The OCCURRENCE, DEVELOPMENT, STABILITY, and REGRESSION of HOUSE FLY (DIPTERA: MUSCIDAE) RESISTANCE to INSECTICIDES in SLOVAKIA

Abstract:
The resistance of the house fly to insecticides is a limiting factor for its control even in Slovakia, where more than 70% of flies are highly resistant to synthetic pyrethroids (permethrin, cypermethrin, deltamethrin, and lambdacyhalothrin), 66% of fly populations are highly resistant to bendiocarb, 40% to azamethiphos, 32% to dimethoate, and 25% to chlorpyriphos. On the other hand, no resistance to diflubenzuron and cyromazin has been detected. The stability of resistance to azamethiphos, bendiocarb ,and deltamethrin was investigated during 4 years (60 laboratory generations) under laboratory conditions in flies not exposed to the selection pressure by insecticides. The highest stability of resistance was observed for bendiocarb, which decreased considerably starting with the 35th laboratory generation. The decrease in resistance to deltamethrin occurred in four stages, characterized by alternative decrease and increase in resistance factor values. In the case of azamethiphos, a marked decrease in resistance was recorded starting from the fourth laboratory generation. The results obtained in laboratory tests were compared with those obtained under practical conditions in pig houses. An intensive use of insecticides induced resistance in the course of 2 to 3 seasons in dependence on the number of residual spray applications during the season, i.e., from May to September. After cessation of selection pressure, resistance to bendiocarb during 7 years and deltamethrin during 4 years remained at a high level. However, the decrease of resistance to moderate or low level did not solve the problem because a repeated use of insecticides resulted in development of high resistance in about one season.