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.

美国东部地区的苹果绕实蝇（Rhagoletis pomonella，双翅目：实蝇科）从原生寄主柔毛山楂（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。不过该实蝇在美国西部地区亦有分布，其大概率是近60年内通过带虫苹果入侵至此。除苹果外，西部种群的苹果绕实蝇还可蛀食两种山楂：一种为本土的道格拉斯黑山楂（C. douglasii），另一种为引入的英国观赏山楂（C. monogyna）。本研究通过飞行隧道测定法（flight tunnel assays），检测西部苹果绕实蝇种群对不同寄主果实挥发性气味混合物（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学证据。结果显示，西部苹果种群、黑山楂种群及观赏山楂种群的实蝇，相较于非原生寄主果实的挥发性气味，对各自原生寄主果实的挥发性气味均表现出显著更强的逆风定向飞行（upwind directed flight）行为，这一结果符合寄主种群分化的判定标准。我们还讨论了该行为学结果对西部苹果绕实蝇起源的启示，其中包括一种可能性：西部的苹果实蝇种群并非由外来入侵而来，而是由当地原生山楂上的实蝇种群近期发生寄主转移演化形成。