Genetic and biochemical mechanisms limiting fipronil toxicity in the LPR strain of house fly, Musca domestica

Fipronil is a new insecticide which exerts its toxic action by interacting with the insect GABA-gated chloride channel. Previous studies have shown th at cyclodiene-resistant insects have low to moderate levels of cross-resist ance to fipronil, while other resistant strains are usually susceptible. In contrast, we recently found a strain (LPR) of house fly (Musca domestica L ) with 15-fold cross-resistance to fipronil that was not associated with cy clodiene resistance. Fipronil cross-resistance in LPR was inherited as an i ntermediately dominant, autosomal, multigenic trait. [C-14]Fipronil was obs erved to penetrate into LPR flies more slowly than into susceptible flies. S,S,S-tributylphosphorotrithioate and diethyl maleate pretreatment did not reduce the level of fipronil cross-resistance, while piperonyl butoxide res ulted in a slight decrease. These results indicate that decreased penetrati on and monooxygenase-mediated detoxification may be mechanisms contributing to fipronil cross-resistance in the LPR strain. (C) 1999 Society of Chemic al Industry.