Insecticide Resistance in the House Fly: Effect of a Modifier Gene in Combination with Major Genes Which Confer Resistance13

The modifying effect of a genetic factor that reduces rates of insecticide penetration in Musca domestica L. was studied in combination with major genes conferring resistance to DDT, dieldrin, and malathion. When the gene for reduced penetration was combined with major resistance genes, resistance was increased by factors of 1.5 to more than 100-fold. The increase was least with malathion, intermediate with DDT, and greatest with dieldrin. The results demonstrate that a decrease in rate of penetration is an important component of insecticide resistance in M. domestica. In other tests, peculiarities involved in transmission of the gene for reduced penetration were investigated. The observed anomalies involved crosses in which a susceptible male parent which apparently contained the Y chromosome or male determining factor attached to chromosome 3 was crossed with females of a strain containing the factor for reduced penetration.