Learning performances of honeybees (Apis mellifera L) are differentially affected by imidacloprid according to the season

Axel Decourtye, Eric Lacassie, Minh-Hà Pham-Delègu

Abstract: To establish the sublethal concentrations domain, acute and chronic oral tests were
conducted on caged honeybee workers (Apis mellifera L) using imidacloprid and a metabolite, 5-OHimidacloprid,
under laboratory conditions. The latter showed a 48-h oral LD50 value (153ng per bee)
five times higher than that of imidacloprid (30ng per bee). Chronic feeding tests indicated that the
lowest observed effect concentrations (LOEC) of imidacloprid and of 5-OH-imidacloprid on mortality
of winter bees were 24 and 120µg/kg respectively. Behavioural effects of imidacloprid and 5-OHimidacloprid
were studied using the olfactory conditioning of proboscis extension response at two
periods of the year. Winter bees surviving chronic treatment with imidacloprid and 5-OH-imidacloprid
had reduced learning performances. The LOEC of imidacloprid was lower in summer bees
(12µg/kg) than in winter bees (48µg/kg), which points to a greater sensitivity of honeybees behaviour
in summer bees, compared to winter bees.

Bron: Pest Management Science, Volume 59, Issue 3, Pages 269-278