SIZE OF THE LARVAL BLACK FLY SIMULIUM-TRUNCATUM (DIPTERA, SIMULIIDAE)IN RELATION TO DISTANCE FROM A LAKE OUTLET

High abundance of filter-feeding lotic insects near lake outlets has b een attributed to the high quality/quantity of seston available in thi s habitat. Accordingly, a decrease in food quality or quantity with in creased distance from a lake outlet might be detectable as a decrease in insect size. We examined changes in larval size of the black fly Si mulium truncatum within the first 120 m of a stream draining a small l ake from the Avalon Peninsula, Newfoundland. The observed decrease in larval size with increased distance from the outlet was consistent wit h a decreasing food hypothesis. Laboratory experiments also showed tha t larval size was dependent on food supply.