Landmark-Based Wing Morphometrics for Three Holotrichia Beetle Species (Coleoptera, Scarabaeoidea)

Abstract

Many species of scarabs are remarkably similar in appearance, with some species showing minimal sexual dimorphism, thereby complicating the differentiation between males and females. Geometric morphology techniques, which rely on landmark-based analysis, have proven effective in distinguishing not only closely related insect species but also different sexes within the same species. Traditionally, the shape and size of the hind wings of Coleoptera have not been considered a primary feature for taxonomic identification. However, the potential taxonomic significance of wing venation characteristics among scarabs within the same genus warrants further investigation. This study employs shape analysis techniques based on landmarks to conduct the spatial analysis of wing venation characteristics across three scarab species. The results indicate that both wing shape and size hold significant reference value for discriminating between species and sexes. After accounting for wing size, the accuracy of distinguishing female and male specimens exceeded 94.12% and 76.67%, respectively. The female wings exhibited a wider and shorter morphology compared to the more slender and elongated wings of males. In terms of interspecific differences, H. oblita females displayed narrow and elongated wings, whereas H. diomphalia females had a more rectangular wing shape. Among males, the degree of wing narrowness decreased in the order of H. oblita, H. titanis, and H. diomphalia. These findings underscore the substantial research value of geometric morphometrics in differentiating closely related insect species and their respective sexes.