1. General principles of feeding bees

Only honey is truly suitable for bees; it has been their food for millions of years. They did not wait for our nutritional knowledge to survive in good health. Ideally, bees should be allowed to build up their reserves at the appropriate time, namely during flowering periods. This occurs in spring. This was also the practice of our ancestors, who recommended in early 19th-century agricultural manuals that honey be harvested only in May, taking the remainder of the previous year’s stores and part of the new flow, then allowing bees to rebuild their reserves during strong nectar flows.

Today we aim to harvest more than 4 or 5 kilograms of honey per colony and deplete their reserves from April to August. As a result, few flowering periods remain for building winter stores, making artificial sugar feeding a necessity.

There is another reason as well: colonies are exposed to predation by Varroa mites combined with neonicotinoids and other systemic phytosanitary products, which, unlike earlier substances such as DDT, affect not only foraging bees but also brood. Colonies are chronically weakened, favouring the emergence of diseases that were previously little known or unknown, particularly viral diseases. Ensuring good nutrition increases colonies’ capacity to defend themselves against disease. Protein supplements are intended to compensate for the protein depletion caused by Varroa, which reduces the ability of nurse bees to produce brood food and wax and shortens their lifespan. Neonicotinoids also appear to promote the development of certain diseases, Nosema in particular.

Although honey remains the best food for bees, our feed inputs will not consist of honey unless we are certain that the honey provided is free from pathogens, especially foulbrood spores. Such certainty is rarely achievable, and sterilisation treatments would destroy honey’s valuable components. Sugar is therefore the feed of choice, except in specific cases where honey is used occasionally for selected colonies, notably in queen rearing. The risk lies in the general distribution of contaminated honey.

Other inputs: protein supplements. Due to their limited diversity, they can never match the richness of pollen proteins. These substitutes are used at specific times, either to bridge the period until the massive arrival of spring pollen or at the end of the season to stimulate or maintain queen laying and to produce winter bees with well-developed fat bodies, their main protein reserve.

Additional supplements such as trace elements and vitamins may also be provided to strengthen the general condition of bees or to improve their gut flora, particularly to reduce Nosema spore loads that develop in the intestinal wall when lesions allow spore entry. Such lesions are notably promoted by neonicotinoids, according to research conducted at INRA and CNRS, particularly by teams led by Yves Le Conte. Nosema reproduction in the intestinal wall promotes bee mortality.

No single factor alone appears sufficient to explain winter losses; however, their combination since the introduction of neonicotinoids seems to be the main cause of winter mortality for nearly 20 years. Other factors are also discussed, such as Varroa treatment products, as suggested by a Spanish study, and the use of antibiotics, which according to a US study published in PLOS One block proteins responsible for eliminating foreign chemical substances from the bee organism.

All of this highlights the importance of feeding, beyond good practices in medication use and apiary site selection. It represents a key response available to beekeepers to counteract the harmful effects of today’s environment.

 

2. Products used: sugars

Sugar: Glucose or fructose would be the most suitable for bees, as they are simple sugars (monosaccharides) that can be assimilated directly. However, pure sucrose derived from beet or cane sugar is readily available commercially. Bee saliva contains enzymes that hydrolyse the sugars present in nectar, which also includes sucrose, as well as the syrup provided. After enzymatic transformation, these sugars become monosaccharides that are directly assimilable.

Low-cost sugars are enzymatic transformation products of wheat or maize starch; when the reaction is carried through to completion, only glucose remains. These syrups are suitable provided their purity is assured. If they contain complex sugars incompatible with the enzymes available to bees (e.g. starch or lactose), they are indigestible, clog the intestine and cause diarrhoea.

The advantage of starch-derived sugars is that the resulting glucose can reach very high concentrations (generally above 70%) without crystallising in feeders, unlike sucrose, which crystallises once concentrations exceed 66%. When available, these sugars are economically attractive, particularly in light of current global sugar price increases and European commitments to source 15% of supplies from producing countries such as Brazil, which can no longer supply due to their focus on biofuel production.

Stimulation syrup (to encourage queen laying) should not exceed 50% sugar. Nectar contains around 20%, at most 30%, sugars (glucose, fructose, sucrose). Given in small quantities (0.5 to 1 litre) daily or two to three times per week, it simulates a nectar flow. Bees redistribute it throughout the colony, maintaining a high nutritional level over time that stimulates abundant production of royal jelly and brood food. The well-fed queen begins laying, and wax production increases. The volume provided should match daily consumption to avoid storage.

Concentrated syrup, given in large quantities, causes rapid accumulation, as the colony quickly becomes nutritionally saturated. Excess exceeds consumption capacity, and bees store syrup wherever cells are free, preventing the queen from laying because syrup occupies cells freed by emerging brood.

Each syrup concentration therefore corresponds to a specific objective.

Syrup should be provided at external temperatures above 15 °C; if it is too cold, bees cannot take it. Feeders at hive temperature allow early-season stimulation of queen laying. Fondant or sugar blocks are used for winter feeding.

 

3. Proteins: protein supplements for bees

These are plant-based proteins, such as freeze-dried brewer’s yeast commonly consumed by humans and available in grocery stores, or defatted soybean flour sold by beekeeping suppliers.

Added at a rate of 3 to 5% to syrup and thoroughly mixed to disperse these insoluble or poorly soluble products, these proteins provide high-quality supplementation.

 

4. Vitamins and trace elements: vitamins for bees

These products are supplied via commercial formulations. Prices vary widely, and some also contain proteins. Due to limited information on composition and mode of action, it is difficult to identify the best value for money. Those knowledgeable in plant identification and preparation may use plant-based decoctions to provide these inputs. Brewer’s yeast also contributes such nutrients. Overall, observed effects on colonies are very convincing.

 

5. Vinegar: control of Nosema in bees

Traditionally used to control Nosema, it is administered at a concentration of 5%. Some double this amount to ensure a strong effect. White vinegar or acetic acid are used; some recommend cider vinegar for its potassium content. No conclusive data support this. I have also prepared, and continue to use, a saturated propolis decoction in 60–70% alcohol, administering 5 cl per litre of syrup.

 

6. When to feed bees? Wintering of colonies

Winter reserves should be built immediately after the honey harvest, at the same time as Varroa treatments. The quality of wintering depends on feeding quality and Varroa control. The importance of stored pollen is often underestimated, both for restarting queen laying during winter and regarding risks associated with spring storage of pollen contaminated by insecticides, pesticides or fungicides. Its absence is not critical if adequate protein supplements are provided, particularly in fondant from January onwards.

As I am not aiming for record harvests, I carry out the last harvest midway through the sunflower flow, allowing this nectar flow to fill the brood boxes.

A balance between concentrated and light syrup is maintained to preserve the indicated ratio between brood area (around one third) and honey area (around two thirds).

Feeding must cease by mid-September so that the bees involved in storage—aged bees—disappear, allowing the development of “house bees” that will overwinter. Their fat bodies preserve hypopharyngeal glands and enable colony restart as day length increases. For late honeydew harvests, late feeding may compromise colony survival.

Proteins are sparingly distributed in summer syrups, except for late queen rearing. They are mainly provided early in the season to boost colonies; appropriate pollen sources should then be available, ivy in particular. Other supplements remain necessary.

 

7. How to feed: bee syrup, honey reserves

As indicated, stimulation is achieved with small doses of light syrup, while storage uses large quantities of concentrated syrup. Stores must extend over the full height of frames. The worst situation is when all frames have only about 10 cm of honey at the top: during prolonged cold spells, a small cluster may starve in one corner while honey remains elsewhere. At the end of August, hive volume should be reduced using dummy boards, removing empty or poorly filled frames so that feeding fills the remaining ones fully.

A hive reduced to five well-filled frames of honey and brood winters perfectly.

All feeders are suitable except entrance feeders, which are prone to robbing. Their size determines refill frequency.

The most important factor is tightness to prevent robbing. During periods of scarcity, populous colonies actively seek food.

Top feeders carry a high risk: a slightly warped roof can lead to drowning of foreign bees. This can be avoided by placing a plastic sheet under the roof to ensure tightness. Reducing entrances and feeding in the evening also limits robbing; syrup is consumed at night when robbers are in their own hives.

 

8. Further reading

► Late-winter feeding: what should we think?
► Which syrup to choose for winter feeding?
► ApiService aide-mémoire: Feeding