Delimitation difficulties in species splits: a morphometric case study on the Euxoa tritici complex (Lepidoptera, Noctuidae)

摘要

Genital characteristics tend to vary greatly between Lepidoptera species, providing helpful features for species delimitation. The differences between species are usually remarkable and suspicions about species identity never arise. However, fairly often, and possibly increasingly, taxa are elevated to species rank on the basis of very slight morphological differences, often without quantitative support. Euxoa tritici (Linnaeus) is a typical example of a variable species split into several morphologically similar species. The present study tested whether the diagnostic genital characters of the current classification, based on nonquantitative methodology, provide safe identification of species. Both traditional distance morphometrics as well as modern geometric morphometrics, which also enables quantitative shape exploration, were used. Moreover, whether the study specimens can be unambiguously categorized into several species with visual comparisons was tested independently using four specialist entomologists. Genital types of several named species as well as considerable variation in genitalia were found, but no support was found for the presence of several morphologically distinguishable species with quantitative morphometric analyses. Neitherwere study specimens categorized unambiguously by specialists. The results suggest that pure visual comparisons may lead to unsound taxonomic conclusions and that a quantitative approach in critical cases should be used more frequently.