Genetic variation for resistance to chlorpyrifos in Drosophila melanogaster (Diptera: Drosophilidae) infesting grapes in Israel.

Five species of drosophilid flies were observed breeding in grapes growing in Israel; of these, 2 species, Drosophila melanogaster (Meigen) and D. simulans Sturtevant, are major pests. Natural populations of both species were sampled and tested for resistance to chlorpyrifos; the 2 more intensively sampled populations were D. melanogaster in commercial vineyards. One vineyard had been treated repeatedly with chlorpyrifos to control this secondary pest species; the other had never been treated with an organophosphorus compound. The LC50 to chlorpyrifos of a genetically heterogeneous line of D. melanogaster from the exposed population (Be'er Tuvia) was 99 ng/cm2, and the LC50 of a corresponding line from the unexposed population (Sde Eliahu) was 52 ng/cm2; the wild-caught lines were much more resistant than a laboratory strain, Canton-S, whose LC50 was 0.25 ng/cm2. Genetic variance for resistance existed in both natural populations but realized heritability did not differ significantly between the populations. In crosses between a highly resistant strain and several sensitive laboratory strains of D. melanogaster, resistance was dominant. A resistance factor was mapped to a locus on chromosome 2 (approximately 2-72).