Analysis of gene flow in North American face fly (Musca autumnalis) populations.

Vertical polyacrylamide gel electrophoresis was used to resolve enzymes at ten putative loci in face flies Musca autumnalis De Geer, a colonizing, Palaearctic species established in North America for at least 210 generations. Flies were sampled in 1991 from six locations in Iowa, two in Maryland, two in Minnesota, two in Tennessee, three in New York, and three in Missouri. Nondirectional temporal variation in gene frequencies over a 4-year interval was detected at farms in central Iowa. Heterogeneity in allele frequencies was detected among farms in Iowa, Maryland, New York and Minnesota but not in Tennessee and Missouri. There were no consistent departures from random mating. Partitioning variances in gene frequencies showed that 58% of the variation occurred in populations among states and 43% between populations within states. Mean reproducing immigrants per population per generation was estimated to be eighteen flies. No regional genetic differentiation was detected, and there were no barriers to gene flow within or among diverse populations in the six states. Earlier data bearing on gene flow among and between Nearctic and Palearctic face fly samples were analysed and significant differentiation was not detected.