Carbamate Insecticides: Toxic Action of Synergized Carbamates against Twelve Resistant Strains of the House Fly1

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Abstract
When various alkyl, alkoxy, xylyl and heterocyclic carbamates were tested in the laboratory with piperonyl butoxide synergist (1:5 ratio) against strains of the house fly (Musca domestica L.) selected with carbamate, chlorinated hydrocarbon, organophosphorus, and nitroparaffin insecticides, the resistance observed was below the 10-fold level. An exception was a strain selected with Chlorthion® (O-(3-chloro-4-nitrophenyl) O,O-dimethyl phosphorothioate) and subsequently with ronnel (O-(2, 4,5-trichlorophenyl) O,O-dimethyl phosphorothioate), which showed a 129-fold level of resistance to synergized Sevin® (1-naphthyl N-methylcarbamate) but only 5.6-fold resistance to synergized Dimetilan® (2-dimethylcarbamyl-3-methyl-5-pyrazolyl dimethylcarbamate). This specificity of cross-resistance was attributed to parallels in the chemical configurations of ronnel and Sevin. Maximal treatment of flies with piperonyl butoxide did not offset resistance entirely, and it was concluded that carbamate resistance is in part due to components insensitive to the action of piperonyl butoxide.