Some effects of low temperature on the photoperiodic clock in Drosophila triauraria

Abstract. Prior studies revealed that the photoperiodic clock in Drosophila triauraria operates during the scotophase and the processes measuring scotophase are composed of two phases: the A phase which lasts 6–7 h from the onset of the scotophase and the B phase which follows the A phase. In this study the photoperiodic clock in this species was analysed by low-temperature pulses. Low temperature (5C) or a low-temperature (2C) pulse of 3 or 4 h decreased the induction of diapause when applied during the scotophase, but not when applied within the photophase. The low-temperature pulse showed two maxima of the effect, 0–4 h and 8–10 h after the onset of the scotophase, approximately corresponding to the A and B phases, respectively. It is considered that low temperature retards the time measurement processes operating during these phases. In the period which was rather insensitive to the diapause-preventing action of low temperature, i.e. 5-7h after the onset of the scotophase, substances or stimuli accumulated during the A phase may be converted to information required for operation of the machinery in the B phase. Experiments using a combination of low-temperature and light pulses suggested that low-temperature decreases the sensitivity to light, especially in the B phase.