Comparative Ultrastructure and Ecological Adaptation of Adhesive Setae in Four Species of Longhorn Beetles (Coleoptera).

Longhorn beetles mainly harm trees, flowers, and certain crops. They are closely associated with their host plants and often climb on vertical trunks, branches, and the underside of leaves. Their tarsi have numerous micro-scale adhesive setae on the ventral side. These setae provide sufficient force to enable the beetles to adhere firmly to smooth or slightly micro-structured surfaces. This study observed and analyzed the ultrastructures of the adhesive setae of three species from different subfamilies of Cerambycidae and one species from Vesperidae using a scanning electron microscope. The comparative analysis focused on characterizing the types, morphology, distribution patterns and adhesion mechanisms of the adhesive ultrastructures in four longhorn beetle species. The results showed that the longhorn beetles generally had pseudotetramerous tarsi (except An. chinensis, which had tetramerous tarsi), and that tarsomeres I-III were expanded and widened to increase the contact area between the tarsi and the substrate. Furthermore, a large number of micro-scale adhesive setae were present on the ventral surface of these tarsomeres. In total, five types of adhesive setae were found in the four species studied. The three species belonging to the Cerambycidae family exhibited adhesive setae with numerous short setules, while in the species Mantitheus pekinensis belonging to Vesperidae, there are two types of adhesive setae without any short setules. The differentiation of the adhesive structures in longhorn beetles is shaped by the combined effects of phylogeny, sexual dimorphism, and host-plant adaptations.