THE EFFECT OF ILLUMINANCE ON THE LETHAL 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 dies in illuminances of 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 and female flies die decrease to a minimum at 600 f. c., and then increase to a maximum temperature at 1600 f. c., about the same as that at which they die in 250 f. c.

3. In illuminances of 250, 600, and 800 f. c., the temperature at which Eristalis dies depends upon the sex of the fly. The females die at higher temperatures in these illuminances than do the males. This sexual difference is not present in illuminances of 1200 and 1600 f. c.

4. There is a correlation between the reversal and lethal temperatures in Eristalis in illuminances of 250, 600, 1200, and 1600 f. c. The higher the reversal temperature, the higher the lethal temperature. This correlation does not apparently exist in an illuminance of 800 f. c.

5. As the light energy to which Eristalis is exposed increases, the resistance of the organisms to heat decreases to a minimum and then rises to a maximum. Consequently, the curve describing these events resembles greatly those curves reported previously by other investigators recording the viscosity changes in certain proteins, lipids, and protoplasms, and changes in rates of certain enzyme reactions, on exposure to rising temperature.