|St. Jean, Gilbert|
Submitted to: Annals of the Entomological Society of America
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 2/11/2013
Publication Date: 3/22/2013
Citation: Hood, G., Yee, W.L., Goughnour, R., Sim, S., Egan, S.P., Arcella, T., St. Jean, G., Powell, T.H., Xu, C.C., Feder, J.L. 2013. The geographic distribution of Rhagoletis pomonella (Diptera:Tephritidae) in the western United States: Introduced species or native population?. Annals of the Entomological Society of America. 106(1):59-65. Interpretive Summary: The apple maggot fly is an important quarantine pest of apples in the Pacific Northwest of the U.S. Knowledge of the fly’s distribution in the western U.S. can be used to identify areas that could be the greatest source of flies threatening the apple industry. Personnel at the Yakima Agricultural Research Laboratory in Wapato, WA, Washington State University in Vancouver, and the University of Notre Dame in Indiana determined the distributions of apple maggot flies in Colorado, Idaho, Montana, Oregon, Utah, and Washington. Flies occurred at low levels or were absent east of the Cascade Mountains in Washington, Oregon, and Idaho. This result is important because it suggests apple growers should be most concerned with movement of infested apples from west of the Cascade Mountains into central apple growing regions.
Technical Abstract: The apple maggot fly, Rhagoletis pomonella Walsh (Diptera: Tephritidae), is a major pest of commercially grown domesticated apple (Malus domestica) in North America. The shift of the fly from its native host hawthorn (Crataegus mollis) to apple in the eastern U.S. is often cited as an example of incipient sympatric speciation in action. However, R. pomonella is also present in the Pacific Northwest region of the U.S. where it infests apple, native black hawthorn (Crataegus douglasii), and introduced English ornamental hawthorn (C. monogyna). It is believed that R. pomonella was introduced to the Portland, Oregon area via larval-infested apples from the east. The fly subsequently spread through the region, shifting onto black hawthorn and ornamental hawthorn as additional hosts as it spread. It is also possible, however, that R. pomonella is native to black hawthorn in the Pacific Northwest and switched to infest apple and ornamental hawthorn following the introduction of these two alternative hosts to the region. Here, we document the distribution of R. pomonella through the Pacific Northwest and Rocky Mountain states of the western U.S. to help clarify the origin(s) of the fly outside the eastern U.S. We report a distribution pattern consistent with the hypothesis that R. pomonella was introduced to the Pacific Northwest via infested apples. In particular, the low levels or general lack of C. douglasii-infesting R. pomonella east of the Cascade Mountains in the states of Washington, Oregon, and Idaho implies that the fly is not native on black hawthorn and is of recent origin. We discuss the evolutionary and applied implications of the results with respect to our current understanding of host race formation and biocontrol for R. pomonella.