Biochemistry and genetics of thiodicarb resistance in the house fly (Diptera: Muscidae).

The biochemistry and genetics of thiodicarb resistance were studied in the house fly, Musca domestica L. Bioassays with several strains revealed that a thiodicarb-resistant strain was also resistant to carbaryl and to several organophosphates. Bioassays with a thiodicarb-synergist combination showed that resistance was only partially blocked by use of a synergist, suggesting the presence of target site resistance. The inheritance of resistance to thiodicarb was studied through crosses of the resistant parent to a multimutant, susceptible strain. Bioassays of backcrosses and the F2 generation showed that the major gene(s) conferring resistance to thiodicarb were on chromosome II. Cholinesterase assays showed that the enzyme of the resistant strain was several times more resistant to inhibition by carbamates than the enzyme of a susceptible strain or a strain with only metabolic resistance to insecticides. The data indicate that resistance to thiodicarb in the house fly was mainly because of target site changes. In addition, metabolism may contribute to resistance.