Fluctuations in the aerial density of Anisopus fenestralis Scop. (Diptera) above sewage bacteria beds

SUMMARY Using a standard 9 in. diameter disc-dropping suction trap, the aerial density of Anisopus fenestralis above bacteria beds was assessed hourly on 410 24-hourly occasions over a period of 19 months, and the prevailing temperatures and wind velocities were recorded. Between o and 10 m.p.h. wind velocity there was a gradual rise in catch associated with a rise in temperature to an optimum, beyond which the catch decreased. This optimum fell as wind velocities rose; it occurred between 70° and 75° F. at winds between 2 and 4 m.p.h., at 65–70° F. with winds between 4 and 6 m.p.h. and at 60–65° F. between 6 and 8 m.p.h. At all temperatures between 30 and 80° F. the catch fell as wind velocity increased from o to 10 m.p.h. By comparing the dusk catches on successive days a significant positive correlation was found between the deviation in log catch from a 3-day running mean and the corresponding temperature deviation, except when the wind velocity deviation exceeded + 2. There was also a significant negative correlation between deviation in log catch from the running mean and the corresponding deviation in wind velocity, except when the temperature deviation exceeded — 2. The average regressions showed that for each °F. rise in temperature the log catch was raised by 0.14 and for each 1 m.p.h. rise in wind velocity the log catch was decreased by 0.19. Expressed arithmetically the catch was doubled by a 2.2° F. rise in temperature or by a fall in wind velocity of approximately 1.5 m.p.h. The aerial density ...