threshold is currently reached. Trap saturation would occur later in the season, and even very soon after threshold was attained. Although trap satur ation of traps with natural pheromone lures can occur at low population densities, with regular two day inspections it should not be a problem during the period when threshold catches are currently attained. Clearly, this would need complete re-evaluation of the threshold catch, as would any change in the spacing of traps. Any improvements considered must not only be possible in theory, but also in practice, i.e improvements that growers might reasonably be expected to adopt. Growers should be kept informed about major developments and possibly involved in large scale field trials. 314 In many ways, the success of the sex-attractant monitoring system for C.niqricana, has been fortuitous, and certain assumptions about the condition of females have now been validated, retrospectively. Nevertheless, the system remains one of the most sophisticated, yet simple to operate, systems available, drawing as it does on information concerning pest biology, weather conditions, and using a computer model to make predictions. During this study two techniques have been developed or improved, namely a sampling technique for low density insect populations in large areas of crops with tramlines and one for the aging of adults of C.niqricana physiolog ically. In order to examine population build up and decline, it is essential to sample quantitatively with a view-to determining absolute density estimates (Southwood, 1970). This may or may not then be compared with other biased or untested methods, of assessing insect numbers (e.g. sex- attractant traps). Suction apparatus, of which the D-Vac. is one form, are an efficient means of extracting insects from vegetation Equipment with a narrow suction hose and sampling head (ca. 5 to 15cm.) has been shown to be very efficient, with extraction rates of 70 to 100% for different taxa in short grassland (Johnson, Southwood & Entwistle, 1957; Whittaker, 1965; Henderson Sc Whitaker, 1976). The efficiency of the D-Vac. type of sampler is affected by the mode of operation. The equipment was designed to sample an area of one square foot (Dietrick, 1961) by moving the nozzle vertically into the foliage and down to the ground surface. When used in this manner it has been shown to be 50 to 70% efficient (Turnbull & Nicholls, 1966; Shepard, Sterling S c Walker, 1972 Smith, Stadelbacher Sc Gantt, 1976) . However, removing the sample from the collection bag , and refitting the collec tion bag ready for the next sample, means the technique is time consuming. When a large area is to be sampled, as in this study, this technique is only suitable when the insect being sought is sufficiently abundant, otherwise too much time will be spent recording 'zeros'. When insects are evidently at low density as with C. niqricana (even 315 though populations encountered, in fields in this study were at atypically high densities for this pest), it is not cost effective in either time or effort to use this approach. If the nozzle is used horizontally in a sweeping mode, efficiency is greatly reduced (Richmond & Graham, 1969) even though a much greater area can be sampled in the same unit time. Sweeping with the D-Vac. was unsatisfactory because of the difficulty of reaching into cereal crops up to lm. in height,which was awkward even in the tramlines; furthermore the damage caused to pea crops by repeated use of this technique was unacceptable. The design and construction of the attachment specifically for use in crops with tramlines was therefore an essential component in the quantitative study of C.nigricana populations. Although the attachment apparently performed satisfactorily and its robust construction stood up to two seasons of intensive use, it is in many ways still a prototype. If adopted for sampling other insects improvements can be envisaged. For example, the interior of the front box section, may cause turbulance which deposits some of the catch in the corners, thus some form of stream lining to guide the catch up into the collection bag could be incorporated. An alternative would be to move the collection bag from its position within the D-Vac. head, and relocate it in the front box section of the tramline attachment. This could be readily achieved by attaching the bag with 'velcro' strips to a flange inside the box inlet opening. Preliminary sampling programmes for this study included emergence cages and ideas for enclosing wheat or pea plants in a sampler akin to a 'Dempster box' (Dempster, 1961) or the clam-shell trap of Leigh, Gonzalez and Van den Bosch (1970), and removing insects by anaesthetising or suction. Given the low densities of C.nigricana however, these techniques would not have proved practical for exten sive sampling. The aerial populations of C.nigricana were sampled by kite netting after considering suction traps (Johnson, 1950; Taylor, 1955) and rotary net trap designs (Prescott & Newton, 1963) . Suction traps were successfully used by Lewis et al(1975) to study C.nigricana and catches used 316 to determine the diel flight periodicity curve, and the temperature threshold for flight. These authors suggested that disturbing eddies at the edge of the crop may have led to reduced catches. The suction traps used were of the exposed cone type (Taylor, 1951) and so the enclosed cone type (Johnson & Taylor, 1955), protected from cross- winds, would seem to have been a better choice. Given the areas involved in this study however, which would have necessitated using a lot of suction traps, and other considerations, such as interference from people, kite netting was the best alternative to study aerial populations, given that Lewis et al(1975) had already determined daily flight curves etc. Nevertheless conversions of suction trap catch to aerial density and then to absolute aerial population are possible (Southwood, 1978), which is not the case with netting. Southwood (1978) outlines several techniques for aging adult insects, viz. daily growth layers in the cuticle, sclerotisation and colour change in the cuticle and wings, changes in male genitalia, and changes in internal organs, both reproductive and non-reproductive. 'Wear and tear' has also been suggested and is admirably suited to Lepidoptera, but was clearly unsuitable for this study, since captured moths had been subjected to considerable physical abrasions with both kite net or D-Vac. collecting techniques. Recording the weight of adult insects that feed little or not at all as adults is also suggested, but again was impractical for this study, since insects must be weighed immediately on death, and this was not possible as the large number of samples collected necessitated freezing then thawing before sorting. Initially female C.nigricana were dissected to assess fecundity, but it became apparent that the appearance of the fat bodies was different in what were obviously newly emerged, and old, spent individuals. This led to the development of an ordinal physiological age scale, which furthermore was also applicable to male C.njqricana. Apart from providing interesting results in its own right the physiological age scale also provided good corroborative evidence for aspects of ecology suggested by other methods. 317 This study has improved techniques for sampling low density insects in crops with tramlines, and for physiological aging of Microlelidoptera using fat body scores. Much more is now known about the biology and ecology of C,nigricana as a result of intensive sampling of populations throughout the season. The use of independ ent sampling techniques to record adult insect density concurrent with sex-attractant traps ( cf . delayed indices e.g. damage or overwintering populations) is an important advancement for the use of monitoring traps. Although the relationship between trap catch and adult moth density is a prerequisite for monitoring (sensu stricto, cf. detection) and remains unidentified for C.niqricana, this is one of the first attempts to do this, and may be unique to date. The major shortcoming of this work is that only one farm, with two or three fields per year, was studied. This was enforced by the labour intensive sampling programme, and while more fields could have perhaps been studied with continual good weather, in practice this would have probably resulted in more poor coverage of all fields studied. As it was some fields in some weeks were regrettably sampled incompletely, which necessitated the calculation of inter polated catches to estimate totals. The study fields were atypically close together, but this did mean that populations in pea fields were, at least for the greater part, from the emergence site studied. Moth densities were certainly uncommonly high (although still low when compared with both other insecti pests, and populations of C.niqricana in other countries). Behaviour and ecology may be different at lower densities, although the densities recorded cannot be described as crowded. The weakest side of the work reported here is that done in the laboratory, due to the difficulty of producing sufficient numbers of adult moths over and above that required for maintaining a culture. This was largely due to synchronising pea pod production with egg hatch, time consuming culture techniques and the failure of controlled environment rooms. The effect of diet on moth fecundity and longevity is probably not worth pursuing, but the effect of host plant phenology remains undetermined even though in the long run it may not greatly alter the use of the monitoring system. 318 Future work should still strive to relate sex- attractant trap catch of males to density of at least males and preferably females. The possibility of using natural pheromone in the traps should be considered. Trap density remains to be optimised and trap positioning can be refined, to minimise the error associated with thresholds. However only those improvements that will be acceptable to trap users should be considered. There is a case for further similar studies (even though it is labour intensive) in commercial fields with more typical (lower) population densities of C.njgricana, and with more enlightened cultural practices (i.e. not with current year's pea crops sown adjacent to emergence sites following heavily damaged pea crops). Further work is required to identify ovipositional cues in the field; certain factors might then be minimised by plant breeding or cultural practices. More direct observation of female ovipositional behaviour, preferably in the field, would complement the above. 319 7. SUMMARY 1. The life cycle and stages of the pea moth, Cydia niqricana (F.), are described. Early methods of, and attempts at controlling the pest are reviewed, culminating in the egg-warning system operated by the agricultural advisory services in the 1960's and early 1970's. This is followed by the development of the sex-attractant monitoring system, and a description of the system as it is currently employed by growers. 2. Field site selection and the physical character of those sites is described. This is followed by a description of the techniques employed to sample active and inactive insect populations at emergence/over- wintering sites and at pea fields. Two techniques have been developed or improved, and these are described calibrated and evaluated with respect to existing techniques. These techniques are i) for sampling low density insect populations in large areas of crops with tramlines and ii) for the aging of adults of C.nigricana physiologically. 3. Emergence of adults of C.nigricana was protandrous; this may have been due to the smaller size of male pupae. Emergence of both sexes showed a very marked peak in the middle of the emergence period. 4. Moths became aggregated in emergence sites at the time of peak density, which coincided with the time of peak emergence. Females tended to be aggregated nearer to pea fields; male aggregation was not associated with the proximity of pea fields. The spatial pattern of emergence was random, but adults became aggregated very soon after emergence. 5. Dispersal from in or around emergence sites to native vegetation, and thence to pea fields, was very rapid so that peak density in pea fields was at most one week later than peak density in emergence sites. Dispersal was adversely affected by unfavourable weather conditions. 320 6. The sex ratio in emergence sites was male biased, while in pea fields it was female biased. The overall sex ratio was 1:1, therefore many more females than males migrated to pea fields. Females left the emergence site while still physiologically young, and no physiologically old females were found at emergence sites. Many male moths remained in the emergence site, boosting the numbers there, and becoming physiologically old. 7. Mating occurred first in or around the emergence site, and probably soon after female emergence; by the time females entered pea crops they were mated. Most females only mated once, supernummerary matings were probably to rectify infertile first matings. 8 Immigration into pea crops was not determined by crop growth stage, rather immigration occurred at flowering or anytime thereafter. Pods of a wide variety of age after pod inflation has occurred, were susceptible to attack. 9. The potential fecundity was 250-300 eggs, and the realised fecundity may have been 150-200. All females were fully gravid when they reached the pea crops, but females did not have a full complement of eggs on emergence. 10. Resting sites may have been very important; when hedge rows were present around pea fields, the highest densities of resting female moths were in the perimeter of the field. When hedgerows were absent and pea plants were sparse and small in the perimeter, the highest densities were in the centre of the field. 11. Larval density was uniform across pea fields, despite aggregated distributions of resting females. This may have been a reflection of uniform, random flight/ distributions of active ovipositing females above the pea crop. There was no suggestion of a "headland effect" in the final distribution of larval damage. 12. Immigration of moths into pea crops was reflected by an increase in sex-attractant trap catch, but trap 321 catch was not related to the density of males or females during the first part of the season, up to and including the time of main female immigration. Most males do not migrate to pea fields, and very few enter the pea crop, so sex-attractant traps may have been attracting males from outside the crop region, leading to premature thresholds. 13. The reasons for the success of the sex-attractant monitoring system are explained in terms of the new findings on the biology and ecology of C.nigricana. Possible improvements or refinements to the monitoring system are discussed. 322 ACKNOWLEDGEMENTS I would like to thank my supervisors, Dr. V. K. Brown at Silwood Park, and Dr. C. Wall at Rothamsted, for all their encouragement, patience and advice throughout this project. I am grateful to Professor M. J. Way, as Director of Silwood Park, for the facilities provided, and to Sir Leslie Fowden, as Director of Rothamsted Experimental Station, and Dr. T. Lewis, as Head of Entomology for facilities provided at Rothamsted. I would like to thank Dr. R. K. Scott, Head of Station,, and Dr. R. A. Dunning at Broom's Barn Experimental Station, for providing facilities, and allowing me to use the Station as my field base. I would like to thank all the farm owners and Estate Managers who allowed me access to their land, and I am particularly grateful to Sir John Richmond at Shimpling Park Farm, and Mr. R. Davey his foreman, for their interest and cooperation. Other people who have helped me, and to whom I extend my thanks are Dr. M. J. Crawley at Silwood Park and also Mr. J. N. Perry at Rothamsted, for statistical advice, and the technicians and glasshouse staff at Silwood Park and Rothamsted for equipment and materials. Finally, I would like to thank my parents for their unfailing support throughout my education, and especially during the last few years while I have been completing my thesis. 323 REFERENCES AD^MS, T.S. S c NELSON, D.R. (1969). Effect of corpus allatum and ovaries on amount of pupal and adult fat body in the housefly, Musca domestica. J. Insect Physiol. 15: 1729-1747. ADKEN, R. (1925). Dispersal of butterflies and other insects. Nature, Lond. 116: 467. ADKISSON, P.L., BULL, D.L. S c ALLISON, W.E. (i960). A compar ison of certain artificial diets for laboratory cultures of the pink bollworm. J. econ. Ent. 53: 791-793. AKINGBOHUNGBE, A.E., A3BEDE, T. S c OLAIFA, J. I. (1980). Oviposition preference by the black cowpea moth, Cydia ptychora (Meyrick) (Lepidoptera:Tortricidae) for different varieties of cowpea. Bull, ent. Res. 70; 439-443. - ALFORD, A.R. S c HAMMOND, A.M. jr. (1982). Plusiinae (Lepidoptera Noctuidae) populations in Louisiana soybean eco systems as determined with looplure-baited traps. J. econ. Ent. 75: 647-650. ALLMAN, S.L. (1930). Studies of the anatomy and histology of the reproductive system of the female codling moth, Carpocapsa pomonella (L.). Univ. Calif. Publ Ent. 5s: 135-164. ANDRE ADIS, T.G. Sc HALL, D.W. (1980). Relationship between physiological age and fecundity in Culex salinarius (Diptera:Culicidae). J. med. Entomol. 17: 485-486. ANDREWS, K.L., BARNES, M.M. S c JOSSERAND, S . A. (1980). Dispersal and oviposition by navel orangeworm moths. Environ. Entomol. 9_: 525-52 9. ANON. (1977). Pea moth. Advisory leaflet no. 334. Ministry of Agriculture, Fisheries and Food, H.M.S.O. ARBOGAST, R.T. (1981). Mortality and reproduction of Ephestia cautella and Plodia interpunctella exposed as pupae to high temperatures. Environ. Entomol. 10: 708-711. ARNOLD, M.T. S c REGNIER, F.E. (1975). Stimulation of hydro carbon biosynthesis by ecdysterone in the fleshfly Sarcophaqa bull ata. J. Insect. Physiol. 21: 15 81-1586. AIWAL, A.S. (1955). Influence of temperature, photoperiod and food on the speed of development, longevity, fecundity and other qualities of the diamondback moth Piute11a maculipennis (Curtis) (Lepidoptera:Tineidae) . Aust. J. Zool. _3_: 185-221. * AYRE, G.L., TURNOCK,* W. J. S c STRUBLE, D.L. (1982). Spatial and temporal variability in sex-attractant trap catches of Euxoa messoria and E.ochrogaster (Lepidoptera: Noctuidae) in relation to their biology in Manitoba. Can. Ent. 114: 993-1001. BAILEY, P. (1980). Oriental fruit moth in South Australian peach orchards: monitoring moth activity and abundance and estimating first egg hatch. Z. angew. Ent. 89: 377-386. 324 BAKER, A.D. (1937). The pea moth, Laspeyresia niqricana Steph., on the Gaspe Coast. Scient. Aqric. 17 : 694-702. BAKER, A.D. & PERRON, J.P. (1944). Life history studies on the pea moth, Laspeyresia niqricana Steph. on the Gaspe Coast. Scient. A^ric. 24: 341-349. BAKER, P B., SHELTON, A.M. S c MDALORO, J.T. (1982). Monitoring of diamondback moth (Lepidoptera: Yponomeutidae) in cabbage with pheromone. J. econ. Ent. 75_: 1025-1028. BAKER, T.C. S c CARDE, R .T. (1979). Courtship behaviour of the oriental fruit moth (Grapholitha molesta): experimental analysis and consideration of the role of sexual selection in the evolution of courtship pheromones in the Lepidoptera. Ann, ent. Soc. Am. 72; 173-188. BAKER, T.C., CARDE, R.T. S c CROFT, B . A. (1980). Relationship between pheromone trap capture and emergence of adult oriental fruit moths, Grapholitha molesta (Lepidoptera: Tortricidae). Can. Ent. 112: 11-15. BALOCH, G.M., MOHYUDDIN, A. I. S c GHANI, M. A. (1969). Biological control of Cuscuta spp. III.Phenology, biology and host specificity of Herpystis cuscutae Bradley (LepidopterarTortricidae). Entomoph ag a 14: 119-128. BANERJEE, A.C. S c DECKER, G.C. (1966a). Studies on sod webworms. I. Emergence rhythm, mating and oviposition behaviour under natural conditions. J. econ. Ent. 5 9 : 1237-1244. BANERJEE, A.C. S c DECKER, G.C. (1966b). Studies on sod webworms. II.Oviposition behaviour of Crambus trisectus under regulated light conditions in the laboratory. J. econ. Ent. 5 9 : 1245-1248. BARDNER, R. (1978). The economic importance of pea moth in the United Kingdom. ADAS Quart. Review 31: 159-172. BARTELL, R.J. Sc SHOREY, H.H. (1969a). A quantitative bioassay for the sex pheromone of Epiphyas postvittana (Lepidoptera) and factors limiting male responsiveness. J. Insect Physiol. 15: 33-40. BARTELL, R.J. Sc SHOREY, H.H. (1969b). Pheromone concentrations required to elicit successive steps in the mating sequence of males of the light brown apple moth, Epiphyas postvittana. Ann, ent. Soc. An. 62: 1206-1207. BATISTE, W.C., BERLOWITZ, A., OLSON, W.H. , DETAR, J.E. Sc JOOS, J.L. (1973). Codling moth: estimating time of first egg hatch in the field - A supplement to sex- attractant traps in integrated control. Environ. Entomol. 2: 387-391. BATISTE, W.C., OLSON, W.H. Sc BERLCWITZ, A. (1973a). Codling moth:diel periodicity of catch in synthetic sex- attractant versus female-baited traps. Environ. Entomol. 2_: 673-676. BATISTE, W.C., OLSON, W.H. & BERLOWITZ, A. (1973b). Codling moth:influence of temperature and daylight intensity on the periodicity of daily flight in the field. J. econ. Ent. 66: 883-892. 325 BECKWITH, R.C. (1970). Influence of host on larval survival and adult fecundity of Choristoneura conflictana (Lepidoptera:Tortricidae). Can. Ent. 102: 1474-1480. BEGON, M. (1976). Temporal variations in the reproductive condition of Drosophila obscura Fallen and D. subobscura Collin. Qecologia (Berlin) 23: 31-47. BERISFORD, C.W. Sc BRADY, U.E. (1972). Attraction of Nantucket pine tip moth males to the female sex pheromone. J. econ. Ent. 65: 430-433. BEROZA, M. , HOOD, C.S., TREFREY, D. , LEONARD, D. A. KNIPLING, E.F. S c KLASSEN, W. (1975). Field trials with disparlure in Massachusetts to suppress mating of the gypsy moth. Environ. Entomol. 4_: 705-711. BIRCH, M.C. (1970). Structure and function of the pheromone producing brush-organs in males of Phloqophora meticulosa (L.) (Lepidoptera:Noctuidae). Trans. R. ent. Soc. Lond. 122: 277-292. BLAIS, J.R. (1952). The relationship of the spruce budworm (Choristoneura fumiferana (Clem.)) to the j_cowering condition of balsam fir (Abies balsamea (L.)). Can. J. zool. 30: 1-29. BLAIS, J.R. (1953). Effects of the destruction of the current year's foliage of balsam fir on the fecundity and habits of flight of the spruce budworm. Can" Ent. 85; 446-448. BLISS, C.I. S c FISHER, R. A. (1953). Fitting the negative binomial distribution to biological data. Biometrics 9: 176-200. BOGGS, C.L. Sc GILBERT, L.E. (1979). Male contribution to egg production in butterflies: evidence for transfer of nutrients at mating. Science, N.Y. 2 06: 83-84. BRADLEY, J.D., TREMEWAN, W.G. S c SMITH, A. .(1979). British Tortricoid moths. Tortricidae:Olethreutinae. Ray Society BRAZZEL, J.R. S c MARTIN, D.E. (1957). Oviposition sites of the pink bollworm on the cotton plant. J. econ. Ent. 50: 122-124. BRITTAIN, W.H. (1921). Notes on the life history, habits and control of the pea moth, Laspeyresia niqricana Steph. Proc. ent. Soc. Nova Scotia 1919: 11-20. BROWER, J.H. (1975). Sperm precedence in the Indian meal moth, Plodia interpunctella. Ann, ent. Soc. Am. §8: 78-80. BUTLER, C.G. (1974). The world of the Honeybee. Revised Edition. Collins, London. BYERS, J.R. (1978) . Biosystematics of the genus Euxoa (Lepidoptera:Noctuidae) X. Incidence and level of multiple mating in natural and laboratory populations. Can. Ent. 110: 193-200. CAMERON, E. (193 8) . A study of the natural control of the pea moth, Cydia niqricana Steph. Bull, ent. Res. 29: 277-313. 326 CALLAHAN, P.S. (1958). Behaviour of the imago of the corn earworm Heliothis zea (Boddie), with special reference to emergence and reproduction. Ann, ent, Soc. An. 51: 271-283. CAMPBELL, I .M. (1961). Polygyny in Choristoneura Led. (LepidopterarTortricidae). Can. Ent. 93: 1160-1162. CARPENTER, J.E., SPARKS, A.N. &GUELDNER, R.C. (1982). Effects of moth population density and pheromone concentration on mating disruption of the corn ear- worm in large screened cages. j. econ. Ent. 75: 333-336. ~ CHARMILLOT, P.J. (1979). Efficacite du piege a carpocapse (Laspeyresia pomonella (L.)) appate d 1attratif sexual synthetique. Ann. Zool. Ecol. anim. 11: 587-598. CHARMILLOT, P.J., VALLIER, R. S c TASINI-ROSSET, S. (1979). Carpocapse des prunes (Grapholitha funebrana Tr.) etude du cycle de developpement en fonction des sommes de temperature et considerations sur 1 1 activite des papillons. Mitt, schweiz. ent. Ge s . 52: 19-33. CHEEMA, P.S. (1956). Studies on the bionomics of the case bearing clothes moth Tinea pellionella L. Bull, ent. Res. 47: 167-182. CHEW, F.S. Sc ROBBINS, R.K. (1984). Egg-laying in Butterflies. Proc. XIth. Symp, R, ent. Soc. Lond. (ed. Vane- Wright, R.I.) (in press). CLAYTON, T.E. Sc HENNEBERRY, T.J. (1982). Pink bollworm: Effect of soil moisture and temperature on moth emergence in field and laboratory studies. Environ. Entomol, 11: 147-149. COLWELL, A.E., SHOREY, H.H., GASTON, L.K. S c VAN VORPHIS KEY, S.E. (1978). Short range precopulatory behaviour of males of Pectinophora gossypiella (Lepidoptera: Gelechiidae). Behav. Biol. 22: 323-355. COMEAU, A., CARDE, R.T. Sc ROELOFS, W.L. (1976). Relationships of ambient temperatures to diel periodicities of sex attraction in six species of Lepidoptera. Can. Ent. 108: 415-418. COMMON, I.F.B. (1954). A study of the ecology of the adult Bogong moth, Acrrotis inf us a (Boisd.) with special reference to its behaviour during migration and aestivation. Aust. J. Zool- 2_: 223-263. CONDR AS HOFF, S.F. (1967). An extraction method for rapid counts of insect eggs and small organisms. Can. Ent. 99: 300-303. CRANE, E. (Ed.) (1975). Honey, a Comprehensive Survey. Heinemann, London. CR/WFORD, C.S. (1966). Photoperiod dependent oviposition rhythm in Crambus teterrellus (Lepidoptera:Crambinae). Ann, ent. Soc. Am. 59: 1285-1288. CR/WFORD, C.S. (1967). Oviposition rhythm studies in Crambus lopiarius (Lepidoptera:Pyralidae:Crambinae). Ann. ent. Soc. Am. 60: 1014-1018. 327 CRAWFORD, C.S. (1971). Comparative reproduction of Crambus harpipterus and Aqriphila plumbifimbriella in northern New Mexico. Ann, ent. Soc. Am. 64: 52-59. CURTIS, R.K. S c BARNES, M.M. (1977). Oviposition and devel opment of the navel orangeworm in relation to almond maturation. J. econ, Ent. 70: 395-398. DANTH ANAR AX'ASIA, W. (1975) . Factors determining variation in fecundity of the light brown apple moth, Epiphyas postvittana (Walker) (Tortricidae) . Aust. j. Zool. 23: 439-451. DAVID, W.A.L. S c GARDINER, B.O.C. (1961). Feeding behaviour of adults of Pieris brassicae (L.) in a laboratory culture. Bull, ent. Res. 5 2 : 741-762. DEAN, R.W. S c ROELOFS, W.L. (1970). Synthetic sex pheromone of red banded leaf roller moth as a survey tool. J. econ. Ent. 63: 684-686. DEMPSTER, J.P. (1961). A sampler for estimating populations of active insects upon vegetation. J. Anim. Ecol. 30: 425-427. DEN OTTER, C.J. S c KLIJNSTRA, J.W. (1980). Behaviour of male summer-fruit tortrix moths, Adoxophyes or ana (LepidopterazTortricidae) , to synthetic and natural female sex pheromone. Ent. exp. Sc appl. 28: 15-21. DeROZARI, M.B., SHCWERS , W.B. S c SHAW, R.H. (1977). Environment and the sexual activity of the European corn borer. Environ. Entomol. 6: 657-665. DETHIER, V.G. (1959). Egg-laying habits of Lepidoptera in relation to available food. Can. Ent. 91: 554-561. DIETRICK, E.J. (1961). An improved backpack motor fan for suction sampling of insect populations. J. econ. Ent. 5 4 : 394-395. DIETRICK, E.J., SCHLINGER, E.I. S c VAN DEN BOSCH, R. (1959). A new method for sampling arthropods using a suction collecting machine and modified Berlese funnel separator. J. econ. Ent. 5 2 : 1085-1091. DIRIMANOV, M. S c SENGALEVICH, G. (1962). The bark borer (Laspeyresia woeberiana Schiff.), morphological and biological peculiarities and possibilities for control. Rastit, Zasht. 10: 33-46. Cited by Hinton (1981). DOANE, C.C. (1968). Aspects of mating behaviour of the gypsy moth. Ann, ent. Soc. Am. 6 1 : 768-773. DOUWES, P. (1968). Host selection and host finding in the egg-laying female Cidaria albulata L. (Lepidoptera: Geometridae). Opusc. ent. 33: 233-279. DROOZ, A.T. (1965). Some relationships between host, egg potential and pupal weight of the elm spanworm, (LepidopterazGeometridae). Ann, ent. Soc. An. 58: 243-245. DROOZ, A.T. Sc SOLOMON, J.D. (1964). Effect of solarisation on elm spanworm eggs (Lepidoptera:Geometridae). Ann. ent. Soc. Am. 57: 95-98. 328 DUNS TAN, G.G. (1964). Mating behaviour of the oriental fruit moth, Grapholitha molesta (Busch)' (Lepidoptera: Olethreutidae). Can. Ent. 96: 1087-1093. EDWARDS, C.A. (1954). Experiments on the control of pea moth. PI. Path. 3_: 66-67. EDWARDS, D.K. (1962). Laboratory determinations of the daily flight times of separate sexes of some moths in naturally changing light. Can. J. Zool. 40; 511-530. EKHOLM, S. (1963). The pea moth, Laspeyresia nigricana Steph., its fluctuation and distribution in Finland. Notul. ent. 43; 1-13. ELLIOT, W.M. (1977). Mating frequency of the female European corn borer, Ostrinia nubilalis (Lepidoptera:Pyralidae) in southwestern Ontario. Can, Ent. 109: 117-122. ELSEY, K.D. (1980). Pickleworm: effect of temperature on development, fecundity and survival (Lepidoptera: Pyralidae) . Environ. Entomol. 9_: 101-103. FAGERSTROM, T. S c WIKLUND, C. (1982). Why do males emerge before females? Protandry as a mating strategy in male and female butterflies. Oecologia (Berlin) 52: 164-166 FATZINGER, C.W. (1973). Circadian rhythmicity of sex pheromone release by the moth Dioryctria abietella (Lepidoptera: Pyralidae:Phycitinae) and the effect of a diel light cycle on its precopulatory behaviour. Ann, ent. Soc. Am. 6 6 : 1147-1153. FENEMORE, P.G. (1979). Oviposition of potato tuber moth, Phthorimaea operculella Zell. (Lepidoptera:Gelechiidae) the influence of adult food, pupal weight and host plant tissue on fecundity. N.Z. Jl. Zool. 6_: 389-395. FINCH, S. (1978). Volatile plant chemicals and their effect on host plant finding by the cabbage root fly (Delia brassicae). Ent. exp. & appl. 24: 350-359. FLETCHER, J.A. (1894). The pea moth. Rep. Dir, exp. F m s . Serv. Can. 1894. FLETCHER, J.A. (1901). The pea moth. Rep. Dir, exp. Fms Serv. Can. 1900. FLINT, H.M. S c KRESSIN, E.L. (1968). Gamma irradiation of the tobacco budworm: sterilization, competitiveness and observations on reproductive biology. J. econ. Ent. 6_1: 477-483. FLINT, H.M. Sc MERKLE, J.R. (1981). Early season movements of pink bollworm moths between selected habitats. J. econ. Ent. 74: 366-371. FLUKE, C.L. (1920a). The pea moth: how to control it. Bull. Wis. aqric. Exp. Stn. 310: 2-12. FLUKE, C.L. (1920b). Pea moth investigations. Bull. Wis. aqric. Exp. Stn. 323: 44-45. FLUKE, C.L. (1921). The pea moth in Wisconsin. J. econ. Ent. 14: 94-98. FORD, E.B. (1972). Butterflies. Collins, London. FRANSSEN, C.J.H. (1954). The biology and control of Enarmonia niqricana. Versl. landbouwk. Onderz. Rijkslandb- Proefstn. 60: 1-50. 329 FRANSSEN, C.J.H. & KERSEN, M.C. (1960). The control of the pea moth Enarmonia niqricana Fab, in the Netherlands. Meded. Inst, plziektenk. Onderz. 232: 1-4. FRETWELL, S.D. (1972). Populations in a Seasonal Environment. Princeton University Press, Princeton. GANE, A. J. , BIDDLE, A. J. Sc KNOTT, C.M. (1984). P.G.R.O. Pea Growing Handbook. Vol. 1. Processors and Growers Research Organisation. GARA, R H. , ALLAN, G.G. , WILKINS, R.M. S c WHITMORE J.L. (1973). Flight and host selection behaviour of the mahogony shoot borer, Hypsipyla grande11a Zell. (Lepidoptera:Phycitidae). Z. angew. Ent. 72: 259-266. GASTON, L.K., KAAE, R.S., SHOREY, H.H. Sc SELLERS, D. (1977). Controlling the pink bollworm by disrupting sex pheromone communication between adult moths. Science, N.Y. 196; 904-905. GEHRING, R.D. S c MADSEN, H.F. (1963). Some aspects of the mating and oviposition behaviour of the codling moth, Carpocapsa pomonella. J. econ. Ent. 56: 140-143. GEIER, P.W. (1960). Physiological age of codling moth females (Cydia pomonella (L.)) caught in bait and light traps. Nature, London. 185: 709. GEORGE, J. A. Sc HOWARD, M.G. (1968). Insemination without spermatophores in the oriental fruit moth, Grapholitha molesta, (Lepidoptera:Tortricidae). Can. Ent. 100; 190-192. GLEN, D.M. Sc BRAIN, P. (1982). Pheromone-trap catch in relation to the phenology of codling moth (Cydia pomonella). Ann, appl. Biol. 101: 429-440. GOSSARD, T. S c JONES, R.E. (1977). The effects of age and weather on egg laying in Pieris rapae. J. appl. Ecol. 14.: 65-71. GOULD, H.J. S c LEGOWSKI, T.J. (1959). Timing sprays for control of pea moth. Agriculture, London. 65: 611-614. GOULD, H.J. S c LEGOWSKI, T.J. (1962). Pea moth on dry harvesting peas, investigations into the timing of sprays; the economics of control measures and fore casting the level of attack. Proc. British Insecticide Sc Fungicide Conf. 1961: 15 9-165. GOULD, H.J. S c LEGOWSKI, T.J. (1964). Spray warnings for pea moth, Laspeyresia niqricana Steph. based on its biology in the field. Ent exp. & appl. 7: 131-138. GOULD, H.J. S c LEGOWSKI, T.J. (1968). Alternatives to DDT for the control of pea moth on dry harvesting peas. Pi, Path. 17: 31-35. GOULD, H.J. LEGCWSKI, T.J. Sc ATKINS, E.C. (1962). Surveys of pea moth damage on dry harvesting peas in East Anglia 1957 - 1959. Pi. Path. 11: 1-6. GRANT, G.G. S c BRADY, U.E. (1975) . Courtship behaviour of Phycitid moths I. comparison of Plodia interpunctella and Cadra cautella, and role of male scent glands. Can. J. Zool. 53: 813-826. 330 GREEN, G.W. (1962). Flight and dispersal of the european pine shoot moth, Rhyacionia buoliana (Schiff.). I. Factors affecting flight and the flight potential of females. Can. Ent. 94: 282-299. GREEN, G.W. Sc POINTING, P.J. (1962). Flight and dsipersal of the european pine shoot moth, Rhyacionia buoliana (Schiff.). II. Natural dispersal of gg laden females Can. Ent. 94: 299-314. GREENBANK, D.O. (1957). The role of climate and dispersal in the initiation of outbreaks of the spruce budworm in New Brunswick II. The role of dispersal. Can. J. Zool. 35: 385-403. GREENWAY, A.R. (1984). Sex pheromone of the pea moth, Cydia nigricana (F.), (Lepidoptera:Olethreutidae). J. Chem. Ecol. 10: 973-982. GREENWAST, A.R. S c WALL, C. (1980) . Sex attractant lures for pea moth. Rep, Rothamsted exp. Stn. 1979, pt. 1: 117. GREENWAY, A.R. S c WALL, C. (1981). Attractant lures for males of the pea moth, Cydia nigricana (F.) containing (E_) -10—dodecen—1-yl acetate and (E, E) - 8, 10-dodecadien- 1-yl acetate. j. Chem. Ecol. 7 : 563-573. GREENW AY, A.R. Sc WALL, C. (1982) . Sex attractants for pea moth. Rep. Rothamsted exp. Stn. 1981, pt. 1: 132. GREENWAY, A.R. , WALL, C. S c PERRY, J.N. (1982). Compounds modifying the activity of two sex-attractants for males of the pea moth, Cydia niqricana (F. ) . J. Chem. Ecol. Jh 397-408. GUPTA, P.D. S c THORSTEINSON, A.J. (1960). Food plant relation ships of the diamondback moth, Plutella maculipennis. II. Sensory regulation of oviposition of the adult female. Ent. exp . Sc appl. 3 : 305-314. HAGEMANN-MEURER, U. S c THALENHORST, W. (1964). Vergleichende untersuchungen uber die Puppengewicht-Eizahl-Relation der foleule Panolis flammea (Schiff.).. Z. angew. Ent. 54: 290-299. HAGLEY, E.A.C. (1973). Timing sprays for codling moth (Lepidoptera:Olethreutidae) control on apple. Can. Ent. 105: 1085-1089. HAGLEY, E.A.C., BRONSKILL, J.F. Sc FORD, E.J. (1980). Effect of the physical nature of leaf and fruit surfaces on oviposition by the codling moth, Cydia pomonella (Lepidoptera:Tortricidae). Can. Ent. 112: 503-510. HAMSTEAD, E.O. S c GOULD, E. (1950). Codling moth oocyte studies. J. econ. Ent. 43: 724-726. HANS, H. Sc THORSTEINS ON, A.J. (1961). The influence of physical factors and host plant odour on the induction and termination of dispersal flights in Sitona cylindrical is Fahr. Ent. exp. Sc appl. 4^: 165-177. HANSON, A J. Sc WEBSTER, R.L. (1936). The pea moth, Laspeyresia niqricana Steph. Bull. Wash, agric. Exp. Stn. no. 327. 331 HARLOW, P.M. (1956). A study of ovarial development and its relation to adult nutrition in the blowfly, Protophormia terrae-novae (R.D .). J. exp. Biol. 33: 777-797. HAWKE, C. (1975). Physiological condition of adult cabbage root fly, Erioschia brassicae (Bouche), attracted to host plants. J. appl. Ecol. 12: 497-506. HENDERSON, I.E. & WHITAKER, T.M. (1976). The efficiency of an insect sampler in grassland. Ecol. Entomology 2z 57-60. HENDRICKS, D.E., GRAHAM, H.M. , GUERRA, R.J. & PEREZ, C.T. (1973). Comparison of the numbers of tobacco budworms and bollworms caught in sex pheromone traps vs. black- light traps in Lower Rio Grande Valley, Texas. Environ. Entomol. 2: 911-915. HENNEBERRY, T . J . Sc CLAYTON, T.E . (1979). Pink bollworm: Movement and distribution of diapause and non-diapause larvae in soil and moth emergence after pupal burial. Environ, Entomol. J3: 782-785. HENNEBERRY, T.J. & CLAYTON, T.E. (1982). Pink bollworm of cotton (Pectinophora gossypiella (Saunders)): male moth catches in gossyplure-baited traps and relation ships to oviposition, boll infestation and moth emerg ence. Crop Protection 1: 497-504. HENNEBERRY, T.J. S c LEAL, M.P. (1979). Pink bollworm: Effects of temperature, photoperiod and light intensity, moth age and mating frequency on oviposition and egg viability. J. econ, Ent, 72: 489-492. HENSON, W.R. (1951). Mass flights of the spruce budworm. Can.Ent. 83: 240. HEY, G.L. (1946). DDT experiments in 1945. Grower 25: 290. HILLYER, R.J. S c THORSTEINS ON, A. J. (1971). Influence of host plant or males on programming of oviposition in the diamondback moth. Can. J. zool. 49: 983-990. HINTON, H.E. (1981). The Biology of Insect Eggs. 3 vols. Pergamon, Oxford. HODJAT, S.H. (1970). Effects of crowding on colour, size and larval activity of Spodoptera littoralis (Lepidoptera: Noctuidae). Ent. exp. & appl. 13: 97-106. HOWELL, J.F. (1974). The competitive effect of field popul ations of codling moth on sex attraction trap efficiency. Environ. Entomol. 3: 803-807. HOWELL, J.F. (1981). Codling moth: the effect of adult diet on longevity, fecundity, fertility and mating. J. econ. Ent. 7 4 : 13-18. HOWELL, J.F. S c THORP, K.D. (1972). The influence of mating on attractiveness of female codling moths. Environ, Entomol. 1: 125-126. INKILA, 0. (1948). Hennekaariaisen (Grapholitha nigricana Steph.) peltohernealle arheuttamiste vakingoista. Maataloust. Aikakausk. 20: 58-66. ISLEY, D. (1938). Codling moth oviposition and temperature. J. econ. Ent. 31: 356-359. 332 JACOBSON, L. A. (1965). Mating and oviposition of the pale western cutworm, Acrrotis orthoaonia Morrison (Lepidoptera:Noctuidae), in the laboratory. Can. Ent. 97: 994-1000. JACOBSON, L. A. S c BLAKELEY, P.E. (1960). Survival, development and fecundity of the pale western cutworm, Aarotis orthogonia Morr. (Lepidoptera:Noctuidae) after starvation. Can. Ent. 92: 184-188. JENNINGS, D.T. S c ADDY, N D. (1968). A staining technique for jack pine budworm egg masses. J. econ. Ent. 61: 1766. JERMY, T. S c SZENTESI, A. (1978). The role of inhibitory stimuli in the choice of oviposition site by phyto phagous insects. Ent. exp . S c appl. 24: 458-471. JOHNSON, C.G. (1950) . A suction trap for small airborne insects which automatically segregates the catch into successive hourly samples. Ann, appl. Biol.- 37: 80-91. JOHNS ON, C.G. (1960). A basis for a general system of insect migration and dispersal flight. Nature, Lond. 186: 348-350. JOHNSON, C.G. (1966). A functional system of adaptive dispersal by flight. A. Rev. Ent. 11: 233-260. JOHNSON, C G., SOUTHWOOD, T.R.E. S c ENTWISTLE, H.M. (1957). A new method of extracting arthropods and molluscs from grassland and herbage with a suction apparatus. Bull, ent. Res. 48: 211-218. JOHNSON, C.G. & TAYLOR, L.R. (1955). The development of large suction traps for airborne insects. Ann, appl. Biol. 4 3 : 51-61. JOHNSON, C.G. Sc TAYLOR, L.R. (1957). Periodism and energy summation with special reference to flight rhythms in aphids. j. exp . Biol. 34: 209-221. JOHNSON, D.R. (1983). Relationship between tobacco budworm (Lepidoptera:Noctuidae) catches when using pheromone traps and egg counts in cotton. J. econ. Ent. 76: 182-183. KAAE, R.S. S c SHOREY, H.H. (1973). Sex pheromones of Lepidoptera 44. Influence of environmental conditions on the location of pheromone communication and mating in pectinophora gossypiella. Environ, Entomol. 2: 1081-1084. KENNEDY, J.S. (1961). A turning point in the study of insect migration. Nature, Lond. 189: 785-791. KENNEDY, J.S. (1977). Olfactory responses to distant plants and other odour sources. In Chemical Control of Insect Behaviour: Theory and Application (eds. Shorey, H.H. S c McKelvey, J.J. jr.) pp. 67-92. Wiley, London. KIRA, M.T., GUTHRIE, W.D. Sc HUGGANS, J L. (1969). Effect of drinking water on the production of eggs by the european com borer. J. econ. Ent. 62: 1366-1368. 333 KIRITANI, K. S c KAN OH, M. (1984). Influence of delay in mating on the reproduction of the oriental tea tortrix, Homona magnanima Diakonoff (Lepidoptera: Tortricidae), with special reference to pheromone- based control. Protection Ecology 6 : 137-145. KLASSEN, W. RIDGWAY, R.L. S c INSCOE, M. (1982). Chemical attractants in integrated pest management programs. In Insect Suppression with Controlled Release Pheromone Systems (eds. Kydonieus, A.F. Sc Beroza, M. ) vol. I. pp. 13-130. CRC Press, Boca Raton, Florida. Cited by Wall (1984). KOLMAKOVA, V.D. (1958). On the biology of Siberian fruit moths of the genus Grapholitha (Lepidoptera :Torticidae) , injurious to fruit trees in Transbaikalia. Trudy vses. Inst. Zashch. Rast. 2 4 : 203-210. Cited by Hinton (1981). KUWAYAMA, S. (1937). Notes on the pea moth, Grapholitha niqricana Steph. in Nippon. Kontyu 11: 1-11. LABANCWSKI, G.S. (1981). Spring emergence of the codling moth, Laspeyresia pomonella (L.) and the possibility of forecasting it in central Poland. Ekol, pol. 29: 535-544. LABEYRIE, V. (1978). Reproduction of insects and co-evolution of insect and plants. Ent. exp. S c appl. 24; 496-504. LABINE, P . A. (1966). The population biology of the butterfly, Euphydryas editha. IV. Sperm precedence, a preliminary- report. Evolution 20; 580-586. LABINE, P. A. (1968). The population biology of the butterfly, Euphydryas editha. VIII. Oviposition and its relation to patterns of oviposition in other butterflies. Evolution 22: 799-805. LANDOLT, P.J. S c CURTIS, C.E. (1982). Effect of temperature on the circadian rhythm of navel orangeworm sexual activity. Environ. Entomo1. 11: 107-110. LANGENBUCH, R. (1941). zur biologie des Erbsenwicklers, Grapholitha pisane Steph. Arb. physiol, anqew. Ent. B e r L _8_: 219-245. LANGILLE, R.H. S c KEASTER, A.J. (1973). Mating behaviour of the southwestern corn borer. Environ. Entomol. 2j 225-226. LEGOWSKI, T.J. S c GOULD, H.J. (1960). Losses of dry harvesting peas due to pea moth in East Anglia and the economics of control measures. Pi. Path. 9: 119-126. LEIGH, T.F., GONZALEZ, D. S c VAN DEN BOSCH, R. (1970). A sampling device for estimating absolute insect populations on cotton. J. econ. Ent. 63; 1704-1706. LEWIS, T. (1969). The distribution of flying insects near a low hedgerow. J. appl. Ecol. 6 : 443-452. LEWIS, T. S c MACAULAY, E.D.M. (1976). Design and elevation of sex attractant traps for pea moth, Cydia niqricana Steph. and the effect of plume shape on catches. Ecol. Entomology 1: 175-187. 334 LEWIS, T. S c STURGEON, D.M. (1978). Early warning of egg hatching in pea moth (Cydia nigricana) . Ann, appl. Biol. 8 8 : 199-210. LEWIS, T. S c TAiTLOR, L.R. (1965). Diurnal periodicity of flight by insects. Trans. R. ent. Soc. Lond. 116: 393-479. LEWIS , T., WALL, C., MACAULAy, E.D.M. S c GREENWAy, A.R. (1975) The behavioural basis of a pheromone monitoring system for pea moth, Cydia niqricana. Ann, appl. Biol. 80: 257-274. LIKVENTOV, A.V (1960). On the suppressive effect of plant ations of oak and_lime on the reproduction of the gypsy moth. Trudy vses. Inst. Zashch. Rast. 15: 33-40 Cited by Hinton (1981). LONG, D.B. S c ZAHER, M. A. (1958). Effect of larval population density on the adult morphology of two species of Lepidoptera, Plusia gamma L. and Pieris brassicae L. Ent. exp. S c appl. 1: 161-173. LUKEFAHR, M.J. S c GRIFFIN, J. A. (1957). Mating and ov.i.position habits of the pink bollworm moth. J~. econ. Ent. 50: 487-490. ~~ je LUKEFAHR, M.J. S c MARTIN, D.F. (1964). The effects of various larval and adult diets on the fecundity and longevity of the bollworm, tobacco budworm and cotton leafworm. J. econ. Ent. 57: 233-235. LUM, P.T.M. (1979). Degeneration of ova in the bulla seminalis of Lepidoptera. J. Insect Physiol. 25: 595-599. LUM, P.T.M. S c FLAHERTY, B.R. (1970). Regulating oviposition by Plodia interpunctella in the laboratory by light and dark conditions. J. econ. Ent. 63: 236-239. MACAULAY, E.D.M. (1979). Field trials with attractant traps for timing sprays to control pea moth. Pi. Path. 26: 179-188. MACAULAY, E.D.M., ETHERIDGE, P., GARTHWAITE, D.G., GREENWAY, A.R. , WALL, C. Sc GOODCHILD, R.E. (1985). Prediction of optimum spraying dates against pea moth (Cydia niqricana (F.)), using pheromone traps and temperature measurements. Crop Protection In press. MACAULAY, E.D.M. S c LEWIS, T. (1977). Attractant traps for monitoring pea moth Cydia niqricana (F.). Ecol. Entomology 2: 279-284. MACLELLAN, C.R. (1978) . Field evaluation of synthetic sex pheromone attractants for the eye-spotted bud moth (Lepidoptera:Olethreutidae) and three leafroller species (Lepidoptera:Tortricidae). Can. Ent. 110: 847-852. MADSEN, H.F. Sc PETERS, F.E. (1976). Pest management: Monitoring populations of Archips arqyrospilus and Archips rosanus (Lepidoptera:Tortricidae) with sex pheromone traps. Can. Ent. 108: 1281-1284. MA3NARELLI, L. A. (1976). Physiological age of Tabanidae (Diptera) in Eastern New York State, U.S.A. J. med. Entomol. 12: 679-686. 335 MARKS, R.J. (1976). Mating behaviour and fecundity of the red bollworm Diparopsis castanea Hmps. (Lepidoptera: Noctuidae). Bull, ent. Res. 6 6 : 145-158. MARSHALL, L.D. (1982). Male nutrient investment in the Lepidoptera: what nutrients should males invest? Am. Nat. 120: 273-279. MARTYN, E.J. (1965). Studies on the ecology of Oncopera intricata Walker (Lepidoptera:Hepialidae) I. Fecundity of the female moths. Aust. J, Zool. 13: 801-805. MILES, H.W. (1926). Life history and control of the pea moth, Laspeyresia niqricana Steph. Bull. Chamber Hortic. 3j 6-9. MILLER, C.A. (1957). A technique for estimating the fecundity of natural populations of the spruce budworm. Can. J. Zool. 35: 1-13. MINDER, I.F. (1959). Leaf-rollers injurious to fruit crops in the flood-plain of the Oka river. Rev, Ent. U.R.S.S. 38: 98-110. Cited by Hinton (1981). MINKS, A.K. & DE JONG, D.J. (1975). Determination of spraying dates for Adoxophyes or an a by sex pheromone traps and temperature recordings. J. econ. Ent. 6 8 : 729-732. MINKS, A.K. Sc NOORDINK, J.W. (1971). Sex attraction of the summerfruit tortrix moth, Adoxophyes orana: evaluation in the field. Ent. exp. S c appl. 14: 57-72. MISKIMEN, G.W. (1966). Effect of light on mating success and egg-laying activity of the sugarcane borer, Diatraea saccharalis. Ann, ent. Soc. Am. 59: 280-284. MITCHELL, B.K. Sc SEABROOK, W.D. (1974). Electrophysiological investigations on tarsal chemoreceptors on the spruce budworm, Choristoneura fumiferana (Lepidoptera). J. Insect Physiol, 20; 1209-1218. MOSCARDI, F., BARFIELD, C.S. S c ALLEN, G.E. (1981). Impact of soybean phenology on velvetbean caterpillar (Lepidoptera:Noctuidae); oviposition, egg hatch and longevity. Can. Ent. 113: 113-119. MULLER, 0. (1957). Biologische studien uber den fruten Kasteinien-wickler Pammene juliana (Stephens) (Lepidoptera:Tortricidae) und seine wirtschaftliche Bedeutung fur den Kanton Tessin. Z. anqew. Ent. 41: 73-111. NAGAUDA, D. S c PITRE, H. (1983) . Development, fecundity and longevity of the tobacco budworm (Lepidoptera: Noctuidae) fed soybean, cotton, and artificial diet at three temperatures. Environ. Entomol. 12: 582-583. NAG AT A, K. , TAMAKI, Y. , NOGUCHI, H Sc YUSHIMA, T. (1971). Changes in sex pheromone activity in adult females of the smaller tea tortrix moth, Adoxophyes fasciata. J. Insect Physiol. 18: 339-346. NEL, R.I. (1940). The validity of the bait trap method of spray timing in codling moth control. Entomology Mem. Pep, agric. tech. Serv, Repub. S, Afr. 2; 55-76. 336 NICOLAISEN, W. (1928). Der Erbsenwickler, Grapholitha (Cydia, Laspeyresia) sp., sein Schaden und seine Bekampfung unter besonderer Berucksichtigung der Anfalligkeit verschiedener Erbsensorten. Kuhn-Arch. 19: 196-256. Cited by Wright et ad (1951). NIEZGODZINSKI, P. (1965). Pachowka strakoweczka- Laspeyresia niqricana Steph. (Lepidoptera:Tortricidae) nowym szkodnikiem bobu w Polsce. Polskie Pismo ent. (B) 37-38: 177-179. NOLTE, H.W. (1959). Untersuchungen zur Bekampfung des Erbsen wickler s (Laspeyresia niqricana Stph.). Albrecht- Thaer-Arch. 2: 146-157. OLAIFA, J.I. S c AKINGBOHUNGBE, A. E. (1981). Aspects of the biology of the black cowpea moth, Cydia ptychora (Lepidoptera:Tortricidae) related to host plant phenology. Ann, appl. Biol. 97: 129-134. OLOUMI-S ADEGHI, H., SHOWERS # W.B. S c REED, G.L. (1975). European c o m borer: lack of synchrony of attraction to sex pheromone and capture in light traps. J, econ. Ent. 6 8 : 663-667. 0N0, T. (1977). Diurnal rhythms of the behavioural components in the mating of the potato tuber moth, Phthorimaea operculella (Lepidoptera:Gelechiidae). Botyu-Kaqaku 42: 203-206. OTAKE, A. & OYAMA, M. (1973). Influence of sex ratio and density on the mating success of Spodoptera litura F. (Lepidoptera:Noctuidae). Appl . Ent. Zool. Qj 246-247. OUTRAM, I. (1971). Aspects of mating in the spruce budworm, Choristoneura fumiferana (Lepidoptera:Tortricidae). Can. Ent. 103: 1121-1128. OUYE, M.T., GARCIA, R.S., GRAHAM, H.M. S c MARTIN, D.F. (1965) Mating studies in the pink bollworm, Pectinophora qossypiella (Lepidoptera:Gelechiidae) based on presence of spermatophores. Ann, ent. Soc. Am. 58: 880-882. OUYE, M.T., GRAHAM, H.M. RICHMOND, C. A. S c MARTIN, D.F. (1964) Mating’ studies of the pink bollworm. J, econ. Ent. 57: 222-225. OVERHULSER, D.L., DATERMAN, G.E., SOWER, L.L., SARTWELL, C. S c KOERBER, T.W. (1980). Mating disruption with synthetic sex attractants controls damage by Eucosma sonamana (Lepidoptera:Tortricidae:Olethreutinae) in Pinus ponderosa plantations II. Aerially applied hollow fibre formulation. Can. Ent. 112: 163-165. OZOLS, E. (1933). Pea pests. Lauksaimn. Menesrak. 3: 130-137 PANTIN, C.F.A. (1962). Notes of Microscopical Techniques for zoologists. Cambridge University Press, Cambridge PARKER, G.A. (1970). The reproductive behaviour and nature of sexual selection in Scatophaqa stercoraria L. II. The fertilisation rate and the spatial and temporal relationships of each sex around the site of mating and oviposition. J. Anim. Ecol. 39: 205-228. 337 PARKER/ G.A. (1974). The reproductive behaviour and the nature of sexual selection in Scatophaga stercoraria L. IX. Spatial distribution of fertilisation rates and evolution of male search strategy within the reproductive area. Evolution 28: 93-108. PENCOE, N.L. S c LYNCH, R.E. (1982). Distribution of Heliothis zea eggs and first instar larvae on peanuts. Environ. Entomol. 11: 243-245. PEREZ, R. S c LONG, W.H. (1964) . Sex attract ant and mating behaviour in the sugar cane borer. J, econ. Ent. 57: 688-690. PERRIN, R.M. (1977). Studies on host-plant selection by the cowpea seed moth, Cydia ptychora (Lepidoptera: Olethreutidae). Ann, appl. Biol. 87: 175-182 PERRY, J.N., MACAULAY, E.D.M. Sc EMMETT, B.J. (1981). Phenological and geographical relationships between catches of pea moth in sex-attractant traps. Ann, appl. Biol. 97: 17-26. PERRY, J.N. S c WALL, C. (1984). Local variation between catches of pea moth, Cydia nigricana (F.) (Lepidoptera: Tortricidae), in sex-attractant traps, with reference to the monitoring of field populations. Protection Ecology 6 : 43-49. PERRY, J.N., WALL, C. & GREENWAY, A.R. (1980). Latin-square designs in field experiments involving insect sex attractants. Ecol. Entomology 5: 385-390. PHILOGENE, B.J.R. (1982). Development rate changes in insects: the importance of photoperiod. Am. Nat. 120: 269-272. PLISKE, T.E. (1975). Attraction of Lepidoptera to plants containing pyrrolizidine alkaloids. Environ. Entomol. 4: 455-473. POINTING, P.J. (1961). The biology and behaviour of the european pine shoot moth, Rhyacionia buoliana (Schiff.) in southern Ontario I. Adult. Can. Ent. 93: 1098-1112. POTTER, D. A. S c TIMMONS, G.M. (1983). Forecasting emergence and flight of the lilac borer (Lepidoptera:Sessiidae) based on pheromone trapping and degree day accumul ations. Environ. Entomol. 12: 400-403. PRESCOTT, H.W. S c NEWTON, R.C. (1963) . Flight study of the clover root Curculio. J. econ. Ent. 56: 368-370. PRUESS, K.P. (1963). Effects of food, temperature and oviposition site on longevity and fecundity of the army cutworm. J. econ. Ent. 56: 219-221. RAHN, R. (1972). The effect of age on sex pheromone release in virgin females of Acrolepia assectella (Z.). C. r. Seanc. Soc. Biol. 166: 1162-1166. RAULSTON, J.R. , SNOW, J.W., GRAHAM, H.M. S c LINGREN, P.D. (1975). Tobacco budworm: effect of prior mating and sperm content on the mating behaviour of females. Ann. ent. Soc. Am. 6 8 : 701-704. 338 REID,, J.A. (1941). Mating and oviposition in Cnephasia chrys anthe an a (Dup.) (Lepidoptera:Tortricidae). Proc. R. ent. Soc. Lond. (A) 16: 24-28. RENWICK, J.A. A. S c RADKE, C.D. (1980). An oviposition deterrent associated with frass from feeding larvae in the cabbage looper Trichoplusia ni (Lepidoptera: Noctuidae). Environ. Entomol. 9: 318-320. RICE, R.E., SADLER, L.L., HOFFMAN, M.L. S c JONES, R. A. (1976). Egg trap for the navel orangeworm, Paramyelois transitella (Walker). Environ. Entomol. 5: 697-700. RICHMOND, C. A. S c GRAHAM, H.M. (1969). Two methods of operating a vacuum sampler to sample populations of the cotton fleahopper on wild hosts. J. econ, Ent. 62: 525-526. RICHMOND, J.A./ THOMAS, H. A. S c BH ATTACH ARYY A, H. (1983). Predicting spring flight of Nantucket pine tip moth (Lepidoptera:Olethreutidaa) by heat unit accumulation. J. econ. Ent. 76 : 269-271. RIEDL, H. (1980). The importance of pheromone trap density and trap maintainance for the development of stand ardised monitoring proceedures for the codling moth (Lepidoptera:Tortricidae). Can. Ent. 112: 655-6G3. RIEDL, H. S c CROFT, B . A. (1974). A study of pheromone trap catches in relation to codling moth (Lepidoptera: Olethreutidae) damage. Can, Ent. 106: 525-537. RIEDL, H. , CROFT, B. A. S c HOWITT, A.J. (1976). Forecasting codling moth phenology based on pheromone trap catches and physiological time models. Can. Ent. 108: 449-460. ROACH, S.H. (1975). Heliothis zea and H. virescens: moth activity as measured by blacklight and pheromone traps. J. econ. Ent. 6 8 : 17-21. ROBERT, P.C. (1971). The effect of host and non-host plants on oogenesis and oviposition in Scrobipalpa ocellatella Boyd. (Lepidoptera:Gelechiidae). Acta Phtyopath. Sci. Hung . 6 : 235-241. ROBINSON, G.S. (1976). The preparation of slides of Lepidoptera genitalia with special reference to the Microlepidoptera. Entomologists* Gaz. 27: 127-132. ROBINSON/ G . S y Sc NIELSEN, E.S. (1983). The Microlepidoptera described by Linnaeus and Clerck, Syst. Entomo 1., Q: 191-242. ROSAif, B. (1969). Anatomical indicators for assessing age of mosquitoes: changes in ovarian follicles. Ann, ent. Soc. Am. 62: 605-611. ROTHSCHILD, G.H.L. & MINKS, A.K. (1974). Time of activity of male oriental fruit moths at pheromone sources in the field. Environ. Entomol. 3: 1003-1007. ROTHSCILD/ G.H.L., VICKERS/ R . A. Sc MORTON, R. (1984). Monitoring the oriental fruit moth, Cydia molesta (Busck) (Lepidoptera:Tortricidae) , with pheromone traps and bait pails in peach orchards in South-Eastern Australia. Protection Ecology 6 : 115-137. 339 ROTHSCHILD, M. Sc SCHOONHOVEN, L.M. (1977). Assessment of egg load by Pieris brassicae (Lepidoptera:Pieridae). Nature, Lond. 266: 352-355. RUTOWSKI, R L. (1979). The butterfly as an honest salesman. Anim. Behav. 27 : 1269-1270. RYGG T.D. (1966). Flight of Qscinella frit L. (Diptera: Chloropidae) females in relation to age and ovary development. Ent. exp. & appl. 9; 74-84. SAARIO, C.A., SHOREY, H.H. Sc GA3TON, L.K. (1970). Sex pheromones of Noctuid moths XIX. Effect of environ mental and seasonal factors on captures of males of Trichoplusia ni in pheromone baited traps. Ann. ent. Soc. An. 63: 667-672. SANDERS, C.J. (1975). Factors affecting adult emergence and mating behaviour of the eastern spruce budworm, Choristoneura fumiferana (Lepidoptera:Tortricidae). Can. Ent. 107: 967-977. SCHMIEGE, D.C. (1965). The fecundity of the black-headed budworm, Acleris variana (Fern.) (Lepidoptera: Tortricidae) in coastal Alaska. Can. Ent. 97: 1226-1230. SCHNEIDER, F. (1962). Dispersal and migration. A. Rev. Ent. 7j 223-242. SCHURR, K. Sc HOLD AW AY, F.G. (1970). Olfactory responses of female Ostrinia nubilalis (LepidopterarPyraustinae). Ent. exp. Sc appl. 13: 455-461. SCHUTTE, F. (1957). Untersuchungen iiber die populationsdynamik des Eichenwicklers (Tortrix viridana(L.)). Z - angew, Ent. 40: 1-36. SCHWAN, B. (1941). Laspeyresia nigricana - a pea pest that cannot easily be reached. Vaxtskyddsnotiser 1941: 41-45. SHAPIRO, A.M. (1982). Survival of refrigerated Tatochila butterflies (Lepidoptera:Pieridae) as an indicator of male nutrient investment in reproduction. Oecologia (Berlin) 53: 139-140. SHEPARD, M. , STERLING, W. Sc WALKER, J.K. (1972). Abundance of beneficial arthropods on cotton genotypes. Environ. Entomo 1, I_: 117-121. SHOREY, H.H. (1963). The biology of Trichoplusia ni (Lepidoptera:Noctuidae) II. Factors affecting adult fecundity and longevity. Ann, ent. Soc. Am. 56: 476-480. SHOREY, H.H. (1964a). The biology of Trichoplusia ni (Lepidoptera:Noctuidae) III. Response to the ovipos- ition substrate. Ain, ent. Soc. Am. 57: 165-170. SHOREY, H.H. (1964b). Sex pheromones of Noctuid moths II. Mating behaviour of Trichoplusia ni (Lepidoptera: Noctuidae) with special reference to the role of the sex pheromone. Ann, ent. Soc. Am. 57: 371-377. SHOREY, H.H. , ANDRES, L. A. Sc HALE, R. L. (1962). The biology of Trichoplusia ni (Lepidoptera:Noctuidae) I. Life history and behaviour. Ann, ent. Soc. Am. 55; 591-597. 340 SHOREY, H.H. Sc GASTON, L.K. (1970). Sex pheromones of Noctuid moths XX. Short range visual orientation by stimulated males of Trichoplusia ni. Ann, ent. Soc. Am. 63; 829-832. SHOREY, H. H ., MCFARLAND, S.U. Sc GASTON, L^K. (1968). Sex pheromones of Noctuid moths XIII. Changes in pheromone quantity, as related to reproductive age and mating history, in females of seven species of Noctuidae (Lepidoptera). Ann, ent. Soc. Am. 61: 372-376. SHOWERS, W.B., REED, G.L., ROBINSON, J.F. Sc DEROZARI, M.B. (1976). Flight and sexual activity of the european corn borer. Environ. Entomol. 5; 1099-1104. SMITH, J.W., STADELBACHER, E. A. Sc GANTT, C.W. (1976). A comparison of techniques for sampling beneficial arthropod populations associated with cotton. Environ. Entomol. 5: 435-444. SNOW, J.W., YOUNG, J.R. Sc JONES, R.L. (1970). Competitiveness of sperm in female fall armyworms mating with normal and chemosterilised males. J. econ, Ent. 63: 1799-1802. SO, J.S. (1975). Studies on the biology and control of the pea moth, Laspeyresia niqricana Steph. (Lepidoptera: Tortricidae). Unpublished D.I.C. Thesis, Imperial College, University of London. SOLOMON, J.D. (1967). Carpenterworm oviposition. J. econ. Ent. 60; 309. SOUTHWOOD, T.R.E. (1978). Ecological Methods with particular reference to the study of insect populations. Chapman and Hall. 2nd. ed. SOWER, L.L., SHOREY, H.H. Sc GASTON, L.K. (1970) . Sex pheromones of Noctuid moths XXI. Light/dark cycle regulation and light inhibition of sex pheromone release by females of Trichoplusia ni. Ann, ent. Soc. Am. 63; 1090-1092. SOWER, L.L., SHOREY, H.H. Sc GASTON, L.K. (1971). Sex pheromones of Noctuid moths XXV. Effects of temper ature and photoperiod on circadian rhythms of sex pheromone release by females of Trichoplusia ni. Ann, ent. Soc. Am. 64; 488-492. SPRADBERY, J.R. Sc SANDS, D.P.A. (1981). Larval fat body and its relationship to protein storage and ovarian development in adults of the screw-worm fly, Chrysomya bezziana. Ent. exp . & appl. 30: 116-122. STAMP, N.E. (1980). Egg deposition patterns in butterflies: why do some species cluster their eggs rather than deposit them singly? Am. Nat. 115: 367-380. STEINER, L.F. (1940). Codling moth flight habits and their influence on the results of experiments. J. econ. Ent. 33: 436-440. STENMARK, A. (1971a) . Studies on the pea moth (Laspeyresia nigricana Steph.) in central Sweden I Sc II. Meddn St. VaxtskAnst. 15;136, 1-47. 341 STENMARK, A. (1971b). Studies on the pea moth (Laspeyresia niqricana Steph.) in central Sweden III. Meddn St. VaxtskAnst. 15;138, 91-110. STENMARK, A. (1972) . Studies on the pea moth (Laspeyresia niqricana Steph.) in central Sweden IV - IX. Meddn St. VaxtskAnst. 15:149, 309-354. STENMARK, A. (1974) . Studies on the pea moth (Laspeyresia niqricana Steph.) in central Sweden. Meddn St. VaxtskAnst. 15;155, 451-475. STINNER R.E., BARFIELD, C.S., STIMAC U.L. Sc DOHSE, L. (1983). Dispersal and movement of insect pests. A. Rev. Ent. 28: 319-335. SWINGLE, H.S. (1928). Digestive enzymes of the oriental fruit moth. Ann, ent. Soc. Am. 21: 469-475. TAYLOR, F. (1981). Ecology and evolution of physiological time in insects. An. Nat. 117: 1-23. TAXLOR, L.R. (1951). An improved suction trap for insects. Ann, appl. Biol. 38: 5 82-591. TAYLOR, L.R. (1955). The standardisation of airflow in insect suction traps. Ann, appl. Biol. 43: 390-408. TAYLOR, L.R. (1961). Aggregation, variance and the mean. N ature, Lond♦ 189: 732-735. TAYLOR, L.R. (1963). Analysis of the effect of temperature on insects in flight. J, Anim. Ecol. 32; 99-112. TAYLOR, O.R. jr. (1967). Relationship of multiple mating to fertility in Atteva punctella (Lepidoptera: Yponomeutidae). Ann, ent. Soc. An. 60 : 583-590. TAYLOR, T . A. (1965). Observations on the bionomics of Laspeyresia ptychora Meyr. (Lepidoptera:Eucosmidae) infesting cowpea in Nigeria. Bull, ent. Res, 5 5 ; 761-773. THIBOUT, E. (1974). Influences respectives de la plant- hote et de la copulation sur la longevite la ponte la production ovarienne et la fertilite de femelles d'Acrolepia assectella Zell. (Lepidoptera:Piute11idae) . Ann, zool. Ecol. anim. 681-96. THIBOUT, E. (1975). Causal analysis of the inhibition of sexual receptivity and of the influence of a second copulation on the reproduction by Acrolepia assectella (Lepidoptera:Plutellidae). Ent. exp . Sc appl. 18: 105-116. THIBOUT, E. Sc RAHN, R. (1972). A study in the variation in volume and fertilising potency of successive sperm- atophores of Acrolepia assectella (Lepidoptera: Plutellidae) . Ent. exp. Sc appl. 15: 443-454. THOMAS, A.W., BORLAND, S . A. Sc GREENBANK, D.O. (1980). Field fecundity of the spruce budworm (Lepidoptera: Tortricidae) as determined from regression relation ships between egg complement, fore wing length and body weight. Can. J. zool. 58: 1608-1611. THOMPSON, L.S. & SASTDERSON, J.B. (1977). Pea moth control in field peas with insecticides and the effect on crop yield. J. econ. Ent. 70: 518-520. 342 THOMPSON, W.R. (1946) . A Catalogue of the Parasites and Predators of Insect Pests. Sect-ion 1. Parasite Host Catalogue. Part 7. Parasites of the Lepidoptera. Imperial Agricultural Bureaux, Institute of Entomology. THORNHILL, E.W. (1978). A motorised insect sampler. Pans 24: 205-207. TOTTMAN, D.R., MAKEPEACE, R.J. Sc BROAD, H. (1979). An explanation of the decimal code for the growth stages of cereals, with illustrations. Ann, appl. Biol. 93: 221-234. TRAYNIER, R.M.M. (1970). Sexual behaviour of the Mediterr anean flour moth, Anagasta kuhniella: some influences of age, photoperiod and light intensity. Can. Ent. 102: 534-540. TRAYNIER, R.M.M. (1975). Field and laboratory experiments on the site of oviposition by the potato moth Phthorimaea operculella (zell.)(Lepidoptera: Gelechiidae). Bull, ent. Res. 65: 391-398. TRUMAN, J.W. (1973). Temperature sensitive programming of the silkmoth flight clock: a mechanism for adapting to the seasons. Science, N.Y. 182: 727-729. TUOVINEN, T. (1981). Prognosis of injury by Cvdia nigricana (Lepidoptera:Tortricidae) using "the oecos pea moth monitoring system": A preliminary report. Acta Entomol, Fenn. 40: 35-38. TURNBULL, A.L. Sc NICHOLLS, C.F. (1966). A "quick trap" for area sampling of arthropods in grassland communities. J. econ. Ent. 59: 1100-1104. TYNDALE-BISCOE, M. Sc HUGHES, R.D. (1969). Changes in the female reproductive system as age indicators in the bushfly Musca velustissima Wlk. Bull, ent. Res. 59: 129-141. USHER, M.B. (1969). Some properties of the aggregations of soil arthropods: Collembola. J. Anim. Ecol. 38: 607-622. USHER, M.B. (1971). Properties of the aggregations of soil arthropods, particularly Mesostigmata (Acarina). Oikos 22; 43-49. VOLNEY, W. JAN A., WATERS, W.E., AKERS, R.P. Sc LIEBHOLD, A.M. (1983). Variation in spring emergence patterns among western Choristoneura spp. (Lepidoptera:Tortricidae) populations in southern Oregon. Can. Ent. 115: 199-209. WALL, C. (1984). The Exploitation of insect Communication by Man - Fact or Fantasy? Proc. Xllth. Symp. R. ent. Soc. Lond. (ed. Lewis, ~T. ) pp. 379-400. WALL, C., GREENWAY, A.R. Sc BURT P.E. (1976). Electro- antennographic and field responses of the pea moth, Cvdia nigricana, to sex attractants and related compounds. Phys. Ent. 1: 151-157. WALL, C. Sc PERRY, J.N. (1978). Interactions between pheromone traps for the pea moth, Cvdia nigricana (F.) . Ent. exp. Sc appl. 24: 155-162. 343 WALL, C. & PERRY, J.N. (1980) . Effect of spacing and trap number on interactions between pea moth pheromone traps. Ent. exp. Sc appl. 28; 313-321. WALL, C. Sc PERRY, J.N. (1981) . Effect of dose and attract- ant on interactions between pheromone traps for the pea moth, Cydia nigricana (F.) . Ent. exp. Sc appl. 30: 26-30.~ WALL, C. Sc PERRY, J.N. (1982). The behaviour of moths responding to pheromone sources in the field: a basis for discussion. Les Collogues de l'INRA _7_: 171-188. WALL, C. , STURGEON, D.M. GREENWAY, A.R. Sc PERRY, J.N. (1981). Contamination of vegetation with synthetic sex- attractant released from traps for the pea moth, Cydia niqricana (F . ) . Ent, exp. Sc app 1. 30: 111-115. WALOFF, N., NORRIS, N.J. Sc BROADHEAD, E.C. (1948). Fecundity and longevity of Ephestia elutella Hubner (Lepidoptera: Phycitidae). Trans. R. ent. Soc, Lond. 99: 245-268. WATSON, T.F., LINDSEY, M.L. &SLOSSER, J.E. (1973). Effect of temperature, moisture and photoperiod on termin ation of diapause in the pink bollworm. Environ. Entomol. 2: 967-970. WEARING, C.H., CONNOR, P.J. Sc AiBLER, K.D. (1973). Olfactory stimulation of oviposition and flight activity of the codling moth, Laspeyresia pomonella, using apples as an automated olfactometer. N.Z. Jl.-Sci. 16: 697-710. WEARING, C.H. Sc HUTCHINS, R.F.N. (1973). oc-F arnesene, a naturally occurring oviposition stimulant for the codling moth, Laspeyresia pomonella. J. Insect Physiol. 19: 1251-1256. WEBB, J.W. Sc BERISFORD, C.W. (1978) . Temperature modific ation of flight and response to pheromones in Rhyacionia frustrana. Environ. Entomol. 7; 278-280. WHEATLEY, G . A. Sc DUNN, J.A. (1962). The influence of diapause on the time of emergence of the pea moth, Laspeyresia niqricana Steph. Ann, appl. Biol. 50: 609-611. WHITE, L.D., HUTT, R.B. Sc BUTT, B. A. (1973). Field dispersal of laboratory reared fertile female codling moths. Environ. Entomol. 2_: 66-69. WHITE, M.R., AMBORSKI, R.L., HAMMOND, A.M. jr. Sc AMBORSKI, G.F. (1973). Ultrastructural changes associated with pheromone production in the sex pheromone gland of Diatraea saccharalis. J. Insect Physiol. 19: 1933-1940. WHITTAKER, J.B. (1965). The distribution and population dynamics of Neophilaenus lineatus (L.) and N. exclamatignis (Thun.) (Homoptera:Cercopidae) on Pennine moorland. J. Anim, Ecol. 34: 277-297. WIKLUND, C. Sc FA3ERSTROM, T. (1977). Why do males emerge before females? A hypothesis to explain the incidence of protandry in butterflies. Qecoloqia (Berlin) 31: 153-158. 344 WIKLUND, C. Sc SOLBRECK, C. (1982). Adaptive versus incidental explanations for the occurrence of pro- tandry in a butterfly, Leptidea sinapis L. Evolution 36: 56-62. WILLIAMS, C.B. (1957). Insect migration. A. Rev, Ent. 2j 163-179. WILSON, L.F. (1959). Branch "tip" sampling for determining abundance of spruce budworm egg masses. J, econ. Ent. 52; 618-621. WILSON, L.T., GUTIERREZ, A.P. Sc HOGG, D.B. (1982). Within plant distribution of cabbage looper, Trichoplusia ni (Hubner) on cotton: development of a sampling plan for eggs. Environ. Entomol. 11: 251-254. WRIGHT, D.W. Sc GEERING, Q. A. (1948). The biology of and control of the pea moth, Laspeyresia nigricana Steph. Bull, ent. Res. 39: 57-84. WRIGHT, D.W., GEERING, Q. A. Sc DUNN, J. A. (1951). Varietal differences in the susceptibility of peas to attack by pea moth, Laspeyresia nigricana Steph. Bull, ent. Res. 41 : 663-677. ZADOKS, J.C., CHANG, T.T. Sc KONZAK, C.F. (1974). A decimal code for the growth stages of cereals. weed. Research 14: 415-421. ZAHER, M. A. Sc LONG, D.B. (1959). Some effects of larval population density on the biology of Pieris brassicae L. and Plusia gamma L. Proc. R. ent. Soc. Lond. (A) 34: 97-109. ZAHER, M. A. Sc MOUSSA, M. A. (1961). Effects of population density on Prodenia litura (Lepidoptera:Noctuidae). Ann, ent. Soc. An. 54: 145-149. 345 APPENDICES Appendix I . D-Vac. Calibration Appendix II. List of samples taken and numbers of male and female C.nigricana in those samples Appendix III. The effect of pea plant presence on the attractiveness of the natural pheromone of C.nigricana in the field Appendix IV. Infestation levels in pea crops Appendix V. Analysis of percentage mating among female populations of c.nigricana 346 Appendix la. D-Vac. Calibration Comparison of sweeping with conventional D-Vac. head versus use of trolley attachment in crops with tramlines. All insects were counted. Counts of insect taxa given. CROP Wheat Wheat , Peas Peas D-Vac. SAMPLING MODE Sweeping Trolley Sweeping Trolley attachment CL ttachment REPLICATE 1 2 1 2 1 2 3 1 2 3 INSECT CATEGORY MICROLEPIDOPTERA 4 1 5 1 0 0 0 0 0 0 DIPTER.-\ >7mm. 1 0 0 0 4 2 1 2 1 0 DIPTERA 5-7mm. 16 3 13 14 3 4 5 4 2 3 DIPTERA 3-5mm. 16 7 5 10 11 4 3 4 5 7 Opomvza sp. 10 14 2 19 16 18 1 6 15 1 HYMENOPTERA >7mm. 0 1 3 2 5 4 2 2 5 2 HYMENOPTERA 5-7mm. 0 0 0 0 6 3 4 2 6 1 HYMENOPTERA 3-5mm. 7 10 4 7 8 5 5 6 8 5 COLEOPTERA 3-5mm. 0 5 8 1 3 0 3 0 1 3 COLEOPTERA <3mm. 3 0 0 0 2 0 0 0 0 1 Sitona sp. 0 0 0 0 387 494 466 68 46 75 HETEROPTERA >5mm. 0 0 0 2 0 0 0 0 0 0 HETEROPTERA <5mm. 0 0 0 1 2 1 2 2 0 2 HOMOPTERA >5mm. 0 0 0 0 0 0 0 0 0 0 HOMOPTERA <5mm. 0 0 0 0 0 0 0 1 0 0 SPIDERS > 5mm. 0 0 1 1 0 0 0 0 0 0 SPIDERS < 5mm. 0 0 0 1 0 0 0 0 0 0 LARVAE 1 1 0 0 1 0 0 0 1 0 CROP Beans Beans D-Vac. SAMPLING MODE Sweeping Trolley attachment REPLICATE 1 2 3 4 1 2 3 4 INSECT CATEGORY MICROLEPIDOPTERA 0 T 0 0 0 0 0 0 DIPTERA > 7mm. 1 3 0 3 0 3 0 1 DIPTERA 5-7mm. 8 6 3 2 0 6 2 1 DIPTERA 3-5mm. 23 b 6 10 17 9 4 1 Opomyza sp. 1 7 3 2 0 3 0 5 HYMENOPTERA >7mm. 0 0 0 0 0 0 1 2 HYMENOPTERA 5-7mm. 1 0 2 2 0 3 2 3 HYMENOPTERA 3-5mm. 0 6 5 7 5 4 4 5 COLEOPTERA 3-5mm. 0 0 1 0 6 1 1 1 COLEOPTERA <3mm. 3 0 1 1 2 3 0 1 Sitona sp. 0 185 117 33 0 115 94 44 HETEROPTERA > 5mm. 0 1 0 2 1 1 0 0 HETEROPTERA <5mm. 2 0 0 2 3 0 0 0 HOMOPTERA 3> 5mm. 2 0 0 0 0 0 0 0 HOMOPTERA < 5mm. 0 1 0 2 0 0 0 0 SPIDERS > 5mm. 0 0 0 0 0 0 0 0 SPIDERS < 5mm. 0 0 0 0 1 2 0 0 LARVAE 1 0 0 0 0 1 0 0 347 Appendix lb. D-Vac. Calibration Comparison of sweeping with conventional D-Vac. head versus use of trolley attachment in crops with tramlines. Crop Number of Insect t Probability categories compared at n-ldf. Wheat 14 0.511 NS Peas 13 1.955 NS Beans 17 0.289 NS Data from replicates pooled (Appendix la) 348 Appendix lc. D-Vac. Calibration Comparison of sweeping with conventional D-Vac. versus quantitative area sampling with conventional D-Vac. head along grassbanks. All insects counted. Counts of insect taxa and totals given. CD O 0 i3 3 £ o > CD b H 3 0 ts H & 0 3 3 t s CD O H i-1 3 3 ts CD P 3 CD CD id q CD 03 3 C—J b- b q Data adjusted Data unadjusted Efficiency Factor H- CD 03 0 «d q b - H- O ft CD Hi CD 03 for sample length b X for sample length CD H- b CD q o ft O q 03 H- 3 h-1 t Probability t Probability x C • E.) Range CD 3 l 03 < P i W 03 1 < tr CD 0 INSECT CATEGORY at n-ldf. at n-ldf. "—' CD CD H i hh O M 3 CD D MICROLEPIDOPTERA 2.965 + <0.05 1.477 + NS O 3 3 3 b 03 1 b 3 CD 03 CD £ < DIPTERA j> 7mm. 1.077 + NS 0.465 + NS F 3 03 . CD CD CD CD O tr CD 0 DIPTERA 5-7mm. 3.879 + <0.01 1.036 NS 4.454 + 1.147 1.25 - 10.00 CD iQ CD hh 03 P o CD b Qj DIPTERA 3-5mm. 2.4 91 + <0.05 2.389 - <0.05 3.380 + 0.700 0.71 - 6.33 0 b- S' 03 b 3 3 n HYMENOPTERA 5-7mm. 1.090 + NS 0.818 NS 1.979 + 0.313 1.25 - 2.50 td CD q x' 0 d! h-1 H HYMENOPTERA 3-5mm. 4.623 + <0.01 1.671 NS 3.974 + 0.897 1.00 - 8.75 b Hib H- £ H- CD + CD 3 H- tr l COLEOPTERA 3-5mm. 1.275 + NS 0.499 NS 6.289 + 2.628 2.00 - 13.33 CD H- 3 id q b ft 3 HETEROPTERA > 5mm. 1.137 + q q CD u> 0.573 + NS 1.482 NS 0.460 0.50 - 2.50 3 —- 03 H- £ CD q HETEROPTERA <5mm. 0.367 - NS 4.835 - <0.01 2.563 + 0.832 1.25 - 5.00 CD q H- 0 b- < 3 3 O CD q 0 0 HQMOPTERA ca 3mm. 3.928 + < 0.01 3.746 - <0.01 2.623 + 0.395 0.67 - 3.71 ft a ft q q 3 3 I • CD 03 b- < SPIDERS <5mm. 0.022 - NS 1.639 NS ft < 0 CD CD CD 0 3 ALL INSECTS >7mm. 2.675 + < 0.05 0.113 + NS 4.750 + 1.888 2.00 - 10.00 3 q H- fD 3 < b- ALL INSECTS 5-7mm. 5.262 + <0.01 1.281 NS 4.650 + 1.222 1.25 - 10.00 3 3 03 CD 0 CD 3 3 A L L INSECTS 3-5mm. 7.806 + <0.001 3.504 - <0.01 2.891 + 0.357 1.36 - 4.32 03 q CD ■S s; O H - h-1 ALL INSECTS 8.593 + <0.001 4.370 - <0.01 3.063 + 0.310 1.36 - 4.14 ts CD CD 0 CD CD q 3 o 3 0 CD 1 q H• S' H < Data adjusted for sample length/ is where counts from quantitative b- 3 b- CD X id 3 O 0 sampling are multiplied by a factor of 5. • id 1 • h-j < 0 id CD q Efficiency factor = quantitative use,count x 5 , • b O CD —’ CD • CD sweeping/ count • CD a q S' means (-S.E.) of efficiency factors for 8 replicates/ where positive CD CD < b CD CD catches were recorded. d b 03 3 03 350 Appendix le. D-Vac. Calibration Comparison of D-Vac. sampling with trolley attachment versus quantitative area sampling with conventional D-Vac. head, in wheat crop tramlines. All insects were counted. Counts of insect taxa and totals given. CTi n PJ ^ 1-3 P' < O > QJ f t + PJ CD CD 0 P X H f t — tr PJ H 3 P CD O PJ h d CP P CD P c O O CD p Pj P H M d h CP h d H- PJ 3 0 H- HH- f t CD 1—1 H P CP Data adjusted Data unadjusted Efficiency Factor O P X PJ H- P CD C 0 f t for sample length for sample length O H CD (+ £ pj P H CD P • U) 1 p j PH CP CP CD < CD f t o • t Probability t Probability x (+ S.E. ) Range h pj PJ H- H H INSECT CATEGORY at n-ldf. at n-ldf. 0 f t f t O p — c PJ O u h 1 CD 0 f t 1 1 Cydia nicjricana 2.499 + NS 1.580 + NS W CO H H < < CD 0 O < PJ pj DIPTERA 5-7mm. 2.325 + NS 5.323 - 0.01 1.512 + 0.501 0.27 - 3.85 PJ iQ P l-h P CD 0 0 • DIPTERA 3-5mm. 0.330 NS 4.158 - 0.01 1.372 + 0.580 0.27 - 3.75 0 CD P 0 CP • PJ 3 H PJ Opomyza sp. 5.007 + 0.01 0.432 - NS 5.464 + 1.555 1.54 - 11.00 Cf £ H CP o f t X CD A H- CD QJ pj HYMENOPTERA 5-7mm. 0.313 + NS 3.795 - 0.05 2.122 + 0.529 1.11 - 3.75 h h P f t PJ 3 H CD + UJ PJ PJ P H- HYMENOPTERA 3-5mm. 3.937 + 0.05 0.750 - NS 4.750 + 1.250 1.00 - 10.00 PJ P CP H cr r+ H 0 H f t Qj H- H ALL INSECTS >7mm. 1.934 + NS 0.575 + NS 3 Hi H- h 3 P pj CD f t QJ P iQ r t ALL INSECTS 5-7mm. 6.349 + 0.01 6.563 - 0.01 2.288 + 0.282 1.48 - 3.20 p f t H OJ § l—' H- f t H P f t H H- £ 0 ALL INSECTS 3-5mm. 2.763 + 0.05 2.251 - NS 3.130 + 0.977 0.85 - 6.43 • PJ CP H H- P H P P CD < P iQ f t ALL INSECTS 4.134 + 0.01 3.790 - 0.05 2.663 + 0.507 1.35 - 4.43 cp 0 CD (D PJ ft H CP £ 0 cp c • H- f t 3 CP H H Data adjusted for sample length, is where counts from quantitative CD f t CD PJ 0 d PJ H sampling are multiplied by a factor of 5. pj n O I-1 d P pj 0 CD Efficiency factor = quantitative use, count x 5 PJ r t p KJ f t f t o < trolley attachment, count P> h p J CD PJ 0 H P f t Means (- S.E.) of efficiency factor for 6 replicates, where positive H P H H H c Q H- PJ catches were recorded. # CD 0 n P ^ iQ P p J CD H PJ 3 P CD H CD d PJ P H- f t D f t X CD 1 H < 1—J pj CD 0 WEEK 123456789 10 11 WEEK sae Cmrdehr, 1980. Cambridgeshire, Estate, D-Vac. samples, emergence site, wheat field P, Childerley Childerley P, field wheat site, emergence samples, D-Vac. Appendix Ila. List of samples and numbers of moths taken taken moths of numbers and samples of List Ila. Appendix \> *o "o *o "o *0 *o *D *o "o "o *o "o Po *o *o *o 04 of of Of O-f Of Of Of Of Of Of Of Of Of Of 04 Of o+ Of Of Of Of - - N O ^ fO (N H oooouooooooouooouuoououuuouuououoouuoouooooooo II I I III 1 1 I I I 1 I 1 I 1 1 I I I II I I II II I I I II II I I II I i iii ii l H 1 C' C O* r—H C"'* O'* CO O r I • I I II III o o.-HCNiroTi m (>i in ^ II I II I I III I < —I i—n I I I i i I v o t ^ - c o c n o r H c M m —I I — | ( — I r - I C N O J C M C M I I I II i—1 I I III N C II I 353 Appendix I lb. List of samples and numbers of moths taken D-Vac. samples, pea field J, Childerley Estate, Cambridgeshire, 1980. WEEK 1 2 3 4 5 6 7 8 9 10 11 b CH- SEX cf$ $ 40 40 o'? Appendix Iid. List of samples and numbers of moths taken Kite net samples, pea field J, Childerley Estate, Cambridgeshire, 1980. W E E K 1 2 3 4 W E E K 1 2 3 4 SEX d" ^ c f ^ d 1 $ SEX ( f $ cT $ c f ? ^ $ _ HI - _ PI H 2 - - P 2 -- H 3 - P 3 - H 4 - P 4 - H 5 P 5 H 6 - P 6 - H 7 -- P 7 - - H 8 - P 8 - H 9 - P 9 — H I 0 - P 1 0 - H l l -- P l l -- H 1 2 - P 1 2 - H 1 3 - P 1 3 - H 1 4 - P 1 4 - H 1 5 - P 1 5 - H 1 6 - P 1 6 - H 1 7 -- P 1 7 -- H 1 8 - P 1 8 - H 1 9 P 1 9 H 2 0 -- P 2 0 — _ H 2 1 P 2 1 H 2 2 - P 2 2 - H 2 3 P 2 3 H 2 4 - - P 2 4 — _ H 2 5 P 2 5 H 2 6 -- P 2 6 _ ' _ H 2 7 P 2 7 H 2 8 - P 2 8 - C l C 2 _ — C 3 — C 4 - _ C 5 _ C 6 _ C 7 _ C8 _ C 9 — CIO — C l l C 1 2 C 1 3 _ C 1 4 — C15 C 1 6 C 1 7 C 1 8 __ C19 C20 C21 356 Appendix lie. List of samples and numbers of moths taken D-Vac. samples, emergence site, wheat field WAl, Shimpling Park Farm, Suffolk, 1981. 357 appendix Ilf- List of samples and numbers of moths taken D-Vac. samples, pea field PAl, Shimpling Park Farm, Suffolk, 1981. 358 Appendix Ilg . List of samples and numbers of moths taken Kite net samples, emergence site, wheat field WAl, Shimpling Park Farm, Suffolk, 1981. WEEK 5 6 7 SEX d £ d j d 5 HI 9 - 3 1 - 1 H 1 2 1 4 - 3 8- H l 7 14_2 17-3 9- H 3 0 11 - H 3 3 8 5 - 1 7 H 3 6 8 - 9 - G 4 14-1 10-1 7- G 8 30-1 19-1 20-3 G 2 0 1 1 - 3 1 1 - 2 G 2 7 7-1 10-1 44-2 P 3 6 - 1 1 5 - P 5 8 - 1 1 4 - 5 - P 9 2 5 - 6 - P 1 4 21 - 6 - P 1 9 1 5 - 9 - P 2 1 1 0 - 2 3 - P 2 6 1 - 6 - 1 2 5 - 1 P 2 8 11 - 2-1 P 3 1 1 9 - 1 3 - 2 P 3 4 1 4 - 5 - 2 C 6 8-2 18-3 7-2 C 7 3 6 - 2 2 3 - 1 CIO 2 9 - 1 2 3 - C l l 7-1 13- 39- C 1 5 5 - 1 1 7 - 1 C l 6 8-2 10-1 C 22 26-3 5-3 19-3 C 2 3 9 - 7 - 2 0 - 2 C 2 4 22-1 7-2 19- C 2 5 1 8 - 12-1 1 8 - 2 Appendix nh. List of samples and numbers of. moths taken Kite net samples, pea field PAl, Shimpling Park Farm, Suffolk, 1981. WEEK 5 6 7 SEX d ? d- ? cf HI 1 - _ 1 2 - 5 H 4 2 1 - 4 4 - 3 3 - 4 G 8 1-1 3 - 1 0 - 1 9 B 1 0 1-1 3 - 2 2 2 - 4 5 P 3 -1 2 - 1 3 - 7 P 6 -1 8-6 1 0 - 3 P 7 - - 8-6 P 9 -1 1 1 - 5 2 6 - 5 C l l 1 6 - 1 1 1 - 5 12-8 C l 2 3 - 2 1- 11-8 C 1 3 5 - - 4 - 6 C 1 4 2 - 2 - 4 4 - 9 359 Appendix IIj_. List of samples and numbers of moths taken D-Vac. samples, emergence site, wheat field WA2, Shimpling Park Farm, Suffolk, 1982. 360 Appendix Ilk. List of samples and numbers of moths taken D-Vac. samples, pea field PA2, Shimpling Park Farm, Suffolk, 1982. 361 Appendix Ilm. List of samples and numbers of moths taken D-Vac. samples, pea field PB2, Shimpling Park Farm, Suffolk, 1982. 362 Appendix Ilia The Effect of Pea Plant Presence on the Attractiveness of the Natural Pheromone of C.niqricana. Experimental proceedures described in Section 2.1.11. Experiment 1 Treatment A: (E,E)-8 ,10-12: Ac. with a selection of fresh pea plant material at all phenological stages. Treatment B : (E,E)-8 ,10-12:Ac. with no pea plant material. Sex-attractant traps provided with sticky inserts on days 1 to 6 / and water traps on days 7 to 10. Results show catch during activity period. DAY'S SITE I II Treatment Catch Treatment Catch 1 A 42 B 32 2 B 27 A 54 3 B 3 A 18 4 A 45 B 27 5 B 41 A 68 6 A 10 B 8 7 A 231 B 146 8 B 200 A 226 9 B 52 A 84 10 A 135 B 112 AN OVA (log' transformed data) S ource SS df MS F-value Squares 3.2578 4 0.8145 32.7088 p < 0.01 Areas in Squares 0.0971 5 0.0194 0.7799 NS Days in Squares 1.1201 5 0.2240 8.9968 P < 0.05 Treatment 0.2519 1 0.2519 10.1165 p <0.05 Error 0.0996 4 0.0249 Total 4.8265 19 The higher within-treatment variance introduced by this approach is accounted for as a day effect. 363 Appendix IIlb The Effect of Pea Plant Presence on the Attractiveness of the Natural Pheromone of C.niqricana Experimental proeeedures described in Section 2.1.11. Experiment 2 Treatment A: (E, E)-8 ,10-12sAc. with fresh pea plant material at old reproductive stages. Treatment B : (E, E)-8 ,10-12:Ac. with fresh pea plant material at young reproductive stages. Results show catch during activity period. DAY'S SITE I II Treatment Catch Treatment Catch 1 B 23 A 16 2 A 3 B 11 3 A 2 B 13 4 B 23 A 9 ANOVA (log transformed data) S ource SS df MS F-value Squares 0.0156 1 0.0156 0.5016 NS Areas in Squares 0.0824 2 0.0412 1.3248 NS Days in Squares 0.4772 2 0.2386 7.6720 NS Treatment 0.4715 1 0.4715 15.1608 NS Error 0.0311 1 0.0311 Total 1.0778 7 ANOVA for realisation of Crossover design (log transfomed data) Source SS df MS F-value S ites 0.0824 1 0.0824 5.2821 NS Days 0.4928 3 0.1643 10.5321 NS Treatments 0.4715 1 0.4715 30.2244 p < 0.05 Error 0.0311 2 0.0156 Total 1.0778 7 364 Appendix IVa. Infestation levels in pea field PAl, 1981, and subsequent moth populations in emergence site WA2, 1982, Shimpling Park Farm Infestation levels and numbers of larvae in three areas of pea field PAl. Infestation levels based on four samples of fifty plants in each of three areas. Moth populations at three D-Vac. sample points within the wheat crop of emergence site WA2, corresponding to the position of infestation samples the previous season. INFESTATION SAMPLE 1981 NORTH c e n t r a l SOUTH % + % Pod Infestation (-S.E.) 51.75 t 1.97ab 46.63 ± 2.44a 60.20 t 2.30b Number of Pods 1607 1692 1347 * % Infested Pods with two or 29.22 ± 2.11c 26.01 ± 1.47c 34.24 t 3.87c more Larvae (is.E.) Number of Infested Pods 833 787 810 Number of Larvae per Plant: Total Population (is.E.) 5.65 ± 0.46d 5.13 t 0.31d 5.74 ± 0.41d 4 ^ and 5 ^ ^ instars (ts.E.) 4.94 ± 0.39e 4.31 t 0.25e 4.80 ± 0.38e j.th+ -[nstars (ts.E. ) 3.44 t 0.35f 3.07 t O.llf 3.03 ± 0.37f D-VAC. SAMPLE 1982 t P2 C8 P6 MALES Total Population 24g 55 17g Population below P.A.10 15g 46 16h Population below P.A.7 12 j 36 10J FEMALES Total Population 8k 30 8k Population below P.A.10 6m 22 6m Population below P.A.7 6np 14n 5p ADULTS Total Population 32r 85 25r Population below P.A.10 21s 68 22s Population below P.A.7 18t 50 15t * Percentages are untransformed values. t 5th instars includes both those in pods and those that have left pods 1 Totals are for the seven weeks 1,2,3,4,7, 8 & 9. Means and counts followed by the same letter are not significantly different below p = 0.05. 365 Appendix IVb Variance ratio, F, from analysis of variance of percentage pod damage (arc-sin transformed) between truss levels and between sub-samples, Pea field PAl, Shimpling Park Farm, Suffolk, 1981 NORTH All truss levels (1 - 9) AN OVA Source F-value Truss level 4.098 p <0.01 8,24df Sub-sample 0.431 NS 3,24df Truss levels 1 - 8 ANOVA Source F-value Truss level 1.601 NS 7,21df Sub-sample 1.525 NS 3,21df Truss levels 1 - 6 ANOVA Source E-value Truss level 2.183 NS 5,15df Sub-s ample 4.478 p <0.05 3, 15 df CENTRE All truss levels (1 - 10) ANOVA Source F-value Truss level 11.509 p < 0.01 9,27df Sub-s ample 3.384 p < 0.05 3,27df Truss levels 1 - 8 ANOVA Source F-value Truss level 6.396 p < 0.01 7,21df Sub-sample 1.863 NS . ' 3,21df Truss levels 1 - 6 ANOVA Source F -value Truss level 2.046 NS 5,15df Sub-s ample 2.155 NS 3,15df SOUTH All truss levels (1 - 10) ANOVA Source F-value T m s s level <1.0 NS 9,27df Sub-s ample 1.791 NS 3,2 7 df Truss levels 1 - 8 ANOVA Source F-value Truss level 1.428 NS 7,21df Sub-sample <1.0 NS 3,21df Truss levels 1 - 6 ANOVA Source F-value Truss level <1.0 NS 5,15df Sub-s ample 1.806 NS 3, 15df 366 Appendix IVc Variance ratio, F, from 3-level analysis of variance of the number of larvae in each instar/ at truss levels, in areas, Pea field PAl, Shimpling Park Farm, Suffolk, 1981. Level A 3 areas, (North, central & South). B 10 Truss levels C 5 instars (5^ instars includes both larvae in pods, and those that have vacated pods). ANOVA Source F-value A’ 2 . 1 5 7 NS 2,oo df B 1 9 3 . 4 6 9 p < 0 . 0 1 9 ,oo d f C 5 0 8 . 6 5 0 p < 0 . 0 1 4 ,oo d f A X B 0.639 NS 20,oo df A X C 2.6 06 p < 0.01 8, oo df B X C 7 4 . 8 5 4 p < 0 . 0 1 4 0, oo df A X B X C 0 . 8 4 1 NS 6 0 , o o d f Appendix IVd Correlation between number of larvae at a truss level and length of exposure of, or number of pods at, that truss level, Pea field PAl, Shimpling Park Farm, Suffolk, 1981 NORTH R-squared r Exposure after week 6 78.37% 0.89 p < 0. 01 7df Exposure after week 7 53.46% 0.73 p <0.05 7df Number of pods 97.62% 0.99 p < 0.001 7df CENTRAL Exposure after week 6 73.54% 0.86 p <0.01 7df Exposure after week 7 48.15% 0.69 p < 0.05 7df Number of pods 94.77% 0.97 p <0.001 7df SOUTH Exposure after week 6 77.18% 0.88 p < 0.01 7df Exposure after week 7 52.82% 0.73 p <0.05 7df Number of pods 99.26% 0.99 p <0.001 7df 367 Appendix IVe Table of 'd' and associated probability for comparison of percentage seed damage within and between fields, Pea fields Shimpling Park Farm, Suffolk, 1982 . Pea field PA2 Number Number of Area of Seeds Damaged Seeds i Nearest to Emergence Site 2304 352 ii Central 2754 390 iii Furthest from Emergence Site 2911 341 Pea field PB2 Area i Nearest to Emergence Site 1932 340 ii Central 1493 218 iii Furthest from Emergence Site 1792 444 where n = number of seeds a = number of damaged seeds a9 n2 k, - - 1 k0 = - 2 h - "-1 + 1 n^ 2 n2 nl + n2 PA2 PB2 i i i i i i i i i i i i PA2 i - i i 1.10 NS - i i i 3 .8 0 * * * 2 .8 0 * * - PB2 i 2 .0 2 * 3 .1 6 * * 5.7 7*** — i i 0.59 NS 0.36 NS 2 .7 4 ** 2 .3 6 * i i i 7 . 6 3 * * * 9 .0 1 * * * 1 1 .7 0 *** 5.38*** 7.25*** 368 Appendix Va. Analysis of variance of percentage of female C.niqricana unmated in crop regions of emergence sites, Shimpling Park Farm, 1981 and 1982 WHEAT FIELD WAl, 1981 Week 2 & 3 4 5 6 7 8 9 10 Number of Females Perimeter 2 6 2 28 22 5 - 2 Centre 3 7 1 102 28 12 - 4 Percentage Unmated Perimeter 50.0 66.7 100 42.9 72.7 40.0 - 50.0 Centre 0 71.4 100 54.9 71.4 41.7 0 ANOVA (arc-sin transformed data) for weeks 2-8, 10. Source SS df MS F value Crop areas 460.58 1 460.58 1.74 NS Weeks 6636.44 6 1106.07 4.17 NS Error 1592.99 6 265.50 Total 8690.01 13 WHEAT FIELD WA2, 1982 Week 1 2 3 4 5 6 7 8 Number of Females Perimeter 1 1 3 14 - 6 1 Centre 0 4 8 42 - 13 3 Percentage Unmated Perimeter 100 0 66.7 78.6 - 33.3 100 Centre - 50.0 75.0 54.8 - 46.2 66.7 ANOVa (arc-sin transformed data) for weeks 2 - 4, 7, 8. Source SS df MS F value Crop areas 6.24 1 6.24 < 1 NS Weeks 2915.55 4 728.89 1.64 NS Error 1776.22 4 444 06 Total 4698.01 9 369 Appendix Vb. Comparison of percentage unmated females in crop area of wheat field emergence sites/ Shimpling Park Farm, Suffolk, 1981 and 1982 Number of Number of Females (n) Unmated Females (a) Wheat crop, 1981 224 (n1) 125 (aj_) Wheat crop, 1982 96 (n2) 56 (a2) Total 320 (n) 181 (a) a k-. = ai k0 t 2 k = — 1 2 n ni n 2 a - *>■• d = 0.413 NS at p = 0.05. 370 Appendix Vc. Analysis of variance of percentage of female C.nigricana unmated in vegetation categories surrounding emergence site/ Shimpling Park Farm, 1981 Week 2 & 3 4 5 6 7 8 9 10 Number of Females Hedgerow 2 8 20 44 13 10 - 0 Understorey 4 7 2 65 10 11 - 3 Grassbank 3 1 0 14 0 2 - 0 Percentage Unmated Hedgerow 50.0 37.5 40.0 18 2 15.4 10.0 - Understorey 50.0 42.9 50.0 32.3 40.0 0 - Grassbank 33.3 0 50.0 50.0 - Hedgerow and Understorey ANOVA (arc-sin transformed data) for weeks 2-8. Source SS df MS F value Category 21.07 1 21.07 < 1 NS Weeks 1692.08 5 338.42 4.94 NS Error 342.68 5 68.54 Total 2055.83 11 Hedgerow, Understorey and Grassbank ANOVA (arc-sin transformed data) for weeks 2 & 3, 4 6, 8. Source SS df MS F value Category 4.98 2 2.49 < 1 NS Weeks 753.03 3 251.01 < 1 NS Error 2314.09 6 385 68 Total 3072.10 11 371 Appendix Vd. Comparison of percentage unmated females in vegetation surrounding wheat field emergence sites, Shimpling Park Suffolk, 1981 and 1982 Number of Number of Females (n) Unmated Females (a) Total Surrounding Vegetation, 1981 219 63 Total Surrounding Vegetation, 1982* 127 22 Total 346 85 d = 2-40 p<0.05 Understorey and Grassbank, 1981 122 40 Total Surrounding Vegetation, 1982* 127 22 Total 249 62 d = 2.82 p<0.01 Grassbank, 1981 20 9 Total Surrounding Vegetation, 1982* 127 22 Total 147 31 d = 2.83 p<0.01 * All vegetation around the 1982 emergence site was classed as grassbank. 372 Appendix Ve. Analysis of variance of percentage of female C.nigricana unmated in the crop and in the surrounding vegetation of emergence sites, Shimpling Park Farm, 1981 and 1982 WHEAT FIELD WAl# 1981 Week 2 & 3 4 5 6 7 8 9 10 Number of Females Crop 5 13 3 130 50 17 - 6 Surrounding 9 16 22 123 23 23 3 Vegetation - Percentage Unmated Crop 20.0 69.2 100 52.3 72.0 41.2 - 16.7 Surrounding ^ ^ 37.5 40.9 29.3 26.1 8.7 0 Vegetation - ANOVA ( arc-sin transformed. data) for weeks 2 - 8, 10- Source SS df MS F value Area 1447.30 1 1447.30 7.796 p <0. 05 Weeks 3268.93 6 544.82 2.94 NS Error 1113.92 6 185.65 Total 5830.15 13 WHEAT FIELD WA2, 1982 Week 1 2 3 4 5 6 7 8 Number of Females Crop 1 5 11 56 -- 19 4 Surrounding Vegetation 0 0 13 15 23 54 16 4 Percentage Unmated Crop 100 40.0 72 7 60.7 - - 42.1 75.0 Surrounding Vegetation - - 23.1 13.3 17.4 22.2 0 0 ANOVA (arc-sin transformed data) for weeks 3, 4, 7, 8. Source SS df MS F value Area 3204.00 1 3204.00 42.14 Weeks 587.91 3 195.97 2 58 Error 304.17 4 76.04 Total 4096.08 7 313 Appendix Vf. Analysis of variance of percentage of female C.niqricana unmated in crop regions of pea fields/ Shirnplinq Park Farm, 1981 and 1982 PEA FIELD PAl, 1981 Week 6 7 8 9 10 11 Number of Females Perimeter 5 37 14 - 4 1 Centre 2 24 3 - 4 1 Percentage Unmated Perimeter 40.0 2.7 0 - 0 0 Centre 0 0 0 - 0 0 ANOVA (arc-sin transformed data) for weeks 6-8, 10, 11. Source SS df MS F value Crop Areas 237.17 1 237.17 1.65 NS Weeks 576.28 4 144.07 1.00 NS Error 576 27 4 144.07 Total 1389.72 9 PEA FIELD P a2, 1982 Week 3 4 5 6 7 8 9 Number of females Perimeter 2 3 -- 30 16 2 Centre 6 -- - 14 8 4 Percentage Unmated Perimeter 0 100 -- 3.3 6.3 0 Centre 0 - - - 0 0 0 ANOVA (arc-sin transformed data) for weeks 3, 7-9. Source SS df MS F value Crop Areas 78.13 1 78.13 2.85 NS Weeks 82.13 3 27.38 1.00 NS Error 82.13 3 27.38 Total 242.38 7 PEA FIELD PB2, 1982 Week 2 3 4 5 6 7 8 9 Number of Females Perimeter 0 1 0 -- 12 4 1 Centre 0 1 0 - - 20 14 8 Percentage Unmated Perimeter - 0 --- 33.3 0 0 Centre - 0 --- 5.0 0 0 ANOVA (arc-sini transformed data) for weeks 3, 7-9. Source SS df MS F value Crop Areas 62.16 1 62.16 1.00 NS Weeks 867.61 3 289.20 4.65 NS Error 186.48 3 62.16 Total 1116.25 7 374 Appendix Vg. Analysis of variance of percentage of female C.niqricana unmated in the crop and in the surrounding vegetation of pea fields, Shimpling Park Farm, 1981 and 1982 PEA FIELD PAl, 1981 Week 3 4 5 6 7 8 9 10 11 Number of Females Crop 0 0 0 7 61 17 - 8 2 Surrounding , 57 45 1 0 Vegetation 6 17 41 - Percentage Unmated Crop - 28.6 1.6 0 - 0 0 q Surrounding 17.5 24.4 0 0 0 Vegetation 33.3 - - ANOVA (arc-sm transformed. data) for weeks 6 - 8, 10 Source SS df MS F value Are as 12.50 1 12.50 2.11 NS weeks 1343.87 3 447.96 75.54 P C o. 01 Error 17.79 3 5.93 Total 1374.16 7 PEA FIELD PA2, 1982 Week 2 3 4 5 6 7 8 9 Number of Females Crop 0 8 3 - 44 24 6 Surrounding „ Vegetation 7 3 8 13 3 0 Percentage Unmated Crop 0 100 - 2.3 4.2 0 Surrounding Vegetation “ 14.3 60.0 25.0 0 0 - ANOVA (arc-sin transformed data) for weeks 3,, 4, 7, 8. Source SS df MS F value Areas 175.78 1 175.78 < 1 NS Weeks 6057.18 3 2019.06 6.40 NS Error 946.43 3 315.48 Total 7179.38 7 PEA FIELD PB2, 1982 Week 2 3 4 5 6 7 8 9 Number of Females Crop 0 2 - - 32 18 9 Surrounding „ Vegetation 7 7 11 36 4 2 Percentage Unmated Crop 0 - - 15.6 0 0 Surrounding Q Vegetation 0 0 0 2.8 0 0 ANOVA (arc-sin transformed data) for weeks 3, 7-9. Source SS df MS F value Areas 23.46 1 23.46 <1 NS Weeks 182.23 3 60.74 < 1 NS Error 294.07 3 98.02 Total 499.75 7 375 Appendix Vh. Analysis of variance of percentaqe of female C.niqricana unmated in the crops of the two pea fields and in the surrounding vegetation of the two pea fields, Shimpling Park Farm, 1982 CROP AREAS, PA2 and PB2, 1982 Week 2 3 4 5 6 7 8 9 Number of Females Crop, Pa 2 0 8 3 - 44 24 6 Crop, PB2 0 2 - - 32 18 9 Percentage Unmated Crop, Pa 2 - 0 100 - 2.3 4.2 0 Crop, PB2 - 0 -- 15.6 0 0 ANOVA (arc-sin transformed data) for weeks 3, 7-9. Source SS df MS F value Pea field 0.98 1 0.98 < 1 NS Weeks 341.82 3 113.94 1.95 NS Error 175.22 3 58.41 Total 518.02 7 SURROUNDING VEGETATION, PA2 and PB2, 1982 Week 2 3 4 5 6 7 8 9 Number of Females Surrounding 0 7 5 8 13 3 0 Vegetation, p a 2 Surrounding 7 7 11 36 4 2 Vegetation, PB2 2 Percentage Unmated Surrounding 14.3 60.0 25.0 0 0 - Vegetation, Pa2 - Surrounding 0 0 0 0 2.8 0 Vegetation, PB2 - ANOVA (arc-sin transformed data) for weeks 3, 4, 6 - 8. Source SS df MS F value Pea field 872.36 1 872.36 3.01 NS Weeks 764.94 4 191.24 < 1 NS Error 1160.46 4 290.12 Total 2797.76 9 376 Appendix Vi. Comparison of percentage unmated females in crops and in surrounding vegetation of pea fields, Shimpling Park Farm, Suffolk, 1981 and 1982 Number of Number of Females (n) Unmated Females (a) Surrounding Vegetation 168 15 Pea field PAl, 1981 Surrounding Vegetation 105 7 Pea fields P a 2 S c PB2, 1982 Total 273 22 d = 0.667 NS at p = 0 .05 Crop Region Pea field PAl, 1981 95 3 Crop Region Pea fields Pa 2 & PB2, 1982 146 10 Total 241 13 d 1.238 NS at p 0.05