Insecticide Resistance in the House Fly: Identification of a Gene that Confers Resistance to Organotin Insecticides and Acts as an Intensifier of Parathion Resistance1

Abstract

A strain of Musca domestica L. known as California Parathion (Cal P-R) possesses an unusually high level (100-fold) of resistance to parathion and is resistant also to organotin toxicants such as tributyltin chloride (TBTC). When the phenomenon of simultaneous resistance to parathion and organotin was investigated toxicologically and genetically, resistance to parathion was found to be conferred only by a single 2nd-chromosomal incompletely dominant gene that is probably allelic with previously reported genes conferring organophosphate resistance. Also, a gene conferring resistance to TBTC was isolated and shown to be a 3rd-chromosomal incomplete recessive; it is designated organotin-R and given the mutant symbol “tin.” When a synthesized strain possessing only the tin gene was crossed with the Tropical “P” classic-wing strain that is moderately resistant to parathion (30-fold), rigorous selection of the F₂ and F₃ generations with parathion resulted in a new strain having 100-fold resistance to parathion and a level of resistance to TBTC identical to that of the parent tin strain. Hence, the tin gene, or a closely linked modifier, acts as an intensifier of resistance and therefore the high level of resistance to parathion in the Cal P-R strain is caused by the interaction of 2 independent major genes.