A particulate formulation of Abate was used to control blackfly (Diptera: Simuliidae) larvae in Newfoundland. The effects of this compound on stream invertebrates during routine field use was observed by using drift fauna collected in relation to five insecticide treatments using dosage ranging from 0.059-0.091 ppm Abate applied for 18-23 minutes in four different streams. Invertebrate populations varied from stream to stream and the effects of the insecticide on the drift reflect community structure and physical parameters in the stream. Numbers of larvae of Chironomidae (Diptera), Trichoptera, Ephemeroptera and Plecoptera increase in drift after dosing at concentrations of insecticide less than those recommended for Abate when administered as an emulsifiable concentrate. Drifting blackfly larvae increased from five percent up to 40 percent of total drifting communities after the insecticide was applied.