Contrasting effects of imidacloprid on habituation in 7- and 8-day-old honeybees (Apis mellifera)

We examined the effects of sublethal doses (0.1, 1, and 10 ng per animal) o f a new neonicotinoid insecticide, Imidacloprid, on habituation of the prob oscis extension reflex (PER) in honeybees (Apis mellifera) reared under lab oratory conditions. In untreated honeybees, the habituation of the probosci s extension reflex is age-dependent and there is a significant increase in the number of trials required for habituation in older bees (8-10 days old) as compared to very young bees (4-7 days old). Imidacloprid alters the num ber of trials needed to habituate the honeybee response to multiple sucrose stimulation. In 7-day-old bees, treatment with Imidacloprid leads to an in crease in the number of trials necessary to abolish the response, whereas i n 8-day-old bees, it leads to a reduction in the number of trials for habit uation (15 min and 1h after treatment), and to an increase 4 h after treatm ent. The temporal effects of Imidacloprid in both 7- and 8-day-old bees sug gest that 4 h after treatment the observed effects are due to a metabolite of Imidacloprid, rather than to Imidacloprid itself. Our results suggest th e existence of two distinct subtypes of nicotinic receptors in the honeybee that have different affinities to Imidacloprid and are differentially expr essed in 7- and 8-day-old individuals. (C) 2001 Academic Press.