Mating behavior and functional morphology of genitalia in longhorn beetle Dorysthenes granulosus (Coleoptera: Cerambycidae: Prioninae)

Abstract

Sexual selection is a driving force behind the evolution of insect genitalia morphology. Understanding the functional morphologies of mating-related structures can help explain the evolution of diverse genital morphologies. However, this research is limited to many insect groups, such as the Cerambycidae. We observed the mating process and morphology of mating-related structures of the longhorn beetle Dorysthenes granulosus (Thomson) (Coleoptera: Cerambycidae: Prioninae). Our observations revealed mating behavior characteristics and the functional morphology of genitalia and leg tarsi. The mating process of D. granulosus can be divided into three stages: mounting, insemination, and guarding. The male usually spends 30 min from mounting to control the female, then extends its endophallus and typically inserts it twice into the female reproductive tract. Each insertion lasts for about 40 s. After that, the male begins a long-time insemination, which lasts for two to three minutes. Then, the male withdraws the endophallus and the female reproductive tract secretes a sperm mass. After insemination, some males continue to mount the female for a postcopulatory guarding period, which can last from one to five hours. During copulation, barbs on the surface of the everted male endophallus directly contact the female reproductive tract. The male fore and mid leg tarsi firmly grasp the female elytra, thorax, and abdomen. We discuss the functional morphologies of mating-related structures and the possible reason for male multiple insertions in the Cerambycidae.