The apple maggot, Rhagoletis pomonella (Walsh, 1867) (Diptera: Tephritidae), is an introduced quarantine pest of apple, Malus domestica Borkhausen (Rosaceae), in Washington State, U.S.A. A morphologically similar native fly, Rhagoletis zephyria Snow, 1894, infests snowberries, Symphoricarpos spp. (Caprifoliaceae), and is also present in Washington. Although it is not a pest of apples, R. zephyria is caught on sticky yellow rectangles baited with ammonia deployed for R. pomonella, which could have implications for apple maggot surveys and understanding differences in the ecology of the flies. Here, we report the relative abundance of R. zephyria and R. pomonella on traps placed in apple maggot host trees during surveys, including in the dry apple-growing regions of central and eastern Washington. Rhagoletis zephyria outnumbered R. pomonella on traps from 3 to 1102 times to one, increasing times required for accurate species identifications and implying that traps that are more specific for R. pomonella would be useful. Despite the high numbers of R. zephyria caught, >94% of all female flies could be identified to species, suggesting that R. zephyria minimally affected the accuracy of surveys. Detections of both fly species were lower in drier than wetter locations; however, mean annual precipitation was more positively correlated with R. pomonella than with R. zephyria captures. The greater relative abundance of native R. zephyria in drier counties implies that it is better adapted to central and eastern Washington than is the invasive R. pomonella or that habitat factors in these regions favor R. zephyria abundance.
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