Bee microbiome responses to bactericides in the foraging environment

There is limited field-data on the impact of sprayed agrochemicals on beneficial insect microbiomes (symbiotic gut bacteria). Understanding these potential impacts is relevant for pollinators as they come into contact with chemical residues in crop pollen and nectar. The risk of microbial depletion is especially concerning for pollinators with core microbiomes, such as bumble bees and honey bees, given their role in mediating bee immunity, nutrition, and behavior.

We examined the impact of bactericide, copper and streptomycin, applications to blooming apple orchards on the microbiome composition of eastern bumble bees (Bombus impatiens) and honey bees (Apis mellifera). Within the same orchard, four Bombus colonies were placed in a copper-sprayed plot and four were placed in a streptomycin-sprayed plot. Three Apis colonies were placed at a streptomycin-sprayed orchard and three near an unmanaged orchard. We collected bees once pre and post spray, dissected whole guts, extracted their DNA and sequenced the 16s rRNA V4 region.

We found that the microbiome of eastern bumble bees was more susceptible to disturbance from antibiotic sprays, relative to honey bees. The initial Bombus microbiome was dominated by core bacteria. However, the proportion of opportunistic bacteria increased across all bumble bee colonies and the community composition was different for copper and streptomycin-exposed bees (P = 0.001). This compositional change was accompanied by a reduction on Snodgrassella (P < 0.05), a core symbiont that mediates bee immunity. The initial honey bee microbiome harbored opportunistic bacteria and the exposure to antibiotics did not evidently alter its composition.