Managing Microbiota Activity of Apis mellifera with Probiotic (Bactocell ® ) and Antimicrobial (Fumidil B ® ) Treatments: Effects on Spring Colony Strength.

Against a backdrop of declining bee colony health, this study aims to gain a better understanding of the impact of an antimicrobial (Fumidil B ® , Can-Vet Animal Health Supplies Ltd., Guelph, ON, Canada) and a probiotic (Bactocell ® , Lallemand Inc., Montreal, QC, Canada) on bees' microbiota and the health of their colonies after wintering. Therefore, colonies were orally exposed to these products and their combination before wintering in an environmental room. The results show that the probiotic significantly improved the strength of the colonies in spring by increasing the total number of bees and the number of capped brood cells. This improvement translated into a more resilient structure of the gut microbiota, highlighted by a more connected network of interactions between bacteria. Contrastingly, the antimicrobial treatment led to a breakdown in this network and a significant increase in negative interactions, both being hallmarks of microbiota dysbiosis. Although this treatment did not translate into a measurable colony strength reduction, it may impact the health of individual bees. The combination of these products restored the microbiota close to control, but with mixed results for colony performance. More tests will be needed to validate these results, but the probiotic Bactocell ® could be administrated as a food supplement before wintering to improve colony recovery in spring.