Comparisons of apple cultivar suitability for Rhagoletis pomonella (Diptera: Tephritidae) from Washington State, United States of America

Authors: Yee, Wee

Submitted to: The Canadian Entomologist
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 8/13/2024
Publication Date: 11/18/2024
Citation: Yee, W.L. 2024. Comparisons of apple cultivar suitability for Rhagoletis pomonella (Diptera: Tephritidae) from Washington State, United States of America. The Canadian Entomologist. 156;2024;e33. https://doi.org/10.4039/tce.2024.33.
DOI: https://doi.org/10.4039/tce.2024.33

Interpretive Summary: Apple maggot fly is a quarantine pest of apple in WA state. Information on types of apples preferred by the fly is important because it may improve fly detection programs in Washington, but little information exists on apple cultivar use by flies in WA. Personnel at the USDA-ARS Temperate Tree Fruit & Vegetable Research Unit in Wapato, WA and Washington State University in Vancouver, WA determined the suitability of five early, mid, and late season apple cultivars for apple maggot from WA. Data showed that the earlier apple cultivars Gala and Golden Delicious produced more maggots than later apple cultivars. Data are important in that they suggest for efficiently protecting orchards against flies in Washington, trap deployment in non-commercial, early apple trees closest to Gala and Golden Delicious orchards should be prioritized over deployment in such trees closest to orchards with late apple cultivars.

Technical Abstract: It is unclear whether larval infestations of Rhagoletis pomonella (Walsh) (Diptera: Tephritidae) in earlier (softer) apple (Rosaceae) cultivars are greater than in later (firmer) apple cultivars in Washington State, United States of America, where flies were introduced and are quarantine pests of apple. Here, a field survey of apples in a noncommercial setting in Washington and experiments testing whether earlier apples are more suitable than later apples for Washington-origin R. pomonella were conducted. Early season ‘Gala’ and ‘Golden Delicious’, midseason ‘Red Delicious’, and late-season ‘Granny Smith’ and ‘Fuji’ were exposed to flies reared from early and midseason apples in laboratory experiments and to wild flies in apple trees in field experiments. The field survey provided evidence for softer apples being more infested and suitable. Likewise, most of the laboratory and field experimental data showed that ‘Gala’ and ‘Golden Delicious’, two of the softer apples tested, produced the most larvae and were most suitable, regardless of whether test apples were conventional or organic and ripe or unripe. To optimise fly trapping protocols in Washington, trapping in early apple trees near ‘Gala’ and ‘Golden Delicious’ orchards should be prioritised over trapping near mid- or late-season apple cultivar orchards.