ARS | Publication request: Behavioral evidence for fruit odor discrimination and sympatric host races of Rhagoletis pomonella flies in the western United States

Submitted to: Evolution
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: July 7, 2012
Publication Date: November 15, 2012
Citation: Linn, Jr, C.E., Yee, W.L., Simm, S.B., Cha, D.H., Powell, T.H., Goughnour, R.B., Feder, J.L. 2012. Behavioral evidence for fruit odor discrimination and sympatric host races of Rhagoletis pomonella flies in the western United States. Evolution. 66(11):3632-3641.

Interpretive Summary: The apple maggot fly damages apple fruit and is a major quarantine concern for apple growers in the western U.S. Personnel at the USDA-ARS Yakima Agricultural Research Laboratory in Wapato, WA, University of Notre Dame, IN, and Cornell University, NY conducted flight tunnel assays of flies from Washington and the eastern U.S. to fruit volatiles from apple, black hawthorn, ornamental hawthorn, and downy hawthorn fruit. Flies that developed in apple and in black, ornamental, and downy hawthorn responded highly to volatile blends isolated from their respective host fruit but not to blends from other host fruit. Results suggest that host races of apple maggot flies exist in Washington, as in the eastern U.S., and that hawthorn-origin flies may not respond highly to apples.

Technical Abstract: 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.