Data from: Behavioral evidence for fruit odor discrimination and sympatric host races of Rhagoletis pomonella flies in the western United States

The recent shift of Rhagoletis pomonella (Diptera: Tephritidae) from its native host downy hawthorn, Crataegus mollis, to introduced domesticated apple, Malus domestica, in the eastern U.S. is a model for sympatric host race formation. However, the fly is also present in the western U.S., where it may have been introduced via infested apples within the last 60 years. In addition to apple, R. pomonella also infests two hawthorns in the West, one the native black hawthorn, C. douglasii, and the other the introduced English ornamental hawthorn, C. monogyna. Here, we test for behavioral evidence of host races in the western U.S. through flight tunnel assays of western R. pomonella flies to host fruit volatile blends. We report that western apple, black hawthorn, and ornamental hawthorn flies showed significantly increased levels of upwind directed flight to their respective natal compared to non-natal fruit volatile blends, consistent with host race status. We discuss the implications of the behavioral results for the origin(s) of western R. pomonella, including the possibility that western apple flies were not introduced, but may represent a recent shift from local hawthorn fly populations.

美国东部的苹果实蝇（Rhagoletis pomonella，双翅目Diptera：实蝇科Tephritidae）从原生寄主多毛山楂（Crataegus mollis）转向引入的栽培苹果（Malus domestica）的演化事件，是同域寄主种群分化（sympatric host race formation）研究的经典模型。不过该实蝇亦分布于美国西部，其种群可能在过去60年内通过带虫苹果被人为引入。除苹果外，美国西部的苹果实蝇还可寄生两种山楂：其一为原生的道格拉斯山楂（C. douglasii，又名黑山楂），其二为引入的英国观赏山楂（C. monogyna）。本研究通过飞行隧道测定（flight tunnel assays）实验，检测美国西部苹果实蝇种群对各类寄主果实挥发性混合物（volatile blends）的行为反应，以验证西部种群是否存在寄主分化的行为证据。结果显示，西部苹果种群、黑山楂种群与观赏山楂种群，分别对各自原生寄主的果实挥发性混合物表现出显著更强的逆风定向飞行（upwind directed flight）行为，该结果与寄主分化种群的行为特征相符。本研究还讨论了上述行为结果对美国西部苹果实蝇起源的启示，其中包括西部苹果种群并非源于引种，而是可能由当地山楂实蝇种群近期发生寄主转移演化而来的可能性。