Genetic population structure in olive fly Bactrocera oleae (Gmelin): gene flow and patterns of geographic differentiation

Four wild Spanish populations of Bactrocera oleae (Gmelin) (Dipt., Tephriti dae) were studied by gel electrophoresis, in order to find out their popula tion genetic structure and the relative importance of gene flow in that str ucture. A great amount of genetic variability was observed. In terms of the pattern of the genetic variability in our populations, the most noticeable characteristics were the similarity of the configuration of allelic freque ncies from locality to locality, the existence of exceptions and quantitati ve differences within that similarity, and the heterogeneity among the vari able loci. Gene flow estimated from Wright's method gave a value of Nm = 8. 9. However, the F-ST statistic in three of the loci ranged from 0.0451 to 0 .0620 indicating a substantial degree of differentiation among populations (P < 0.001). The present observations seem to support the hypothesis that a lthough gene flow could be high (Nm = 8.9), 'natural' selection, probably d ue to agricultural practices, may be the major factor responsible for the p attern of the genetic variability observed in B. oleae.