Wireworm (Coleoptera: Elateridae) intoxication symptoms indicate the postharvest presence of broflanilide residues in soil collected from potato fields

Abstract

Abstract Wireworms are primary pests of potatoes in Canada with relatively few effective control options. Recently, a new meta-diamide insecticide, broflanilide, was registered in Canada and the United States as an in-furrow spray applied at planting that provides protection of tubers from feeding damage and dramatically reduces wireworm populations. As part of our routine screening of wireworm response to novel insecticides, we exposed wireworms (predominantly Agriotes obscurus; N=2320) to field soil collected from plots to which either bifenthrin (Capture 2EC) or broflanilide (Cimegra) had been applied at registered rates 124–145 and 314–335 days previously in 2018, 2019, and 2021. Wireworm behavioral responses were assessed using a previously developed numerical scale, and indicated residues were present in sufficient quantity in all broflanilide and most bifenthrin-treated plots to induce morbidity. Transfer of affected wireworms to untreated soil indicated morbidity was generally reversible after exposure to bifenthrin, but not after exposure to broflanilide. There was an inverse relation between wireworm size and the degree of morbidity induced by exposure to broflanilide, but not bifenthrin. Analyses of soil residues indicated readily quantifiable levels of broflanilide still present in undisturbed (not harvested) field soil 314–335 days after application. Insecticide residues in soil samples from disturbed (harvested) sections of the potato plots were lower, as was the degree of morbidity of wireworms exposed to this soil. The use of wireworms as bioindicators of insecticide residues, and the implications of insecticide persistence for wireworm management are discussed.