SUMMARYLaboratory and field experimentation has shown that resistant and susceptible diazinon genotypes of flies collected from the field may have similar fitness in an environment free of diazinon. If the genetic background of resistant genotypes from the field is disrupted, the fitness of the resistant genotype declines. These results, in conjunction with previous data, indicate a modification of the genetic background in field populations following the spread of the resistance allele some ten years earlier. It is suggested that this outcome is dependent on the availability of genetic variability, the intensity of selection and the duration of insecticide usage after resistance develops.

Linkage data and revised maps for 52 autosomal loci in L. cuprina are presented. Examination of the linkage relationships of biochemically and morphologically similar mutations in L. cuprina, Musca domestica L. and Drosophila melanogaster (Mg) suggests that the major linkage groups have survived largely intact during the evolution of the higher Diptera.

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