Resistance to a particular class of insecticides, the cyclodiens (e.g. dieldrin), seems to be widely distributed throughout the world in two species of vinegar flies, Drosophila simulans and Drosophila melanogaster/. In ten resistant strains studied so far, resistance is inherited at a single locus (called Rdl for 'resistance to dieldrin") that is homologous between two species. The region containing the susceptible allele of the Rdl gene in D. melanogaster has been cloned and mapped via restriction fragments. The important next step is to determine whether the resistance alleles in each species have a single origin by detailed six-cutter restriction enzyme site analysis of the Rdl gene regions for resistant and susceptible alleles isolated from both species from around the world.
