Assessment of Sublethal Effects of Neonicotinoid Insecticides on the Life-History Traits of 2 Frog Species.

Neonicotinoid insecticides are used extensively in agriculture and, as a consequence, are now detectable in nearby aquatic environments. Few studies have evaluated the effects of neonicotinoids on amphibians in these aquatic environments. In the present study, we examined the effects of 2 commercial formulations of neonicotinoids (active ingredients clothianidin and thiamethoxam) on survival and life-history traits of wood frogs (Lithobates sylvaticus) and northern leopard frogs (Lithobates pipiens). We used artificial pond mesocosms to assess the effects of these neonicotinoids, at nominal concentrations of 2.5 and 250 µg/L, on amphibian larval development through metamorphosis. We found no differences between controls and neonicotinoid exposure for any of the endpoints assessed for either wood frogs or leopard frogs. The present study suggests that concentrations meeting or exceeding observed levels of clothianidin and thiamethoxam in surface waters will not directly affect metamorphosis in 2 amphibians. Environ Toxicol Chem 2019;38:1967-1977. © 2019 SETAC.

Sensitivity of the early-life stages of freshwater mollusks to neonicotinoid and butenolide insecticides.

Neonicotinoid insecticides can be transported from agricultural fields, where they are used as foliar sprays or seed treatments, to surface waters by surface or sub-surface runoff. Few studies have investigated the toxicity of neonicotinoid or the related butenolide insecticides to freshwater mollusk species. The current study examined the effect of neonicotinoid and butenolide exposures to the early-life stages of the ramshorn snail, Planorbella pilsbryi, and the wavy-rayed lampmussel, Lampsilis fasciola. Juvenile P. pilsbryi were exposed to imidacloprid, clothianidin, or thiamethoxam for 7 or 28 d and mortality, growth, and biomass production were measured. The viability of larval (glochidia) L. fasciola was monitored during a 48 h exposure to six neonicotinoids (imidacloprid, thiamethoxam, clothianidin, acetamiprid, thiacloprid, or dinotefuran), or a butenolide (flupyradifurone). The 7-d LC50s of P. pilsbryi for imidacloprid, clothianidin, and thiamethoxam were ≥4000 µg/L and the 28-d LC50s were ≥182 µg/L. Growth and biomass production were considerably more sensitive endpoints than mortality with EC50s ranging from 33.2 to 122.0 µg/L. The 48-h LC50s for the viability of glochidia were ≥456 µg/L for all seven insecticides tested. Our data indicate that neonicotinoid and butenolide insecticides pose less of a hazard with respect to mortality of the two species of mollusk compared to the potential hazard to other non-target aquatic insects.