Genetic Structure of Apple Maggot Fly (Diptera: Tephritidae) Populations

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Abstract
Patterns of genetic variation in the apple maggot, Rhagoletis pomonella (Walsh), were analyzed at 19 enzyme genes by starch gel electrophoresis. Eleven populations from the eastern United States, the native range of the fly, showed high levels of genetic variation within, but relatively low levels of heterogeneity among populations. In contrast, R. pomonella from parts of the western United States, where it has been widely found only during the past decade, were significantly different from flies in the native range. Flies from Utah were depauperate in genetic variation, had diagnostic allele frequency shifts at remaining polymorphic genes, and exhibited substantial heterogeneity among populations. Samples from the Pacific Northwest had somewhat less genetic variation than eastern flies and showed evidence of hybridization with the snowberry maggot, R. zephyria Snow, endemic to that region. A sample of R. pomonella from Colorado is more similar to eastern than to Utah flies. Comparisons of fly populations from sympatric hawthorn and apple reinforce previous findings of genetic differences between apple maggot host races.