1. Why this question comes up regularly in the apiary

Objective To frame the central question precisely: not whether bees need protein — they obviously do — but whether protein supplementation truly provides a net benefit under ordinary Swiss beekeeping conditions.

Every spring, and more generally whenever a colony appears sluggish, the question of protein feeding returns in beekeeping discussions. It arises especially when weather limits flights, when pollen availability seems low, when young colonies struggle to develop or, more simply, when a pollen shortage is feared. In this context, protein patties, commercial substitutes and homemade recipes are often presented as ways of “supporting” colonies.

Pollen is indeed essential for brood rearing, the physiology of young workers, metabolism, digestion and several dimensions of organismal defence (Keller et al., 2005a, 2005b ; Ritter & Kast, 2021). In the Swiss context, most sites normally provide pollen in sufficient quantity and acceptable quality, even though this varies according to region, season, weather, available flora and local colony density. The colony also finely regulates its pollen collection according to brood status and internal needs, with the capacity to compensate within about a fortnight when reserves vary substantially (Seeley, 1997, cited in Ritter & Kast, 2021).

Development judged to be insufficient therefore does not automatically mean that a protein supplement is indicated. Weather, queen quality, health status, parasite pressure, a break in the nectar flow or seasonal dynamics can produce similar effects. Even when a pollen resource becomes objectively limiting, a protein patty or homemade recipe does not necessarily reproduce the biological value of natural pollen. Trials by Di Pasquale et al. (2013) show that the effects of pollen on survival, hypopharyngeal glands and certain disease-resistance parameters depend on its quality, not on crude protein content alone. A recent literature review further concludes that the effects of pollen substitutes remain highly variable depending on formulation, environmental conditions and the objectives pursued, and that natural pollen feeding remains the nutritional reference for colonies (Noordyke & Ellis, 2021).

Data collected in two Swiss apiaries illustrate the natural richness of a good site. At Allschwil (BL, 290 m), a multi-year study identified 134 different pollen species, 25 of which each represented more than 1% of total pollen intake over a season. At Vogorno (TI, 600 m), 74 species were recorded. This diversity reminds us that the nutritional richness of a good site cannot realistically be reproduced by a protein patty (Roncoroni, 2020, cited in Guichard et al.).

2. What exactly are we talking about?

Objective To distinguish the different realities that beekeeping practice often conflates: natural pollen, a pollen frame, harvested pollen, commercial substitutes and homemade recipes do not follow the same biological logic and do not involve the same risks.

Natural pollen is the reference resource. It is collected from flowers, brought back as pollen pellets, consumed rapidly or stored. About two thirds of pollen is consumed fresh during the brood-rearing season, while the remainder is packed into cells, mixed with nectar or honeydew and preserved as bee bread. Foragers do not simply assess the presence or absence of pollen; rather, they obtain information about the colony’s needs through social regulation based on inhibitory feedback (Camazine, 1993).

A pollen frame is a special case: it is a targeted transfer of natural pollen that has already been stored, not an artificial substitute. In certain limited situations — late-formed artificial swarms facing pollen shortage — Ritter and Kast (2021) consider that a pollen frame from a healthy colony, ideally from the parent colony, may offer more advantages than the risks associated with the pathogens adhering to it. This type of transfer does not raise the same issue as a patty or a formulated substitute.

Harvested or purchased pollen raises a distinct sanitary issue. Nutritionally, it remains pollen; from a health perspective, however, it can become a vector of pathogens when it comes from other colonies — notably European foulbrood, American foulbrood, chalkbrood or certain viruses (Imdorf et al., 1984, cited in Ritter & Kast, 2021).

Commercial substitutes and homemade recipes form a different category: their logic is to provide a formulated supplement based on ingredients chosen for their apparent protein richness. This is where the main practical confusion arises. A patty may contain a great deal of crude protein without reproducing the biological value of natural pollen, whose lipids, minerals and other nutrients are as important as protein (Keller et al., 2005a, 2005b). Finally, an “effective” product must be assessed over time: brood development, adult population, longevity, physiological state of nurse bees, resistance to pathogens — not on the basis of a one-off observation (Di Pasquale et al., 2013 ; Ritter & Kast, 2021).

3. Why natural pollen is difficult to replace

3D amino acid molecule

Objective To show that the biological value of pollen cannot be reduced to crude protein: the balance of essential amino acids, lipids, sterols and the way pollen is digested make natural pollen a resource that substitutes only rarely reproduce.

Natural pollen is not just a protein raw material. Its biological value depends on the balance of essential amino acids, lipids, sterols, and the way it is digested and redistributed within the colony — a set of properties that substitutes and homemade recipes only rarely reproduce (Keller et al., 2005a ; Ritter & Kast, 2021).

The balance among amino acids cannot be reduced to protein content alone. Dandelion illustrates this point: although low in protein, this pollen is rich in lipids, which promotes development of the fat body, important for metabolism and the organism’s defence (Ritter & Kast, 2021). Recent work also shows that colony performance depends more on the balance of essential amino acids than on crude protein percentage alone: in a trial involving 144 colonies, deficits in essential amino acids explained average bee weight and colony size better than macronutrients (Ricigliano et al., 2022). Hoover et al. (2022) observed that lysine and arginine remained below optimal proportions in almost all commercial patties tested. A feed can therefore be “rich in protein” and still remain nutritionally imperfect for the colony.

Lipids and sterols play a role of their own. Experimental trials have shown that the lipid content of pollen diets influences bee longevity (Manning et al., 2007). Bees do not synthesise their own sterols; under natural conditions, they obtain them from plant pollen. A study published in Nature had to rely on genetically modified yeast to provide rare but essential pollen sterols in an artificial diet capable of supporting brood rearing in the absence of floral pollen (Moore et al., 2025). The message is not that replacement is impossible in principle, but that any credible replacement requires a level of formulation precision far removed from the logic of homemade recipes.

Pollen digestion adds yet another level of complexity. The pollen grain is surrounded by a double envelope that is virtually indigestible; nutrients are extracted only through the germination pores after passage through the crop, proventriculus and intestine. Nurse bees are specialised for this digestion, and digestive efficiency declines with age (Ritter & Kast, 2021). Recent work confirms that the form in which nutrients are delivered matters as much as their composition: diets rich in free amino acids have been associated with high DWV levels and increased mortality, whereas diets based on intact proteins produced better virological outcomes (Tapia-Rivera et al., 2025).

4. What scientific studies show about protein supplementation

Objective To present an honest assessment of the scientific studies: effects are sometimes positive, sometimes neutral, sometimes negative depending on conditions, with no solid basis for a general recommendation of protein supplementation.

The scientific studies reviewed do not justify a general recommendation of protein supplementation. The effects of pollen substitutes appear at times positive, at times neutral and at times negative depending on formulation, environmental conditions and the criteria measured (Noordyke & Ellis, 2021 ; Ritter & Kast, 2021). Under good pollen conditions, the effect of a protein supplement often appears weak or absent; under unfavourable conditions, a positive effect may be arguable (Guichard et al.). There is therefore no solid basis for considering protein supplementation a routine measure.

Specific situations nevertheless exist. Hoover et al. (2022) observed that spring protein feeding could increase colony population before summer pollination, especially in an apiary where natural pollen was scarce; where natural pollen was abundant, differences between treatments became much less marked. Ritter and Kast (2021) explicitly mention late-formed artificial swarms, especially when pollen availability is reduced or dominated by low-protein pollen such as maize.

Other trials did not reveal any net benefit. Mortensen et al. (2019), working with 75 colonies distributed across several treatments, found no differences either in colony strength or in the intensity of Nosema infection between supplemented and control colonies. DeGrandi-Hoffman et al. (2016) showed that colonies with access to natural forage had lower pathogen loads — Black Queen Cell Virus, Nosema, queen losses — and better overwinter survival than colonies given protein supplements; nurse bees also digested proteins from supplements less efficiently than those from natural pollen.

Agroscope’s caution is based on several concrete and clearly identifiable disadvantages. Pollen from external sources can transmit pathogens — European foulbrood, American foulbrood, chalkbrood, viruses (Imdorf et al., 1984, cited in Ritter & Kast, 2021). Administering protein feed reduces natural pollen-collecting activity. A spring supplement may alter nutritional balances in undesirable ways and possibly promote nosema (Ritter & Kast, 2021). Finally, to be truly effective, supplementation would need to be administered during the brood-production season, which often coincides with the nectar flow — with a high risk of compromising the honey.

A protein supplement may therefore be of interest in specific, well-identified cases. Under ordinary conditions, however, its advantages often remain limited, uncertain or highly context-dependent, whereas the sanitary, behavioural and technological disadvantages are very real. Protein supplementation follows an exception logic, not a standard response.

5. Why homemade recipes pose a scientific problem

Objective To identify the three fundamental problems with homemade recipes: nutritional, functional and validation-related — including a Swiss field result that contradicts a widely held assumption.

Homemade recipes are based on an intuitive but overly simple idea: that providing a protein-rich mixture — yeast, soy flour, milk powder — would be enough to compensate for a lack of pollen. Three fundamental problems undermine this logic.

The first is nutritional. The biological value of pollen cannot be reduced to crude protein: the balance of essential amino acids, lipids and sterols plays a role of its own that the common ingredients of homemade recipes do not reproduce. No simple adjustment in the amount of yeast or soy can, by itself, reproduce the nutritional profile of plant pollen. A feed can therefore be “rich in protein” and still remain biologically incomplete for the colony.

The second is functional. For protein feeding to be useful for larval rearing, it must be consumed by nurse bees. However, Agroscope indicates that it is suspected that foragers are mainly the ones consuming it in large quantities. In addition, adding only 10% natural pollen to a substitute already significantly improved digestion, the size of the hypopharyngeal glands and certain health-related parameters compared with a substitute alone (Watkins de Jong et al., 2019). Diets based on free amino acids may be associated with high DWV levels and increased mortality (Tapia-Rivera et al., 2025).

The third is a validation problem — and concerns a widely held assumption that a Swiss field trial helped correct. It is often said that bees take only as much patty as they need and do not store it in the frames. A study conducted by Agroscope in two apiaries (Witzwil, BE and Bellechasse, FR) demonstrated the opposite: feed patty is indeed stored within the colony, and when the brood box is full, bees move it into honey frames. Baker’s yeast (Saccharomyces cerevisiae) was thus found in spring honey only two weeks after the last feeding in April, and still in summer honey harvested in August. The control colonies, which had not been fed, contained none. The presence of baker’s yeast in honey is an indicator of added sugar, incompatible with good-quality honey (Roetschi et al., 2017 ; Kast & Roetschi, 2017).

These recipes are not necessarily without effect in situations of documented shortage. But they generally remain biologically under-specified: they attempt to correct a complex problem on the basis of an overly simple criterion, whereas natural pollen is a much more complete resource and much harder to reproduce credibly (Moore et al., 2025 ; Ritter & Kast, 2021).

6. What to do in practice in the Swiss context?

Objective To provide concrete practical guidance: when to observe rather than intervene, in which limited cases a supplement may be considered, and how to assess a product critically.

The first response to concern about pollen supply is generally not to use a protein patty. The most relevant starting point remains the site, the quality of the floral resources and careful observation of the colony.

A pollen shortage should not be presumed, but documented concretely: brood status, visible pollen stores, quality of the local floral resources and flight conditions over the preceding days. The colony regulates its pollen collection very finely; the absence of good stores does not by itself mean that protein feeding is necessary. Slower development may also be linked to weather, queen quality, parasite pressure or seasonal timing. Very low pollen stores during the brood-rearing period, or a very limited visual diversity of pollen pellets and pollen stores, may raise concern about a quantitative or qualitative deficiency (Guichard et al.).

The situations in which a supplement may genuinely be considered remain limited: artificial swarms or young colonies formed during a period of pollen shortage, areas with low floral diversity, weather conditions that prevent flights for a prolonged period, and certain periods when an abundant but pollen-poor resource dominates locally — for example, strong maize dominance in June–July. In such cases, a pollen frame from a healthy colony, ideally from the parent colony, is the best documented option.

When a supplement truly becomes necessary, the composition of a product alone cannot guarantee its real biological value. A few guidelines are nevertheless more useful than others. A simple crude protein percentage is not enough: the balance of essential amino acids appears more informative, especially for often-limiting amino acids such as lysine or arginine (Hoover et al., 2022 ; Ricigliano et al., 2022). Formulations containing pollen, or biologically closer to pollen, seem more favourable than pure substitutes (Watkins de Jong et al., 2019). In practice, a product should therefore be judged less on general claims than on the existence of independent colony-scale trials and on the transparency of its formulation (Noordyke & Ellis, 2021).

Neither homemade recipes nor commercial protein patties should be the reflex response to development judged to be insufficient. The practical hierarchy remains simple: examine the site and floral resources, observe the colony closely, place observations back into their seasonal context, and reserve any supplement for limited, well-identified situations.

Conclusion

Objective To summarise the position of scientific studies and Agroscope: protein supplementation is not a neutral measure. Under ordinary conditions, its benefits often appear limited or uncertain, whereas several disadvantages are well documented.

Pollen remains the colony’s reference nutritional resource. Its biological value depends on a set of dimensions — essential amino acids, lipids, sterols, digestibility and integration into nurse bee physiology — that no simple recipe reproduces faithfully (Di Pasquale et al., 2013 ; Keller et al., 2005a ; Moore et al., 2025 ; Ritter & Kast, 2021).

Scientific studies do not support the routine use of protein supplementation. Positive effects may exist in situations of real shortage or objectively compromised development, but they remain contextual; outside such cases, sanitary, behavioural and technological disadvantages often outweigh the benefits (DeGrandi-Hoffman et al., 2016 ; Mortensen et al., 2019 ; Noordyke & Ellis, 2021 ; Ritter & Kast, 2021).

Homemade recipes are generally biologically under-specified: they attempt to correct a complex situation on the basis of an overly simple criterion. In the Swiss context, Agroscope’s formulation remains fully relevant in practice: supplementary protein feed for bees only rarely offers advantages, but much more often presents disadvantages. The priority remains the site, careful observation of colonies and the diagnosis of a real shortage before any intervention.

Protein supplementation is therefore not a neutral measure. Under ordinary conditions, its benefits often appear limited or uncertain, whereas several disadvantages are well documented. One cannot therefore reason here according to the idea: “if it does no good, at least it does no harm”.

See also:

• How do bees choose pollen?
• Preserving the bees’ life capital
• Microbes beneficial to bee health
• Controlling the water content of honey
• Internal anatomy: the digestive system

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Bibliography

Camazine, S. (1993). The regulation of pollen foraging by honey bees: How foragers assess the colony's need for pollen. Behavioral Ecology and Sociobiology, 32, 265–272. https://doi.org/10.1007/BF00166516

DeGrandi-Hoffman, G., Chen, Y., Rivera, R., Carroll, M., Chambers, M., Hidalgo, G., & Watkins de Jong, E. (2016). Honey bee colonies provided with natural forage have lower pathogen loads and higher overwinter survival than those fed protein supplements. Apidologie, 47(2), 186–196. https://doi.org/10.1007/s13592-015-0386-6

Di Pasquale, G., Salignon, M., Le Conte, Y., Belzunces, L. P., Decourtye, A., Kretzschmar, A., Suchail, S., Brunet, J.-L., & Alaux, C. (2013). Influence of pollen nutrition on honey bee health: Do pollen quality and diversity matter? PLoS ONE, 8(8), e72016. https://doi.org/10.1371/journal.pone.0072016

Furse, S., Koch, H., Wright, G. A., & Stevenson, P. C. (2023). Sterol and lipid metabolism in bees. Metabolomics, 19(9), Article 78. https://doi.org/10.1007/s11306-023-02039-1

Guichard, M., Droz, B., & Ritter, R. (s.d.). Le pollen : besoins, diversité et qualité [Présentation Agroscope / apiservice].

Hoover, S. E., Ovinge, L. P., & Kearns, J. D. (2022). Consumption of supplemental spring protein feeds by western honey bee colonies: Effects on colony growth and pollination potential. Journal of Economic Entomology, 115(2), 417–429. https://doi.org/10.1093/jee/toac006

Kast, C., & Roetschi, A. (2017). Evaluation of baker's yeast in honey using a real-time PCR assay. Food Microbiology, 62, 282–287. https://doi.org/10.1016/j.fm.2016.12.011

Keller, I., Fluri, P., & Imdorf, A. (2005a). Pollen nutrition and colony development in honey bees: Part I. Bee World, 86(1), 3–10. https://doi.org/10.1080/0005772X.2005.11099641

Keller, I., Fluri, P., & Imdorf, A. (2005b). Pollen nutrition and colony development in honey bees: Part II. Bee World, 86(2), 27–34. https://doi.org/10.1080/0005772X.2005.11099650

Manning, R., Rutkay, A., Eaton, L., & Dell, B. (2007). Lipid-enhanced pollen and lipid-reduced flour diets and their effect on the longevity of honey bees. Australian Journal of Entomology, 46(3), 251–257. https://doi.org/10.1111/j.1440-6055.2007.00598.x

Moore, E., de Sousa, R. T., Felsinger, S., Arnesen, J. A., Dyekjær, J. D., Farman, D. I., Gonçalves, R. F. S., Stevenson, P. C., Wright, G. A., & Kildegaard, K. R. (2025). Engineered yeast provides rare but essential pollen sterols for honeybees. Nature, 646(8084), 365–371. https://doi.org/10.1038/s41586-025-09431-y

Mortensen, A. N., Jack, C. J., Bustamante, T. A., Schmehl, D. R., & Ellis, J. D. (2019). Effects of supplemental pollen feeding on honey bee colony strength and Nosema spp. infection. Journal of Economic Entomology, 112(1), 60–66. https://doi.org/10.1093/jee/toy341

Noordyke, E. R., & Ellis, J. D. (2021). Reviewing the efficacy of pollen substitutes as a management tool for improving the health and productivity of western honey bee colonies. Frontiers in Sustainable Food Systems, 5, Article 772897. https://doi.org/10.3389/fsufs.2021.772897

Ricigliano, V. A., Williams, S. T., & Oliver, R. (2022). Effects of different artificial diets on commercial honey bee colony performance, health biomarkers, and gut microbiota. BMC Veterinary Research, 18, Article 52. https://doi.org/10.1186/s12917-022-03151-5

Ritter, R., & Kast, C. (2021). Le pollen, essentiel pour le développement des colonies d'abeilles. Revue suisse d'apiculture, 3, 108–117.

Roetschi, A., Kilchenmann, V., & Kast, C. (2017). Des levures de boulanger dans le miel ? Revue suisse d'apiculture, 3, 39–41.

Tapia-Rivera, J. C., Tapia-González, J. M., Alburaki, M., Chan, P., Sánchez-Cordova, R., Macías-Macías, J. O., & Corona, M. (2025). The effects of artificial diets containing free amino acids versus intact proteins on biomarkers of nutrition and deformed wing virus levels in the honey bee. Insects, 16(4), Article 375. https://doi.org/10.3390/insects16040375

Watkins de Jong, E., DeGrandi-Hoffman, G., Chen, Y., Graham, H., & Ziolkowski, N. (2019). Effects of diets containing different concentrations of pollen and pollen substitutes on physiology, Nosema burden, and virus titers in the honey bee. Apidologie, 50, 845–858. https://doi.org/10.1007/s13592-019-00695-8