The Geographic Distribution of Rhagoletis pomonella (Diptera: Tephritidae) in the Western United States: Introduced Species or Native Population?

Abstract

ABSTBACT The apple maggot fly, Rhagoletis pomonella Walsh (Diptera: Tephritidae), is a major pest of commercially grown domesticated apple (Malus domestica Borkhausen) in North America. The shift of the fly from its native host hawthorn (Crataegus mollis) to apple in the eastern United States 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 United States 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, OR, 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 after 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 United States to help clarify the origin (s) of the fly outside the eastern United States. 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 lack of C. dougliasii-infesting R. pomonella east of the Cascade Mountains in the states of Washington, OR, 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 control for R. pomonella.

New records ofRhagoletisLoew, 1862 (Diptera: Tephritidae) and their host plants in western Montana, U.S.A.

“…Similarly, R. pomonella is rare in black hawthorn in central Washington State and patchily distributed in the plant elsewhere throughout the northwestern U.S. (Yee 2008). The same also appears to be true throughout most of the western U.S., supporting the contention that R. pomonella was introduced to the region and is not native (Hood et al 2013). It remains unclear if black hawthorn fruit is unsuitable for sustaining high fl y densities or whether environmental conditions where black hawthorns thrive, in combination with the plant's fruiting phenology, are not optimal for R. pomonella survival.…”

“…Rhagoletis pomonella was likely introduced from eastern North America into the western U.S. in the 1950s or 1970s (AliNiazee & Westcott 1986). In the western U.S., R. pomonella is found in Idaho, Washington, Oregon, Utah, Colorado, and California (Brunner 1987, Dowell 1989, Yee & Goughnour 2008, Hood et al 2013), but its presence in Montana has never been confi rmed. A recent survey conducted by Hood et al (2013) found the fl y absent from fi ve sites in three counties (Gallatin, Missoula, and Mineral) in southwestern and west-central Montana.…”

“…In the western U.S., R. pomonella is found in Idaho, Washington, Oregon, Utah, Colorado, and California (Brunner 1987, Dowell 1989, Yee & Goughnour 2008, Hood et al 2013), but its presence in Montana has never been confi rmed. A recent survey conducted by Hood et al (2013) found the fl y absent from fi ve sites in three counties (Gallatin, Missoula, and Mineral) in southwestern and west-central Montana. The National Agricultural Pest Information System database compiled from information provided by the Cooperative Agricultural Pest Survey program (National Agricultural Pest Information System 2013) indicates that R. pomonella was found in Flathead and Lake Counties in 2005, but there are no supporting data for this record.…”

Status of <I>Rhagoletis</I> (Diptera: Tephritidae) Pests in the NAPPO Countries

“…Populations in Mè xico (below) may also be native. Populations in the western United States are almost certainly introduced (Dowell 1991, Hood et al 2013, likely from the eastern United States.…”

“…Berlocher and Enquist (1993), Berlocher and McPheron (1996), Powell (2012), Hood et al (2013) High -C. monogyna Jacq.…”