STUDIES ON THE ECOLOGY AND BEHAVIOUR OF XJ4E- I S 13i--(vrt - t-t Q:!1.\<-(-41- IPC-_,r■rs. tS) L SE GAF 1214WIEta xylostella(1/4-61414441-&.14.6 -) if,LEPIDOPTERA fe#0451=1A7k04FE2 y Pedro Jose Salinas, lng. Agr., M.Sc., D.I.C. A thesis submitted for the Degree of Doctor of Philosophy in the Faculty of Science, University of London. Department of Zoology and Applied Entomology Imperial College of Science and Technology Field Station, Silwood Park Ascot, Berkshire. June 1972 ABSTRACT Plutella xylostella (L.) (Lepidoptera : Plutellidae) is a universal pest of cabbage.. Populations of this species were studied both in constant environment rooms and in field conditions. The lengths of the different instars, and the fecundity,, were determined in the laboratory at 20°C. The behaviour of the larvae was recorded with particular emphasis to the recently hatched larvae and to density. The effects of size and shape of the leaves on behaviour. and ' survival of the larvae as well as the effects of starvation in later instar larvae, in the laboratory, were recorded. The. dispersion pattern of the larvae was recorded throughout development. The effects of the leaf toughness on survival was studied. The behaviour of the adults was recorded. In the field, mortality factors were studied by exclusion cage techniques. These included exclusion of birds, soil predators, small aerial predators, parasites and rainfall. Mortalities from the different causes were assessed for the different instars. The importance of overlapping causes of mortality was demonstrated and as an exercise life tables were constructed. Suggestions are made on how natural methods of'control could be enhanced in order to minimise dependance on insecticides for control of this pest. 1 TABLE OF CONTENTS Page ABSTRACT 1, INTRODUCTION 10 1 1 THE CONCEPT OF PEST 10 1,2. CONTROL OF INSECT PESTS 10 1,3, Plutella xylostella (L.) AS AN IMPORTANT PEST 11 REVIEW OF LITERATURE C . 14 2,1. ECOLOGY OF LEPIDOPTERA 14 2.2. ECOLOGY OF CRUCIFEROUS CROPS.PESTS.. 15 2.2.1, General crucifers pests .15 2.2,2. Pieris spp. 15 2.2,3. Mamestra brassicae L 16 2,2,4. Trichoplusia ni Hubner 17 2, 2.5, Plutella xylostella (L.) 17 2.3. EFFECTS OF DENSITY 19 2.3,1, Effects of density on insects 19 2.3.2, Effects of density on Lepidoptera . 22 2..3,3. Effects of density on Lepidoptera attacking crucifers 24 3. DESCRIPTION OF THE DIFFERENT STAGES OF P. xylostella 26 3.1, THE EGG 26, 3,2, THE LARVA 27 3.3. THE PRE-PUPA 27 • 3,4. THE PUPA 28 2 Page 3. 5. THE ADULT 29 4. LIFE HISTORY• 31 4.1. INTRODUCTION 31 4.2, MATERIALS AND METHODS 31 4,2.1. The rooms 31, 4.2.2. The cages 32 •4,2, 3. The leaf discs 32 4,2,4. The experiments 33 4,3, RESULTS 33 4, 3, 1. Developmental time 33 4.3.2, Longevity and fecundity 34 4.4, DISCUSSION 40 5. BEHAVIOUR 43 5„ 1. INTRODUCTION 43 5.2. MATERIAL AND METHODS 44 5.3. RESULTS 45 5.4. PRE-HATCHING AND HATCHING BEHAVIOUR. 46 5.5. BEHAVIOUR OF THE LARVAE 46 5., 5; 1. stFir.• instar. From hatching to first feeding place 47 Larvae from groups of eggs 47 Larvae from isolated eggs 49 5. 5. 2. First instar 51 5. 5. 3.- Second instar 53 5. 5.4. Third instar 54 5.5,5. Fourth instar 55 5, 5.6. Pre-pupa 55 5.5.7. Pupa 56 • 3 Page 5.6. "SPACING" BEHAVIOUR OF THE LARVAE 57 6. EFFECTS OF THE SIZE AND SHAPE OF THE LEAVES, AND OF THE DENSITY OF THE LARVAE ON THE BEHAVIOUR, DISPERSION AND SURVIVAL OF P. xylostella 61 6.1. INTRODUCTION 61 6. 2. MATERIALS AND METHODS 61 6.3. RESULTS 62 6. 3.1. EFFECTS ON LARVAL BEHAVIOUR, DEVELOPMENT, AND MORTALITY. 62 6.3.1.1. Gallery-making stage 62 6. 3. 1. 2. Developmental time (including pr e- pupation) 64 6.3.1.3. Larval mortality 65 6.3.2. EFFECTS ON SIZE AND WEIGHT OF PUPAE AND WEIGHT OF ADULTS . 66 6.4, DISCUSSION 70 7, BEHAVIOUR OF THE LARVAE UNDER STARVATION (THIRD AND FOURTH INSTARS) 72 8. ADULT BEHAVIOUR 75 8.1. NORMAL BEHAVIOUR „ 75 8.2. MATING BEHAVIOUR ....... • • . 75 8.3. OVIPOSITION BEHAVIOUR 78 8. 3. 1. Oviposition substrate preference . 80 Materials and Methods 80 Results . 81 4 Page 8. 3, 2, Leaf position preference 83 Materials and Methods 83 Results .84 9. STUDIES ON CAUSES OF MORTALITY AND ON DIS- PERSION IN LABORATORY POPULATIONS OF P. xylostella .86 9.1. INTRODUCTION 86 9.2. MATERIALS AND METHODS 86 9.2.1. The rooms 86 9.2.2. The cages 87 9.2, 3. The plants • -87. 9.2.4. The leaves 87 9, 2, 5. The oviposition cages 90 9.2.6. The stock culture of the larvae 90 9. 3. EXPERIMENT TO DETERMINE DEVELOP- MENT, MORTALITY AND DISPERSION 91 9.3.1. Materials and Methods 92 9, 3.2. Results and Discussion 94 9.4. EXPERIMENT TO DETERMINE DEVELOP- MENT, MORTALITY AND DISPERSION • 97 9 . 4. 1 . Materials and Methods 97 9.4.2. Results and Discussion 99 9.5. EXPERIMENT TO DETERMINE DEVELOP- MENT, MORTALITY AND DISPERSION AT LOW TO HIGH DENSITIES 102 9. 5. 1. Materials and Methods 103 9.5.2. Results and Discussion 104 41 5 Page 9.6. EXPERIMENT TO COMPARE DEVELOP- MENT, MORTALITY AND DISPERSION AT LOW, HIGH AND VERY•HIGH DENSITIES 107 9.6.1. Materials and Methods 107 9.6.2. Results and Discussion 108 9.7. EXPERIMENT TO COMPARE DEVELOP- MENT, MORTALITY AND DISPERSION AT HIGH, LOW AND EXTREMELY LOW (ISOLATED LARVA) DENSITIES, ON TOUGH AND TENDER LEAVES ..... 112 . 9.7,1. Materials and Methods •113 9.7.2. Results and Discussion 114 9.8. EXPERIMENTS TO DETERMINE DEVELOP- MENT, MORTALITY AND DISPERSION OF ISOLATED AND PAIRED LARVAE, ON TENDER LEAVES 117 9.8.1. Materials and Methods 118 9.8.2, Results andDiscussion 118 9.9. EXPERIMENTS TO COMPARE THE DE- VELOPMENT, MORTALITY AND DIS- PERSION OF THE LARVAE AT DIFFERENT DENSITIES (ISOLATED LARVAE TO HIGH DENSITY) ON DIFFERENT TOUGHNESS AND SIZES OF LEAVES .121 9.9.1. Materials and Methods .121 9.9.2. Results and Discussion 122 • 6 • Page 9.10. EXPERIMENTS WITH PENETROMETER TO COMPARE TEXTURE OF LEAVES . 125 9.10.1. Materials and Methods 125 9.10.2. Results and Discussion 125 9.11. DISPERSION OF THE LARVAE 128 9.11.1. Introduction 128 9.11.2. Materials and Methods 130 • 9.11.3. Results 130 9.11.4. Discussion 131 10. STUDIES ON CAUSES OF MORTALITY IN FIELD POPULATIONS OF P. xylostella .148 10.1. INTRODUCTION 148 10.2. MATERIALS AND METHODS 150 10.2.1. The field 150 10.2.2, The plants .150 10.2.3. The exclusion cages 151 10.3. SETTING UP THE FIELD EXPERIMENTS .155 10.3.1. Establishment of field populations. .155 10.3.2. Method of counting .155 10.3.3. Analysis of the data .156 10.4. FIRST FIELD EXPERIMENT (SUMMER 1969) 158 10.4.1. Materials and Methods 158 10.4.2. Results 158 Effects of excluding parasites and predators 158 Effects of excluding birds 170 Effects of excluding rainfall 171 Effects of exposure to all natural enemies and to rain 172 7 Page 10.4.3. Discussion 173 10.5. SECOND FIELD EXPERIMENT (LATE SUMMER-AUTUMN 1969) 182 10, 5.1. Materials and Methods 183 10. 5.2. Results 194 Effects of excluding parasites and predators 194 Effects of excluding birds 195 Effects of excluding rainfall • 195 Effects of exposure to all natural enemies and to rain 197 10. 5. 3. Discussion .198 10.6. THIRD FIELD EXPERIMENT (LATE SUMMER -AUTUMN 1970) 205 10.6.1. Materials and Methods 206 10.6.2. Results 208 Effects of excluding parasites and predators 208 Effects of excluding birds 219 Effects of excluding soil predators 220 Effects of exposure to all natural enemies and to rain 221 Discussion 225 10.7. DISCUSSION 227 10, 7.1. Effects of birds predation 229 10.7.2. Effects of soil predators 230 10.7.3. Effects of parasites 231 10. 7.4. Effects of rainfall 231 10. 7.5. Effects of other factors 232 a 8 • Page 100 8. LIFE- TABT 235 10.8.1 . Introduction o 235 10. 8.2. Materials and methods 235 10. 8. 3. Results -238 10.8.4. Discussion 238 11. DISCUSSION 243 11 . 1, LABORATORY EXPERIMENTS 244 11, 2 FIELD EXPERIMENTS 245 11.2.1. Early instar mortality (up to 3rd instar) 246 11.2, 2. Late instar mortality 247 Parasites 247. - Birds. 248 Soil predators 248 Other predators 249 Other mortality causes 249 11.3. GENERAL REMARKS 249 12. SUMMARY • 252 13. ACKNOWLEDGEMENTS 255 14. REFERENCES 256 15. APPENDICES 15.1. APPENDIX 1. BEHAVIOUR OF THE LARVAE • • • A. 1. Behaviour of the recently hatched larvae • . • A.1.1. Single larva from egg within a batch A.1.2. Single larva from egg separated from batch A.1.3. Group of larvae within a batch . * 8 • Page 10.8. LIFE- TABLES 235 10.8.1, Introduction 235 10.8.2. Materials and methods 235 10.8.3. Results 238 10.8.4. Discussion 238 11. DISCUSSION 243 11.1. LABORATORY EXPERIMENTS . 244 11.2. FIELD EXPERIMENTS 245 11.2.1, Early instar mortality (up to 3rd instar) • 246 11.2.2. Late instar mortality 247 Parasites 247 Birds 248 Soil predators 248 Other predators 249 Other mortality causes 249 11.3.