Benton-FP-1975-Phd-Thesis.Pdf
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LARVAL TAXONOMY ANA BIONOMICS OF SOME BRITISH PIPUNCULIDAE by Forbes Peter Benton A Thesis submitted for the Degree of Doctor of Philosophy, University of London Imperial College Field Station, Silwood Park, Sunninghill, Ascot, Berkshire. February, 1975• ABSTRACT The thesis contains a taxonomic and ecological study of a family of insect parasites, the Pipunculidae (Diptera) which are exclusively endoparasitic in Homoptera, Auchenorrhyncha. Little detailed biological information about them exists; this is surprising in view of their potential in the biological control of leafhopper pests. The present studies extend the basic information on pipunculid biology and for the first time examine the taxonomy of the larvae. Nearly half the total of 77 British species have been found at Silwood Park and 17 of these have been bred out. It was found that several species, particularly in the genus Eudorylas, could not be positively identified with the recently available key (Coe, 1966). Drawings of the male genitalia of most species studied are included and these provide, almost exclusively, good absolute characters for species identification. In studies of biology a Malaise trap was used to sample adult Pipunculidae. Observations on the times of emergence of the larvae from the hosts, together with the analyses of the catches of adults in the Malaise trap, elucidated the life histories of the most common species. Pipunculidae can vary considerably in size intraspecifically depending on the species of leafhopper host attacked. A large number of measurements were made in investigating this phenomenon and some relationships between overall variability and host specificity are suggested. The last part of the thesis contains descriptions of the larvae which were bred out. A key has been prepared for their identification up to generic, and in some instances up to the specific, level. Scanning electron micrographs have been included as an aid to illustrations of characters referred to in the key. Micrographs of the labial plates of the mature larvae of some species show probable sensory receptors which are believed to be hitherto undescribed in the Diptera. TABLE OF CONTENTS • ?AM INTRODUCTION 1 SECTION A Methods of Rearing Pipunculidae 3 Duration of the Pupal Stage 4 Differences in the Pupal Duration between Species 6 Pupal Diapause 7 Effects of Hosts upon Insect Parasites 8 Range of Different Hosts attacked by Pipunculidae 12 The Variability of Adult Pipunculidae in relation to the Number of Different Host Species attacked 17 Other Factors causing Intrinsic Size Variation to vary with Species 28 Graphical Analysis of Polymodal Frequency Distributions 30 Summary and Discussion of Size Variation in Adult Pipunculidae 38 SECTION B' LIFE HISTORIES OF BRITISH PIPUNCULIDAE 62 SECTION C FIELD OBSERVATIONS ON THE OVIPOSITION BEHAVIOUR OF VERRALLIA SETOSA 77 SECTION D THE TAXONOMY OF PIPUNCULID LARVAE 79 Key to Mature Larvae and Puparia of Pipunculidae bred at Silwood Park 81 Detailed Descriptions of Larvae and Puparia 83 Sensory Receptors on the Labial Plates 87 SECTION E THE TAXONOMY OF ADULT PIPUNCULIDAE 117 Descriptions of some British Pipunculidae 119 DISCUSSION 163 SUMMARY 169 Page • ACKNOWLEDGMENTS 171 REFERENCES 172 APPENDIX A 174 APPENDIX B 176 APPENDIX C 178 Descriptions of Pipunculinae from Plattenhardt, W. Germany 179 • 1 INTRODUCTION Pipunculidae are a family of Diptera which are exclusively endoparasitic in auchenorrhynchous Homoptera. The little biological information about them which is available comes from studies on species parasitic on economically important leafhopper pests. This consists mainly of host records and percentages of parasitism. The recent work of Waloff (1975) at Silwood Park, which is probably the most detailed study to date, assesses the importance of Pipunculidae as mortality factors. The present study was undertaken with a view to extending the basic information on pipunculid biology and also to examine the taxonomy of the larvae. It was found in these investigations that some species, particularly those of the genus ERioalsa could not be positively identified with Coets key (1966). Descriptions and drawings of the male genitalia of most species studied have been included in the thesis. During 1974 a large collection of adult Pipunculidae was made near Stuttgart in West Germany. This collection proved very valuable for comparative work with the British species and further descriptions and drawings are given. Particular emphasis was again placed on the male genitalia. Nine new species are described (see Appendix C). Whittaker (1969) used a Malaise trap to sample Verrallia aucta L, a parasite of the common cuckoo spit insect,in his studies at Wytham Woods. Similarly, a Malaise trap was successfully used in the present study at Silwood Park. Data on the seasonal abundance of Pipunculidae were obtained. Several species were taken in sufficiently large numbers to elucidate voltinism. 2 It has been possible to show the extent to which the intra- specific variation in size of adult Pipunculidae is related to the number and sizes of the host species attacked. A large number of head width and wing length measurements were made in investigating this phenomenon and about a third of the thesis is devoted to this subject. In the cyclorrhaphous Diptera the integument of the last larval instar becomes the puparial wall. The chitinised parts of the mature larva are therefore -left in or attached to the wall. Examination of the puparia of bred Pipunculidae of known species is thus necessary in the study of larval taxonomy. Eighteen species were bred and drawingsand stereoscan electron micrographs of seventeen are given in Section D, together with a key for the identification of larvae and puparia to the generic level and in some instances up to the species. Probable sensory receptors are ••• described on the labial plates of some species. No previous electron microscope studies have been made of these receptors. 3 SECTION A METHODS OF REARING PIPUNCULIDAE Apart from the single breeding records scattered in the literature and collected together by Coe (1966) the only other biological work on Pipunculidae comes from economic studies such as Williams (:x.957) on the sugar-cane Delphacidae and their natural enemies in Mauritius and Esaki and Hashimoto (1936) on the leafhoppers injurious to the rice plant and their natural enemies. Little quantitative work is included in the economic studies apart from the recording of percentages of parasitism. Probably the most extensive ecological study of Pipunculidae is that of Waloff (1975) at Silwood Park, where several species were bred out for the first time. Descriptions of rearing methods were also included. During 3 the present study 18 species of Pipunculidae were bred out from 26 different species of leafhopper. The hosts represented a broad coverage of the taxonomic groups of Auchenorrhyncha. Methods The most rewarding results were obtained by collecting parasitised leafhoppers in the field with a sweep net and setting up the infected hosts in tubes in the laboratory. Hosts containing mature larvae are usually quite easy to recognise, at least in the male sex, because the abdomens are greatly distended. As Perkins (1905, p.126) remarks, the host's cuticle may become discoloured (usually to a paler colour). Part of the overall effect of discolouration is due to the stretching of the host's abdomen, revealing the intersegmental membranes, these latter appearing white because the pale internal tissue becomes visible through them. 4 The parasitised leafhoppers were placed individually, with a small piece of food plant, into 3" x 1" glass tubes containing sand to a depth of about The sand was kept moist to keep the humidity up and the tubes were closed by a cork with a large central hole covered with fine muslin to allow free circulation of air. When the mature larvae emerged, which was invariably within three days of collection, they pupated on or just below the surface of the sand. The two species Dorylomorpha haemorrhoidalis Zetterstedt and Dorylomorpha xanthopus Thomson provide interesting exceptions in that they pupated either on the wall of the glass tube or on the food plant (see Section D). Emergence of the larvae took place in all observations by rupturing of the host's integument at the junction of the thorax and abdomen. It has already been established that only a single pipunculid larva develops to maturity in the abdomen of the host; e.g. Williams (1957, p.101) and Keilin and Thompson (1915, p.4). This was also confirmed in the present study although shrivelled and apparently encapsulated first instar larvae were occasionally found together with a normal first instar larva in the same host. Puparium formation was completed within forty-eight hours in laboratory conditions. The duration of the pupal stage was about two and a half weeks. Attempts to get field collected female pipunculids to mate and parasitise leafhopper nymphs in the laboratory a were not successful. DURATION OF THE PUPAL STAGE Several bred Pipunculidae were kept in a 2000 constant temperature room and the time in days was recorded from the beginning of puparium formation to the time of emergence of the imago from the puparium. The data are summarised in Table 1. 5 TABLE 1 Duration in Days of the Pupal Stage at 200C Mean Standard Standard Parasite No. Duration Deviation Error Cephalops semifumosus Kowarz 5 15.30 0.67 0.29 C. semifumosusgv 5 13.50 1.12 0.50 Pipunculus campestris Latreille ? 5 14.80 0.57 0.25 P. campestris dv, 3 13.33 0.58 0.33 Eudorylas subterminalis Collin 6 17.75 0.42 0.17 E. subterminalis dicr 5 17.60 0.55 0.24 The above table shows that the duration of the pupal stage is greater in females than in males in all species. 't' tests were carried out to test for the significance of the difference between sexes (Table 2(a)) and between species (Table 2(b)).