Performance of honeybee colonies located in neonicotinoid‐treated and untreated cornfields in Quebec

Twenty‐two honeybee (Apis mellifera) colonies were placed in four different cornfield areas in order to study the potential in situ effects of seed‐coated systemic neonicotinoid pesticides used in cornfields (Zea mays spp) on honeybee health. Two apiaries were located in two independent neonicotinoid‐treated cornfield areas and two others in two independent untreated cornfield areas used as controls. These experimental hives were extensively monitored for their performance and health traits over a period of one year. Trapped pollen was collected and microscopically identified to define the visited flowers and the amount of corn pollen collected by bees. Liquid chromatography–mass spectrometry was performed to detect pesticide residues in honeybee foragers and trapped pollen. Honeybee colonies located in neonicotinoid‐treated cornfields expressed significantly higher varroa mite loads than those in untreated cornfields. However, brood production and colony weight were less disturbed by the treatment factor. Sublethal doses of neonicotinoids were detected in the trapped corn pollen and none in bee foragers. Overall, our results show that forager bees collected 20% of corn pollen containing variable concentrations of neonicotinoids. Colonies located in treated cornfields expressed higher varroa loads and long‐term mortality than those in untreated cornfields. On the other hand, no significant differences were observed regarding the brood production and colony weight.