Evidence for adaptation of Rhagoletis pomonella (Diptera: Tephritidae) on large-thorn hawthorn, Crataegus macracantha, in Okanogan County, Washington State, USA

Authors: Yee, Wee; MILNES, JOSHUA - Washington Department Of Agriculture; GOUGHNOUR, ROBERT - Washington Department Of Agriculture; BUSH, MICHAEL - Washington Department Of Agriculture; HOOD, GLEN - Wayne State University; FEDER, JEFFREY - University Of Notre Dame

Submitted to: Environmental Entomology
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 3/3/2023
Publication Date: 4/9/2023
Citation: Yee, W.L., Milnes, J., Goughnour, R., Bush, M., Hood, G.R., Feder, J. 2023. Evidence for adaptation of Rhagoletis pomonella (Diptera: Tephritidae) on large-thorn hawthorn, Crataegus macracantha, in Okanogan County, Washington State, USA. Environmental Entomology. 52(3):455-464. https://doi.org/10.1093/ee/nvad026.
DOI: https://doi.org/10.1093/ee/nvad026

Interpretive Summary: Apple maggot fly is a quarantine pest of apple in western North Apple maggot fly is a quarantine pest of apple in western North America. Determining whether a fly population has adapted to non-apple host plants can affect fly management, in that managing the fly in apple alone would be insufficient to reduce the threat of flies attacking apples. Personnel at the USDA Temperate Tree Fruit & Vegetable Research Unit in Wapato, WA, Washington State Department of Agriculture in Yakima, WA, and the University of Notre Dame in Indiana determined whether populations of flies attacking large-thorn hawthorn in north-central WA have adapted to the plant. We found evidence that the flies have adapted to large-thorn hawthorn, as flies from large-thorn hawthorn emerged earlier than flies attacking apple and the flies preferred to attack and lay eggs in the hawthorn over apple. Results are important in that they suggest apple maggot flies can adapt quickly to hawthorn species, which could lead to host race formation and problems for pest management.

Technical Abstract: The apple maggot fly, Rhagoletis pomonella (Walsh) (Diptera: Tephritidae), was introduced from eastern North America into western North America via infested apples (Malus domestica Borkhausen) about 43 years ago, where it subsequently adapted to two hawthorn species, Crataegus douglasii Lindley and C. monogyna Jacquin. Here, we test whether R. pomonella has also adapted to large-thorn hawthorn, Crataegus macracantha Loddiges ex Loudon, in Okanogan County, Washington state, U.S.A. In 2020, 2021, and 2022, fruit of C. macracantha were shown to ripen in late September and were infested at rates from 0.7 to 3.0%. In laboratory rearing studies, flies from C. macracantha eclosed on average of 9–19 d later than flies from earlier ripening apple (August–early September), consistent with large-thorn hawthorn flies having adapted to the later fruiting phenology of its host. In a laboratory no-choice test, significantly fewer (35.2%%) large-thorn hawthorn than apple flies visited apples. In choice tests, greater percentages of large-thorn hawthorn than apple flies resided on and oviposited into C. macracantha versus apple fruit. Hawthorn flies were also smaller in size than apple flies. Our results support the recursive adaptation hypothesis proposed by Mattsson et al. (2021). Rhagoletis pomonella appears to have rapidly and independently specialized phenologically and behaviorally to different novel hawthorn hosts since its introduction into the Pacific Northwest of the U.S., potentially leading to host race formation.