Circannual Rhythms in Insects

Abstract

Although many insects adapt to seasonal changes by photoperiodism, a small proportion of insect species use a circannual rhythm for seasonal adaptations. The circannual pupation rhythm of the varied carpet beetle Anthrenus verbasci shows a periodicity of approximately 40 weeks under constant conditions, and the change in photoperiod acts as a zeitgeber. The circannual rhythm of A. verbasci, of which the larval duration varies from one to several years, probably plays an important role for synchronizing the pupation and breeding times with spring each year. There are only slight differences in the critical daylength for circannual entrainment among geographically distinct populations in Japan, and they pupate in the same period under natural conditions in Osaka. Therefore, A. verbasci can adapt to seasonal changes in different regions without changing the parameters of the circannual rhythm. Long-term endogenous rhythms have also been reported in oviposition and pupation of some ant species. These insects are considered to refer not only to external cues but also to the phase of an endogenous clock for maintaining appropriate seasonality.