Laboratory evaluation of fipronil, a phenylpyrazole insecticide, against adult Anopheles (Diptera : Culicidae) and investigation of its possible cross-resistance with dieldrin in Anopheles stephensi

Adult mosquitoes from two strains of Anopheles gambiae and from three strai ns of Anopheles stephensi were exposed to 0.25% fipronil-treated papers in WHO test kits or to 500 mg fipronil m(-2) impregnated mosquito netting in b ioassay spheres. For comparison, tests were also carried out with the pyret hroid permethrin, using the same methods and doses, and on papers treated w ith 0.4 and 4% of the cyclodiene insecticide dieldrin. Compared with the sa me doses of permethrin, fipronil showed less and delayed activity. Two of t he An stephensi strains were resistant to fipronil and dieldrin. To investi gate whether this was due to a resistance mechanism in the An stephensi str ains acting against both insecticides, the most fipronil- and dieldrin-tole rant strain was further selected in two separate lines with one of the inse cticides, followed by tests with the insecticide that the line had not been selected with. This indicated a concomitant rise of resistance to dieldrin in the fipronil-selected line and vice vel sa. Repeated back-crossing of t he two lines with a susceptible strain and re-selection with either dieldri n or fipronil gave evidence for the involvement of a single resistance mech anism to both insecticides. Permethrin resistance in both lines declined wi th selection for dieldrin or fipronil and confirms the absence of cross-res istance between fipronil and pyrethroids. (C) 2001 Society of Chemical Indu stry.