Diazinon and V-C-13 granular formulations, applied as furrow treatments at the rate of 1 and 2 pounds toxicant per acre, and diazinon wettable powder as seed treatment at [Formula: see text] ounces toxicant per pound of seed, effectively controlled populations of the onion maggot, Hylemya antiqua (Meigen) resistant to cyclodiene insecticides in southwestern Quebec, in both mineral and organic soils. EN 18133 granular formulation was also very effective but caused a slight delay in germination without, however, affecting the stand or decreasing the yield to any extent. Ethion, Trithion and Guthion granular formulations as furrow treatments at either 1 or 2 pounds toxicant per acre, and also as wettable powder seed treatments at the rate of 1 ounce toxicant per pound of seed, were significantly inferior to Diazinon, V-C-13 and EN 18133. Dylox water soluble powder, applied as a drench post-emergence treatment at 4 pounds toxicant per acre, gave poor control.