PHOTOPERIODIC INDUCTION OF DIAPAUSE IN AN INSECT

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Abstract
The European corn borer, Ostrinia (=Pyrausta) nubilalis (Lepidoptera: Pyralidae), diapauses as a mature larva in response to short day lengths (< 14.5 hours of light per day). Insects were reared on a synthetic culturing medium and exposed to experimental photo-periods during entire larval growth. Diapause induction was dependent upon numbers of hours of light (photophase) and dark (scotophase) in the photoperiodic cycle, rather than upon the photophase: scotophase ratio. Duration of scotophase was far more critical than that of photophase. Scotophase of from 10 to 14 hours induced diapause, with a 12 hour scotophase being of maximum efficiency. Significant incidence of diapause occurred when a 12 hour scotophase was combined with photophase of any length between 4.5 and 32 hours. Interruption of scotophase by a 1 hour period of light modified the response, the exact effect depending on the position of the light interruption within the scotophase.