Effects of imidacloprid and deltamethrin on associative learning in honeybees under semi-field and laboratory conditions

We have compared the sublethal effects of two insecticides in the honeybee (imidacloprid and deltamethrin) in both semi-field and laboratory conditions. A sugar solution containing 24 μg kg−1 of imidacloprid or 500 μg kg−1 of deltamethrin was offered to a colony set in an outdoor flight cage. In contrast to imidacloprid, deltamethrin had lethal effect on workers bees. The contamination of syrup with imidacloprid or deltamethrin induced a decrease in both the foraging activity on the food source and activity at the hive entrance. Negative effects of imidacloprid were also observed in an olfactory learnt discrimination task. Free-flying foragers were taken from the contaminated feeder and subjected to a conditioned proboscis extension response (PER) assay under laboratory conditions. As with free-flying bees, no impact of deltamethrin was found on the learning performances of restrained individuals in the PER procedure, whilst significant effects were found with imidacloprid in both semi-field and laboratory conditions.