Abstract
The photoperiodic clock in Drosophila triauraria was analyzed with thermoperiods and temperature pulses. In thermoperiods of TCs (thermophase : cryophase) 10 : 14, 12 : 12 and 15 : 9h, a light pulse at the warm (18°C) phase lowered the rate of diapause incidence, but a light pulse at the cool (5°C) phase did not. This suggests that the process measuring night length is retarded at low temperatures (5°C). Both low-(2 and 8°C) and high-temperature (23°C) pulses also decreased the rate of diapause incidence when applied during the scotophase, but not when applied within the photophase. It is assumed that the temperature rising stimuli reset or stop the night-length measurement processes ; i. e., acts as a Zeitgeber. The effectiveness of temperature change as a Zeitgeber was modified by the duration of the temperature pulses. The temperature pulse showed two maximum peaks for this effect, one at 0-4h and one at 8-10h after the onset of teh scotophase. The complex response of the species to low-temperature pulses is considered to be attributable to the combined effects of low temperature itself and temperature changes.
