Resistance stability and coadaptation in diazinon-resistant house flies (Diptera: Muscidae)

The mean frequency ( plus or minus SD) of the diazinon resistance allele in Musca domestica L. recently collected from the field in Mississippi was 0.265 plus or minus 0.051. Estimates of reproductive potential (fecundity and developmental time) indicated no differences between resistant and susceptible strains of house flies isolated directly from the field. A backcrossing scheme was used to isolate the resistance allele in a susceptible genetic background. The RR genotype was not at a significant disadvantage compared to the SS genotype, even in the apparent absence of fitness modifiers. Therefore, coadaptation of resistance and fitness does not appear to be important in these populations.