The use of acoustic signals as characters in systematic studies is unusual, probably because of a lack of required detailed data, even for relatively well-studied groups. Tishechkin here (Chapter 24) shows how, for the Hemiptera Auchenorrhyncha, when a sufficient database is accumulated, useful conclusions and pointers may be made to systematic relationships.
At the level of biological species, acoustic studies have been widely and effectively used to establish the status of related populations of a wide variety of insects. The term biosystematics, sometimes biotaxonomy, has come in recent years to be used as synonymous with systematics. This is unfortunate as it was originally used in the narrower and more useful sense to include all sorts of studies which might illuminate the genetic, and therefore specific, status of groups of related organisms (Claridge and Morgan, 1987; Claridge, 1988, 1991). A plea is made elsewhere in this book by Drosopoulos (Chapter 18) to return to this usage, a plea which I heartily endorse.
In this narrower sense, biosystematics is a necessary prelude to understanding the process of speciation and therefore of evolutionary divergence in any group. Critical to such studies is the identification of the signalling methods which particular insects use in their specific mate recognition systems (Paterson, 1985; Claridge, 1988; Claridge, Dawah and Wilson, 1997a). These may be of any sensory modality and often mixtures of several. When these are acoustic, recording, analysis and playback are relatively simple. It is therefore not surprising that, unlike general systematics, acoustic studies have been central to much biosystematic work on insects. In this book,
Sueur (Chapter 15) has reviewed this widely in the context of species concepts. Many examples are included elsewhere in this volume — Heller for bushcrickets (Chapter 9); Henry for Neuropterida (Chapter 10); Hoch and Wessel for cave-inhabiting planthoppers (Chapter 13); Drosopoulos et al. and Quartau and Simoes, for different genera of European cicadas (Chapters 16 and 17); Cocroft and McNett for treehoppers (Chapter 23); Strubing for some leafhoppers (Chapter 19); Kanmiya for whiteflies and some Diptera (Chapters 28 and 29) and Kasper and Hirschberger for some dung beetles (Chapter 31). In addition Drosopoulos (Chapter 18) shows how the use of acoustic analyses, in conjunction with other genetic techniques, may illuminate unexpected complications and even parthenogenesis and pseudogamy.
It is clear then that the past 40 years or so have seen enormous developments in the study and understanding of insect acoustic behaviour. It is worthy of study, not only as a subject in its own right, but also for the light it may shed on many fundamental, and indeed also applied, fields of biology, from cell biology and physiology to ethology and evolution. In this volume we have brought together an unprecedented range of expertise from many different countries on all aspects of our subject. We hope that the resulting book adds to the diversity of information now easily available to the general reader, but also that it will stimulate new interests and exciting lines of research.
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