Exhibition of circannual rhythm under constant light in the varied carpet beetle

Abstract

The varied carpet beetle Anthrenus verbasci shows a clear circannual pupation rhythm under light/dark (LD) 12:12. We examined whether this rhythm is exhibited under constant light (LL) of 0.002 Wm[−2] and 0.9 Wm[−2] intensities. Rhythmic pupation was not observed when the larvae were continuously maintained under LL. Moreover, the circannual rhythmicity of pupation was not observed under LL after pre-exposure to LD 12:12 for 2 or 4 weeks but was observed after exposure for 8 weeks. Under LL of both light intensities, as the pre-exposure to LD 12:12 was longer, the first pupation peaks occurred earlier and almost synchronized with pre-exposure for 8 weeks with the first peak under continuous LD 12:12. However, the transition from LD 12:12 to LL did not reset the phase of this circannual rhythm. Pre-exposure to LD 12:12 probably synchronizes the asynchronous rhythm observed under LL so that a clear circannual pupation rhythm is exhibited.