Variation of the number and size of spines on the adult body in Dactylispa Weise 1897 (Coleoptera: Chrysomelidae: Cassidinae)

The three-dimensional morphologies of insects, such as spines and horns, have recently garnered attention as an effective system for elucidating the processes underlying dramatic changes in external morphology. Adult leaf beetles of Dactylispa Weise 1897 exhibit sharp spines on their pronotum and elytra, while their pupae lack such features. In order to obtain foundational data for future investigations into the developmental mechanisms governing spine formation, this study assessed variations in spine numbers across ten body regions and in spine size across three body regions in adults of Dactylispa higoniae (Lewis in Ann Mag Nat Hist (Ser. 6) 17:329–343, 1896. https://doi.org/10.1080/00222939608680376) and D. issikii (Chûjô in Bull Umeno Entomol Lab 6:5–13, 1938). As a result, the degree of variation in spine numbers and size was variable among body regions even within single species. However, the number of spines on the pronotal front margin in D. higoniae and the elytral interval 4 in D. issikii was stable. The spine numbers of these two species did not exhibit significant differences between the right and left sides of the body and was not likely to be influenced by sex or elytral length. Furthermore, we observed pronotal and elytral spines that formed inside the pupal cuticle of late-stage pupae of these two species. Our observations suggested neither pronotal nor elytral spines exhibit a formation pattern resembling concentric folded structures, as seen in beetle horns.