: Popular and non-native probiotics have no overall effect, and do not rescue antibiotic treatment: A longitudinal field study of commercial honey bees.

Probiotics are widely used in agriculture including commercial beekeeping, but there is little empirical evidence supporting their effectiveness. Antibiotic treatments can greatly distort the gut microbiome, reducing its protective abilities and facilitating the growth of antibiotic resistant pathogens. Commercial beekeepers regularly apply antibiotics to combat bacterial infections, often followed by an application of probiotics advertised to ease the impact of antibiotic-induced gut dysbiosis. We tested whether probiotic application affects the gut microbiome or disease prevalence, or rescues the negative effects of antibiotic induced gut dysbiosis. We found no difference in the gut microbiome or disease markers by probiotic application or antibiotic recovery associated with probiotic treatment. A colony-level application of the antibiotics oxytetracycline and tylosin produced an immediate decrease in gut microbiome size, and over the longer-term, very different and persistent dysbiotic effects on the composition and membership of the hindgut microbiome. Our results demonstrate the lack of probiotic effect or antibiotic rescue, detail the duration and character of dysbiotic states resulting from different antibiotics, and highlight the importance of the gut microbiome for honeybee health.