Studies on the biology of black-fly larvae (diptera: simuliidae) with reference to the structure and function of the feeding organs

The morphology of the rays of the primary fans, the main food collecting organ, of 25 species of black-fly larvae (Diptera: Slmuliidae) were studied using the scanning electron microscope. The form, arrangement, spacing and dimensions of the microtrichia on the rays of these species was recorded. The flicking action of the primary fan was found to be frequent and irregular. The actions of the primary fan and mandible were also studied and their mode of action outlined. Experiments on black-fly larvae of four species (Simulium omatim Mg., S. variegatum Mg., S. monticola Fried, and S. reptans (L. ) ) were conducted in an artificial environment in which current velocity, food concentration and light level could be controlled. Each species was found to differ from the others in its rate of food intake over a range of current velocities. Species with similar patterns of miorotrichia on their head fans had comparable rates of food Intake at the same current velocities. Experiments were done, using a dye-tracer technique, on S. omatum, S. variegatum, S. reptans, S. venustum and S. pictipes- longistylatim in the natural stream habitat of these larvae to determine the rate of intake of natural food. Intake rates varied widely from species to species and within a species depending on current velocity and probably the amount of suspended matter in the stream Larvae of P. ferruglneum (Wahlb.) from Eastern Norway were found to predate on other aquatic arthropods including other species of black-fly larvae. Experiments were conducted on the space requirements of S. omatum larvae in an artificial environment. Densities of up to l4l larvae per sq. cm. were obtained. These densities were much higher than those found in nature. Densities in nature varied widely. Analysis was made of the movements of larvae on an attachment site of limited area