Imidacloprid-induced facilitation of the proboscis extension reflex habituation in the honeybee

Imidacloprid. is a new insecticide from the family of the neonicotinoids, w hich interact with the insect nicotinic acetylcholine receptor. The effects of imidacloprid at a dose that does not affect sensory or motor functions are studied on nonassociative learning abilities in the honeybee. The behav ioral procedure is the habituation of the proboscis extension reflex (PER). Imidacloprid topically applied on the thorax (1 mul) at the doses of 5, 10 , and 20 ng/bee induces an increase of the gustatory threshold defined as t he lowest concentration of a sucrose solution applied to the antennae able to elicit the PER. The ability of the honeybee to move in an open-field-lik e apparatus is impaired at the doses of 2.5, 5, 10, and 20 ng/bee. These ef fects are amplified with time and reach a maximum 60 min after application. The lowest dose of 1.25 ng/bee has no effect on the gustatory function but increases the motor activity and facilitates the PER habituation independe ntly of time. This result fits our hypothesis that a slight activation of t he cholinergic system with a low dose of imidacloprid can facilitate a simp le form of learning in the honeybee. (C) 2001 Wiley-Liss,Inc.