Phototaxis in the walking male and female fly (Calliphora erythrocephala Meig.) I: The spontaneous phototactic reaction

Investigations into the phototactic behavior of the walking blowfly (C.erythrocephala Meig.) led to the following results: 1. The phototactic behavior of female flies under the controlled test conditions is three-phase: (a) a short phase in the first hours after the final moult, in which no one of the two base orientation directions (towards the light or away from it) is preferred, (b) a strongly photopositive phase on the second day, (c) an intensively photonegative phase during the course of the third day of life. This is preserved with a constant strength until at least the tenth day (Figs. 3a, 4a). 2. The phototactic behavior of the male flies is multiphase: the tactic direction changed rhythmically during the total test duration (12 days) with a cycle of about 3 days. The first photopositive phase on the second day after the final moult coincides exactly with that of the females (Figs. 3 b, 4b). 3. At constant test intensity (I t = 300 Lux) the strength of the positive and the negative phototaxis varies, in both sexes, inversely to the illumination intensity (0 Lux≦Ic≦400 Lux) to which the flies had been exposed in their rearing cages for several hours before beginning the test (Figs.4a, b; 5). 4. With constant rearing illumination in the cage (I c = 40 Lux), deviations from the light direction of the courses walked depend on the test intensity in the following complex manner: with stepwise increase in the test intensity from 10−3 Lux to about 101 Lux the standard deviation in the angles walked decreases; from approximately 102 Lux on, it increases. The variance in the walking angles is larger in the case of young flies (2 days) than with older ones (6 or 12 days; Fig. 6). 5. Long-duration measurements at two-hourly test intervals with constant between-test illumination (40 Lux) show no indication of a correlation, under these test conditions, between the strength of phototactic reaction and the daily light-dark cycle (Fig. 7)