Assessing the impact of broadcast-sprayed antibiotics on bee gut microbiome composition and presence of antibiotic-resistant genes

Crop pollination typically increases the risk of bee exposure to traces of agrochemicals. To date, much remains unknown about the potential exposure of bees to field sprayed antibiotics used to control crop pathogens. It is important to fill this knowledge gap due to the increased use of antibiotics in fruit tree orchards that rely on pollinators. According to the literature, we could expect contrasting impacts of antibiotic exposure: (1) in the lab; antibiotics can disrupt the bee gut microbiome that mediates bee immunity and response to pathogen invasion; (2) there is evidence for antimicrobial resistance development in bee gut symbionts when bee colonies are treated with antibiotics.


To tease apart the impact of field sprayed antibiotics on the bee microbiome composition, antibiotic resistance, and pathogen abundance, three times during the blooming period, we sampled crop flowers, wild bees, and honey bees at three apple orchards (antibiotics applied on blooms) and three strawberry farms (control) located in North Georgia. In the lab, we analyzed residual antibiotic concentrations in flowers and bees, carried out 16s amplicon sequencing to track changes in microbiome composition, quantified the presence of antibiotic-resistant genes, and determined the abundance of the environmental pathogen Serratia marcescens, known to invade bee guts disrupted by antibiotics. We are still analyzing data, but preliminary results show high concentrations of streptomycin on apple flowers (147 to 216 ppm) and bees (11 to 113 ppm). Our results will provide baseline information on the direct impact of agricultural antibiotics on the bee microbiome composition.