THE EFFECT OF ILLUMINANCE ON THE REVERSAL TEMPERATURE IN THE DRONE FLY, ERISTALIS TENAX

¹ Department of Biology, University of Buffalo, Buffalo, N. Y.

1. Observations were made on 2700 young flies in ascertaining the temperature at which Eristalis tenax becomes negative to light in the following illuminances: 250, 600, 800, 1200, and 1600 f. c.

2. As the illuminance increases from 250 to 1600 f. c., the mean temperatures at which the male flies reverse decrease to a minimum at 800 f. c., and then increase.

3. As the illuminance increases from 250 to 1600 f. c., the mean temperatures at which the female flies reverse decrease to a minimum at 800 f. c. Further increase in the illuminance causes no further significant change in the mean reversal temperature.

4. In illuminances of 600 and 800 f. c., the temperature at which Eristalis changes in its reaction to light depends upon the sex of the fly. Females cease their positive reaction to light and become negative at higher temperatures than do the males. This difference between the sexes does not exist at the following illuminances: 250, 1200, and 1600 f. c.