The Development and Characterization of Resistance to Carbamate Insecticides in the House Fly, Musca domestica1

Two subcolonies of a house fly strain of near normal susceptibility to all insecticides except to members of the cyclodiene group were selected with Isolan® (1-isopropyl-3-methylpyrazolyl-(5)-dimethylcarbamate) and Compound III (3-isopropylphenyl N-methylcarbamate), respectively, during all life stages. After 20 generations of selection with Isolan, a 7- and 19.5-fold resistance to this compound was present in adults and larvae, respectively. Selection with Compound III resulted, respectively, in > 50- and 7.5-fold resistance in these stages. Injection of Compound III indicated a 4.9-fold level of adult resistance. Cross-resistance in the selected strains was nearly complete to carbamates of the general formula where R- was either 2-isopropyl, S-isopropyl, 2-isopropoxy, or 3-tert-butyl; to Pyrolan® (1-phenyl-3-methylpyrazolyl-(5)-dimethylcarbamate); and to Sevin® (1-naphthyl N-methylcarbamate). Cross-resistance to 3,5-dimethoxyphenyl N-methylcarbamate and phenyl N,N-dimethylcarbamate was approximately 10- and S-fold, respectively. Both carbamate-selected strains showed low cross-tolerance ((3-fold) to DDT, Prolan®(1,1-bis (p-chlorophenyl)-2-nitropropane), parathion, Chlorthion®(O-(3-chloro-4-nitrophenyl) O, O-dimethyl phosphorothioate) and dicapthon, and higher cross-tolerance or low cross-resistance (3-to 6-fold) to methoxychlor, malathion, Diazinon® (O, O-diethyl 0-(2-isopropyl-4-methyl-6-pyrimidinyl) phosphorothioate), ronnel and allethrin. Chlorinated hydrocarbon and organophosphorus insecticide-resistant strains manifested cross-resistance levels toward carbamates approximating those exhibited by the carbamate-selected strains. In all cross-resistance tests, some specificity within the N-methyl and N,N-dimethyl carbamate groups was evident. Cross-tolerance to either Isolan or Compound III in combination with piperonyl butoxide (1:5 ratio) was <6- and <3-fold, respectively, in all resistant strains, regardless of history of exposure. Selection of the Compound III-resistant strain for eight additional generations with Compound III plus piperonyl butoxide resulted in only threefold tolerance to this combination.