Resetting of the circannual rhythm of the varied carpet beetle Anthrenus verbasci by low‐temperature pulses

Abstract

AbstractThe varied carpet beetle Anthrenus verbasci L. has a circannual pupation rhythm and pupates in the spring in the wild. The change in photoperiod acts as a predominant zeitgeber for this rhythm. However, it is unclear whether the change in ambient temperature acts as a zeitgeber. The present study examines the effects of low‐temperature pulses on this circannual rhythm by exposing larvae kept under constant short‐day conditions (LD 12 : 12 h) at 20 °C to a lower temperature of 15, 10 or 5 °C for 8 or 12 weeks at various phases. Larval development and pupation are suppressed during exposure to low temperature, with this pupation being induced in sufficiently grown larvae within 2 months of a return to 20 °C. These results are attributed to the exogenous suppression and stimulation of pupation, rather than being related to the circannual rhythm (i.e. masking of the circannual rhythm by temperature). Furthermore, long‐term observations demonstrate the existence of phase‐dependent phase shifts of circannual rhythm as a result of low‐temperature pulses. Circannual phase response curves to low temperature are constructed on the basis of the phase shifts obtained. A low‐temperature pulse as a winter signal can reset the circannual rhythm of A. verbasci. It is probable that both temperature and photoperiod play a role in the entrainment of this circannual rhythm to a natural year.