ARS | Publication request: Abundances of apple maggot, Rhagoletis pomonella, across different areas in central Washington, with special reference to black-fruited hawthorns

Submitted to: Journal of Insect Science
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: February 11, 2012
Publication Date: December 10, 2012
Citation: Yee, W.L., Cha, D.H., Linn, Jr, C.E., Klaus, M.W., Goughnour, R.B., Feder, J.L. 2012. Abundances of apple maggot, Rhagoletis pomonella, across different areas in central Washington, with special reference to black-fruited hawthorns. Journal of Insect Science. http://www.insectscience.org/12.124/i536-2442-12-124.pdf.

Interpretive Summary: The apple maggot fly is an important quarantine pest of apples in the Pacific Northwest of the U.S. that also infests hawthorns. Knowledge of fly population densities near apple-growing regions in central Washington can help with management of the fly and with predicting its pest status. Researchers at the USDA-ARS Yakima Agricultural Research Laboratory, Wapato, WA, and Cornell University, Washington State Department of Agriculture, Washington State University, and University of Notre Dame are determining the abundances of apple maggot in native black-fruited hawthorns in central Washington. They found that apple maggot flies in central Washington occurred in low numbers in thickets of black hawthorns in dry areas but occurred in higher numbers in wetter areas, suggesting that apple maggot population densities are limited by moisture. This result is important in that it can be used for predictions of population growth of the fly in differing habitats, which could affect shipment of apples from commercial apple-growing regions of Washington to foreign markets.

Technical Abstract: The apple maggot fly, Rhagoletis pomonella (Walsh), has infested native black-fruited hawthorn (mostly Crataegus douglasii Lindl.) in central Washington since at least 2003, but little is known about the fly’s ecology in hawthorns there. The main objective here was to determine adult and larval abundances of R. pomonella in these hawthorns in central Washington. Flies were first caught in Klickitat, Yakima, and Kittitas Counties in non-commercial apple trees in 1981, 1995, and 1997, respectively. During 2007–2010, ammonia-baited spheres placed in C. douglasii in Yakima and Kittitas Counties caught 0.03–0.18 flies per d and caught more flies than fruit volatile-baited spheres. In 2008 and 2010, there were 0–0.00248 larvae per hawthorn fruit in relatively warm and dry sagebrush and/or bunchgrass habitats in Yakima and Kittitas Counties. In 2010, there were 0.20813 larvae per C. douglasii fruit in two Klickitat County sites in relatively cool and wet ponderosa pine habitat located ~70–153 km south of Yakima and Kittitas County sites. However, at a drier bunchgrass habitat site (Goldendale) ~16 km away from Klickitat sites, there were only 0.00200 larvae per fruit, suggesting precipitation affects R. pomonella abundance. Our adult and larval abundance data combined with the long history of low numbers of R. pomonella in drier areas of central Washington suggest that R. pomonella population growth in C. douglasii is limited by moisture, although there are other possible explanations for observed abundance patterns. The results can be useful for predicting population growth of R. pomonella in non-endemic areas.