Fate and effects of flupyradifurone and sulfoxaflor on non-target soil-dwelling invertebrates

Flupyradifurone and sulfoxaflor are two novel insecticides registered for global use. They were developed as alternates to neonicotinoids, and their subsequent use restrictions, based on impacts on non-target organisms. Although structurally distinct, both alternatives share the same mode of action as neonicotinoids, raising concerns about their potential risks to non-target soil invertebrates. The fate and toxicity of flupyradifurone and sulfoxaflor in soil was assessed, tested both as pure chemicals and in commercial formulations (Sivanto™ Prime and Closer™ Insecticide, respectively). The half-life of flupyradifurone in soil ranged from 68 to 75 days for the commercial formulation (Sivanto™ Prime) and extended to 89 days as the pure chemical, reflecting the influence of adjuvants on degradation. In contrast, sulfoxaflor degraded rapidly with a half-life of only 2 to 3 days in soil for both the pure chemical and Closer™ Insecticide. Toxicity (adult survival and reproduction) was evaluated in three soil invertebrate species: Oppia nitens, Eisenia andrei, and Folsomia candida. No toxic effects were observed for O. nitens for all substances tested at the highest concentrations (≥15.5 mg a.i./kg dry soil) after a 28-day exposure. However, E. andrei was the most sensitive species to sulfoxaflor (median lethal concentration [LC50] = 0.25 mg/kg [pure chemical]; median inhibitory concentration [IC50] = 0.11 mg/kg [Closer™ Insecticide] and IC50 = 0.15 mg/kg [pure chemical]), with demonstrated bioaccumulation. Conversely, F. candida was the most sensitive to flupyradifurone, exhibiting significant effects on survival (LC50 <1.16 mg/kg [pure chemical]) and reproduction (IC50 <0.28 mg/kg [pure chemical]). Compared to neonicotinoids evaluated previously using the same test conditions, flupyradifurone and sulfoxaflor were less toxic than clothianidin to F. candida. However, sulfoxaflor was more toxic to E. andrei than thiamethoxam, clothianidin, and flupyradifurone.