Effects of chronic neonicotinoid exposure on expression of antimicrobial peptides in the bumble bee (Bombus impatiens)

Bumble bees are an important pollination resource across the world. However, in recent years, there has been concern for the health of bumble bee populations due to a range of factors including parasitism and pesticide exposure. Previous study of the European bumble bee Bombus terrestris has shown that exposure to neonicotinoid pesticide reduces colony growth and queen production. Here we explore the possibility of a synergy between pesticide exposure and immune function. Specifically, we test whether chronic exposure to the neonicotinoid pesticide imidacloprid at field-realistic concentrations impacts the expression of four antimicrobial peptides (AMPs). AMPs play an important role in the insect immune system, and have been shown to defend bees against gram negative and positive bacteria, fungi, and trypanosome infections. Using commercial B. impatiens colonies in small field enclosures, baseline variations in AMP expression were explored over 3 weeks.  Imidacloprid exposures were then made during a 4-week period. Our data demonstrate that chronic low-dose exposure to imidacloprid in sugar syrup and pollen resources result in altered expression of AMPs, compared to controls. This may represent a direct effect of imidacloprid or a stress-like response to other physiological and behavioral effects of the pesticide.