Effects of a chronic dietary exposure of the honeybee Apis mellifera (Hymenoptera: Apidae) to imidacloprid.

Previous studies have shown that imidacloprid and insecticidally active imidacloprid plant metabolites are rapidly metabolized by honeybees. Accordingly, no striking differences were expected between the acute and the chronic dietary toxicity of imidacloprid to honeybees. More recently, however, an unexpectedly high chronic dietary toxicity to honeybees was reported for imidacloprid and imidacloprid plant metabolites, and a novel pharmacologic mechanism unrelated to the parent toxophor was postulated. In an extensive literature survey, no further evidence was found for the reported high difference between the acute and the chronic dietary toxicity of imidacloprid and its plant metabolites to honeybees. The majority of data indicated a dietary no observed lethal-effect concentration >0.04 and 0.02 mg/L 50% sucrose solution, respectively, for an acute and a chronic dietary exposure of honeybees to either imidacloprid or its plant metabolites. Findings of chronic feeding studies with those plant metabolites where the toxophor had already been cleaved did not support the hypotheses of a novel pharmacologic mechanism unrelated to the parent toxophor. No increased treatment-related mortality or behavioral abnormalities were recorded in four independent research facilities during a 10-day dietary exposure of honeybees of different ages to sucrose solutions spiked with the respective metabolites at 0.0001, 0.001, and 0.010 mg/L 50% sucrose solution.