Diapause Responses to Photoperiod and Night Interruption in Mamestra brassicae (Lepidoptera : Noctuidae)

Abstract

The pupae of Mamestra brassicae underwent two distinct types of diapause in response to the larval photoperiod. A long winter diapause was induced in 13L11D or longer night-lengths, and a short summer diapause in 15L9D or shorter night-lengths. Nondiapause development was prevalent in 14L10D and extremely short or long night-lengths. A 1hr light break more or less reversed the long-night effects of 4L20D to 13L11D only when it occurred about 9 hr after dusk. In the early scotophase, a light pulse of 3 hr reversed the long-night effect, but a 2hr and shorter ones were ineffective. Nevertheless, such short pulses modified the responses to later night interruptions. In 14L10D, night interruptions induced winter diapause at hour 4-6 from dusk and summer diapause at hour 8. In 15L9D and 16L8D, the incidence of summer diapause varied with the time of night interruption in reciprocal ways. These results seem to suggest various actions of an interrupting light pulse on the time-measuring dark reaction : (i) resetting, (ii) exerting a coincidence effect and (iii) modifying the rate or shifting the phase. Moreover, the involvement of a light reaction in the time-measurement was suspected particularly from the summer-diapause response.