Activation of mating-related behavior by serotonin in males of the Japanese yellow hornet Vespa simillima.

The behavioral physiology of males in social wasps has received little attention, despite the importance of male behavior adapted to complex social environments. To explore the roles of brain biogenic amines in mating-related behavior in male Japanese yellow hornets (Vespa simillima), we first determined the development of mating-related behavior and age-related changes to biogenic amines in the brain. The activities of locomotion, flight, and mating in the males increased with day-age by 1 week after emergence. Testes size decreased within 1 week after adult emergence, suggesting that male sexual maturation may be complete with the development of mating-related behavior. Serotonin levels in the brain increased with age in parallel to the behavioral activities. Dopamine levels in the brain peaked at 2 days of age and then decreased with age, whereas octopamine levels in the brain decreased with age. Thus, serotonin was a candidate compound activating mating-related behavior in males. We then examined the effects of serotonin on the mating-related behavior of males using serotonin injections. Injections of serotonin significantly enhanced activities of locomotion, flight, and mating, depending on serotonin concentration. Those results suggested that serotonin activates mating-related behavior in male hornets.