Chronic toxicity of clothianidin, imidacloprid, chlorpyrifos, and dimethoate to Apis mellifera L. larvae reared in vitro.

Abstract

The effects of chronic exposure to two neonicotinoids (clothianidin and imidacloprid) and two organophosphates (chlorpyrifos and dimethoate) on survival, developmental rate and larval weight of honey bee larvae reared in vitro were determined. Diets containing chemicals were fed to larvae with the range of concentrations for each compound based on published acute toxicity experiments and residues found in pollen and nectar, both components of the larval diet. Four concentrations of each compound and controls were tested: chlorpyrifos: 0.5, 0.8, 1.2, 8 mg/L; clothianidin: 0.1, 0.4, 2, 10 mg L-1 ; dimethoate: 0.02, 1, 6, 45 mg L-1 ; imidacloprid: 0.4, 2, 4, 10 mg L-1 ; positive control: dimethoate (45 mg L-1 ); solvent control: acetone or methanol; and negative control. A significant decrease in survival, relative to the solvent control, occurred in the 0.8, 1.2 and 8 mg L-1 chlorpyrifos, 0.4, 2 and 10 mg L-1 clothianidin, and 45 mg L-1 dimethoate diets, but not the imidacloprid diets. The treatment of larval diets with clothianidin, dimethoate and imidacloprid did not affect survival, developmental rate, or weight of immature honey bees; however, treatment with chlorpyrifos did. Overall, our results are valuable for evaluating the chronic toxicity of these pesticides to developing honey bees. © 2018 Society of Chemical Industry.