Phase-shifting effects of a light pulse interrupting scotophase on locomotor activity rhythm and photoperiodic time measurement for diapause in the onion fly, Delia antiqua


Dr Yasuhiko Watari, Laboratory of Biotechnology, Faculty of Education, Ashiya University, Rokurokuso-cho 13-22, Ashiya, Hyogo, 659-8511 Japan. Email:


When a light pulse of 1 h duration was given 3 h after lights off in a photoperiod of 11 h light : 13 h dark (LD 11 : 13) at 20°C, the phase of the major peak of locomotor activity rhythm in Delia antiqua was delayed for approximately 0.6 h. In contrast, it was advanced by approximately 0.6 h by a light pulse given 9 h after lights off. It is suggested that in the circadian clock, a pulse falling in the early scotophase is taken as a new dusk and a pulse falling in the late scotophase is taken as a new dawn. Although a sharply defined critical photoperiod did not exist in the diapause response to photoperiod in D. antiqua, the percentage of pupal diapause decreased by these pulses in LD 11 : 13 at 20°C. The effect of a 15 min light pulse on both locomotor activity rhythm and pupal diapause induction was stronger at 3 h than at 9 h after lights off, while a 1 min light pulse was ineffective at both times. The parallel effects of light pulse on locomotor activity rhythm and diapause response might be based on the same chronobiological functions.