British and Irish Pug Moths: A guide to their identification and biology by & . Harley Books , 2003 . 264 pp. ISBN-13 978 0946589517 .
The Eupitheciini are one of the most speciose and difficult tribes of the Geometridae, Eupithecia alone having well over 1000 described species worldwide, and even with a comparatively restricted fauna in Britain, they constitute a real source of difficulty for workers on Lepidoptera. They are small, generally very similar in external appearance, and more often caught in poor than fresh condition at standard light trapping. The appearance of a specialist book on the British eupitheciine fauna is therefore very welcome.
Riley and Prior bring together in this volume a good summary of the historical records, distribution as presently known, and biology of all the British species, presented in a readily digestible form. They also deal comprehensively with the confusing mass of synonymic names, forms and aberrations which crop up in the literature. There is a good historical review in the introduction, though it is a little surprising that no mention is made in this of the important work done on the continent by such people as Dietze and Petersen: although this was not specifically about the British fauna, it had many implications for it.
As a tool for identification, the book is however somewhat less useful than it should be. The authors are undoubtedly right in asserting that conventional keys are of little use when dealing with this group, and that comparison with good quality colour plates of both fresh and worn specimens is essential. However the plates leave much to be desired, and do not include illustrations of worn specimens: the figures are small, approximately life size, while figures at least twice life size are desirable when dealing with such small insects. The figures are also marred by shadows.
A brave attempt has been made to illustrate groupings with similar characteristics, which is useful as far as it goes, though ‘similarity’ is a somewhat subjective quality. But there are some strange anomalies: for instance, among species listed as having ‘distinct arrow markings on forewing postmedian line’, E. exiguata has been omitted, although it does have such markings very similar to those species which are illustrated.
As the authors suggest, confident confirmation of the identity of many worn specimens requires examination of the genitalia. This is where the book really falls down: illustrations of the male aedeagus and the female bursa copulatrix are reproduced in larger format and more accurately than in Agassiz et al. (1981), and correct at least one error in the latter, but there are no illustrations of the male valves and associated structures other than very crude outlines of valves considered to be distinctive, and the female genital apparatus posterior to the neck of the bursa has been omitted. The genital plates of the male eighth sternite are illustrated only as they would appear in situ on the insect (which of course varies depending on the degree of retraction of the eighth segment), and not in their entirety. This is a step backwards from the illustrations in the work cited above. While many of the male valves in Eupithecia are indeed uniform, there are other structures associated, as for instance the uncus, which are diagnostically very helpful. The same goes in many cases for the female papillae, eighth tergite and apophyses, particularly as the patterns of spining in the bursa can be rather more variable than the authors suggest. The point of attachment of the ductus seminalis is also important, and is not always shown clearly.
The text is more helpful on identification, and some very useful pointers are given, though the user might be forgiven for thinking in some cases that virtually all other British Eupithecia appear under individual entries as ‘similar species’. But that is, after all, the problem with Eupithecia.
This book was a long time in the preparation, no doubt partly due to the sad death of Gaston Prior before it was completed. It has in the meantime been rather overtaken by the appearance of volume four of The Geometrid Moths of Europe, which contains all the European Eupitheciines (Mironov 2003), and which has larger and better produced illustrations and excellent genitalia diagrams. Workers in the UK may well find it helpful to make use of the specifically British information in the present volume, but in my opinion the latter will be found more useful for identification, particularly where examination of genitalia is required.