Genetic evidence for the introduction of Rhagoletis pomonella (Diptera: Tephritidae) into the northwestern United States

Authors: Sim, Sheina; DOELLMAN, MEREDITH - University Of Notre Dame; HOOD, GLEN - Rice University; Yee, Wee; POWELL, THOMAS - Binghamton University; SCHWARTZ, DIETMAR - Western Washington University; GOUGHNOUR, ROBERT - Washington State University Extension Service; EGAN, SCOTT - Rice University; ST. JEAN, GILBERT - University Of Notre Dame; SMITH, JAMES - Michigan State University; ARCELLA, TRACY - University Of Notre Dame; DZURISIN, JASON - University Of Notre Dame; FEDER, JEFFREY - University Of Notre Dame

Submitted to: Journal of Economic Entomology
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 8/11/2017
Publication Date: 10/6/2017
Citation: Sim, S.B., Doellman, M.M., Hood, G.R., Yee, W.L., Powell, T.H., Schwartz, D., Goughnour, R.B., Egan, S.P., St. Jean, G., Smith, J.J., Arcella, T.E., Dzurisin, J.D., Feder, J.L. 2017. Genetic evidence for the introduction of Rhagoletis pomonella (Diptera: Tephritidae) into the northwestern United States. Journal of Economic Entomology. 110(6):2599-2608. https://doi.org/10.1093/jee/tox248.
DOI: https://doi.org/10.1093/jee/tox248

Interpretive Summary: The presence of apple maggots (Rhagoletis pomonella) in apple growing regions of the Pacific Northwest can potentially pose a threat to the apple growing industry. In an effort to identify the origin of these flies, we performed a genetic analysis using nuclear microsatellite markers and mitochondrial DNA sequences to discriminate between the hypotheses that R. pomonella are native to the west or represent an invasive population. The results of this study show that the western population of R. pomonella have lower genetic diversity than the eastern population and thus support the hypothesis that western flies represent an invasive population.

Technical Abstract: The apple maggot fly, Rhagoletis pomonella (Walsh) (Diptera: Tephritidae), is a serious quarantine pest in the apple-growing regions of central Washington and Oregon. The fly is believed to have been introduced into the Pacific Northwest via the transport of larval-infested apples near Portland, Oregon within the last 40 years. However, R.pomonella also attacks native black hawthorn, Crataegus douglasii (Lindley), and introduced ornamental hawthorn, C.monogyna (Jacquin), in the region. It is therefore possible that R.pomonella was not introduced but has always been present on black hawthorn. If true, then the fly may have independently shifted from hawthorn onto apple in the Pacific Northwest within the last 40 years after apples were introduced. Here, we test the introduction hypothesis through a microsatellite genetic survey of 10 R.pomonella sites in Washington and five in the eastern USA, as well as a comparison to patterns of genetic variation between populations of R.cingulata (Loew) and R.indifferens (Curran), two sister species of cherry-infesting flies known to be native to the eastern and western USA, respectively. We report results based on genetic distance networks, patterns of allelic variation, and estimated times of population divergence that are consistent with the introduction hypothesis for R.pomonella. The results have important implications for R.pomonella management, suggesting that black hawthorn-infesting flies near commercial apple-growing regions of central Washington may harbor sufficient variation to utilize apple as an alternate host, urging careful monitoring and possible removal of hawthorn trees near orchards.