A Gross Genetic Analysis of Two DDT-Resistant House Fly Strains

Abstract

A genetical analysis was undertaken for factors conferring DDT resistance in 2 strains of the house fly, Musca domestica L. The Grothe strain possesses a moderate (200-fold) resistance to DDT and is susceptible to the nondehydrochlorinatable analog of DDT, ortho-chloro DDT. The Orlando DDT strain is more highly resistant (>3000-fold) to both insecticides. Both strains were found to possess a fifth chromosomal dominant which confers moderate (100- to 200-fold) resistance to DDT, but does not confer resistance to o-chloro DDT. In addition, the Orlando DDT strain possesses a second chromosomal recessive which confers moderate (100- to 150-fold) resistance to DDT and high tolerance to o-chloro DDT (>3000-fold). The presence of both factors in a single strain confers virtual immunity (more than 5000-fold resistance) to DDT. From crosses between the Orlando DDT strain and susceptible marker strains, 2 substrains were isolated, each possessing only 1 major factor for resistance. Appropriate crosses and bioassays provided confirmation of the nature of the 2 independent factors for resistance. Resistance associated with the fifth chromosomal dominant is that for DDT dehydrochlorinase. The second chromosomal recessive is probably hdr-o as described by Milani (1960, Misc. Pub. Entomol. Soc. Amer. 2: 75-83). The mechanism of resistance associated with this factor is unknown, but apparently it does not involve dehydrochlorination.