This study assesses the value of currently available multivariate morphometric techniques in the analysis of the Culicoides pulicaris complex. This midge complex is typical of species groups which are difficult to separate into discrete clusters (species). Initially, emphasis is given to the study of eight nominal taxa in Britain: C. delta Edwards, fagineus Edwards, grisescens Edwards, impunctatus Goetghebuer,.lupicaris Downes & Kettle, newsteadi Austen, pulicaris Linnaeus and punctatus Meigen. Subsequently, material from other parts of the Palaearctic Region is included.
Morphological characters of adults are tested to evaluate the nature and extent of variation. Size is rejected as unreliable, since both intraspecific and seasonal variation is excessive. Allometry of size in legs, antennae and palps is studied in large homogeneous samples of three species and the implications for taxonomy discussed.
A new system for coding wing pattern, utilising pattern elements, is developed and compared to a mechanical scanning method. The former, based on only 13 characters, is preferable, on practical and theoretical grounds, to the scanning method involving 420 characters.
In constructing a classification, two points are considered. Firstly, whether a large number of characters is required for a reliable classification and secondly, whether the recognised species are homogeneous. Using subsets from a total of 72 characters, selected by inspecting inter—character correlations, loadings on principal components, or traditional use, approximately three quarters are found to be superfluous. Using individual specimens as operational taxonomic units to test the homogeneity of species, lupicaris is rejected and another, sp. A, is recognised as new.
Percentiles about the means of each species are incorporated into canonical variate diagrams, for the accurate identification of additional specimens.
A system of classification is developed, in which species are considered as sets with indistinct boundaries. Under these conditions, transition from membership to non—membership of each set is gradual rather than abrupt. The relationship of these findings with current species concepts is discussed.