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2 November 2022 Alfalfa Weevil (Coleoptera: Curculionidae) Resistance to Lambda-cyhalothrin in the Western United States
E. A. Rodbell, M. L. Hendrick, I. M. Grettenberger, K. W. Wanner
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Forage alfalfa (Medicago sativa L. [Fabales: Fabaceae]) is a key agricultural commodity of the western region of the United States. The key insect pest of alfalfa, Hypera postica Gyllenhal (Coleoptera: Curculionidae), has developed resistance to the most common class of insecticide used to manage its damage. Alfalfa weevil samples from 71 commercial alfalfa fields located in Arizona, California, Montana, Oregon, Washington, and Wyoming were assayed for susceptibility to lambda-cyhalothrin during 2020–2022 using a laboratory concentration-response assay. Seventeen field sites representing all six states were highly resistant to lambda-cyhalothrin (resistance ratios >79.6) and bioassay mortality often did not exceed 50% even at the highest concentration tested (3.30 µg/cm2 in 2020 and 10.00 µg/cm2 in 2021–2022). Field sites assayed with more than one pyrethroid active ingredient indicated likely cross-resistance between lambda-cyhalothrin and zeta-cypermethrin (type II pyrethroids) and variable and/or limited potential cross-resistance to permethrin (type I pyrethroid). Thirty-two field sites representing five states were susceptible to lambda-cyhalothrin (resistance ratios ranging from 1 to 20). While resistance is widespread, integrated resistance management strategies including rotating mode of action groups, applying chemical control tactics only when economic thresholds have been met, and utilizing cultural control tactics can be employed to slow the further development of resistance.

© The Author(s) 2022. Published by Oxford University Press on behalf of Entomological Society of America. All rights reserved. For permissions, please e-mail:
E. A. Rodbell, M. L. Hendrick, I. M. Grettenberger, and K. W. Wanner "Alfalfa Weevil (Coleoptera: Curculionidae) Resistance to Lambda-cyhalothrin in the Western United States," Journal of Economic Entomology 115(6), 2029-2040, (2 November 2022).
Received: 25 July 2022; Accepted: 19 September 2022; Published: 2 November 2022

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Forage crop
insecticide resistance
integrated resistance management
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