Chronic exposure to a neonicotinoid increases expression of antimicrobial peptide genes in the bumblebee Bombus impatiens

Bumblebees are important pollinators in wild and agricultural settings. In recent decades pollinator declines have been linked to the effects of increased pesticide use and the spread of disease. Synergy between these factors has been suggested, but no physiological mechanism has been identified. This study examines the connection between neonicotinoid exposure and innate immune function in the bumblebee Bombus impatiens, which is an important wild and commercial pollinator in eastern North America. Experimental colonies in the field were enclosed and provided pollen and sugar syrup containing an agriculturally relevant range of imidacloprid concentrations. Bumblebees were collected from colonies over four weeks, and the expression of antimicrobial peptides was measured using multiplex quantitative real time PCR. Significant increases in the expression of abaecin, apidaecin and hymenoptaecin were found over time in treatments receiving moderate to high concentrations of the pesticide. Responses were dependent on time of exposure and dose. These results indicate that immune function in bumblebees is affected by neonicotinoid exposure and suggest a physiological mechanism by which neonicotinoids may impact the innate immune function of bumblebee pollinators in wild and agricultural habitats.