Hymenoptera and Conservation E-Book

T. R. New

• Herausgeber: John Wiley & Sons
• Kategorie: Wissenschaft und neue Technologien
• Sprache: Englisch

Seitenzahl: 507

Veröffentlichungsjahr: 2012

Beschreibung

Hymenoptera, the bees, wasps and ant, are one of the largest insect orders, and have massive ecological importance as pollinators and as predators or parasitoids of other insects. These roles have brought them forcefully to human notice , as governors of some key ecological services that strongly influence human food supply. Recent declines of pollinators and introductions of alien pests or biological control agents are only part of the current concerns for conservation of Hymenoptera, and of the interactions in which they participate in almost all terrestrial ecosystems. Both pests and beneficial species abound within the order, sometimes closely related within the same families. Many taxa are both difficult to identify, and very poorly known. This global overview, the first such account for the whole of the Hymenoptera, discusses a broad range of themes to introduce the insects and their conservation roles and needs, and how their wellbeing may be approached. The book is intended as a source of information for research workers, students, conservation managers and naturalists as an introduction to the importance of this dominant insect order.

Leseprobe

Table of Contents

Cover

Title page

Copyright page

Preface

Acknowledgements

1 Introducing Hymenoptera and their Conservation

Perspective

Classification and diversity

Importance for conservation

Social life and conservation

2 Alien Hymenoptera in Classical Biological Control

Introducing a dilemma

Conservation concerns

3 The Junction of Biological Control and Conservation: Conservation Biological Control and Cultural Control

4 Introduced Bees: Threats or Benefits?

5 Social Wasps and Ants as Aliens

Social wasps

Ants

Current perspective

6 Pollinator Declines

Introducing the concerns

Threats to pollinators

7 Levels of Conservation Concern and the Shortcomings of Current Practice

Foci for conservation

Species focus

Biotope and habitat focus

8 Habitat Parameters and Manipulation

Defining and assessing habitats in the landscape

Habitat manipulations for conservation

Practical conservation

9 Species Case Histories

Franklin’s bumblebee (Bombus franklini)

The great yellow bumblebee (Bombus distinguendus)

Wallace’s bee (Chalicodoma pluto)

Neopasiphae simplicior in Western Australia

The antennal-waving wasp (Tachysphex pechumani)

The dinosaur ant (Nothomyrmecia macrops)

The red-barbed ant (Formica rufibarbis) in Britain

10 Assessing Conservation Progress and Priorities for the Future

Introduction: The basic need

Monitoring

The milieux of concern

References

Index

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Library of Congress Cataloging-in-Publication Data

New, T. R.

 Hymenoptera and conservation / T. R. New.

p. cm.

 Includes bibliographical references and index.

 ISBN 978-0-470-67180-1 (cloth)

 1. Hymenoptera–Conservation. 2. Endangered species. I. Title.

 QL563.N49 2012

 595.79–dc23

2012008091

A catalogue record for this book is available from the British Library.

Wiley also publishes its books in a variety of electronic formats. Some content that appears in print may not be available in electronic books.

Cover image: Hornet © iStockphoto.com/Antagain

Cover design: Design Deluxe

Preface

Hymenoptera, generally believed to be the most advanced of all insect groups, are highly unusual insects in that the worth of many species to humanity and natural ecosystems is recognized widely, and acknowledged by people in many walks of life. The critical roles of bees and other insects in pollination are readily acknowledged as vital in crop production, and so they are key contributors to sustaining food supplies for people, with their losses calamitous and economically damaging both to primary industry and human welfare. Likewise, the widespread values of other Hymenoptera as predators or parasitoids of crop pests anchor them firmly into pest management strategies and accompanying reduction of chemical pesticides, with benefits to both agricultural and more natural environments. Apiary has for long valued bees as sources of honey and wax. On a more esoteric level, the complex social existence of ants and some bees and wasps has for long fascinated ethologists, evolutionary biologists, social commentators (from ‘Go to the ant, thou sluggard’, as said by King Solomon in Prov. 6.6, onward) and science fiction aficionados alike, with numerous – often fanciful – parallels sought between Hymenoptera and human society, and the discipline of sociobiology founded largely in the complex phenomena they display. A practical outcome from such widespread recognitions is that, in marked contrast to many other insects, the needs for conservation of many Hymenoptera are accepted easily in a variety of contexts spanning human needs and interests, and maintenance of biodiversity and ecological integrity. Other species, some of them aggressive invaders outside their natural range, are major economic pests or perceived as harmful because of their painful stings, so that this goodwill is by no means universal.

This book is an overview of the importance of Hymenoptera and their conservation, the contexts that drive this appreciation and need and facilitate progress and the problems that still await solutions. It complements understandings of insect conservation stemming from other groups, notably the Lepidoptera (in particular, butterflies as the single most popular and charismatic insect group that many people intrinsically ‘like’ and on which much insect conservation advocacy and practice is founded) and Coleoptera (also with a strong traditional collector interest and many individual species considered as conservation targets as their declines have become apparent). Both these large orders have received considerable conservation attention, but the rather different foci and major issues needed for Hymenoptera imply that a general appraisal may complement other work in insect conservation constructively, and contribute to a wider synthesis for the discipline to progress through demonstrating the rather different shaping of conservation tactics by the variety of taxa and contexts involved.

Perhaps the major contrast in conservation awareness with Lepidoptera and Coleoptera – all three of these orders massively diverse and ecologically varied – is that single threatened species studies have played a lesser part in Hymenoptera conservation than for either of the other orders. Interest in butterfly conservation had its genesis largely in declines and losses of individual species, signalled mainly by concerned hobbyist collectors amongst well-studied faunas of the northern hemisphere, an approach that flowed naturally to considerations for better-known ‘collectable’ beetle families such as stag beetles (Lucanidae) and ground beetles (Carabidae). Broader approaches to conservation have been stimulated largely by the realization that there are far too many needy species for each to be considered individually by expensive individual management plans, but such exercises are still a core component of many Lepidoptera and Coleoptera conservation exercises. Although some species of Hymenoptera, particularly some bees and ants, have indeed received such individual treatments, and continue to do so, the major impetus for their conservation have been process driven and stimulated by practical needs to sustain their roles in maintaining human needs, or to reduce adverse impacts on natural ecosystems and other biota – for example from invasive alien species of ants or wasps or non-target impacts of biological control agents. Perhaps nowhere are the contrasts between needs for pest suppression and conservation brought into stronger relative focus and – in some cases – conflict, based on both fact and strongly held opinions.

Superimposed on this is simply that Hymenoptera are enormously diverse, as discussed later, and that many groups are very poorly known and difficult or impossible to identify to species levels. Parasitoid wasps, as the largest and most confusing broad category, have been suggested to include more than 20% of all insect species. Both the facts and consequences of losses of species and ecological functions are thus largely unheralded. Enormous numbers of species have yet to be named, and distributional and biological knowledge for many described species is entirely lacking beyond data fortuitously provided on the labels of the type specimen(s). Even within the best-documented faunas – the Hymenoptera of Britain, parts of Western Europe and North America – many gaps in knowledge persist and conservation understanding is limited largely to a restricted subset of the better-known groups, mainly within the so-called Aculeata (p. 2). In many other parts of the world, even diversity of major aculeate groups is very incompletely documented, and their ecological variety can be inferred only in rather general terms: Hymenoptera of much of the tropics, in particular, remain substantially undercollected and undocumented.

My own appreciation of the diversity of tropical aculeate wasps arose in part from within the masochistic ‘personal sauna’ environment of being enveloped in thick clothing, plastic raincoat and full-face protection in the humid tropics of central Brazil. The protective armour was vital in attempts to collect entire nests of social wasps with their occupants, and sometimes from high in trees, for studies on nest architecture and social composition by Professor O.W. Richards and Dr (later, Professor) W.D. Hamilton in which, simply through being there, I participated occasionally with them in the inevitability of getting stung by representatives of almost every local species. The substantial variety of nest structures and habitat preferences of different species (discussed by Richards 1978) were an impressive demonstration of social wasp variety and coexistence of many species in an environment that, even in the late 1960s, was rapidly being changed as road access increased and led to vegetation clearance for large-scale cattle grazing. The contrasts between the central Mato Grosso (where the giant pepsine wasps, ‘tarantula hawks’, seeking equally gargantuan mygalomorph spiders were amongst other memorable Hymenoptera) and my upbringing amongst the British fauna remain vivid. In Britain, my boyhood reference texts [such as Step 1932 and the first edition of The Hymenopterists’ Handbook (Cooper 1943) and early Royal Entomological Society ‘Handbooks’] enabled more or less accurate recognition of many species of sawflies and aculeates, and broader identification of some parasitoid groups. Such accessible but detailed works extending beyond specialist literature simply did not exist for the Neotropical taxa then. Contrasts in our knowledge of different regional faunas of Hymenoptera, and the paucity of up-to-date or comprehensive information on some of these, are difficult for many people to understand but severely hamper appraisals of conservation status and need at other than very general levels. A partial analogy can be made by comparing knowledge across major groups of Hymenoptera in the better-documented countries where, as discussed later, the vast arrays of small parasitoid wasps are amongst the most poorly known insects, in marked contrast to the larger and more typical, ‘popular’ bees, ants and wasps for long familiar to collectors. This contrast becomes striking in examining the lists of Hymenoptera species proposed as of conservation concern on Red Lists and similar compilations – parasitoids (even those, such as the spider wasps, Pompilidae, from within the more popular section of the order) are rarely represented, even for western Europe or North America, and such documentation is almost wholly for other aculeates (Chapter 7).

Literature relevant to Hymenoptera conservation is widely dispersed and, as inferred above, highly biased taxonomically towards some ‘flagship’ groups that collectively represent a rather small proportion of the species involved. Threats to Hymenoptera devolve on habitat changes, many of them associated with changes in resource supply through loss of natural vegetation, impacts of alien species, and effects of pesticides on arthropods and weeds in crop and domestic environments, leading to both direct losses and declines of ecologically sensitive species, and parallel but more indirect impacts through effects on hosts or prey. In contrast to rare Lepidoptera and Coleoptera, accusations of losses of Hymenoptera from ‘overcollecting’ are few, with commercial trade in deadstock markedly less than for those orders. However, trade in living pet ants poses some potential concerns. Much of the current practice and need for Hymenoptera conservation depends on understanding their resource requirements and tailoring or managing environments – including both natural and anthropogenic ecosystems – to supply these without compromising human needs. The major taxonomic biases, controversies, practical problems and ongoing scenarios are exemplified in the sequence of chapters in this book.

The first chapter is a broad introduction to the Hymenoptera, exemplifying their richness, biological variety and ecological roles as a basis for their importance in conservation and some of the problems that arise in pursuing measures for their sustainability. The next group of chapters emphasize the various contexts of Hymenoptera as alien organisms, from being deliberately introduced as classical biological control agents of major importance in pest management but with non-target impacts of parasitoids and predators a persistent concern (Chapter 2) with the allied themes of neoclassical and cultural controls (Chapter 3), to the ambiguous roles of alien bees introduced as pollinators (Chapter 4) and, finally (Chapter 5), the more certain adverse impacts of some alien ants and wasps as among the most harmful of all alien insects, with massive impacts in areas they invade and that can demand sustained and ingenious efforts for their suppression and other control. The twin themes of ‘biological control’ and ‘pollination’ dominate much of the interest in conservation and Hymenoptera, and recent pollinator declines (Chapter 6) are perhaps the single most important impetus for interest in these insects. The wider causes of such declines are summarized within a range of conservation concerns in Chapter 7, leading to emphasis on the roles of habitat and critical resources, with some manipulations of these for conservation management discussed in Chapter 8. The fine-scale attention needed for species-level conservation is noted through examples in Chapter 9, and the extension of conservation scale from species to landscape underpins much of the current priority in hymenopteran conservation. The final Chapter 10 includes a perspective for possible future priorities and actions.

This book is a complement to Beetles in Conservation (New 2010) in exemplifying the roles of another vast insect order in advancing the appreciation of, and needs for, insect conservation. The differing emphasis reflects increased and widespread attention to ecological functions of direct value to humanity as a primary driver of interest, rather than protecting individual species for their own sake. Fowles’ (1996) perceptive comment that ‘Aculeates are a key piece in the ecological jigsaw’ would expand easily to cover the whole of the Hymenoptera. I must confess to similar feelings of inadequacy in preparing each of these two books. The published literature on Hymenoptera rivals that of Coleoptera in bulk, complexity and variety, and several lifetimes would be needed to study more than a fraction of this; the unpublished ‘grey literature’ covering much of recent conservation interest is also complex. The books and papers cited are amongst the most important of those I have encountered and sought (up to September 2011) during only a small fraction of one lifetime, in trying to assess the biological background on which much insect conservation practice depends. I can plead only that I believe the theme of this book to be important and, for such a broad synthesis, ‘someone has to start it off’. I thus reiterate my comment in Beetles that I hope that better-informed hymenopterists concerned about conservation may take up the challenge to ‘refine, correct and expand on the perspective presented here’. If the inadequacies of this book stimulate such a response, it will have been eminently worthwhile to produce it.

T.R. NewDepartment of ZoologyLa Trobe UniversityMelbourne, Australia

Acknowledgements

The following organizations and publishers are thanked for their permission to use or modify material to which they hold copyright: The Australian Entomologist (Entomological Society of Queensland), Brisbane; CSIRO Publishing, Collingwood; The Formica rufibarbis Steering Group (through Scotty Dodd, Chairman, and Paul Lee, Hymettus Ltd), UK; The Glasgow Natural History Society, Glasgow; Écoscience, Université Laval, Quebec; Entomological Society of America, Lanham, MD; Elsevier, Oxford; European Journal of Entomology, eské Budjovice; International Bee Research Association, Cardiff; Finnish Zoological and Botanical Publishing Board, Helsinki; GAIA, Zurich; National Academy of Sciences (USA); Oryx, Fauna and Flora International, Cambridge; Springer Science and Business Media b.v., Dordrecht; Wiley-Blackwell Publishing, Chichester. Every effort has been made to obtain permissions for such use. The publisher apologizes for any inadvertent errors or omissions, and would welcome news of any corrections that should be incorporated in future reprints or editions of this book.

I thank Ward Cooper for his encouragement and continuing advice in initiating and planning this book. Also at Wiley-Blackwell, Kelvin Matthews has dealt patiently and efficiently with my queries during its gestation and Ken Chow with production. Later production was facilitated by the careful copyediting of Maria Teresa M.Salazar of Toppan Best-Set Premedia Ltd, and later preparation by Ruth Swan and Kevin Fung.

1

Introducing Hymenoptera and their Conservation

Perspective

Hymenoptera have many influences on the well-being of natural communities and of people. Perhaps best known to many lay people either as stinging or nuisance pests (wasps, ants), or providers of honey (bees), their complex ecological roles give them central importance in the maintenance of ecological processes and systems. Pollination by bees and wasps is critical in both crop production and floral maintenance in nature, and the complex interactions of numerous hymenopteran predators and parasitoids with prey and hosts are integral components of some pest management programmes and of natural food webs, in which such species are commonly amongst the most diverse and influential taxa present. Yet defining and categorizing these influences, recognizing and enumerating the insects involved and evaluating their ecological roles and the ways in which these can be sustained and the agents themselves conserved are all complex exercises. Perceptions of Hymenoptera thus span the range from being essential and highly beneficial to being serious pests, affecting human welfare and ecological systems in many ways – from being essential to sustaining them to serious agents of change or loss and threats to other biota. Those widely polarized views can sometimes apply even to the same species in different contexts. In particular, conflicts over the roles and impacts of introduced honeybees, bumblebees, and some classical biological control agents have stimulated much debate on the impacts of alien species and the needs to monitor and screen them carefully.

Classification and Diversity

Very broadly, the Hymenoptera conventionally comprises two suborders of insects, with one divided into two large sections. The suborder Symphyta is regarded as the more primitive group of Hymenoptera, and comprises the sawflies and woodwasps, all plant-feeding species on foliage and wood, respectively, and some being serious pests of forestry. The sole exception to this herbivorous habit is the family Orussidae, often included within the Symphyta and the only non-apocritan wasp parasitoids, attacking the larvae of wood-boring insects, although the hosts of only a few of the approximately 75 species are known (Vilhelmsen 2003). The primary feature for the recognition of Symphyta is that they lack the ‘wasp waist’ of more advanced Hymenoptera, so that the thorax and abdomen are joined broadly, without any constriction between them (or, more accurately, between the first and second abdominal segments). Relationships between the various families of Symphyta – globally 14 families are recognized – are still debated, but the group comprises several distinct lineages. This is by far the smaller suborder, with fewer than 10 000 species described throughout the world, and comprising well fewer than 10% of described species within the order. By far the larger suborder, Apocrita, are fundamentally carnivorous, with many of the species being predators or parasitoids, but some have secondarily reverted to plant-feeding habits, as in the gall wasps (of markedly different families), sometimes causing abundant spherical galls on wattles in Australia or oak trees in the northern hemisphere, or as nectar feeders (bees, some ants). However, around 75–80% of species are parasitoids, even though the adult wasps may feed on pollen or nectar or other plant products. With the unifying structural feature of the waist, Apocrita are divided into two major groupings, both taxonomically complex and with an array of rather different groups. The Aculeata are those in which the ovipositor has been modified as an envenomating sting, and the ‘Parasitica’ (sometimes ‘Terebrantia’, but with this name applied more formally to a suborder of thrips) retain a conventional ovipositor. More familiarly, the Aculeata are the conventional ants, bees and wider array of wasps, and so, the Hymenoptera of public perception, and the Parasitica almost wholly parasitoid wasps, depending on other insects and related arthropods as hosts for their survival. The ‘stinging Hymenoptera’ (including stinging parasitoids such as Pompilidae, the spider wasps) are far better known than the non-stinging parasitoids, and contain far fewer species. Unlike the caterpillar-like larvae of Symphyta, the typical larva of Apocrita is grublike, being legless, lacking eyes and, in most, also without antennae. However, the evolutionary unity of these major groups, whilst accepting the use of their names as broad descriptors, is by no means universally accepted amongst hymenopterists, and much of the intraordinal arrangement remains unclear.

Thus, whilst there is little doubt that the Apocrita are a natural group of insects, with a single origin (possibly through the group of ectoparasitoid Symphyta, the Orussoidea, Orussidae), relationships within it are more open to debate. If, as commonly thought, orussids are the sister group to Apocrita, the latter are founded in the parasitoid lifestyle. Different authorities cleave to slightly different taxonomic arrangements and the boundaries between some families are not wholly settled, so that the concept and scope of any large family of Hymenoptera used in publications may need to be defined carefully if comparative appraisals of diversity or abundance are to be made. Grissell’s (2010) refreshing comment on the enormous parasitoid family known as the Pteromalidae is highly pertinent. He wrote: ‘The family…with 39 subfamilies, is actually an aggregation of genera and species, some of which may belong in 10 different other families, but we don’t yet know what those families might be, whether we should name some new families to solve the situation, or even if we should combine all the families in Chalcidoidea into one…. So we just talk about the family Pteromalidae as if it actually existed’. Parallel dilemmas occur elsewhere, as amongst the bees and related wasp groups. Some of the largest families are themselves very complex. Ichneumonidae contains some 35 subfamilies and the related Braconidae 29 subfamilies, for example, with the precise number of such groups depending on the opinion of the individual specialist providing that figure.

With few exceptions, Hymenoptera are not well understood, and members of most non-aculeate groups, in particular, are difficult for non-specialists to identify to genus or species levels, and many specialists also encounter difficulties in this. As Huber (2009) put it, ‘The order Hymenoptera contains far more, and more diverse, species than simply ants, bees and wasps’ and ‘Most Hymenoptera belong to groups unknown to the general public’. Many groups lack non-technical common names. Vast numbers of species remain undescribed, and estimates of richness in many taxa are very variable, with suggestions of total species of Hymenoptera ranging as high as a million (Ulrich 1999) and with around 150 000 so far formally named. Whereas at least half of the Symphyta and Aculeata species have probably been described, perhaps fewer than 10% of Parasitica yet have names (Huber 2009) and, even for most of the named species, biological knowledge (such as of host ranges) does not exist. Even formal names may not represent real species, because of earlier propensity to erect new taxa on small differences of colour or structure, without appreciating the variations within species, and many taxonomic revisions not only add new species but also eliminate many of those described earlier as synonyms. Thus, for the ‘tarantula hawks’ noted in the preface, Vardy (2000) found an initial total of 612 species names, of which 546 remained in the genus Pepsis, but 419 (77%) were considered synonyms after his study. With other changes, including new species, his revised total of these spider wasps was 133 species.

This taxonomic and ecological abundance is largely based in terrestrial biomes, with Hymenoptera virtually ubiquitous wherever any exploitable resources occur. However, Hymenoptera have also developed aquatic associations, with 150 species (representing 11 families) of parasitoids occurring in freshwater environments (Bennett 2008) and the habit apparently originating independently some 50 times. Three major categories are involved: (i) species in which females enter water to seek aquatic hosts; (ii) species with endoparasitoid larvae in aquatic larval hosts, even if oviposition is terrestrial; and (iii) species in which newly emerged adults must travel to the water surface after pupation. Bennett considered his enumeration likely to be minimal because of lack of detailed knowledge for many regions. Ichneumonoidea were the most diverse records (39 species of Ichneumonidae, 26 of Braconidae), and the only apocritan reported is a pompilid (spider wasp), Anoplius depressipes, that captures aquatic spiders and moves them onto land before oviposition (Roble 1985). Collectively, aquatic parasitoid hymenopterans have been reported from at least 25 host families across seven insect orders. Bennett (2008) suggested that the habit may have evolved through wasps parasitizing semiaquatic hosts around the water surface. The variety indicated so far is yet further evidence of the evolutionary exuberance within the order.

Beetles (Coleoptera) have traditionally been considered the group of animals with the most species, but many entomologists feel that Hymenoptera may in fact be leading contenders for this status as more information accumulates. Both orders are hyperdiverse and appear to be well ahead of the other two large holometabolous orders, Lepidoptera and Diptera, in numbers of species. Historically, Coleoptera have been better documented as the subjects of more assiduous collector attention, albeit based largely on the more spectacular groups of beetles. Historical interest in Hymenoptera has been much more uneven, and also biased largely towards the larger and more conspicuous life forms. Groups such as bumblebees and ants are relatively well known, but the enormous array of tiny parasitoids remains one of the most daunting ‘black holes’ in insect documentation. The title of ‘most diverse insect group’ must remain conjectural for the time being, but the ambivalence emphasizes how little we know about the diversity of our predominant animal groups. In addition, quoting from Hawkins (1993), ‘the stunning variety of parasitoids in general and parasitic Hymenoptera in particular, as well as that of their insect hosts almost certainly precludes our ever having a complete record of all the species involved’. Searches for ecological patterns to aid predictions of their diversity and distribution continue, but generality and accuracy are both difficult to achieve at any global scale. As with other hyperdiverse and poorly known invertebrate groups, many approaches to estimating richness have been advanced based on extrapolations from various assumptions or correlations. Dolphin and Quicke (2001) examined some of these for Braconidae, and the various shortcomings can commonly involve regional collecting bias and uncertainty over species integrity and identity; whilst valiant, many such cases still leave much uncertainty over the central question of species numbers. Likewise, the use of biodiversity databases, increasing rapidly in complexity and importance, depends on the reliability and completeness of the information they contain (see approach by Santos et al. 2010 for Ichneumonidae). Any such ‘data-mining’ exercises may be informative, but their limitations must be assessed carefully.

For many Hymenoptera the basic templates are not yet sufficiently complete to form an effective substitute for original investigations. Gauld (1991) suggested, for example, that diversity of tropical Ichneumonidae remains underappreciated because ‘scores of sympatric species’ look very similar whilst flying, and many others are small and inconspicuous. His studies (Gauld 1991 and later volumes) on the Ichneumonidae of Costa Rica imply that this single country has an immensely diverse array of the family; he also commented that if some earlier estimates of the magnitude of insect diversity are correct, this family alone could include more than a million species, but he regarded this as very unlikely.

In contrast to tropical Lepidoptera and Coleoptera, Hymenoptera – particularly many of the small parasitoid groups – were not accumulated abundantly during the nineteenth-century exploration era, so that the bulk of foundation knowledge of their systematics arose largely from studies on temperate region faunas. Even since then, the great majority of Hymenoptera have not been attractive to hobbyists, in part reflecting their small size, difficulties of preservation and study, and inability to identify them without good microscopical equipment, considerable preparation and access to first-class institutional collections and library facilities. The problems have been exacerbated by reared parasitoids commonly being ‘unwelcome’; hobbyists rearing Lepidoptera have frequently been disappointed to find small wasps rather than the butterflies or moths they expected and, historically, many such specimens have been discarded without their importance to documentation being recognized. In short, many parasitoid groups have tended to remain in the domain of the specialist, of whom there are far too few. Some very large families of wasps, for example, of massive taxonomic and ecological complexity are studied by only a handful of specialists throughout the world at any time, and many smaller groups are essentially ‘orphaned’ other than from sporadic attention. Yet some of these insects are amongst the most numerous animals in many terrestrial biomes, and many have complex and often highly specific interactions – for example, as pollinators, predators, parasitoids or competitors – vital to the continuation of other species within those communities. Entomologists seeking to document and understand these processes and the influences of Hymenoptera in natural ecosystems over much of the world must inevitably seek guidance from the perspective gained from study of the best-documented faunas, those of Britain and Western Europe. Even there, however, significant problems remain in identifying species. Representative comments on the British parasitoid wasps (from Barnard 1999) include them being still ‘extremely poorly known’ (British Ichneumonidae), having ‘numerous cryptic species’ (British aphid parasitoids), ‘difficult to identify’ (British Figitidae), ‘frequently posing problems with their identification’ (British Trichogrammatidae) and so on. Collectively, such hymenopterous parasitoids were described in a recent text (Foottit and Adler 2009) as ‘exhibiting incredible levels of species richness, accompanied by an equally high level of diversity in biological habits’.

Evolutionary radiations within parasitoid groups of wasps can become immensely complex to interpret as measures of ‘real diversity’, and are perhaps particularly difficult amongst some of the taxa that have become phytophagous and their parasitoid complexes. Initially, host plant species and associations (such as form of galls induced by the wasps) are often highly specific, and each may then found a unique partnership or community. Specific mutualisms of pollinating fig wasps (Agaonidae) and figs (Ficus) or the community of gall-forming cynipoids on oak trees (Quercus) are two such examples. Both have for long attracted the attention of ecologists, and their study has provided pivotal points in understanding evolutionary processes and some of the factors generating diversity, but both still have many questions of detail unanswered. As examples, recent molecular appraisals have revealed previously unsuspected diversity amongst species of a major genus of fig wasps, Pleistodontes. For Pleistodontes imperialis in Australia, Haine et al. (2006) found four major clades that overlapped in distribution along the eastern border of the continent. They inferred that many fig species host two wasp species as pollinators, so that fig wasp speciation may have proceeded more rapidly than fig speciation, countering the ‘one-to-one’ reciprocal relationship for long traditionally accepted. In some cases, wasp speciation seems to have occurred without a shift in host species. Many such instances of ‘cryptic species’ may occur, with the conservation implication that many local populations presumed to be conspecific may indeed each be unique at this level of differentiation. The oak gall wasps have attracted attention over many years in the Northern Hemisphere, with considerable variety of parasitoids, hyperparasitoids and inquilines associated with the primary gall formers. The complexity of relationships with galls of either a single cynipoid species (such as Andricus quercuscalifornicus; see Joseph et al. 2011 for a representative recent study) or wider assemblage on oaks (such as the 48 parasitoid communities of oak-galling cynipoids discussed by Bailey et al. 2009) is a salutary counter to accepting bland generalities on richness as a basis for conservation management.

The formidable intellectual and practical difficulties of assessing species limits and biological diversity within parasitoid wasps are illustrated well by another recent study, using the modern analytical approach of DNA barcoding to complement more traditional approaches for a suite of microgastrine braconid wasps reared from lepidopterous hosts in Costa Rica (Smith et al. 2008). This, part of a major survey of biodiversity as the most comprehensive study yet undertaken in the tropical fauna, indicated a scenario of variety that may prove to be far more widespread. Initial morphological appraisal of 2597 individual braconids revealed 171 entities assessed as ‘provisional species’; barcoding revealed a further 142 such categories, many of them validated by further and more detailed morphological study stimulated by those results, and by host–species records. Within a single putative ‘morphospecies’ (Apanteles leucostigmus), 36 provisional species were delineated. This study, incorporating only six genera of braconids from a single locality, has emphasized the need to examine many other taxa in equivalent detail as essential to interpreting their ecology and levels of host specificity. Thus, A. leucostigmus was previously considered to be a single species with a broad host range – in the Costa Rica study, comprising caterpillars of 32 species of hesperiid butterflies – but the DNA results implied, rather, that this name is actually applied to 36 distinct species, each of which is restricted to one or very few host species. Smith et al. (2008) noted that even before their study, ‘[identification] of species within this hyperdiverse group is impossible in the field and difficult in the laboratory, requiring a specialist for a particular genus’. Molecular studies help to reveal this variety, but the boundaries between ‘real species’ often remain somewhat unclear. Together with elementary or fragmentary understanding of host relationships, the extent of many such parasitoid assemblages may be impossible to define clearly. More generally, Smith et al.’s (2008) study suggests that, at least for lepidopterous parasitoids within the Area de Conservación Guanacaste, the common presumption of broad host ranges amongst parasitoids may give way to a more frequent scenario of high host specificity and narrow host ranges. That this might be the case also for many other ‘species groups’ of small wasps urges caution in estimating taxon richness, with conventional morphology-based estimates unlikely to reflect reality other than as very minimal estimates. Importantly, their conclusions are based on carefully reared and archived specimens and data that are available for reinterpretation as information accumulates or additional analyses become available. From other studies, such as that by Strange et al. (2009) on museum-stored bumblebees, DNA can be extracted and interpreted meaningfully from insects at least several decades old; in their study, some success was achieved even in many long-dead Bombus up to 101 years old, but was considerably greater in specimens up to 60 years of age. In short, much of the uncertainty over the real diversity of many lesser known Hymenoptera flows from recent molecular studies that have revealed numerous distinctive forms that are morphologically identical (or almost so), and whether these are considered to be separate species.

The more general practical and philosophical point that arises is how to define ‘a species’, and the vast array of different species concepts (see Wilkins 2011) also need to be considered carefully in interpreting and comparing published studies, because different meanings can easily be confounded and lead to inconsistencies and errors. As Gaston (1993) emphasized, lack of consistency over definitions seriously compromises estimating diversity of Hymenoptera, and there is little realistic option at present but to accept any consensus on ‘recognizable taxonomic units’, whilst recognizing that differences in approach across different groups may render comparisons misleading. Individual variations and interpopulation and geographical differences in appearances add to difficulty. Thus, with the Pelecinidae (below), small (individual or regional) differences in extent of fore wing shading within the widespread Pelecinus polyturator implies possible complexity and, together with sex ratio differences in populations in different parts of its range, that more than one entity might be involved. Males and females of some other groups differ markedly in appearance and some have historically been described as separate species.

On traditional approaches, globally, the two ichneumonoid families (Ichneumonidae and Braconidae) are considered the largest families of Hymenoptera and – as with many other families within the order – their real suggested size can be little more than ‘guesstimates’. Both families contain enormous numbers – perhaps a substantial majority – of species as yet undescribed or undiagnosed: in Australia, for example, at least several hundred ichneumonids and braconids lack names at present. Globally, Ichneumonidae may prove to be one of the richest of all insect families, with reasoned suggestions that it might contain up to 100 000 species, with even the more conservative estimates suggesting 60 000 species. As Gauld (1986) commented, ‘There are more ichneumonid species than there are vertebrates’ (see comment on p. 4). Braconidae are presumed less diverse, but still contain an estimated 40 000 or more species. At the other extreme, the global fauna of Heloridae, a distinctive group of parasitoids of green lacewings (Neuroptera, Chrysopidae) barely reaches double figures (12 species recognized in a recent appraisal). Similarly, the Pelecinidae consists of one genus (Pelecinus) containing only three species confined to the New World, although other names and erroneous records (from India, Malaysia and Australia) leave a residual historical impression of greater diversity and distribution, as discussed by Johnson and Musetti (1999). However, fossils of this family indeed imply wider occurrence in the past, and that it might have originated in northern China (Shih et al. 2010).

Table 1.1 indicates the relative species richness of major groups of Hymenoptera; for some, these figures may prove to be substantial underestimates, although the relativity is likely to persist. Two recent authoritative listings of species numbers are included in the table and two caveats are needed for these: firstly, recognition of particular families and their content, and allocation of taxa to family or other higher group is sometimes inconsistent and influential on numbers projected – whether ants are treated as part of the Vespoidea or as an independent superfamily, Formicoidea, for example, affects placement of an agreed entity of considerable richness. Secondly, details of individual numbers inevitably vary with concept and recency of appraisal – both the authorities quoted in this table list source references and temporal ‘end points’ for their data. Ongoing taxonomic work can lead to rapid revisions of any figure, in reflecting an individual worker’s concepts of species.

Table 1.1 The major groups of Hymenoptera and their indicative relative diversity as numbers of described extant species reported by Grissell (2010) (column A) and Huber (2009) (column B).

However, appraising ‘species limits’ is only one aspect of assessing hymenopteran diversity. The other major practical problem is to enumerate the entities, however they are defined, reliably in the field, from samples and collections that may be used to furnish inventories of the species present, both to define diversity at particular sites or in particular biotopes and to compare these across space and time. Much of conservation management depends on such information, both to select priorities and to evaluate progress through monitoring. The difficulties of gaining adequate comparative samples of Hymenoptera on which to base estimates of richness and abundance are in themselves formidable (Morrison et al. 1979; Noyes 1989a,b). Site features such as elevation and aspect are often not heeded sufficiently in comparison, and a wide range of climatic (including microclimate) and vegetation variables render the community at almost any site unique in detail. The individual sampling method used, the ‘sampling effort’, and the deployment of traps in space and season usually produce highly heterogeneous results. Seasonal pattern may mask turnover amongst species that cannot be reflected from short-term or ‘spot’ samples, and that hampers comparative studies. Noyes (1989b) noted that assessments of diversity that incorporate relative abundance of all species present are preferable to species richness alone in facilitating comparisons between samples of different sizes.

A considerable variety of collecting techniques (and more formal ‘sampling methods’, with more quantitative approaches to facilitate interpreting changes over time, or differences across sites) are available, and most hymenopterists have their own favourite approaches, often tempered and modified from personal experience. Some of the methods used to collect adult Hymenoptera are noted in Table 1.2, with comments on their uses. Its purpose is simply to demonstrate some of the broad approaches available, and to urge critical planning and background reading before embarking on any study from which quantitative or semiquantitative assessment or comparison is needed. Most of these have been employed extensively, and perhaps the most important point to emphasize is that they differ markedly in their applications and catch, so that the objectives of a study or survey should be defined as fully as possible as an aid to selecting the ‘best’ approach. Even a technique as apparently straightforward as ‘sweep netting’ (basically, swinging a net back and forth amongst low-growing vegetation to dislodge and retain the insects present) is replete with variables that influence catch spectrum and size – as Noyes (1982) commented for chalcidoids, catches can vary over a range of 1–100% with different techniques and net types. Whilst investigating any method to be used for quantitative surveys or comparisons, some preliminary trials for calibration are wise. As another example, the term ‘pitfall trap’ is deceptively simple and small differences in trap size or deployment can have dramatic influences on the catch. In any report or publication, details of the methods used should be described fully, because without this information it is largely impossible to compare information from different studies; even with it, many problems may persist. If attempting to provide an inventory of the species present in an area or site, the methods used bound the catch in largely unknown ways. Because of the selectivity of methods, and differing behaviours, responses and activity, any attempt to make an inventory by field collecting may need to involve a selection of complementary techniques (a ‘sampling set’; see Disney 1986) because any single one will not alone approach this objective. Numerous compendia of insect sampling and collecting techniques (such as Southwood and Henderson 2000; Samways et al. 2010) indicate the methods available and show the two major categories of ‘active methods’ (in which the collector does the work, such as by netting, sweeping or beating) and ‘passive methods’ [setting traps that the insect encounters through its own activity, such as pan traps (water traps), Malaise traps, intercept traps and others]. These compilations also deal with methods of preserving, processing and examining the catches, an aspect of particular importance for many small Hymenoptera for which examination becomes difficult without well-curated specimens and in which such examination may be vital in order to identify already described species, and to diagnose undescribed taxa.

Table 1.2 Examples of collecting and sampling methods used for Hymenoptera, and contexts for application.

Netting

. Individual netting (e.g. from flowers) used widely for bees and other larger aculeates; can be highly selective, but any factors that affect insect activity can cause bias, so better for ‘collecting’ than for quantitative sampling.

Sweep netting

. Very rewarding, particularly for small parasitoids not obtained easily by other means; mesh and size of net can be very influential. Use only under dry conditions.

Beating

. Useful method for collecting from shrubs and low branches; may be high losses due to flight in warm weather.

Pitfall trapping

. Standard method for ants and other ground-foraging taxa; many biases but employed widely for inventory and other survey contexts. Cheap, convenient for use in remote areas.

Vacuum (suction) sampler

. Useful for grassland and dense vegetation (such as tussocks) not amenable to sweep netting. As with pitfall traps, sorting of catches can be laborious, here compounded by inclusion of much general debris.

Yellow pan or ‘bowl’ traps; water traps

. Excellent technique, recommended highly by many hymenopterists as yielding taxa not collected easily by other methods. Materials cheap and easy to transport; different coloured traps may augment overall catch during inventory surveys.

Intercept traps, such as Malaise trap or window trap

. Passive traps that can be deployed for longer-term catches of flying insects intercepted as they encounter a barrier. Can yield considerable variety, including many small species.

Suction traps

. Useful for aerial insects, but cumbersome to transport and deploy, expensive and dependent on reliable power source.

Light trap

. Can yield nocturnal aculeates and some ichneumonoids, but used only rarely as a main technique in surveys for Hymenoptera.

Litter extraction: Tullgren funnels

. Used commonly for leaf litter, soil and debris, with the insect driven out by heat/desiccation provided by an overhanging light bulb. Laborious, but can yield taxa – such as cryptic soil-dwelling ants – rarely collected by other techniques.

Litter extraction: Winkler bag extractor

. Useful for leaf litter and dense cut vegetation/foliage (such as dense tussocks) and applications similar to Tullgren funnels, except lightweight, transportable and power supply not needed.

Direct searching, litter sifting

. A valuable complement to any other method, with care taken not to destroy limited habitats or resources, such as by digging up ant nests or stripping bark from trees, breaking up rotting wood and so on during targeted searches for particular taxa. Sieving of litter in addition to/prior to extractions as above can reduce volume and allow collection of the larger or more mobile (conspicuous) taxa present.

Insecticide spraying or fogging

. Based on ‘knockdown’ of insects by pyrethrin-based insecticides and collection of specimens from trays or funnels supported below. There are various scales of use, from large mist blowers hoisted to the forest canopy to small hand-held aerosol cans applied to individual plants or substrates such as wooden fence posts.

Emergence traps, emergence boxes

. Samples of putative hosts or of vegetation (foliage, galls, seed pods etc.) retained in the laboratory in dark boxes with an outlet into a collecting tube, and through which emerging parasitoids and others move, attracted by light, and from where they can be retrieved.

Trap nest surveys

. Deployment in the field of artificial nest substrates such as reeds, hollow stems or drinking straws. After some months of exposure, some of these may be colonized as nest sites by various bees and wasps (together with their parasitoids) that are otherwise largely unseen by other methods of inspection.

Transect walks

. Observers walk along predetermined routes, noting and counting the aculeates seen under given limits of weather and times of day to help standardize likely activity. Voucher specimens may be netted for inspection or identification, and outcomes are dependent on individual observer skill.

Numerous field studies on Hymenoptera have involved applications of the above methods, but small details usually differ, so that, whereas different sites or seasons compared by the same workers may be validly assessed as having used identical (or near-identical) sampling, cross-study comparisons are commonly more difficult to appraise. Nevertheless, some consensus on ‘the best methods’ for various Hymenoptera can be made. Thus pitfall trapping is by far the most frequently used survey methods for ants, and is a standard component of wider sampling protocols (Agosti et al. 2000); yellow pan traps are useful for many parasitoids, with the cross-method comparisons by Noyes (1989a) a useful summary; and a combination of pan (bowl) traps and direct netting for bees. For any target group of Hymenoptera, inventory or comparative surveys necessitate highly standardized approaches, with details made available for subsequent reference and enable possible replication or repetition. In conservation studies, detections of trends in species incidence and abundance, species richness and relative abundance and overall community composition are prime needs, so that consistency of sampling over substantial periods is necessary.

Much recent field study emphasis has been on pollinators and ants, and sampling protocols for these groups are, perhaps, better understood than those for many less conspicuous Hymenoptera. The confines of any single sampling method are demonstrated in a recent survey of bees, in which results from ‘bowl traps’ (replicated triplets coloured white, fluorescent blue, and fluorescent yellow) and direct netting across 25 Indiana (United States) sites spanning vegetation from grassland to forests were compared (Grundel et al. 2011) Together, 172 species were captured (57 only in bowls, 44 only by netting and 70 by both methods), with many by only one method. Of the 30 most common species, seven were biased heavily towards one or other method (Table 1.3). The differences from the two methods were largely amongst the rarer species, with many of those recovered in only one trapping series. However, the limitations of this survey, discussed extensively by Grundel et al., include that very much larger samples than those usually accomplished are needed to approach completeness in inventory, with the consideration that such massive sampling effort, even if feasible, might increase threats to rarer species from overcollecting. This and other studies emphasize that the aims and purpose of any inventory survey must be assessed seriously and responsibly in any such context. Perhaps the broadest comparative study of sampling methods yet made for bees across five countries in Europe and comparing agricultural and semi-natural biotopes appraised the values of six commonly used approaches to appraising bee diversity (Westphall et al. 2008). From this, several recommendations of more general value were made to increase standardization and reliability of monitoring (Table 1.4). Across all regimes tested, pan traps were considered most suitable because of high sample coverage, collection of the highest numbers of species, minimum collector bias, detection of generally similar species as transect sighting methods and their overall best indication of bee species richness. Their advantages over transect walks, also valuable for sampling, arose because of the marked observer/collector bias that can occur in that approach. However, use of trap nests yielded species not found by any other approach, so that addition of these to pan trapping was considered likely to maximize survey returns effectively in inventory studies.

Table 1.3 Relative catches (numbers) of North American bees in bowl traps and by direct netting.

Table 1.4 Suggested recommendations for studies for estimating bee species richness.

After Westphall et al. (2008).

Careful consideration of the method/s used to achieve the objectives of the survey most efficiently.

Development of standardized sampling protocols.

Estimation of the amount of time needed for preparation, field work and processing.

Standardization of collector experience, for example through training courses in bee taxonomy, species identification and application of sampling methods.

Sound evaluation of indicator methods prior to the survey.

Validation of sampling effort based on species richness estimators.

Application of rarefaction curves to identify potential collector bias.

As a further informative case study, near Sydney (Australia), Lassau and Hochuli (2005) compared catches of wasps (aculeates and parasitoids) in pitfall traps and flight intercept traps. Of 583 species in total, only 30 species were taken by both methods, and 15 of the 22 families had no species in common. Many of these were represented in only very low numbers but, for example, none of the 36 species of Bethylidae (Aculeata), and only 12 of the most diverse family (Scelionidae, with 186 species) were found in both sets. In this study, the traps essentially separate ground-active (pitfalls) from aerially active (intercept) species, so that the low overlap is not surprising – but awareness of such limitations is clearly important. Many parallel caveats are noted throughout this book. One recurring dilemma is the inability to delimit and name the taxa encountered, a problem common in many other samples of invertebrates and that has led to widespread use of terms such as ‘morphospecies’ as surrogates for taxonomic species in inventory studies. For many groups, the reality of morphospecies as valid surrogates is doubtful, and careful ‘quality control’ through comparisons with material identified by specialists is necessary. One limited field test on Hymenoptera in New Zealand (Derraik et al. 2010) confirmed that different families have differing ‘degrees of difficulty’, and suggested careful selection of suitable groups, coupled with prior training of the nonspecialist people to be involved.

Studies continue, together with energetic debate, over the ‘best’ methods to survey and analyse the richness and diversity of ants and other aculeates. The related debate is over ways to ‘streamline’ surveys and reduce costs through reducing sampling effort but without compromising the reliability of the information obtained. Thus, whereas there is some consensus that pitfall traps are essential for ant surveys, there are wide expressions of variations in their optimal number, spacing and how they may be complemented effectively by other techniques. Optimal combination of methods can differ with habitat features. Thus, in Austria, pitfall trap surveys for ants in montane areas were usefully complemented by colony sampling (direct, timed searches for ant colonies, with voucher workers taken from each for identification of every colony encountered), whereas in floodplain forest, a reduced number of pitfall traps can be augmented by use of Winkler extractions (Tista and Fiedler 2011). Part of the rationale of that study was to explore modification of the ALL protocol (‘Ants in Leaf Litter’; Agosti et al. 2000) for a wider variety of biotopes. The interpretations were based in a pool of 37 species (five of them represented by singletons, so they were excluded from analysis) across 12 genera. Only eight of the remaining 32 species were captured by all four methods used, and catches in pitfall traps (with 30 species) were by far the most representative, with Winkler extractors (19 species), hand sampling (18) and colony searches (18) all closely similar in richness. The important inference from this survey was that a combination of pitfall traps with some other method(s) is ‘essential for a representative survey of resident ant species’, with the most informative comparisons based on complete or near-complete values for the richness present.

Choice of methods for sampling ants or other Hymenoptera must therefore depend on a combination of objectives, habitat characteristics and the resources available for the study. Delabie et al. (2000) emphasized that methods and numbers of samples to be collected depends on what proportion of the resident ant fauna found on the site(s) the inventory is intended to capture. In their comparative trial (in a cacao plantation in Brazil), Winkler extractors yielded more species (63) than any of 16 other methods investigated.

The almost endless variations on methods and permutations employed by different workers to sample any group of Hymenoptera render comparative appraisal of most published studies tentative, with ambiguities sometimes enhanced by incomplete details of the techniques given in reports. Strongly held viewpoints and continuing flow of publications detailing novelties or further modifications of methods seem unlikely to abate in the near future. As for surveys of most other invertebrates, every such survey involves compromise. Establishing and describing hymenopteran diversity, whether species richness or at higher levels involving abundance and distribution, is largely impracticable in any short-term study. Simple detection of species, of course, is far different from understanding their biology. For many parasitoids, only unambiguous rearings in captivity from identified hosts can partially elucidate their needs, so that field capture of adult wasps should ideally be accompanied by collections of possible hosts kept alive in laboratory conditions to detect emergences of wasps at some later stage. Scenarios of daunting complexity can emerge (p. 22), with factors determining host range, and so biological amplitude, of many parasitoid species are very difficult to study comprehensively.

Importance for Conservation

The conservation needs of Hymenoptera must thereby encompass a full spectrum (i) from well-known and sympathetically received groups, with increasing public awareness of their decline and some of the consequences of this: pollinators are the best example; through (ii) pest species, some in their natural range, others distributed widely and considered undesirable aliens in parts of their introduced range; and (iii) to vast numbers of undocumented and undescribed species, many not yet collected or recognized, but accepted as abundant components of local faunas, major facets of natural biodiversity and likely to have evolved specialized and intricate ecologies that may render them vulnerable to changes in local environments. Very broadly, most of the species of sawflies and woodwasps that impinge on human well-being are regarded as ‘pests’ (through feeding on or in vegetation: North American forests, for example, can suffer sawfly defoliation over very large areas) and most of the higher Hymenoptera are rather regarded as beneficial (as pollinators, predators or parasitoids, with some of the latter groups having massive economic importance in biological control programmes). As Gauld and Bolton (1988) remarked in introducing their book: ‘Economically, aesthetically and biologically, there are few groups of animals that are as important to man as the Hymenoptera’. That importance, whether deemed beneficial, harmful or simply unknown, helps to endorse both the need and urgency of their conservation and the variety of contexts in which it may be needed across different taxa, interactions and processes and biotopes. Hymenoptera have been designated as the most biologically varied of all insect groups and, as Riek (1970) noted, the relatively small number of pest species is vastly outnumbered by taxa regarded as beneficial to human interests. Provision of ‘ecological services’ is a particularly strong argument in promoting conservation of Hymenoptera, because these can be demonstrated much more readily than in many other insects, include many of immediate and substantial economic value, and their links with the insects shown to be unambiguous.

Demonstrable, even economically quantifiable benefits from Hymenoptera have thus been a prime motivator for conservation interest. By far the greatest attention to Hymenoptera conservation has been fostered by widespread reports of declines of aculeates, many of these attributed directly to human activity. Major concerns flow, in particular, from losses of the key pollinating species whose impacts on crop production have wide economic ramifications (Matheson et al. 1996), and which have spawned an enormous published literature, some of which is cited in context later. Those concerns have led to additional ecological ones because alien pollinators are often introduced to compensate functionally for these losses. Some of the controversies over introductions of bees have led to heated debate and are discussed later. More broadly within the theme of alien introductions and invasions, some ‘tramp ants’ and vespid wasps in many parts of the world are amongst the most harmful of all invasive species, and some have become the targets of major eradication campaigns to counter their ecological predominance and threats to native animals and plants. By comparison with interests (for conservation or suppression) of such aculeates, calls for conservation of parasitoids are relatively rare, other than in idealistic terms as particular declines – mainly of the hosts – are documented. Most parasitoids are much less tangible and more difficult to recognize than aculeates and Symphyta, but their ecological importance in natural communities and food webs may be just as critical. They also generally lack the common names attractive in fostering communication, although several workers have called for these to be increased – for example, S. Shaw (2006) suggested a range of epithets for an important genus of braconids, Aleiodes, in North America. Even if individual species are not recognizable, the collective guild roles parasitoids dominate attest to their impacts and suggest some of the consequences of their loss. Impressively high figures can be provided for species richness within many of the major parasitoid groups, and numerous studies of the impacts of environmental changes on Hymenoptera assemblage composition and richness, at a variety of spatial scales, have led to suggestions that they can have values as ‘biological indicators’ in association with many environmental changes and in different environments. Any such uses presuppose that the ecology of the taxa is sufficiently well understood that changes across sites and sampling occasions can be interpreted reliably. Particularly in intersite comparisons, undetected differences in species biology may thwart interpretation so that defining ‘ecological subsets’ of species that may respond to similar imposed changes can itself be difficult. Nevertheless, various ecological guilds or ‘functional groups’ of Hymenoptera have been proposed and some are discussed later (p. 18). Henson et al. (2009) noted that presence of such higher trophic level taxa as parasitoids can in itself be an indicator of ecosystem health, as they are often ‘key players’ in complex food webs.