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CABI SILWOOD LIBRARY 24 0066169 2 INSECT HERBIVORE LOAD AND PLANT SUCCESSION GARETH EDWARDS-JONES B.Sc. (Hons) Manchester 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 A sc o t Berkshire September 1988 TABLE OF CONTENTS Sum m ary 1 List of figures 7. List of tables 3 CHAPTER 1 : Introduction 17 1.1 O v e rv ie w 17 1 . 2 .i Host plant spatial distribution 18 1, 2 .ii Host plant density 19 Patch composition 1. 2 . ii 19 1.3 Nutrient availability in the host plant 20 1.4 Chemical defences 21 1 .4 ,i C y a n id e 22 1 .4 . ii A lk a lo id s 23 1 .4 . i i i Glucosinolates 26 1 ,4 .iv F la v e n o id s 28 1 . 4 . v S a p o n in s 28 1 ,4 .iv Terpenes & Resins 29 1 .4 . vii T a n n in s 31 1,4 .v iii Miscellaneous defences 33 1.5 Review of plant/herbivore community and 34 evolutionary theory C H A P T E R 2: M ethods 44 2.1 Experimental sites 44 2.1 .i Site preparation 44 2 . 1. i i Site age and nomenclature 44 2. 1. iii Marking sites 45 2.2 Sam pling 46 2. 2 . i Insect sampling 47 2 . 2 .ii Plant sampling 48 2.3 Data handling and analysis 50 2 . 3 . i Rationale behind database 50 2 . 3 . ii Distribution of the data 52 2 .3 . iii Gamma distribution 52 2.3. iv Generalised linear interactive models (GLIM) 53 2.3.v Other statistics 56 CHAPTER 3: Community Patterns Through Succession 57 3.1 Introduction 57 3.2 Methods 59 3.3 R e su lts 60 3.3. a Plant community 60 3.3. a . i Plant species composition 65 3.3. a.ii Leaf area and the plant community 65 Total leaf area Annual fluctuations in leaf area in a serai stage Trends in the leaf area of major plant families within and between serai stages Proportion of serai stage leaf area, provided by each major plant family Contribution of individual plant species to the total leaf area of a serai stage 3 . 3 . b. Insect Community 84 3.3. b.i Total insect abundance during succession 84 3.3. b.ii Abundance of major herbivore taxa associated with 84 different serai stages 3 . 3 . b.iii Annual variation in insect abundance 86 Total numbers Adult numbers 3 . 3 . b.iv Annual variation in abundance of insect groups 92 3.3. b.v Herbivore species composition 92 Variation in species richness with serai stage Annual variation in species richness Annual variation in species richness of insect g ro u p s Species richness of insect groups feeding on major plant families 3 . 3 .b.vi Variation in insect species composition with 100 successional age Annual variation in insect herbivore species composition 3 . 3 . b . v i i The birch community 1 0 2 Variation in species richness between canopies and y e a rs Proportion of adult individuals in each insect g ro u p Variation in abundance of Oncopsis between canopies and dates 3 .4 D iscu ssio n 1 0 5 C H A P T E R 4: Absolute Abundance over a Successional Gradient 1 1 0 1 1 0 4.1 Introduction 4.2 M ethods i n 4.3 R esults 1 1 2 4 .3 . i Distribution of absolute abundance 1 1 2 4 . 3 . ii Absolute abundance in relation to serai stage 1 1 2 Cicadellidae Delphacidae Curcuiionoidea Heteroptera Minor insect groups - Psyllidae, Cercopidae, Chrysomelidae 4 .3 . ii i Absolute abundance of woody and non-woody 1 2 6 plants 4 .3 . iv Absolute abundance on major plant families 1 2 6 4 .3 .V Absolute abundance and species composition of Cicadellidae feeding on Holcus and Agrostis spp 1 4 1 4 . 3 . vi Comparison of absolute abundance of phloem and 1 4 1 mesophyll-feeding Cicadellidae 4 .4 D iscu ssio n 1 4 4 C H A P T E R 5: Vegetation Structure and the Insect Community 1 4 9 5.1 Introduction 1 4 9 5.2 M ethods 1 5 3 5.3 R esults 1 5 3 Vegetation structure and small scale variation in 5 .3 . i 1 5 3 herbivore abundance and species richness 5 .3 . i i Variation in absolute abundance of species 1 5 8 between different serai stages 5 .3 . i i i Variation in overwintering strategies and species 168 ric h n e s s 5 .3 . iv Variation in absolute abundance of birch 168 herbivores associated with the upper and lower ca n o p y 178 5.4 D iscu ssio n C H A P T E R 6 : Variation in Food Quality and Performance of 182 Erannis defoliaria (Lepidoptera: Geometridae) 6.1 Introduction 6.2 Experiment 1 : The effect of leaf age on the 184 performance of Erannis defoliaria 6.2.i Aim s 184 6 . 2 . i i Materials and methods 184 6.2.11. a The organisms 184 6 . 2 .11. b Sampling and experimental procedure 185 M oths B irc h 6 . 2 . i i . c Measurement of food quality 185 Water content T o u g h n e s s Nitrogen and tannin content Nitrogen content Tannin content 6 . 2 . iii R esu lts 187 6 . 2 . i i i . a M oths 187 6 . 2 . i i i . b Food quality 6.3 Experiment 2 : The effect of the freezing of B . pendula leaves on larval growth 197 6 . 3 . 1 Aim s 197 6 .3 .ii Materials and methods 197 6 .3 . i i . a M oths 197 6 . 3 . i i . b Food 197 6 .3 . iii R esults 197 6.4 Experiment 3: Investigation of the early spring 198 phenology of E^ defoliaria 6 . 4 . 1 Aim s 198 6 .4 . ii M ethods 198 6 . 4 . iii R esults 198 6.5 Experiment 4: The effect of leaf toughness on 200 survival of early instar larvae 6 . 5 . i Aim s 200 6 .5 . i i Materials and methods 202 6 .5 . i i i R e su lts 202 6.6 D is c u ssio n 208 6.7 C o n c lu sio n 209 CHAPTER 7: General Discussion 210 Acknowledgements 214 Bibliography 215 A p p e n d ic e s 232 SUMMARY 1. The thesis aims to test Lawton S M cN eill's (1979) h y p o th e sis that the absolute abundance of herbivorous insects (expressed as number/leaf area of host plant), associated with plants of early succession, is greater than that of herbivores associated with late successional plants. 2. The predicted differences in absolute abundance is related to the postulated differences in the chemical defences of early and late successional plants, being defended by qualitative and quantitative defences respectively. 3. The hypothesis was tested for herbivorous Hemiptera and C oleo ptera d u r in g 1985 a n d 1986 o v e r an e x perim en tal successional gradient at Silwood Park, Berkshire U.K., spanning from very early colonisation of bare ground, through mature pasture to a birch woodland. 4. The hypothesis was found to be true. Differences in absolute abundance between serai stages dominated by herbs and grasses is most likely due to variation in factors other than that in chemical defences, eg predation or nutrient availability. 5. Small scale variation in several community attributes., was correlated with the abundance and species richness of herbivores. Curculionoidea and Auchenorrhyncha differed in their response to small scale variation. Host plant leaf area and structure were important for some species. 6 . Examination of patterns of abundance and diversity of herbivorous insects and plants revealed that diversity of plants is greatest in early midsuccession and insects in early succession. Species richness and abundance of insects were comparable between years. 2 7. Experiments under controlled conditions examined the effect of food quality on the performance of Erannis defoliaria (Lepidoptera: Geometridae). The development time and pupal weight of larvae fed young and old birch leaves were compared. Larvae fed on older leaves generally performed better. These results are contrary to current theory, and are discussed in the light of current plant/herbivore th e o ry . 3 LIST OF TABLES 2.1 Age and nomenclature of serai stages 2.2 Model analysis of deviance table for two-way analysis of deviance (ANODEV) (taken from McCullagh & Nelder, 1985). 3.1 Sorensons Index of Similarity for plant species in each major plant family between in different serai stages. 3.2 Proportion of leaf area provided by the dominant species to the community and major plant families on each date, (a) ruderal 1985, (b) ruderal 1986, (c) early 1985, (d) early 1986, (e) early mid 1985 , (f) early mid 1986, (g) late mid 1985, (h) late mid 1986, and species richness of each plant family and co m m u nity. 3.3 Total, adult and nymphal abundance of each major insect group on sites of different successional age over two years (* = significant at P < 0.05). 3.4 Sorensons Index of Similarity for species in each major insect group between years on serai stages of the same a g e .