Pest Management Science (2021) 77, 5439-5444

Ju-Chun Hsu, Ming-Yi Chou, Ronald FL Mau, Colby Maeda, Ikkei Shikano, Nicholas C. Manoukis and Roger I. Vargas (2021)
Spinosad resistance in field populations of melon fly, Zeugodacus cucurbitae (Coquillett), in Hawaii
Pest Management Science 77 (12), 5439-5444
Abstract:
BACKGROUND
Control of Zeugodacus cucurbitae, a serious agricultural pest worldwide, often includes or is dependent on the use of spinosad-based insecticides. This is especially the case in Hawaii, where GF-120, a protein bait containing spinosad as the active ingredient, has been in use as a key integrated pest management (IPM) tool against this Tephritid for the last two decades. Here, we report on resistance to spinosad [resistance ratios (RRs) and median lethal concentration (LC₅₀)] in Hawaii's populations of Z. cucurbitae.
RESULTS
High resistance was found in populations from three farms on Oahu (RR = 102–303; LC₅₀ = 191–567 mg L^–1) and in a population from Maui (RR = 8.50; LC₅₀ = 15.9 mg L^–1). These will be problematic for control given that the most concentrated dilution ratio on the GF-120 label is 96 mg L^–1 of spinosad (1 part GF-120 to 1.5 parts water). Background resistance in a naïve wild population from the Island of Hawaii (RR = 2.73; LC₅₀ = 5.1 mg L^–1) was relatively low compared with a spinosad-susceptible laboratory colony (LC₅₀ = 1.87 mg L^–1). Resistance in the three Oahu and one Maui populations declined over generations in the absence of spinosad but remained elevated in some cases. Moreover, melon flies collected from one of the Oahu farms 1 year after the cessation of spinosad use revealed high persistence of resistance.
CONCLUSION
Compared with a 2008 survey of spinosad resistance, our findings indicate a 34-fold increase in resistance on one of the Oahu farms over 9 years. The evolution and persistence of high levels of resistance to spinosad in Z. cucurbitae in Hawaii highlights the need for alternative control tactics, particularly rotation of active ingredients.
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Full text of article
Database assignments for author(s): Ju-Chun Hsu, Roger I. Vargas

Research topic(s) for pests/diseases/weeds:
pesticide resistance of pest

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Pest and/or beneficial records:

Beneficial	Pest/Disease/Weed	Crop/Product	Country	Quarant.
	Zeugodacus cucurbitae	Cucumber (Cucumis sativus)	U.S.A. (Hawaii)
	Zeugodacus cucurbitae	Melon (Cucumis melo)	U.S.A. (Hawaii)
	Zeugodacus cucurbitae	Watermelon/colocynth (Citrullus)	U.S.A. (Hawaii)