Effect of light pulses in early scotophase on resetting of the night‐measuring diapause clock of the Indian meal moth, Plodia interpunctella

Abstract

Abstract. The Indian meal moth, Plodia interpunctella Hübner (Lepidoptera: Pyralidae) may enter diapause in the last larval instar in response to the photoperiod during the preceding instars. An hourglass‐type photoperiodic clock may measure night length for this purpose. The present study describes the resetting of the hourglass by light pulse(s) in the early scotophase and by scanning the subsequent clock phase by another light pulse (P). When the lights‐off time of a first light pulse is fixed at 4 h after dusk under LD 4 : 20 h and LD 6 : 18 h photoperiods and its duration is increased from 1 to 3 h, the critical night length (CNL) from dawn is decreased, but that from dusk to P increases. A 3‐h first light pulse efficiently resets the time measuring system. If this 3‐h light pulse is split into two 1‐h light pulses (L 1 and L 2 ) by 1 h of darkness, the dark‐time measuring function appears to be impeded and CNL from P to dawn disappears, but that from L 2 to P is expressed. This indicates that the receptivity to light pulses varies among individual insects.