Genetic variation and correlations among responses to five insecticides within natural populations of Drosophila melanogaster (Diptera : Drosophilidae)

To investigate the genetic basis of cross-resistance to insecticides, natur al populations of Drosophila melanogaster (Meigen) were first collected fro m four different locations in Japan. After 10-80 isofemale lines of each po pulation had been established in a laboratory, the susceptibility of each l ine to each of the insecticides permethrin, malathion, fenitrothion, prothi ophos, and DDT was examined. Broad ranges of continuous variation in suscep tibility to all the chemicals were observed within each natural population as a whole. In addition, highly significant correlations among responses to organophosphates were observed. However, based on the coefficients of dete rmination, about less than half of variation in responses to one insecticid e could be explained by variation in responses to another insecticide, sugg esting that not only a common resistance factor but also other factors coul d be involved in a natural population. Genetic analyses by using resistant and susceptible inbred lines from the same natural population demonstrated that resistance to organophosphates in some resistant lines could be due to a single or tightly linked factors, and that resistance in the other line may be due to more than one major factor. These observations could suggest that several resistance factors may be involved within each natural populat ion, and that some of major factors could contribute to correlations among responses to organophosphates. These major factors could then contribute to the broad ranges of continuous variation observed at the level of the popu lations.