Comparative antennal morphology of male Drilini with special reference to the sensilla (Coleoptera: Elateridae: Agrypninae)

Abstract

The click-beetle tribe Drilini (Coleoptera: Elateridae: Agrypninae) contains species with soft-bodied, fully winged males and larviform apterous females. Currently, three genera comprising approximately 120 species have been classified in Drilini – Drilus Olivier, Malacogaster Bassi, and Selasia Laporte. The relationships within the group remain unclear due to the confused taxonomy and variable traditionally used morphological diagnostic characters. To obtain a better understanding of the detailed antennal morphology and its potential taxonomic use within Drilini, we conducted a scanning electron microscopy study of the antennal sensilla of the males of nine species representing all known genera. Additionally, we examined the specimens from three geographically distinct populations of the widely distributed D. flavescens (Geoffroy) to infer the intraspecific variability in their antennal morphology. We observed 20 different sensilla structures in Drilini, belonging to four main types: sensilla chaetica (subtypes C1–C2), sensilla basiconica (B1–B16), Böhm sensilla, and sensilla campaniformia. We found that some sensilla basiconica are useful for the identification of Drilini at the generic and species levels. Malacogaster and Selasia bear several genus-specific sensilla; however, we have not found any sensillum typical for only Drilus. What is more, even the distant geographic populations of D. flavescens differ in the number of sensilla basiconica subtypes. Our results strongly support the close relationship of Drilus and Malacogaster due to their similar antennal sensillar equipment. This study provides the first step towards furthering research on antennal morphology within Drilini and its significance for the taxonomy of the group.