DEVELOPMENT OF RESISTANCE TO PERMETHRIN AND DICHLORVOS BY THE HOUSE FLY (DIPTERA: MUSCIDAE) FOLLOWING CONTINUOUS AND ALTERNATING INSECTICIDE USE ON FOUR FARMS

Abstract The rate at which adult house flies, Musca domestica L. developed resistance to permethrin and dichlorvos, in response to two spray regimes, was studied on eight farms near Guelph, Ontario during 1980 and on four of these farms during 1981. These regimes were: continuous reliance on permethrin or permethrin alternated with dichlorvos throughout the spray season. Where sanitation was comparable, resistance to permethrin developed more rapidly in fly populations from the farms on the continuous permethrin regime than on the farm in which permethrin and dichlorvos had been alternated. Resistance to dichlorvos did not decline under the continuous regime while in the alternately selected flies resistance ratios dropped from 11 to 6 after 2 years. Frequent sanitation delayed the development of resistance in a population continuously selected with permethrin. Alternation of dissimilar insecticides appeared to be a viable means of delaying resistance in the field.