EFFECTS OF PHOTOPERIOD AND AGING ON LOCOMOTOR-ACTIVITY RHYTHMS IN THEONION FLY, DELIA-ANTIQUA

At photoperiods longer than 8 h per 24 h, adults of the day-active oni on fly Delia antiqua showed a major peak of locomotor activity in the late photophase and also bursts of activity induced. by lights-on or l ights-off, At shorter photoperiods the activity peaks fused. After tra nsfer from long photoperiods to constant darkness (DD), the rhythm fre e-ran, but only the major peak persisted. This suggests that only the major peak is controlled by the circadian pacemaker. At long photoperi ods, the daily phase of the major peak occurred progressively later wi th age, As a result, the activity at short photoperiods often shifted from photophase to scotophase in old flies. The free-running period (t au) also changed with age; tau was shorter than 24 h until 14-20 days after eclosion and thereafter became longer, but a few individuals rep eated changes in tau. The phase delay of locomotor activity with age i n D. antiqua would be attributable to the increase in tau. (C) 1997 El sevier Science Ltd.