Methoprene was evaluated in commercial caged-layer houses as a poultry feed additive at 7.5 ppm (AI in feed) in the 1974 fly season and at 10 ppm (AI in feed) in the 1975 fly season. In both seasons, the methoprene treatment caused an inhibition of house fly emergence. However, the average percentage of inhibition did not exceed 53 percent in 1974 or 40 percent in 1975. Both levels of inhibition were too low to result in acceptable control of the resulting adult populations of house flies. Also, the level of inhibition gradually decreased throughout the latter part of both seasons until the methoprene treatment had little if any significant inhibition of house fly emergence. In both seasons, it was concluded that the primary causes of these problems were an existing cross-resistance to methoprene in the field strains followed by an induction in resistance resulting from the continuous exposure to methoprene.

Ph. D.