Abstract: The zygaenid moth Pseudopidorus fasciata enters winter diapause as the 4th instar larvae under short daylight with a critical night length of 10.5 h. In the present study the effects of night-interruption experiments, in which the scotophase of a photoperiod was interrupted by a simple light, on diapause-averting were systematically investigated in P. fasciata. The experiments were carried out by using 1 h or 30 min light pulse to interrupt the scotophases of short photoperiods of L9∶D15 (Light 9 h∶Dark 15 h), L10∶D14, L11∶D13 and L12∶D12 at 25℃ at different phases. The results showed that whether diapause was averted by light pulse mainly depended on whether the pre-interruption (D₁) or the post-interruption (D₂) scotophase exceeded the critical night length (10.5 h). When D₁ or D₂ exceeded the critical night length, diapause was always induced. When both D₁ and D₂ were shorter than critical night length, diapause was averted at different degree, mainly depending on the photoperiod applied and the length and position of light pulse. The results revealed that the nightinterruption response of diapause induction in P. fasciata was based on a time measurement of the critical night length.

Key words: Pseudopidorus fasciata, night-interruption, diapause induction, light pulse, critical night length