1. Key Points

This review document explains why the gut microbiome matters for bee nutrition and health, and why feeding is therefore more complex than simply supplying sugars or proteins.

• The document does not present a single trial, but a synthesis of research on gut flora, its functions, and the implications for beekeeping. 
• The gut microbiome of the bee contributes to digestion, the utilisation of certain pollen nutrients, and protection against various pathogens. 
• Natural pollen remains the biological reference; substitutes, probiotics, and vitamin supplements have not been sufficiently validated in field conditions here to justify routine use. 
• Antibiotics, certain pesticides, and inappropriate feeding can disrupt this microbiome. 
• For the apiary, the main interest is practical but cautious: attending to apiary site, pollen supply, and feeding quality appears more soundly supported than adding multiple supplements.

2. What the Study Shows

The document brings together work from microbiology, physiology, and nutrition to connect bee gut flora with apiary management decisions.

Research question. The author seeks to clarify three points: how the gut flora of the bee is established and changes according to caste and life stage, what roles it plays in nutrition and immunity, and what this implies for feeding or potential supplementation.

Method. This is a review document based on numerous prior studies, not a single experiment conducted at a specific apiary. The text draws on research into larvae, workers, winter bees, and queens, as well as studies on the effects of feeding, antibiotics, and certain pesticides. 

Results. The document first demonstrates that gut flora is neither fixed nor uniform. It changes from the larval stage to the adult bee, differs between workers and queens, and also varies according to social function and season. In adult workers, a relatively stable bacterial core recurs consistently, whereas in queens the composition differs, linked to a very specific diet and lower environmental exposure.

The second important finding concerns the functions attributed to this microbiome. Gut bacteria participate in carbohydrate metabolism, the production of organic acids and certain vitamins, and also contribute to the utilisation of pollen components. The document also emphasises a biological barrier function: the microbiome helps make the gut environment less hospitable to certain pathogens and can stimulate local immune defences. 

The third section links this biology to beekeeping practice. The text highlights that a diet based on natural pollen supports this flora better than a simple artificial nutrient mixture. It also notes that disruptions can occur following certain antibiotic treatments, in the presence of certain pesticides, or through poorly adapted feeding. Finally, it judges commercially available probiotics for bees to be insufficiently validated, and protein or vitamin supplementation as difficult to formulate correctly.

Interpretation. For the beekeeper, the main message is not that the microbiome should henceforth be "fed" with specialised products. The document points in rather the opposite direction: it recalls the biological value of natural pollen, the genuine complexity of bee nutritional requirements, and the caution needed before generalising the use of additives or supplementation protocols. In this logic, the microbiome serves primarily as an explanatory framework for understanding why certain practices support the colony better than others.

3. Critical Assessment

The document is rich and useful, but it is important to distinguish what rests on robust findings from what still represents a cautious extrapolation to apiary conditions.

Strengths of the document. Its primary strength is that it connects several levels rarely presented together: microbiome development, digestion, immunity, queens, winter bees, and feeding practice. It also usefully recalls that bees cannot be reduced to a simple sugar-processing machine, and that pollen supply retains a central place in colony biology. For a beekeeping readership, this contextualisation is valuable. 

Methodological limitations. The document is not, however, a systematic review with an explicit study selection protocol. The research drawn upon is highly heterogeneous: some data come from the laboratory, others from controlled trials, and others from more field-based observations. This makes the synthesis instructive, but not equivalent to a homogeneous and directly transferable body of evidence. Moreover, several findings concern biological mechanisms or intermediate measures, without consistently demonstrating a net benefit at the level of the whole colony. 

Possible biases and uncertainties. A further caution concerns context. The studies cited in the document come from varied geographical and experimental settings, not exclusively from Switzerland nor always from temperate European conditions. The general biology of the microbiome appears broadly relevant to the Swiss apiary, but detailed recommendations on supplements, probiotics, or the ideal composition of a feed input should not be read as recipes directly validated under local conditions.

What cannot be concluded. This document does not allow one to conclude that a commercial probiotic reliably improves colony health or productivity at the apiary. Nor can a universal formula for protein or vitamin supplementation be derived from it. Finally, the document does not show that every measurable disruption of the microbiome will automatically result in disease or colony loss. It illuminates plausible mechanisms and points for vigilance, but does not replace well-controlled comparative field trials. 

4. What the other related studies show

Source: Engel et al. (2012)

The related studies strongly confirm the biological role of the gut microbiota, while calling for caution regarding practical applications at the apiary.

Since the synthesised dossier does not present a single trial, it is useful to confront its claims with a few primary studies and recent reviews. Research on the bee's microbiota benefits from a relatively powerful experimental model: the adult worker has a fairly simple, specialised and experimentally tractable gut community. These works confirm several points of the dossier, but they also show that effects measured in the laboratory do not always translate into direct recommendations for the apiary.

Well-documented nutritional functions. Engel et al. (2012) showed that the bacteria of the bee's gut microbiota display considerable functional diversity, notably for interaction with the host, biofilm formation and the breakdown of complex carbohydrates. Some of the capacities identified are compatible with the breakdown of components of the pollen walls. Kešnerová et al. (2017), in a controlled experimental system, subsequently showed that the bee's gut bacteria use numerous pollen-derived substrates, including flavonoids and components of the outer pollen coat, and produce organic acids as well as other metabolites. These results provide a solid mechanistic basis for the digestive role mentioned in the dossier.

A biological barrier, but not an absolute shield. The protective role of the microbiota is also well supported. Steele et al. (2021) showed that an intact microbiota allows Serratia marcescens, an opportunistic pathogen, to be eliminated more rapidly, whereas this pathogen persists more in guts lacking a normal microbiota or disrupted by antibiotics. Dosch et al. (2021) showed that bees with a normal microbiota survived better after oral exposure to deformed wing virus. In this latter case, however, the viral load remained comparable: the microbiota therefore seems to favour a form of tolerance to the virus rather than direct elimination of the virus. The "biological barrier" must thus be understood as a support for health balance, not as absolute protection.

Nutrition and nutritional stress. The literature also supports the importance of diverse, good-quality pollen. A recent review on the interactions between foraged pollen, nutrition and microbiome concludes that a varied pollen diet helps to maintain a more stable microbiota and better resilience. Castelli et al. (2020) showed in the laboratory that pollen of low nutritional quality alters the composition of the microbiota, decreases the expression of immunity-related markers and favours the multiplication of Nosema ceranae, compared with polyfloral pollen. These results reinforce the dossier's practical message: the quality of the pollen resource remains more fundamental than a late artificial correction through additives.

Antibiotics and pesticides: documented disruptors. Raymann et al. (2017) showed that exposure to antibiotics durably alters the size and composition of the gut microbiota and increases bee mortality, particularly after exposure to opportunistic bacteria. Motta and Moran (2020) likewise showed that sublethal doses of glyphosate can disrupt the gut microbiota, with effects depending on the concentration, the duration of exposure and the timing of exposure relative to the establishment of the microbiota. These works reveal plausible mechanisms, but they do not allow the health status of a colony to be diagnosed from a single exposure factor.

Probiotics: a scientific avenue, not yet a beekeeping routine. Recent studies support the dossier's caution. Damico et al. (2023) observed no restoration of the microbiota after antibiotic treatment with a commercial probiotic widely sold in the United States; the product's microorganisms were not recovered from the gut of the sampled workers. Anderson et al. (2024), in a longitudinal study of commercial colonies, likewise conclude that non-native probiotics do not restore the effects of antibiotic-induced dysbiosis and bring no clear general benefit. These commercial products must, however, be distinguished from experimental work with native strains: Powell et al. (2021) show that a cocktail of native gut bacteria can improve the survival of bees exposed to a pathogen after antibiotic disruption. This avenue is of interest, but it does not yet correspond to a simple recommendation for the apiary.

Season and temperate context. Seasonal variations also deserve attention. Li et al. (2022) showed that winter is accompanied by a substantial reshaping of the microbiota, probably linked to the decline in pollen consumption and the change in diet. These results are consistent with the constraints of temperate climates, but they remain to be interpreted with caution for Switzerland: they shed light on the possible mechanisms of overwintering without providing a specific feeding recipe.

Overall, the other related studies strongly confirm the role of the microbiota in nutrition, immunity and resistance to stress. They reinforce the importance of a diverse pollen environment, of reasoned feeding and of great caution towards disruptors. By contrast, they do not justify the routine use of probiotics or commercial supplements that have not been validated under local conditions. The convergence is strong on the biological mechanisms, but more limited on the practical interventions.

5. Practical Takeaways for the Apiary

At the apiary, this document above all encourages reinforcing the biological foundations of colonies before seeking additive solutions.

• Wherever possible, favour an apiary site offering a varied and consistent pollen supply: this is the lever most coherent with the document's findings.
• Clearly distinguish energy feeding from protein supplementation: these address different needs and carry different risks.
• Remain cautious towards probiotics and "booster" supplements for bees: the document is not sufficient to justify routine use.
• Pay attention to the quality of food stores and to digestive disorders, especially at the end of winter, without attributing every problem too hastily to the microbiome alone.
• In the Swiss context, this text above all reinforces a straightforward principle: good floral resources, well-reasoned feeding, and caution towards extrapolations from the laboratory.

Read the original study

►Understanding gut flora

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Further reading:

• Protein supply for bees: useful or overrated?
• Beneficial microbes for bee health
• Pollen consumption and colony development
• Practical Guide: 4.2 Feeding
• Which feeding syrup for winter feeding?
• Practical Guide: 2.5 Dysentery

Bibliography

Colin, M.-É. (2024). Connaître la flore intestinale et réussir le nourrissement de l'abeille, dossier comprenant « La flore intestinale évolutive de l'abeille », « Les multiples rôles de la flore intestinale » et « L'influence de la pratique apicole sur la flore intestinale de l'abeille ». La Santé de l'Abeille, 322, juillet-août, p. 42-82.

 

Anderson, K. E., Allen, N. O., Copeland, D., Kortenkamp, O. L., Erickson, R. J., Mott, B., & Oliver, R. (2024). A longitudinal field study of commercial honey bees shows that non-native probiotics do not rescue antibiotic treatment, and are generally not beneficial. Scientific Reports, 14.

Castelli, L., Branchiccela, B., Garrido, M., Invernizzi, C., Porrini, M., Romero, H., Santos, E., Zunino, P., & Antúnez, K. (2020). Impact of nutritional stress on honeybee gut microbiota, immunity, and Nosema ceranae infection. Microbial Ecology, 80, 908–919.

Damico, M. E., Beasley, B., Greenstein, D., & Raymann, K. (2023). Testing the effectiveness of a commercially sold probiotic on restoring the gut microbiota of honey bees: A field study. Probiotics and Antimicrobial Proteins, 17, 991–1000.

Dosch, C., Manigk, A., Streicher, T., Tehel, A., Paxton, R. J., & Tragust, S. (2021). The gut microbiota can provide viral tolerance in the honey bee. Microorganisms, 9.

Engel, P., Martinson, V. G., & Moran, N. A. (2012). Functional diversity within the simple gut microbiota of the honey bee. Proceedings of the National Academy of Sciences, 109, 11002–11007.

Kešnerová, L., Mars, R. A. T., Ellegaard, K. M., Troilo, M., Sauer, U., & Engel, P. (2017). Disentangling metabolic functions of bacteria in the honey bee gut. PLoS Biology, 15.

Li, C., Tang, M., Li, X., & Zhou, X. (2022). Community dynamics in structure and function of honey bee gut bacteria in response to winter dietary shift. mBio, 13.

Meehan, D., & O’Toole, P. W. (2025). A review of diet and foraged pollen interactions with the honeybee gut microbiome. Microbial Ecology, 88.

Motta, E. V. S., & Moran, N. A. (2020). Impact of glyphosate on the honey bee gut microbiota: Effects of intensity, duration, and timing of exposure. mSystems, 5.

Powell, J. E., Carver, Z., Leonard, S. P., & Moran, N. A. (2021). Field-realistic tylosin exposure impacts honey bee microbiota and pathogen susceptibility, which is ameliorated by native gut probiotics. Microbiology Spectrum, 9.

Raymann, K., Shaffer, Z., & Moran, N. A. (2017). Antibiotic exposure perturbs the gut microbiota and elevates mortality in honeybees. PLoS Biology, 15.

Steele, M. I., Motta, E. V. S., Gattu, T., Martinez, D., & Moran, N. A. (2021). The gut microbiota protects bees from invasion by a bacterial pathogen. Microbiology Spectrum, 9.