Field-evolved pyrethroid resistance in Tychius picirostris (Coleoptera: Curculionidae) populations in Oregon white clover seed crops

Authors: TIWARI, GRACE - Oregon State University; KAUR, NAVNEET - Oregon State University; ANDERSON, NICOLE - Oregon State University; LIGHTLE, DANI - Oregon State University; TANNER, K - Oregon State University; WILLETTE, ALISON - Oregon State University; OTANI, JENNIFER - Agriculture And Agri-Food Canada; JORGENSEN, AMANDA - Agriculture And Agri-Food Canada; YODER, CALVIN - Sarda Agricultural Research; Dorman, Seth

Submitted to: Journal of Economic Entomology
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 1/11/2024
Publication Date: 1/29/2024
Citation: Tiwari, G., Kaur, N., Anderson, N.P., Lightle, D., Tanner, K.C., Willette, A., Otani, J.K., Jorgensen, A., Yoder, C., Dorman, S.J. 2024. Field-evolved pyrethroid resistance in Tychius picirostris (Coleoptera: Curculionidae) populations in Oregon white clover seed crops. Journal of Economic Entomology. 117(2):609-617. https://doi.org/10.1093/jee/toae012.
DOI: https://doi.org/10.1093/jee/toae012

Interpretive Summary: The clover seed weevil (CSW) is a serious pest of white clover grown for seed production in western Oregon that causes feeding damage to flowers and developing seeds. Since 2019, white clover seed producers have reported field control failures using pyrethroid insecticide applications for clover seed weevil management. Pyrethroids are an important chemical control option for clover seed weevil management. To evaluate insecticide resistance development to pyrethroids (bifenthrin) and other chemistries labeled for clover seed weevil management (malathion, chlorantraniliprole), adult populations were collected from eight commercial white clover fields in the Willamette Valley, Oregon, in 2022 and 2023. All collected populations in Oregon exhibited high resistance to bifenthrin in glass vial bioassays compared to a susceptible Canadian field population. Moreover, >273 percent of the label rate of formulated product containing bifenthrin (Brigade 2EC) was required to kill half of clover seed weevil populations using topical assays in the laboratory. Research determined that several enzymes present in clover seed weevil populations may confer metabolic resistance to bifenthrin. Moderate resistance to malathion was also detected in Oregon clover seed weevil populations. This is the first report of clover seed weevil insecticide resistance development to pyrethroid and organophosphate insecticides. Results will inform continued resistance monitoring and insecticide resistance management (IRM) plans to slow the evolution of clover seed weevil insecticide resistance development in Oregon white clover seed production systems.

Technical Abstract: The clover seed weevil (CSW), Tychius picirostris Fabricius, is a serious pest of white clover, Trifolium repens L., grown for seed production in western Oregon, inflicting feeding damage to flowers and developing seeds. Since 2019, white clover seed producers have anecdotally reported T. picirostris control failures using foliar pyrethroid insecticide applications. This mode of action (MoA) is an important chemical control option for T. picirostris management. To evaluate insecticide resistance development to pyrethroids (bifenthrin) and other MoAs labeled for T. picirostris management (malathion, chlorantraniliprole), adult populations were collected from eight commercial white clover fields in the Willamette Valley, Oregon, in 2022 and 2023. Evaluated Oregon populations exhibited high resistance ratios (RR50 = 178 to 725) to technical grade bifenthrin in glass vial bioassays compared to a susceptible Canadian field population. Moreover, >273 percent of the label rate of formulated product containing bifenthrin as the sole MoA (Brigade 2EC) was required to kill half of T. picirostris populations using topical assays. Synergistic assays with a mixed-function oxidase inhibitor, an esterase inhibitor, and a glutathione S-transferase inhibitor revealed phase I and II detoxification enzymes are present in T. picirostris populations and may confer metabolic resistance to bifenthrin. Moderate resistance to malathion was also detected in Oregon T. picirostris populations. This is the first report of T. picirostris insecticide resistance development to pyrethroid and organophosphate insecticides. Results will inform continued monitoring and insecticide resistance management (IRM) strategies to slow the evolution of T. picirostris insecticide resistance development in Oregon white clover seed production systems.