Meta-analysis on the effect of bacterial interventions on honey bee productivity and the treatment of infection

The concerns over honey bee health and colony collapse have led to an increased interest in the potential for beneficial bacteria as an intervention. However, the efficacy of this approach is mostly unknown because the application of bacterial adjuncts to hives has not often proceeded by understanding the strains being applied or how they function. This article summarizes the effects reported from published studies (2004-2020) that have experimentally tested the influence of beneficial bacteria, including probiotics, on honey bee immune function, pathogen resistance, or colony productivity. The meta-analysis shows that bacterial intervention can improve bee survival against American foulbrood and Nosema infection, and increase honey yields, but the underlying molecular correlates remain poorly understood. There is some evidence that honey bee-derived bacteria could be superior to exogenous bacterial species, although further evaluation is needed. We advocate for a more organized and transparent approach that includes the rationale for strain choice and delivery, a thorough description of treatment formulations, viable counts and their application to hives, and improved design of experimental field trials to consistently include controls and other features that allow interpretation of results. Successful studies should also be validated for efficacy and reproducibility.