1 FACTORS AFECTING PROGENY AND SEX ALLOCATION BY THE EGG PARASITOID Trichogramma evanescens WESTWOOD by P.K.T.N.S. Pallewatta A thesis submitted for the degree of Doctor of Philosophy of the University of London and for the Diploma of Imperial College of Science and Technology. Department of Pure and Applied Biology Imperial College, Silwood Park Ascot, Berkshire. September 1986 2 ABSTRACT Understanding the reproductive strategy of Trichogramma can be a powerful tool in improving production and quality in mass rearing produced wasps. A comparison was made of the reproductive strategy of T. evanescens Westwood, on one of its natural hosts, Mamestra bras sicae L. and on Sltotroga cerealella 01. a factitious host commonly used for mass rearing. Density dependent decreases in survival of the immature stages with increasing wasp density was obtained for both these hosts. Fitness estimates of females likewise decrease, and the sex ratio becomes more male biased. The sex ratio of T. evanescens was found to be influenced by the density of ovipositing females as well as by the size of the host resource. A method was developed for determining the primary sex ratio and clutch size. Individual wasps possess a pattern of allocation whereby males are produced at intervals of female eggs. The first egg laid by a mated female is always female and this pattern was observed to be maintained at three different rates of host encounter and when superparasitising. Superparasitoids laid a smaller clutch size than primary parasitoids but superparasitoids did not allocate a more male biased sex ratio than primary parasitoids. Clutch size was found to change with rate of host encounter. Previous literature on Trichogramma is reviewed and related to factors affecting sex and progeny allocation. 3 ACKNOWLEDGEMENTS I am greatly indebted to my supervisor Dr. J.K. Waage for the supervision of my work and his patience and understanding shown to me during my stay at Silwood Park . I am also very grateful to Dr A.R. Ludlow for the many hours which he spent explaining statistical tech­ niques and also for providing several computer progra­ mmes for my data analyses. My especial thanks go to Professor M.P. Hassell and Dr. M.J. Crawley who have readily provided advice. Mrs Brenda Flavell has helped me to use the Computer Facilities and has also been generous with her friendship. My sincere thanks go to Dr. Patricia Reader and Hefin Jones for spending their time reading drafts of my thesis. Mrs Annette Greathead has taken the trouble to find me some references. I wish to thank all my past and present collegues of the Munro Laboratory and the Ecology Group for their friendship which has made my stay at Silwood a very pleasant one. I gratefully acknowledge the assistance given by Dr. J. Shemilt, Robin Becker and Mark Lee of the Imperial College Computer Centre during the printing of this thesis. The Association of Commonwealth Universities provided me with a Scholarship to carry out my postgradute3 studies.... m Britain. 4 TABLE OF CONTENTS PAGE Abstract 2 Acknowledgements 3 Table of Contents 4 List of Figures 9 List of Tables 13 List of Appendices 16 Chapter 1 Introduction 17 Chapter 2 Biology ofTrichogramma spp. Westwood 26 2.1 Development 26 2.2 Emergence and Mating 30 2.3 Longevity 31 2.4 Dispersal and Host Finding 33 2.5 Egg maturation and Oviposition 42 2.5.1 Hostacceptanceand 4.4 suitability 2.5.1.1 Host species 46 2 . 5 . 1 .2 Host Age 49 2.5.1.3 Previously Parasitised 52 Hosts Chapter 3 Host Biology and Rearing Methods 56 3.1 Biology and Rearing of Mamestra 56 bra ssicae (L. ) 3.1.1 Biology of Mamestra brassicae (L.) 56 3.1.2 Laboratory Rearing of Mamestra 57 brassicae (L.) 3.2 Biology and Rearing of Sitotroga 59 cerealella (01.) 3.2.1 Biology of Sitotroga cerealella 59 3.2.2 Laboratory Rearing of Sitotroga 60 cerealella 5 PAGE 3.3 Rearing 7. evanescens Westwood 61 3.3.1 Rearing 7. evanescens in eggs 61 of M. bra ssicae 3.3.2 Rearing 7. evanescens in eggs 62 of S. cerealella Chapter 4 Mass Rearing and Quality Control Of 63 Trichogramma species 4.1 Mass Rearing 63 4.1.1 Host species 64 4.1.2 Preparation of Hosts 65 4.1.3 Exposure of Hosts to Trichogramma 66 4.1.4 Storage 67 4.2 Factors Affecting the Quality of 68 Laboratory reared Trichogramma 4.2.1 Physical Conditions of Rearing 69 4.2.2 Densities of Parasitoids and 70 Hosts 4.2.3 Host Species 73 4.2.4 Genetic Changes 75 4.3 Quality Control of Mass Reared 76 Trichogramma species 4.3.1 Manipulation of Rearing 76 Procedures 4.3.2 Genetical Manipulation 80 4.3.3 Alternation of Host Species 82 4.4 Artificial Rearing of Trichogramma and 83 its Hosts Chapter 5-Part I The Theory of Progeny Allocation 86 5.1.1 Introduction 86 5.1.2 Optimal Clutch Size 87 5.1.3 Superparasitism 105 6 PAG 5-Part II The Theory of Sex Allocation 109 5.2.1 Local Mate Competition 109 5.2.2 Superparasitism and the Sex Ratio 116 5.2.3 Host Quality Effects 117 5.2.4 Some Other Factors Affecting the 120 Sex Ratio G Effect of the Host Mamestra brassicae (L.) On 122 Clutch Size, Brood Size, Sex ratios and the Fitness Changes of T. evanescens Westwood 6.1 Material and Methods 122 6.1.1 Standardisation of Female Wasps 123 6.1.2 Experimental Design 123 6.1.3 Dissection of Host Eggs 124 6.1.4 Measurement of Tibia Length 124 6.2 Results 125 6.2.1 Effect of the Host M. brassicae 125 on Parasitism by T. evanescens 6.2.2 Statistical Analysis-Analysis of 128 of Deviance 6.2.3 Changes in Clutch Size 133 6.2.4 Within Brood Mortality 142 6.2.5 Progeny Production 145 6.2.6 Production of Males and Females 154 and Sex Ratio Shifts 6.2.6.1 Production of Males 154 and Females 6 .2.6.2 Sex Ratio Shifts 160 6.2.7 Fitness Changes of Progeny 6 . 3 Discussion 7 PAGE Chapter 7 Effect of the Host Sitotroga cerealella 194 (Olivier) On the Clutch Size, Brood size, Sex ratio and Fitness Changes of T. evanescens Westwood 7.1 Materials and Methods 194 7.1.1 Experimental Design 195 7.1.2 Dissection of Host Eggs 197 7.1.3 Measurement of Tibia Length 198 7.2 Results 198 7.2.1 Effect of the Host S. cerealella 198 on Parasitism by T. evanescens 7.2.2 Changes in' Clutch Size 201 7.2.3 Within Brood Mortality 213 7.2.4 Progeny Production 217 7.2.5 Production of Males and Females 227 and Sex Ratio Shifts 7.2.5.1 Production of males and 227 Females 7.2.5.2 Sex Ratio Shifts 233 7.2.6 Fitness Changes of Progeny 235 7.3 Discussion 246 Chapter 8 A Behavioural Method of Detecting the Primary 256 Sex Ratio and Clutch Size 8.1 Introduction 8.2 Materials and Methods 2^ 8.3 Results 261 8.3.1 Sequences of Behavioural Events in 261 Oviposition by Mated Females 8.3.2 Accuracy of the Behavioural Method 266 of Investigating Patterns of Allocation 8.3.3 Time Taken for Oviposition of Male 212 and Female Eggs by Mated females 8 8.3.4 Oviposition Behaviour of Unmated 282 Females 8.3.5 Superparasitism by Mated Females 291 8.4 Discussion 296 Chapter 9 Sequences of Sex and Progeny Allocation 305 and Fitness changes 9.1 Introduction 3®~* 9.2 Materials and Methods 308 9.2.1 Effect of Rate of Host Encounter 308 on Sex and Progeny Allocation. 9.2.2 Broods produced by Two 310 Conspecifics 9.3 Results 310 9.3.1 Patterns of Sex Allocation and 311 Effect of Rate of Host Encounter on Sex Allocation 9.3.2 Sequences of Progeny Allocation 318 9.3.3 Clutch sizes and Sex Ratios laid 325 in Superparasitism 9.3.4 Within Brood Mortality 326 9.3.4.1 Broods produced by Single 327 Females 9.3.4.2 Broods produced by Two 329 Conspecifics 9.3.5 Fitness Changes of Offspring 330 9.4 Discussion 341 Chapter 10 Summary and Discussion 347 Bibliography 357 Appendices 387 Appendix 1 Progeny Production 387 Appendix 2 Experimental Results- Chapter Six 397 Appendix 3 Experimental Results- Chapter Seven 408 9 LIST OF FIGURES FIGURE PAGE 5.1(a) Brood sizes produced by Trichogramma spp. 92 from spherical hosts. 5.1(b) Brood sizes produced by Trichogramma spp. 94 from non-spherical host species. 5.1(c) Change of brood sizes of T. minutum with 96 hosts of different sizes. 5.1(d) Brood sizes produced by some species of 98 Trichogramma from Estigmene acraea . 5.1(e) Brood sizes produced by some species of 98 Trichogramma from Heliothis zea . 5.1(f) Brood sizes produced by some species of 100 Trichogramma from Mamestra b ra s s ic a e. 5.1(g) Brood sizes produced by some species of 100 Trichogramma from Trichoplusia n i. 6 . 2 . 1 (a-e) Effect of parasitoid to host ratios on 127 parasitism by T. evanescens. 6.2.3(a) Overall effect of host patch sizes on clutch 137 sizes . 6.2.3(b) Overall effect of wasp densities on clutch 137 sizes . 6 . 2.3 ( c 1 ) Change of clutch sizes with host patch size.