Figure 2. Locomotor activity rhythms (actograms) of the blow fly, Calliphora vicina in constant dark at 26 °C (double plotted). It shows unperturbated free-running activity with = 20.9 h in the pre-treated fly. On Day 9, 0.5 µg of 5,7-DHT in 1µl of insect saline/ascorbic acid was injected (arrow) in early subjective day. This caused phase delay by a few hours. The level of locomotor activity was greatly reduced and period was lengthened to 21.4h. The reduction in activity level started 2 days after drug injection and after 4 more days normal level of locomotor activity was regained. Periodograms for the appropriate sections of the activity records are shown alongside the actograms. Lines are drawn through activity periods for better visual inspection of the phase shifts.