Light Control of Aquatic Insect Activity and Drift

Investigations on aquatic insect activity, measured as drift in an artificial stream system with rigid light and temperature conditions, demonstrated a light—controlled, labile, exogenously—mediated activity rhythm. A threshold value for light, incident at the water surface, which when decreased led to high drift rates, and when increased suppressed activity, was determined to lie between 10 — 3 and 10 — 4 ft—c (10 — 2 and 10 — 3 lux). Preliminary experiments showed variations in wavelength to have little effect on the activity patterns of the insects.