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

Imidacloprid is a new insecticide from the family of the neonicotinoids, which 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 non-associative learning abilities in the honeybee. The behavioral procedure is the habituation of the proboscis extension reflex (PER). Imidacloprid topically applied on the thorax (1 microl) at the doses of 5, 10, and 20 ng/bee induces an increase of the gustatory threshold defined as the 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-like apparatus is impaired at the doses of 2.5, 5, 10, and 20 ng/bee. These effects 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 independently of time. This result fits our hypothesis that a slight activation of the cholinergic system with a low dose of imidacloprid can facilitate a simple form of learning in the honeybee.