Field efficacy of soil insecticides on pyrethroid‐resistant western corn rootworms (Diabrotica virgifera virgifera LeConte)

BACKGROUND Field‐evolved pyrethroid resistance has been confirmed in western corn rootworm (WCR) populations collected from the United States (US) western Corn Belt. Resistance levels of WCR adults estimated in lab bioassays were confirmed to significantly reduce the efficacy of foliar‐applied bifenthrin. The objective of the present study was to investigate the impact of WCR pyrethroid resistance levels on the performance of common soil‐applied insecticide formulations (23.4% tefluthrin, 17.15% bifenthrin, and 0.1% cyfluthrin + 2.0% tebupirimphos). Field trials were conducted in 2016 and 2017 in three Nebraska, US, counties (Saunders, Clay, and Keith) where distinct levels of WCR susceptibility to pyrethroids (susceptible, moderately resistant, and highly resistant) had been previously reported in adult and larval bioassays. RESULTS All soil insecticide treatments effectively protected maize roots from a pyrethroid‐susceptible WCR population at Saunders. In contrast, the efficacy of bifenthrin and tefluthrin soil insecticides was significantly reduced at Clay and Keith, where pyrethroid‐resistant WCR populations were reported. At Keith, where an additional failure of the cyfluthrin + tebupirimphos soil insecticide was observed, WCR laboratory dose–response bioassays showed a consistent ∼5‐fold resistance level to the active ingredients bifenthrin, tefluthrin, and cyfluthrin. CONCLUSION The efficacy of common soil insecticides used in the US for WCR management was significantly reduced in populations exhibiting relatively low levels of WCR pyrethroid resistance. Using a multitactical approach to manage WCR within an integrated pest management framework may mitigate resistance evolution and prolong the usefulness of WCR insecticides within the system. © 2019 Society of Chemical Industry Western corn rootworm (WCR) pyrethroid resistance has been confirmed in the US western Corn Belt. This research evaluates the resulting impact on the performance of soil‐applied insecticides.