Arguments against a fifth chromosomal factor in control of aldrin epoxidation and propoxur resistance in the Fc strain of the house fly

The DDT-resistant Fc strain of house flies, Musca domestica L., was analyzed genetically by means of crosses with a susceptible strain carrying a recessive mutant marker for each of the five autosomes. Progeny (substrains) retaining combinations of two, three, or four chromosomes of the resistant parent were selected for measurement of their microsomal aldrin expoidase activity and its correlation with chromosomal makeup and level of resistance to DDT and propoxur. There was no evidence that microsomal epoxidation of aldrin or resistance to propoxur, is associated with chromosome V in the Fc strain as has been reported. Instead, the well-known oxidase regulating factor on chromosome II was of major importance in the strain's microsomal oxidation of aldrin. There was also evidence, though not conclusive, that a factor on chromosome I has an influence on the oxidative metabolism of insecticides in this strain, possibly through an interaction with the factor on chromosome II. The reasons for the conflicting reports on the genetic control of microsomal oxidation in the Fc strain are discussed.