Behavior of wireworms (Coleoptera: Elateridae) exposed to wheat seed treated with novel (broflanilide, isocycloseram) and previously registered insecticides in a soil bioassay.

Following the de-registration of lindane as a cereal crop seed treatment for wireworm control in North America, most of the research efforts to find replacements have focused on neonicotinoid, diamide, pyrethroid, phenyl pyrazole, and most recently, meta-diamide and isoxazoline insecticide classes. Although insecticides within these classes have been shown to provide cereal crop protection from wireworm damage, not all insecticides will significantly reduce wireworm populations in the field. To investigate this, we exposed wireworms (Agriotes obscurus L. and Agriotes lineatus L.) to wheat seeds treated with insecticides in the above insecticide classes in soil bioassays in the lab, with a focus on the newly developed meta-diamide broflanilide and the isoxazoline isocycloseram. Various wireworm behaviors (eg repellency) were observed in soil window studies for 3 h, and symptoms of toxicity were recorded upon wireworm removal at 24 h and again at 7 d. No repellency was recorded from seed treated with broflanilide, isocycloseram, thiamethoxam (neonicotinoid), cyantraniliprole (diamide), and fipronil (phenyl pyrazole), but moderate repellency occurred with the pyrethroid λ-cyhalothrin. After 24 h exposure, thiamethoxam, cyantraniliprole, and λ-cyhalothrin treatments had elicited only minor morbidity symptoms, which had mostly disappeared after 7 d. Broflanilide, isocycloseram, and fipronil treatments, however, progressed from initial minor morbidity symptoms to more irreversible morbidity symptoms after 7 d. These data and earlier lab and field trials explain why field populations of wireworms are reduced by broflanilide, isocycloseram, and fipronil treatments relative to neonicotinoid, diamide, and pyrethroid insecticides.