Polymorphism in Hawkmoth Caterpillars
Total Page：16
File Type：pdf, Size：1020Kb
POLYMORPHISM IN HAWKMOTH CATERPILLARS - AN ECOLOGICAL AND BIOCHEMICAL STUDY OF CRYPSIS IN SMERINTHUS OCELLATA (L.) AND LAOTHOE POPULI (L.) by JOY C. GRAYSON B.Sc. A thesis presented for the degree of DOCTOR OF PHILOSOPHY awarded by the Council for National Academic Awards School of Applied Biology, Lancashire Polytechnic, Preston. July, 1986 ACKNOWLEDGEMENTS I would like to thank my supervisor Professor Malcolm Edmunds of Lancashire Polytechnic for his help, advice and useful discussions throughout the project. ± would also like to express my gratitude to Dr. Hilary Evans of Lancashire Polytechnic and Dr. George Britton of Liverpool University for their help with the biochemical aspects of the work. Many thanks to the research staff and students at the Polytechnic for interesting lunchtime discussions and also to the teaching and technical staff for helping with experimental equipment. My special thanks to Dr. Janet Edmunds for her hospitality during the summer months of 1983 and 1984, when the breeding experiments were carried out in the garage of her home in Goosnargh. I am grateful to the Natural Environmental Research Council for financial support. Finally I would like to thank Bridget Cook for typing the manuscript. -1- DECLARAT ION The work presented in this thesis was carried out in the School of Applied Biology, Lancashire Polytechnic (formerly Biology Division of Preston Polytechnic) . Unless otherwise stated it is the original work of the author. While registered as a candidate for the degree of Doctor of Philosophy, for which submission is now made, the author has not been a registered candidate for another award of the C.N.A.A. or of a University. This thesis has not been submitted in whole, or in part for any other degree - - ii - J. GRAYSON POLYMORPHISM IN HAWKMOTH CATERPILLARS - AN ECOLOGICAL AND BIOCHEMICAL STUDY OF CRYPSIS IN SMERINTHUS OCELLATA (L.) AND LAOTHOE POPULI (L.) Extensive field surveys in Lancashire and Merseyside have shown that for both Smerinthus ocellata (the eyed hawkmoth) and Laothoe populi (the poplar hawkmoth) there is a correlation between larval and foodplant coloration. For L. populi, experiments have shown that foodplant determines the colour of full grown caterpillars. Siblings reared on Salix fragilis L. (which has green leaves) became yellow-green, intermediate-green or dull-green whereas those reared on Populus alba L. became either white or green. Further experiments have shown that reflected light intensity may be the vital cue which determines whether a caterpillar becomes white or green. Thus for this species. the polymorphism is environmentally rather than genetically determined. However, the genetic background appears to have some effect on the proportion of dull-green and intermediate-green morphs in broods. For S. ocellata, both laboratory and field experiments have shown that the coloration of caterpillars is also determined by some environmental factors related to light. There is no simple genetic or nutritional control of larval colour in this species. Pigment extraction and analysis have shown that the proportions of different carotenoids in the main foodplants are very similar, as are the chlorophyll a to b ratios and carotenoid to chlorophyll ratios. The principal carotenoid in the food of both species of caterpillar, lutein, is sequestered by the insects in the integument and contributes to the animal's coloration. Cis-lutein is also present in small quantities in the integuments of both L. populi and S. ocellata caterpillars. Yellow-green L. populi larvae contain more lutein in the integument than dull-green morphs and in white caterpillars this carotenoid is barely detectable. Field predation experiments indicated that white caterpillars of L. populi are at a selective advantage compared with yellow-green morphs on the white undersurface of P. alba leaves. However, both white and green morphs suffered similar predation on S. fragilis bushes. - iii - CONTENTS CHAPTER 1 INTRODUCTION Page 1.1 Crypsis and Colour Change in Animals 1 1.2 Polymorphism 4 1.3 Pupal Polymorphism 5 1.4 Polymorphism in Caterpillars 9 1.4.1 The Citrus Swallowtail Papilio demodocus Esper. 9 1.4.2 The Mediterranean Flour Moth Ephestia kUhniella (Zeller) 10 1.4.3 The Pine Looper Caterpillar Bupalus piniarus L. 11 1.4.4 The New World Hawkmoth Errinyis ello L. 12 1.5 Physico-Chemical Basis of Colour in Insects 13 1.6 Green Insect Pigmentation 13 1.7 Pigments in Lepidoptera 15 1.8 The Present Work 1.8.1 Introduction 19 1.8.2 Aim 19 1.8.3 The Species 20 1.8.4 Organisation of the Thesis 21 CHAPTER 2 FIELD SURVEYS 2.1 Introduction 22 2.2 Method 22 2.3 The Sites 2.3.1 Cuerden Valley Park, Lancashire 22 2.3.2 Lytham St. Annes, Lancashire 23 2.3.3 Formby Point Nature Reserve, Merseyside 26 2.3.4 Haslaam Park, Preston, Lancashire 26 2.3.5 Mill Lane, Goosnargh, Lancashire 29 2.4 The Foodplants 29 2.5 Colour and Resting Behaviour of Poplar and Eyed Hawkmoth Larvae 30 2.6 Results and Discussion 2.6.1 Eyed Hawkmoth 32 2.6.2 Poplar Hawkmoth 38 CHAPTER 3 BREEDING PROGRAMME 3.1 Introduction 41 3.2 Rearing Methods 41 3.3 Establishment of the Number of Instars in Laothoe Populi and Smerinthus ocellata Caterpillars 44 3.3.1 Introduction 44 - iv - Page 3.3.2 Method 46 3.3.3 Results and Discussion 46 3.3.3.1 Poplar Hawkmoth 46 3.3.3.2 Eyed Hawkmoth 49 3.4 Growth, Development and Survival of Poplar Hawkmoths on S. fragilis and P. alba 3.4.1 Introduction and Aims 54 3.4.2 Method 54 3.4.3 Results and Discussion 58 3.4.3.1 Mortality of L. populi larvae on S. fragilis and P. alba 58 3.4.3.2 Larval Developmental Time 62 3.4.3.3 Pupal Weights, Adult Wingspan and Egg Production of L. populi Reared as Larvae on S. fragilis or P. alba 63 3.5 Summary of Sections 3.3 and 3.4 67 CHAPTER 4 LABORATORY REARING PROGRAMME - LAOTHOE POPULI 4.0 Aim 68 4.1 Experiment 1 4.1.0 Aim 68 4.1.1 Method 68 4.1.2 Results and Conclusion 69 4.2 Experiment 2 4.2.0 Aim 69 4.2.1 Experiment 2a 4.2.1.1 Method 71 4.2.1.2 Results and Conclusion 71 4.2.2 Experiment 2b 4.2.1.1 Method 71 4.2.1.2 Results and Conclusion 74 4.2.3 Experiment 2c 4.2.3.1 Method 74 4.2.3.2 Results and Conclusion 75 4.2.4 Conclusion for Experiment 2 75 4.3 Experiment 3 4.3.0 Preamble and Aim 76 4.3.1 Method 77 4.3.2 Results and Conclusion 77 4.3.2.1 Frequency of Dull-Green and Intermediate-Green Morphs 77 4.3.2.2 Frequency of Red Spotted Morphs 78 4.4 Experiment 4 4.4.0 Aim 78 4.4.1 Method 83 4.4.2 Results and Conclusion 83 4.5 Experiment 5 4.5.0 Aim 86 4.5.1 Method 86 4.5.2 Results and Conclusion 87 IN Page 4.6 Experiment 6 4.6.0 Aim 87 4.6.1 Method 87 4.6.2 Results and Conclusion 89 4.7 Experiment 7 4.7.0 Aim 91 4.7.1 Method 91 4.7.2 Results and Conclusion 91 4.8 Experiment 8 4.8.0 Introduction 93 4.8.1 Aim 95 4.8.2 Method 95 4.8.3 Results and Conclusion 95 CHAPTER 5 LABORATORY REARING PROGRAMME - SMERINTHUS OCELLATA 5.0 Introduction 99 5.1 Experiment 1 5.1.1 Aim 99 5.1.2 Method 99 5.1.3 Results and Discussion 99 5.2 Experiment 2 5.2.1 Aim 101 5.2.2 Experiment 2a 102 5.2.2.1 Method 102 5.2.2.2 Results and Discussion 102 5.2.3 Experiment 2b 103 5.2.3.1 Method 103 5.2.3.2 Results and Discussion 103 5.3 Experiment 3 5.3.1 Aim 104 5.3.2 Method 104 5.3.3 Results and Discussion 105 5.4 Experiment 4 5.4.1 Aim 105 5.4.2 Method 105 5.4.3 Results and Discussion 106 CHAPTER 6 FIELD PREDATION EXPERIMENTS 6.1 Aim 108 6.2 Experiment 1 6.2.1 Method 108 6.2.2 Results and Discussion 108 6.2.3 Conclus ion 112 6.3 Experiment 2 6.3.1 Method 112 6.3.2 Results and Discussion 113 - vi - CHAPTER 7 BIOCHEMICAL ANALYSIS OF PLANT AND LARVAL Page PIGMENTATION 7.1 Introduction 119 7.2 Aim 121 7.3 Methods 7.3.2 The Larvae 121 7.3.2 The Foodplants 123 7.3.3 Pigment Analysis 123 7.3.4 Extraction of Pigments 123 7.3.5 Estimation of Chlorophylls a and b 125 7.3.6 Separation of Carotenoids 125 7.3.6.1 Preparation of Silica Gel Plates 125 7.3.6.2 Thin Layer chromatography 126 7.3.6.3 Carotenoid Identification 126 7.3.6.4 Hcl Test for Carotenoid Epoxides 128 7.3.6.5 Quantitative Estimation of Carotenoids 128 7.4 Results and Discussion 7.4.1 The Foodplants 128 7.4.2 Laothoe populi Larvae 129 7.4.3 The Gut Sacs 138 7.4.4 The Frass 140 7.4.5 The Fat Body 140 7.4.6 The Eggs 142 7.4.7 Smerinthus ocellata Larvae 142 7.5 Summary of Results 142 CHAPTER 8 GENERAL DISCUSSION AND CONCLUSIONS 8.1 Environmental Polymorphism in Lepidopterous Larvae 145 8.2 Environmental Polymorphism in Laothoe populi Larvae 147 8.3 Environmental Polymorphism in Smerinthus ocellata Larvae 148 8.4 Genetic Polymorphism in L.