Genetic studies on glutathione-dependent reactions in resistant strains of the house fly,Musca domestica L

Genetic studies of glutathione-dependent reactions were conducted with a diazinon-resistant house fly strain in which resistance is controlled primarily by genes on chromsome II. The resistant strain was crossed with a susceptible strain which had mutant markers on chromosomes II, III, and V, and the F₁ was backcrossed to the susceptible strain. Glutathione transferase activities of the resultant eight phenotypes were measured using 3,4-dichloronitrobenzene, methyl iodide, and γ-benzene hexachloride as substrates. High levels of all these activities are controlled by gene(s) on chromosome II. Further analysis was made by introducing diazinon resistance into a susceptible strain via genetic crossing-over. Intermediate activity levels for 3,4-dichloronitrobenzene and methyl iodide conjugations were introduced along with intermediate levels of resistance. Assays of individual flies of the synthesized strain revealed they were heterogeneous for glutathione-dependent activities, consisting of individuals with low, intermediate, and high transferase activity. Based on these results, high levels of the glutathione-dependent enzymes are not a major biochemical mechanism responsible for diazinon resistance. It was also demonstrated that glutathione S-aryltransferase and S-alkyltransferase in the house fly, as measured with 3,4-dichloronitrobenzene and methyl iodide, are inseparable genetically and may, therefore, be the same enzyme.