|HSU, JU-CHUN - National Taiwan University|
|CHOU, MIN - Taiwan Agricultural Research Institute|
|MAU, RON - University Of Hawaii|
|SHIKANO, I - University Of Hawaii|
Submitted to: Pest Management Science
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 7/27/2021
Publication Date: 7/31/2021
Citation: Hsu, J., Chou, M.Y., Mau, R., Maeda, C.T., Shikano, I., Manoukis, N., Vargas, R.I. 2021. Spinosad resistance in field populations of melon fly, Zeugodacus cucurbitae (Coquillett), in Hawaii. Pest Management Science. 77(12):5439-5444. https://doi.org/10.1002/ps.6583.
Interpretive Summary: The melon fly is a serious agricultural pest, often controlled with reduced-risk insecticides based on Spinosad, such as GF-120. Here we report on high levels of resistance of this fruit fly to Spinosad in populations collected on Oahu and Maui islands. Resistance dropped over generations kept in the lab without exposure to Spinosad, but slowly. Field collections suggest resistance has been increasing. This poses a serious problem for management and suggest the need for novel active compounds to be used and for a Resistance Management Plan (RMP).
Technical Abstract: 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 has been in use as a component of IPM against this Tephritid for the last two decades. This study reports on high levels of resistance to Spinosad (resistance ratios and LD50) in Z. cucurbitae from three farms on Oahu where it was in use until the time of sampling in 2017 (RR = 102 – 303; Average LC50 = 191 - 567 mg/L), as well as in a population from Maui (RR = 8.56; LC50 = 16 mg/L). There was a relatively low background resistance in a naïve wild population from Hawaii island (RR = 2.73; LC50 = 5.1 mg/L) compared with a lab colony (LC50 = 1.87 mg/L). These will be problematic for control given the concentration of Spinosad in GF 120 (80 mg/L). Resistance in the three Oahu and one Maui samples dropped over generations (tested up to F8) but remained elevated in some cases. Moreover, for a fourth Oahu farm resistance was still high (RR = 25) a year after cessation of Spinosad use, suggesting that loss of resistance might be slower than expected. Comparison with flies collected at an Oahu farms and assayed in 2008 indicates a 34-fold increase in resistance over 9 years. The evolution of high levels of resistance to Spinosad in Z. cucurbitae in Hawaii highlights the need for alternative control tactics, particularly roation of active ingredients.