In the Great Lakes region, Rhagoletis zephyria Snow (Diptera: Tephritidae) infests snowberries, Symphoricarpos albus variety laevigatus (Fern.) Blake, a western North American native plant that has been introduced widely into eastern North America. These R. zephyria infestations have been hypothesized to be the result of flies that were introduced into eastern North America along with their host plants. In its native range, R. zephyria infests S. albus variety laevigatus, but it infests a related host, Symphoricarpos occidentalis Hook., in the northern Great Plains. Knowledge of the natural geographic and host ranges of R. zephyria is important. R. zephyria is a sibling species of the apple maggot, Rhagoletis pomonella (Walsh), and aspects of R. zephyria biology can be applied to work on speciation mechanisms. Additionally, the possible co-occurrence of morphologically similar R. zephyria and R. pomonella in apple (Malus spp.)-growing regions complicates the positive identification of trap-caught flies in the R. pomonella species group. Here, we examine the hypothesis that R. zephyria in the Great Lakes region has been introduced. Collections of R. zephyria yielded new state/provincial records in Idaho, South Dakota, Nebraska, Wisconsin, Michigan, Pennsylvania, New York, Massachusetts, Maine, and Ontario and Quebec, Canada, and a new host record, S. albus variety albus, which is native to eastern North America. Finding R. zephyria infesting native host plants in the eastern United States leads us to hypothesize that R. zephyria infestations in the Great Lakes region may not be the result of recent (historical) introductions of R. zephyria, but rather they may represent native R. zephyria populations.