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.苹果实蝇（Rhagoletis pomonella，双翅目Diptera: 实蝇科Tephritidae）近期在美国东部从其原生寄主毛叶山楂（Crataegus mollis）转移至引入的栽培苹果（Malus domestica）的案例，是同域寄主宗分化（sympatric host race formation）研究的经典模型系统。 但该实蝇亦分布于美国西部，其大概率于过去60年内通过携带实蝇的苹果被引入该区域。 除苹果外，美国西部的苹果实蝇还可寄生两种山楂：其一为本土的黑山楂（C. douglasii），其二为引入的英国观赏山楂（C. monogyna）。 本研究通过飞行隧道生物测定（flight tunnel assays）实验，检测美国西部苹果实蝇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宗。研究结果显示，西部取食苹果、黑山楂及观赏山楂的实蝇种群，相较于非原生寄主的挥发性混合物，其对各自原生寄主挥发性混合物的逆风定向飞行（upwind directed flight）频次显著升高，该结果与寄主宗的特征相符。 本研究还探讨了上述行为学结果对美国西部苹果实蝇起源的启示，其中包括一种潜在可能：西部的苹果实蝇种群并非通过带虫苹果引入，而是由当地原有的山楂实蝇种群近期发生寄主转移演化而来。