Morphological differences on the mouthparts among six species of cockchafer (Coleoptera: Melolonthinae), with discussions on their feeding habits

Abstract

Melolonthinae represent a megadiverse assemblage of scarab beetles, exhibiting dramatic diversity of feeding habits on the tribal or generic level. As the core feeding apparatus, mouthparts have been relatively underexplored morphologically among genera or tribes within Melolonthinae. In this study, we conducted a detailed dissection and scanning electron microscopic (SEM) analysis of the adult mouthparts from six species across four tribes within Melolonthinae, to provide new morphological characters. The mouthparts exhibit considerable morphological diversity, including variations in labral notches, invaginations on epipharynx, mandibular structures, and the arrangement of setae on the labia. Using SEM, we observed paired invaginations on the epipharynx in Brahmina faldermanni, Hilyotrogus bicoloreus, Polyphylla laticollis and Melolontha incana, which are absent in the Miridiba trichophora, and Apogonia niponica. The structural diversity may be linked to the different feeding habits of these beetles, a relationship that is briefly discussed in the study.