Circannual control of the life cycle in the Varied Carpet Beetle Anthrenus verbasci

Abstract

1. Anthrenus verbasci shows a circannual pupation rhythm, and a transfer from long-day to short-day conditions caused a phase shift. Short-day conditions produced synchronous pupation, and the critical day-length was between 13 and 14 h, which corresponded to the natural day-length in September. 2. A decrease in temperature does not seem to act as a zeitgeber under natural conditions, because a change from 25 to 20°C caused no or little phase shift. 3. Under conditions of natural photoperiod and temperature, larvae pupated synchronously in April, although under natural day-length at 20°C larvae pupated in February. Therefore, a decrease in day-length crossing the critical value in September probably shifts the phase of the circannual rhythm so that the gate to pupation opens in February, and probably low temperatures in winter suppress pupation until April. 4. Newly hatching larvae transferred outdoors pupated successfully only when transferred between late April and mid-September, although larvae transferred after mid-July developed into smaller pupae than those transferred earlier. Therefore, synchronous pupation and emergence in spring are needed to allow larvae of the next generation to grow sufficiently before winter.