Hymenoptera Introduction and Key to Families
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Royal Entomological Society HANDBOOKS FOR THE IDENTIFICATION OF BRITISH INSECTS To purchase current handbooks and to download out-of-print parts visit: http://www.royensoc.co.uk/publications/index.htm This work is licensed under a Creative Commons Attribution-NonCommercial-ShareAlike 2.0 UK: England & Wales License. Copyright © Royal Entomological Society 2012 Handbooks for the Vol. VI, Part 1 Identification of British Insects HYMENOPTERA INTRODUCTION AND KEY TO FAMILIES Second edition By Owain Westmacott Richards Department of Zoology and Applied Entomology Imperial College of Science and Technology London SW7 5BD Editor: Allan Watson ROYAL ENTOMOLOGICAL SOCIETY OF LONDON Published by the Royal Entomological Society of London 41 Queen's Gate, London SW7 5HU © Royal Entomological Society of London First published 1956 Second (revised) edition 1977 Printed in Great Britain by Adlard and Son Ltd, South Street Dorking, Surrey CONTENTS Page FOREWORD iv CORRIGENDA lV INTRODUCTION 1 COMPARATIVE MORPHOLOGY Sculpture 2 Head and Appendages 2 Thorax 13 Prothorax 13 Mesothorax 15 Metathorax 22 Propodeum 22 Wings 24 Legs 35 Abdomen 37 LIFE-HISTORY 52 KEY TO FAMILIES. 64 RELATIONSHIPS 76 FIGURES OF WHOLE INSECTS • 77 LITERATURE 88 REFERENCES 88 TERMS AND ABBREVIATIONS 93 GENERAL INDEX • 98 FOREWORD The author has incorporated new morphological, behavioural, life-history and taxonomic information in this new edition, and brought up-to-date the whole of his text. The original drawings have been retained, but modified where necessary; many are reproduced to a larger scale than in the first edition. EOITOR 3rd January 1977 CORRIGENDA Page 3, fig. 7: for epicranial suture read epicranial sulcus Page 17, fig. 34: for pleural suture read pleural sulcus Page 73, fig. 194:for HALICTUS read LASIOGLOSSUM HYMENOPTERA INTRODUCTION AND KEY TO FAMILIES OWAIN WESTM.A.COTT RICHARDS INTRODUCTION THE order Hymenoptera possibly contains more species than any other group of British insects. The smaller parasitic species are still not well known but seem to be very numerous. Nixon, for instance, in the 1940's described more than seventy new British species in the genus Dacnusa. In the IcHNEUMONID.A.E, many genera are thought to contain twice as many British species as have as yet been recorded. There is also a very great deal to discover about the biology of most groups. The most generalized Hymenoptera are found amongst the sawflies. In this group most of the characters of a primitive winged insect may be found, though not necessarily all combined in one species. The wing-venation alone is always of a peculiar Hymenopterous type which has proved difficult to interpret. The structure of the higher Hymenoptera has become extremely specialized and has presented many problems in morphology. Most of the more important of these have now been solved, though there are still many minor points unsettled. Our knowledge of their structure has grown piece meal and terminology has often been devised for a single family or group rather than for the whole order. Only rather recently has much attempt been made to unify the nomenclature with that employed in other insect orders. A thorough survey of the structure of the whole order is therefore necessary, together with an attempt to co-ordinate the terms which have been applied to the same structures in different groups. It may be noted here that the greatest specialization of structure occurs in some of the Parasitica, whereas the greatest specialization of behaviour occurs in the Aculeata. Such insects as the Proctotrupids are much more specialized in structure than a wasp or even a honey-bee, though the social Hymenoptera show the highest peak in the evolution of invertebrate beha viour. It is a pleasure to acknowledge the help I have received from numerous colleagues in the British Museum (Natural History). Dr Perkins, in parti cular, has made a number of discoveries in structure or interpretation which have been incorporated without further acknowledgement. He also greatly helped me with the key to the families. Dr M. G. Fitton updated my nomen clature of the Ichneumonidae. The illustrations of whole insects numbered in Roman figures were drawn by Mrs C. A. O'Brien. 2 VI (1). HYMENOPTERA COMPARATIVE MORPHOLOGY SCULPTURE The surface of the body in Hymenoptera is often sculptured in a variety of ways (punctate, striate, etc.). The paper by Eady (1968) is useful in explaining the descriptive terms in general use. HEAD AND ITS APPENDAGES The head of Hymenoptera is characteristically orthognathous (fig. 2) with its long axis vertical and the mouthparts directed downwards, though all stages to a prognathous head (fig. 1) with mouthparts directed forwards occur. Its dorsal surface is, therefore, normally directed anteriorly and its ventral one posteriorly. It is probably more convenient to describe the head in the orientation in which it will normally be found when the insect is at rest (or dead). The most obvious landmarks for the study of a Hymenopterous head are the compound eyes, the antenna! sockets, the clypeus, the ocelli, the foramen and the proboscidial fossa. The compound eyes (figs 5, 6) in most Hymenop tera occupy the greater part of the side of the head. They are very reduced in many worker ants, though in British forms always represented by at least one facet, and are relatively small in some of the Parasitica. Sometimes numerous hairs arise from between the facets, and not infrequently the inner margin is excised just above the level of the antenna! sockets (e.g., Vespa). The part of the head within this excision is known as the ocular sinus. The front of the head between the eyes is termed the face; it is made up of the clypeus, lower face and upper face (see below). Normally, the antennae are articulated in sockets at about the middle of the face, but the exact position of the antennal sockets (fig. 5) varies in different groups and they may be situated very low down, near the mandibles. The antennal socket is sur rounded by a sulcus defining a narrow antennalsclerite (fig. 3); in IcHNEU MONIDAE the shape of this sclerite is of importance in classification and in some genera (e.g., Tryphon) is produced into large dorsal processes. The clypeus (figs 5, 6) includes the greater part of the face below the antenna! sockets in most Symphyta and Aculeata; in ants it may even extend up between them. It is usually smaller and much further removed from the antennal sockets in the Parasitica (figs 3, 15); in such forms the area between the antenna! sockets, the clypeus and the compound eyes may be termed the lower face. Laterally and dorsally the clypeus is defined by the curved epistomalsulcus (fig. 5). On each side, usually near the top of the epistomal suture is a small pit, the anterior tentorial pit (figs 5, 6, 14), which is a useful landmark in species whose epistomal sulcus is largely obliterated. The pit marks the point where an arm of the tentorium, the internal skeleton of the head, is invaginated. The ventral margin of the clypeus supports the labrum and, primitively, one articulation of the mandibles (p. 9) is at each outer corner. The ocelli (figs 5, 6) lie near the top of the face; they are typically three in number but may be reduced or absent in wingless forms. They vary much in position; the distance from the outer edge of a lateral ocellus to the compound eye is the ocular-ocellar line, OOL, and the distance between the inner edges of the two lateral ocelli is the postocellar line, POL. HEAD 3 Ptcromalus 2 anterior tentorial pit """-____mandible __,~--- clypeus --. cplstomal sulcus "1/~~~=t== antt:nna I sockrt frontal cTest "' frontal arca -4=:::;d------==fro.ntal carina ---frontal line compound f!Yf! ---t'----mf!dian ocf!llus '---!._.!.--==--~--lateral ocf!llus 5 Formica molar space 1----1--"t--onuriortcntoriolpit --',f---+~.- _outu subontennal sulcus 1-~-~~~~ !nner Fms 1-7. (Scale-line, figs 1-2 = 0.5 mm; 3-7 = 1.0 mm) I, Bethylua cephalotea (Fiirst.) (Bethylidae) <jl. Head and prothorax from left side. Prognathous head. 2, Pteromalua puparum (L.) (Pteromalidae) <jl. Head and prothorax from left side. Orthognathous head. 3, Buathra laborator (Thunb.) (Ichneumonidae) cJ. Head in anteroventral view (antennae removed). 4, The same, head in antero-dorsal view (antennae removed). 5, Formica rufa L. (Formicidae) ~- Head in anterior view (antennae removed). 6, Andrena jacobi Perk. (Andrenidae) <jl. Head in anterior view (antennae removed, hairs omitted). 7, Rhogogaster viridia (L.) (Tenthredinidae) <jl. Head in antero-dorsal view (antennae removed). 4 VI (1). HYMENOPTERA The ratio POL: OOL is of importance in the separation of species in several groups; the distance of the lateral ocelli from the back of the head may also be important. The foramen (fig. 8) (perhaps more correctly foramen magnum) is an approximately circular gap in the skeleton of the back of the head through which the internal organs pass from the head to the thorax, these two parts of the body being attached to one another by the cervical mem brane. The proboBcidial fo88a (figs 9, 10, 11) is the hollow in the lower part of the posterior surface of the head into which the mouthparts are received when at rest. Primitively, it is nearly continuous with the foramen but in many forms a bridge (p. 7) is formed which separates them. When these landmarks have been recognized, it is possible to study the morphology of the head in greater detail. The labrum (figs 6, 9, 10), primi tively, is hinged to the ventral margin of the clypeus and is a transverse flap of not very different texture. Such a condition is seen, for instance, in Tenthredo (TENTHREDINIDAE), Brachymeria (CHALCIDIDAE) or ApiB (APIDAE).