INCREASED SUSCEPTIBILITY TO BACILLUS-THURINGIENSIS ASSOCIATED WITH PYRETHROID RESISTANCE IN BOVICOLA (DAMALINIA) OVIS (PHTHIRAPTERA MALLOPHAGA) - POSSIBLE ROLE OF MONOOXYGENASES

A comparison of the toxicity of Bacillus thuringiensis (Berliner) to pyethroid-susceptible and -resistant strains of Bovicola (Damalinia) ovis showed that B. thuringiensis and pyrethroid toxicity were inversely related. The B, ovis strain with an apparent monooxygenase-mediated pyrethroid resistance mechanism was significantly more susceptible to B. thuringiensis. Susceptibility to B. thuringiensis in both the pyrethroid-susceptible and -resistant strains was significantly reduced after administration of the monooxygenase inhibitor piperonyl butoxide. Susceptibility to B. thuringiensis in the pyrethroid-susceptible strain was significantly enhanced after administration of a monooxygenase inducer, sodium phenobarbital. These results suggest that monooxygenases may be important in increasing the toxicity of B. thuringiensis against B, ovis. We discuss the potential use of B. thuringiensis to control pyrethroid-resistant lice.