THE BIOLOGY AND POPULATION ECOLOGY OF flACROSTELES SEXNOTATUS (FALLEN) (CICADELLIDAE, HEnIPTERA) by Miriam Becker, M.Sc. (Brazil) December, 1974 A thesis submitted for the degree of Doctor of Philosophy of the University of London and for the Diploma of Imperial College Imperial College of Science and Technology, Silwood Park, Ascot, Berkshire. 2 ABSTRACT Studies in the laboratory and under field conditions were made on the biology and population ecology of Macrosteles sexnotatus (Fall6n) (Cicadellidae, Hemiptera). Laboratory studies on the biology were carried out under a set of constant temperature conditions. The rela- tionship between temperature and rates of egg and nymphal development are presented and discussed. Effects of tempera- ture on fecundity and longevity were also studied, and choice of oviposition sites under laboratory and field conditions were investigated. Studies were carried out to induce hatching of diapausing eggs and also to induce diapause in the eggs. The internal reproductive organs of males and females are described and illustrated. Illustrated descrip- tions are also given of the five nymphal stages and sexes are distinguished from third instar onwards. Descriptions and illustrations are given of a short winged form which occurred in the laboratory cultures. Population studies_of M. sexnotatus in an catfield • were carried out from 1972 to 1974. Adults and nymphs were sampled regularly with a D-vac suction sampler and occa- sionally with a sweep net. Weekly population estimates were made from June to late September for 1973 and 1974 and for August and September of 1972. Population budgets are presented and causes of mortality are discussed. Losses caused by parasitism in the nymphal and adult stages are 3 shown to be smaller than those within the egg stage. Predation studies on nymphal and adult stages are also included. Dispersal studies on immigration to and emigration from the oatfield were carried out. Dispersing insects were sampled by means of water traps, sticky traps and specially by aerial suction traps. The mode of coloni- zation of the oatfield was analysed and the following period of trivial flight by males was determined. The state of sexual maturity of the females was used as an index of migratory activity. The emigration from the oatfield by the young second generation adults throughout August and September was followed. The relation of flight to weather conditions was analysed. 4 CONTENTS Page INTRODUCTION 9 SECTION I. Biology of Macrosteles sexnotatus 11 1. Life history 11 2. Host plants 12 3. The habitats of M. sexnotatus and of some of its closely related species 14 4. Methods of rearing 19 A. Stock cultures 19 B. Eggs 20 C. Nymphal stages 22 D. Adults 22 E. Parasites 23 (i) Egg parasites 23 (ii) Nymphal and adult parasites 23 F. Predators 24 •5. The nymphal stages 24 A. Description of the nymphal stages 24 (i)Introduction 24 (ii)Descriptions 26 B. The rate of growth 33 • 6. The adult stage ,35 A. Taxonomic literature 35 B. A short winged form 38 7. The internal reproductive organs and sexual maturation 48 A. The male organs 48 B. The female organs 50 C. Mating 54 t 5 Page 8. Laboratory studies on the rates of egg development 56 A. Introduction 56 B. The direct effect of temperature on developmental rates 61 , (i) Material and methods 61 (ii) Results 62 (iii) Discussion 64 C. The effect of acclimatization to temperature on developmental rates 66 D. The 'developmental zero' 68 E. The effect of humidity 69 (i) Introduction 69 (ii) Material and methods 72 (iii) Results 74 (iv) Discussion 74 9. Laboratory studies on diapause 75 A. Introduction 75 B. Induction of diapause in the eggs 79 C. The hatching of diapausing eggs subjected to a period at low temperatures 81 (i) Introduction 81 (ii) Material and methods 82 (iii) Results and discussion 83 10. Laboratory studies on the rate of development of the nymphal stages 84 A. Rearing under constant temperatures 84 (i)Introduction 84 (ii)Material and methods 84 (iii)Results 85 (iv) Discussion 94 4 B. The 'developmental zero'. 95 6 Page 11. Laboratory studies on fecundity 102 A. Fecundity under constant temperatures 102 (i)Introduction 102 (ii)Materials and methods 104, (iii)Results 106 (iv)Discussion 115 B. Fecundity and weight changes in the females 118 C. Ageing effects 122 12. Oviposition sites 126 A. On oat seedlings under laboratory conditions 126 B. On field oats in an outdoor insectary 131 (i)Material and methods 131 (ii)Results 133 (iii)Discussion 135 13. Longevity of the adults 136 SECTION II. Population studies 1. The study area 143 A. Natural grassland 143 B. An oatfield 144 2. Meteorological records 151 • 3. Methods of sampling the population 155 A. Introduction 155 B. Suction sampling 156 C. Sweep net sampling 161 D. Efficiency of suction sampling 164 E. Effectiveness of sweeping: meter equivalent sweeps 174 4. Weekly population estimates 177 • 7 Page 5. The total number of eggs laid 188 A. Estimation of the daily fecundity 188 (i)Materials and methods 188 (ii)Results 189 (iii)Discussion 192 B. Estimation of the numbers of ovipositing females and natality 197 6. Estimation of incubation rates and nymphal duration in the field 197 7. Integration of population estimates 198 8. The population budgets 213 9. The analysis of budget data 219 10. Parasitism in the egg stage 220 A. In natural grasses 220 B. In the oatfield 223 (i)Material and methods 223 (ii)Results 225 (iii)Discussion 229 11. Parasitism in the nymphal and adult stages 231 A. Introduction 231 B. Parasitism by Pipunculidae 233 C. Parasitism by Dryihidae 236 (i)In field populations 236 (ii)Infection tests 238 12. Predation in the nymphal and adult stages 243 A. Predator feeding trials 243 B. Detection of predation by the precipitin test 246 (i)Introduction 246 (ii)Preparation of antigen 247 • (iii) Preparation of the antiserum 248 8 Page (iv) Titre of antiserum 248 (v) Specificity of antiserum 249 (vi) Tests on predators from the field 251 SECTION III. Studies on dispersal 256 1. Introduction 256 2. Methods of sampling dispersing insects 258 A. Aerial suction traps 258 B. Sticky traps 260 C. Water traps 263 D. Regular netting and suction sampling 264 3. The invasion of the oatfield 264 A. Macrosteles spp. as invaders 264 B. The mode of colonization 268 (i) Introduction 268 (ii) Local immigrants 269 (iii) Immigrants from other sources 275 4. The trivial flights of males 281 5. The state of maturation of female ovaries as an indication of migratory activity 284 6. The emigration from the crop by second generation adults 291 • 7. Flight and weather conditions 302 GENERAL DISCUSSION AND SUMMARY 305 ACKNOWLEDGEMENTS 315 REFERENCES 317 S 9 INTRODUCTION The genus Macrosteles Fieber occurs in the Palearctic and Nearctic regions and about fifty valid species have been described within it. Some of the species- occur in natural grasses only while others invade culti- vated crops. All the species of the genus consist of macropterous forms. Cicadellidae in general are slow fliers, easily blown off course by weak winds and are particularly prone to high altitude transport (Johnson, 1969). In North America, M. fascifrons (Stal)engages in long-distance displacements from the breeding grounds. Both in terms of numbers of individuals and in numbers of species, leafhoppers form a most important component of the phytophagous fauna of temperate grass- lands (Waloff & Solomon, 1973). Leafhoppers can be important pests of agricultural crops either by direct feeding and oviposition on green tissues or by their role as vectors of plant diseases caused by mycoplasma-like organisms. M. fascifrons (Stal) is, the principal vector of the aster-yellows disease to plants on a number of • economically important crops in the United States and Canada. In Europe, some of the species of Macrosteles have been detected as vectors of diseases and to cause economic losses to cultivated crops. In England, as other leaf- hoppers, no economic importance is attached to Macrosteles species. • 10 M. sexnotatus is a highly mobile species. In any Population system there are three pathways through which numbers may change: natality, mortality and migration. Most arable crops are initially 'ecological vacuums' (Southwood, 1971) where the whole area is open to coloni- zation and once the insect has invaded it, settled and commenced reproduction population growth in the young crop may be exponential. In the present study, this system was followed in an annual crop which was invaded each year. Laboratory studies supplied and complemented infor- mation on the biology of the species and its relations with natural enemies. • 11 SECTION I BIOLOGY OF MACROSTELES SEXNOTATUS (FALLEN) 1. Life History Maerosteles sexnotatus is a bi-voltine species in Britain and overwinters in the egg stage. It is a widespread species in the Palearctic region and is rather common in grasslands throughout the British Isles. It has polyphagous habits and some of its related species are economically important as vectors of mycoplasmas of the 'aster-yellows' group to cultivated crops. M. sexnotatus is a mobile species though not as much as some other species within the genus. In southern England the overwintered eggs, laid in grasses, begin to hatch in late April. The first generation nymphal £nstars are spent in grassland. During the spring and summer of 1972 to 1974 M. sexnotatus occurred in very low densities in the acidic • grasses of Silwood Park. An experimental plot planted with oats was available for the study of invasion of crops by this species. Invasion commences at the beginning of June and may extend over a few weeks. The immigrants are young adults and soon after settling down shot•: a period of intense flitting, probably trivial flights of males in search of females.