Traces of a neonicotinoid pesticide stimulates activity in honey bee colonies, but not productivity

Abstract

How neonicotinoid contamination effects honey bees remains controversial. Studies have yielded contradictory results, and few have examined effects on colony development. Here we report the results of a comprehensive five-year study of the effects of the neonicotinoid imidacloprid on honey bee colonies. Colonies fed 5 ng/g (ppb) imidacloprid showed increased brood production, lower temperature variability, higher CO2 production and had more foragers compared to control colonies. Even so, treatment did not affect adult bee numbers or average hive temperatures, and did not increase food stores, daily food acquisition or colony survivorship. Imidacloprid contamination increased colony metabolism without improving colony productivity, which is consistent with the pharmacological action of imidacloprid as a stimulant. Our findings explain why some studies have reported no, or even positive, effects of neonicotinoids. We provide an explanation for the diverse effects of pesticide contamination on honey bees, and a thorough understanding of how colonies are impacted.