Exposure to a fungicide for a field-realistic duration does not alter bumble bee fecal microbiotas

Social bees are frequently exposed to pesticides when foraging on nectar and pollen. Recent research has shown that pesticide exposure not only impacts social bee host health but can also alter the community structure of social bee gut microbiotas. However, most research on pesticide-bee gut microbiota interactions has been conducted in honey bees; bumble bees, native North American pollinators, have received less attention and, due to differences in their ecology, may be exposed to certain pesticides for shorter durations than honey bees. Here we examined how exposure to the fungicide chlorothalonil for a short, field-realistic duration altered bumble bee fecal microbiotas (used as a proxy for gut microbiotas) and host performance. We exposed Bombus impatiens microcolonies to field-realistic chlorothalonil concentrations for five days, tracking changes in fecal microbiotas during the exposure period and a nine-day recovery period, and comparing microcolony production between treatments at the end of the experiment. We also assessed the use of fecal microbiotas as a gut microbiota proxy by comparing community structures of fecal and gut microbiotas. We found that chlorothalonil exposure did not alter bumble bee fecal microbiota structure or affect microcolony production at any concentration, but that fecal and gut microbiotas differed significantly in community structure. Our results highlight the importance of considering ecologically relevant exposure periods when investigating the effects of toxicants on animal microbiotas and host health, and the importance of sampling gut microbiotas directly, when possible.