The Ecology of the Viburnum Whitefly, Aleurotrachelus Jelinekii (Frauenf
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The Ecology of the Viburnum Whitefly, Aleurotrachelus jelinekii (Frauenf.). by Patricia Mary Reader B.Sc, A thesis submitted for the Degree of Doctor of Philosophy of the University of London. Department of Zoology and Applied Entomology Imperial College at Silwood Park Ascot Berkshire April 1981 2. ABSTRACT A long term study on the Viburnum whitefly, Aleurotrachelus jelinokii (Frauenf.) was begun in 1962. This is an introduced species to Britain, originally from the Mediterranean, with southern England representing the northern edge of its range. Previously, (Southwood & Reader, 1976), it had been shown that the major controlling factors for the population on the bushes at Silwood Park were adult mortality and factors affecting fecundity. Consequently this thesis focuses on the adult stage and examines, in the first place, the effects of such factors as host plant, density and temperature, on the fecundity of the insect, all of which have some influence on the number of eggs produced. The extent of migration is then discussed, with the conclusion that this is not likely to be a major cause of population dilution. Indeed, tests show that this whitefly will not pursue the prolonged flights expected in a migrating insect. The impact of various predators on the whitefly populations was also examined and only one, Conwentzia psociformis, responded numerically to changes in population densities mainly because it is multivoltine; all the other predator species had one generation a year. Finally, the relation- ship between the host plant and the insect was assessed. Food quality was expressed in amino acid levels found in the leaves both within and between seasons, and it was concluded that a relationship between total levels and egg numbers per leaf could be established. The increased ratio of favourable to unfavourable amino acids in new leaves was linked to the brief egg laying period. The thesis ends with a comparison of all these components indicating their relative importance and contribution to the population dynamics of this whitefly. 3. TABLE OF CONTENTS PAGE ABSTRACT 2 CHAPTER 1 INTRODUCTION 11 CHAPTER 2 FECUNDITY 19 2.1 Introduction 19 2.2 Larval conditions 19 2.2.1 Introduction 19 20 2.2.2 Methods and Results 21 1. Length of larval development a. Aleurotrachelus 21 b. Trialeurodes 23 2. Density during development 25 3. Temperature during development 25 4. Weight of female at emergence 31 2.3 Adult conditions 32 2.3.1 Host Plant 32 1. Effect of leaf age on fecundity 34 2. Seasonal variations in fecundity 35 3. Effect of host plant 36 2.3.2 Density 41 1. Aleurotrachelus 41 2. Trialeurodes 49 2.3.3 Climate 54 Methods and Results 54 2.4 Discussion 57 CHAPTER 3 DISPERSAL 67 3.1 Introduction 67 3.2 Methods 69 3.2.1 fir-Id i"ivx^nts 69 4. PAGE 3.2.2 Experimental assessments 70 3.3 Results 74 3.3.1 Field experiments 1. Daily totals on sticky traps and trap plants. 2. Climatic effects on the total numbers caught. 77 3. Dispersal with distance 4. Numbers caught at different heights 5. Sex ratio - 6. The influence of population size and density. 100 3.3.2 The experimental assessment of flight and landing characteristics. -^3 1. Effect of age on flight activity 2. Flight and landing in a flight chamber 104 a. The duration of flight. b. The length of individual flights 107 c. Landing site preference 3.3.3 Dissections 3.4 Discussion m CHAPTER 4 PREDATORS 117 4.1 Introduction 4.2 Methods and Results 120 4.2.1 Spiders 120 4.2.2 Other Predators 127 4.3 Discussion 138 5. ?AGE CHAPTER 5 THE NITROGEN LEVEL IN THE HOST PLANT 142 5.1 Introduction 142 5.2 Methods 142 5.3 Results 144 5.3.1 Total Amino Acid levels 144 5.3.2 Individual Amino Acid levels 152 5.3.3 Seasonal Variation in Amino Acid levels 152 5.4 Discussion 161 CHAPTER 6 ADULT POPULATION DYNAMICS 6.1 Introduction 169 6.2 Methods 169 6.3 Analysis of natality 172 CHAPTER 7 GENERAL DISCUSSION 188 SUMMARY 196 ACKNOWLEDGEMENTS 198 REFERENCES 199 APPENDICES 217 6. LIST OF FIGURES PAGE FIGURE 1.1 The study sites at Silwood Park 13 FIGURE 1.2 Leaves from bushes A and B showing differences in scale of larval populations 16 FIGURE 2.1 Design of clip cages 22 FIGURE 2.2 Effect of length of development on-the fecundity of Aleurotrachelus . 24 FIGURE 2.3 Effect of length of development on the fecundity of Trialeurodes ' 26 FIGURE 2.4 Effect of larval density on the fecundity of Trialeurodes ' FIGURE 2.5 Effect of temperature on the fecundity of Trialeurodes . 30 FIGURE 2.6 Seasonal variations in fecundity of Aleurotrachelus— ' 38 FIGURE 2.7 Effect of host plant on fecundity of Aleurotrachelus ; 40 FIGURE 2.8 Effect of density on fecundity of Aleurotrachelus 44 FIGURE 2.9 Relationship between available space for female and eggs laid. 46 FIGURE 2.10 Relationship between the total eggs per female and the total number laid 48 FIGURE 2.11 Effect of density on fecundity of Trialeurodes on tomatoes 51 FIGURE 2.12 Effect of density on fecundity of Trialeurodes on beans 51 FIGURE 2.13 Effect of increased space of fecundity of Trialeurodes 53 7.. PACE FIGURE 2.14 Daily total of eggs laid by Trialeurodes 56 FIGURE 2.15 Effect of temperature on the fecundity of Aleurotrachelus 59 FIGURE 2.16 Effect of June temperature on the fecundity of Aleurotrachelus in the field 6L FIGURE 3.1 Position of sticky traps round Bush A 72 FIGURE 3.2 Daily totals of whitefly caught on the first annulus 76 of traps 1972-1974 76 FIGURE 3.3 Daily totals reaching the nearest trap plant 79 FIGURE 3.4 Numbers of adults caught on each annulus of sticky traps * SI FIGURE 3.5 Fit of Hawkes1 and Paris1 equations to the data from the sticky traps 87 FIGURE 3.6 Fit of Hawkes' and Paris' equations from the data from the trap plants ^ FIGURE 3.7 Fit of Paris'& Hawkes'- models to the mean catches 94 FIGURE 3.8 Numbers caught at different heights 96 FIGURE 3.9 Relationship between the number of males caught on the sticky traps and adult numbers 99 FIGURE 3.10 Percentage of the population caught on each annuli of sticky traps ^2 FIGURE 3.11 Effect of age on take off by Aleurotrachelus 105 FIGURE 3.12 Relationship between length of flight and age of female —— 109 FIGURE 3.13 Decline in aerial density with distance FIGURE 4.1 Phenology of Aleurotrachelus and its associated species H9 FIGURE 4.2 Number of spiders compared with whitefly density- 1-22 8. PAGE FIGURE A.3 Relationship between number of whitefly trapped and spider numbers. 124 FIGURE 4.4 Number of whitefly trapped per spider 126 FIGURE 4.5 Number of whitefly trapped per spider compared with adult density 129 FIGURE 4.6 Percentage trapped compared with population density 131 FIGURE 4.7 Relationship between whitefly density and predator species richness 133 FIGURE 4.8 Seasonal fluctuations in numbers of predator species 135 FIGURE 4.9 Relationship between total numbers of individual predators and population density 137 FIGURE 4.10 Relationship between number of coniopterygids and whitefly density 140 FIGURE 5.1 Seasonal variations in total amino acid levels 147 FIGURE 5.2 Comparison between number of eggs laid per leaf and amino acid levels 150 FIGURE 5.3 Individual amino acid levels 153 FIGURE 5.4 Seasonal variations in amino acid levels 156 FIGURE 5.5 Seasonal variations in the percentage of individual amino acids 158 FIGURE 5.6 Seasonal differences in amino acid quality 163 FIGURE 6.1 Functional response of mirids to Aleurotrachelus 174 FIGURE 6.2 kQ and its component values. 179 FIGURE 6.3 kQ and the corresponding values for quality density and temperature 184 9. LIST OF TABLES ?AGE TABLE 2.1 Weights of whitefly from Bushes A and B 31 TABLE 2.2 Numbers of eggs laid on old and young leaves 34 TABLE 2.3 Numbers of eggs laid on 1 year and older leaves— 34 TABLE 2.4 Survival of 1st and 2nd instar 35 TABLE 2.5 Significance of host plant on fecundity Al TABLE 3.1 Six models for density with distance 82 TABLE 3.2 Total numbers caught of ten sticky traps during 1968-1976 82 TABLE 3.3 Total numbers caught on the trap plants 83 TABLE 3.4 Fit of the six equations to the data from the sticky traps 84 TABLE 3.5 Fit of the six equations to the data from the trap plants 85 TABLE 3.6 Departure from a 50 : 50 sex ratio of adults caught on the sticky traps 92 TABLE 3.7 Sex ratio of adults from the inner and outer annuli of sticky traps 97 TABLE 3.8 Sex ratio of adults from the trap plants 100 TABLE 3.9 Comparison between numbers caught on outer and inner annuli 103 TABLE 3.10 Population density and percentage of the population caught on trap plants 103 TABLE 3.11 Flight development time 104 TABLE 3.12 Flight willingness of 1 day old Aleurotrachelus 106 TABLE 3.13 Flight willingness of whitefly of different ages 106 TABLE 3.14 Frequency of individual flights of females 107 TABLE 3.15 Landing site preference 110 10. PACE TABLE 3.16 Effects of host plant on landing site preference- 110 TABLE 5.1 Amino acids identified during analysis 145 TABLE 5.2 Amino acid amounts found in old leaves — 151 TABLE 5.3 Index of amino acid quality — 161 TABLE 6.1 Estimate of adult numbers 175 TABLE 6.2 k - values for egg loss — 176 TABLE 6.3 Percentage egg loss — 181 TABLE 6.4 Values of k .