Separation of photoperiodic and circadian effects on the termination of diapause in the spider miteTetranychus urticae

Abstract

The same critical nightlength was found for both photoperiodic induction and termination of diapause inTetranychus urticae, indicating that the same clock mechanism operates during both induction and termination of diapause in these mites. Resonance experiments revealed the involvement of the circadian system in the photoperiodic termination of diapause. The period of the circadian oscillation involved in diapause termination was about 1.5 h shorter, however, than that of the oscillation involved in diapause induction. Moreover, the time course of the appearance of the first peak of diapause termination appeared to be different from that of the subsequent peaks in the resonance experiment, suggesting that the mechanism of diapause termination in regimes with nights shorter than the critical nightlength is different from that with nights longer than the critical nightlength. These results lead to the conclusion that the circadian system does not operate as the photoperiodic clock in these mites, as suggested already by experiments on diapause induction.