Analysis of isozyme loci in the face fly, Musca autumnalis DeGeer

North American face flies Old World origins: mitochondrial evidence

Analysis of a 513 base sequence of mitochondrial cytochrome oxidase I gene in Musca autumnalis De Geer (Diptera: Muscidae) from the U.S.A., England, Russia and Kazakhstan confirms that North American flies originated in Western Europe. Flies from the U.S.A., England and southern Russia shared most of their mitochondrial diversities, but face flies from Kazakhstan were substantially dissimilar, suggesting highly restricted gene flow and a species complex within the Palearctic.

Bionomics of the face fly, Musca autumnalis

The face fly was introduced from the Palearctic region and spread across North America in 20 years after World War II. Adults feed on cattle and horses, and larvae develop in fresh cattle dung. Little genetic differentiation appears between European and North American populations and among regions within North America. After an autumnally initiated diapause, overwintered flies emerge in spring and reproduce through late spring and summer. Generations after the first overlap, and age structure develops toward a stable age distribution. After three to ten generations, depending on weather, facultative diapause interrupts host feeding and oogenesis, and flies with hypertrophied fat body enter overwintering hibernaculae. Life table statistics and factors affecting population growth and diapause are reviewed. Early views on the fly's effects on animal productivity may have been exaggerated. On-farm control by conventional means has not been effective because of the fly's population dynamics and mobility. We suggest that the alternatives of classical biological control and area-wide control with the sterile insect technique should be considered.

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.

Allozyme variation in stable flies (Diptera: Muscidae)

Polyacrylamide gel electrophoresis was used to resolve allozymes in the cosmopolitan blood-feeding stable fly, Stomoxys calcitrans (L.). Nineteen of 38 loci were polymorphic (53%). Mean heterozygosities among all loci and among only polymorphic loci were 0.096 and 0.182, respectively. These gene diversity measures are about half those among other muscid Diptera. Variation in gene frequencies was examined in 10 natural stable fly populations from Iowa and Minnesota. Gene frequencies were homogeneous at five of eight loci among six populations in 1990 and eight of eight loci among four populations in 1992. Wright's F statistics showed no significant departure from random mating among stable flies. It was concluded that gene flow compensates for any local differentiation in stable fly populations.