1. Honey consumption

Plant nectar and, to a lesser extent, honeydew linked to insect exudation are the main sources of carbohydrates for the bee. Nectar also provides water, minerals, and a few other biological substances. The sugar concentration of nectar can vary from 4 to 60% depending on the case. Bees will favour nectar sources with a concentration between 30 and 50% and will neglect nectars below 15% sugar.

Bees are able to transform nectar by partially drying it and modifying its composition by incorporating digestive enzymes from their saliva. When the product of the transformation is stable, bees store it in cells that they cap. The honey thus produced constitutes the colony’s collective reserve and provides most of the carbohydrates and part of the minerals (its average composition is given in Table 1).

Honey has several characteristics that are of interest to the bee colony. Indeed, its low water content and high sugar concentration allow:

• long-term preservation, among other things due to a limited risk of fermentation
• high nutritional value for the bee
• higher digestibility of honey compared to nectar

Highly diluted substances such as nectar require a significant concentration of enzymes during digestion in the bees’ intestine, with a higher energetic cost of digestion. As a result, bees generally consume relatively little nectar directly.

According to various authors (e.g., Rosov, 1944; Pouvreau, 1981), a colony consumes between 50 and 120 kg of honey per year, including 10 to 30 kg during winter (depending on climate and weather, colony size, and its thermoregulation capacity (e.g., Farrar, 1952; Dyce and Morse, 1960).

Carbohydrates represent an important part of the bees’ diet and are mainly used for their energy expenditure. We can mention the main ones below (in decreasing order of energetic cost):

• Thermoregulation (ventilation, heat production). This activity depends on the outside temperature: During the season, brood must be maintained at 35 +/- 2 °C. When the outside temperature is low, bees produce heat (see our “Beekeeper’s word” synthesis, “How do your bees get through the winter?” from January 2015). Thermogenesis (heat production) is the most energy-expensive activity for the bee. When the temperature is high, bees introduce drops of water into the brood area, which, as they evaporate, lower the temperature.
• Motor functions (in particular foraging, storing pollen and nectar, cleaning cells, walking), which entail high energy consumption.
• Building activities (wax production).
• Feeding the brood (royal jelly production).

Carbohydrates can also be transformed and stored in the bees’ fat bodies: excess assimilated sugars are digested and the resulting fragments reassemble to form lipids. These lipids are intended for storage in the bee’s body reserves (see page 9 - Individual and collective reserves).

The plastic role of carbohydrates also deserves mention: for example, the main constituents of chitin (bee cuticle) are glucose derivatives.

The sugars usually present in honeys are assimilated by bees. The most common are the most digestible (glucose, fructose, sucrose, maltose). There is no absolute certainty in the literature, but it is clear that bees are unable to digest certain disaccharides (composed of 2 sugars, such as lactose), certain trisaccharides, and all polysaccharides. They are therefore able to digest certain types of disaccharides and trisaccharides. Somerville (2005) indicates that the most complex sugars have no energetic value for the bee. Some are poisons at low concentration (galactose, arabinose, xylose, melezitose, mannose, raffinose, stachyose, and lactose). Pectin and many gums are also toxic to bees. Thus, certain honeydews (containing, among other things, raffinose and gums) are problematic.

Among the most palatable sugars for the bee, we find (from most to least attractive): fructose, sucrose, then glucose. Anecdotally, this order of preference is also that of humans.

The bee must hydrolyse sucrose into glucose and fructose, then glucose into fructose, in order to fragment it and use it (for energy production or synthesis of molecules). To do this, it uses enzymes present in its saliva. Whatever sugars are ingested, the enzymes will always be present in the bee’s saliva and the organism of bees will not stop synthesising them. Moreover, these enzymes are not “lost” after use: each has an active site that, in the presence of sugars, will carry out hydrolysis and will become available again after the reaction. Even though, obviously, there are enzyme losses over time.

2. Pollen consumption

Pollen, to which bees add nectar, glandular secretions, and lactic acid bacteria, undergoes fermentation by lactic acid bacteria to form bee bread.

 

 

These lactic acid bacteria are present in the bees’ intestinal flora. They are inoculated when bees mix pollen with nectar from their crop and with saliva to agglomerate it, and later to remove air bubbles in the cells when it is stored.

The bacteria introduced will allow:

• optimisation of digestibility, among other things by degradation of pollen grain walls and digestion of carbohydrates
• an increase in the presence of enzymes useful for pollen maturation
• production of amino acids, peptides, vitamins, trace elements (including omega-3 and omega-6 fatty acids) increasing the nutritional value of bee bread
• a reduction in the content of non-acidophilic pathogenic bacteria and fungi (Ascosphaera, etc.) thanks to the action of lactic acid bacteria (Čeksterytė, 2012), which produce lactic acid, lowering the pH of bee bread
• seeding of the intestine of young bees with these bacteria (and therefore acquisition of their benefits on digestion and vitamin synthesis).

The composition of bee bread is broadly similar to that of fresh pollen, but it contains more interesting compounds, bacteria, enzymes, and moulds (Guilliam, 1997). Its biological value is therefore higher.

Bee bread provides proteins, amino acids, fibres, lipids, vitamins, and minerals to the colony. It thus helps to balance the bees’ diet in order to avoid deficiencies (particularly in vitamins and minerals).

According to Somerville (2005), we assume that pollen represents 10% to 20% of the bee’s total consumption, respectively in broodless situations and during the rearing period.

 

The average composition in proteins, lipids, minerals, etc. varies greatly depending on plant species. Lamiaceae pollens (rosemary and sunflower, for example) are low in proteins (less than 20%); fruit trees, thistles, rapeseed, and legumes contain a medium amount (20 to 30%), while viper’s bugloss and phacelia contain more (Stace, 1996). Thistle, sunflower, and viper’s bugloss pollens, for example, are low in lipids (2%), unlike cistus (up to 6%) and Brassicaceae (6–7%) (Cordon, 2005). If we consider pollen composition as a whole, Brassicaceae (rapeseed, ...), Ericaceae (heathers), and Rosaceae (fruit trees) pollens seem the most complete and interesting for the bee. Conversely, Gramineae pollens, when dominant, should be avoided.

 

The protein needs of the adult bee are described by Crailsheim (1986) in the graph (Figure 3). It illustrates the variation in the amount of leucine in the haemolymph of the adult bee. Leucine is a very good indicator of protein consumption because:

• it is the major amino acid in haemolymph proteins,
• it is an essential amino acid (see Figure 4 - next page) that can only be provided by diet.

 

 

In the first days after emergence, the adult bee requires a protein-rich diet, much of which is used for the development of hypopharyngeal glands and the production of royal jelly (Maurizio, 1954). Pain and Maugenet (1966) estimated that nearly 60 mg per bee are consumed during the first ten days.

Protein feeding decreases rapidly and stabilises at 20% of initial needs from 15 days after emergence (Crailsheim, 1986). Often, nurse bees ensure via trophallaxis the feeding of older workers such as foragers (Crailsheim et al., 1998).

Important: If nurse bees do not find the proteins necessary for their diet (as well as in the case of heavy Varroa infestation), their hypopharyngeal glands do not develop fully and their royal jelly production does not allow normal brood development and/or correct feeding of the queen. The latter’s egg-laying is reduced. Hypopharyngeal gland secretions represent about 95% of the total amount of proteins necessary for the development of a larva (Babendreier et al., 2004). For Pernal and Currie (2000), pollen is involved in vitellogenesis and, in the absence of a queen, it increases the development of the bees’ ovaries.

Larvae are fed with larval jelly. This jelly has a composition similar to that of royal jelly during the first three days. Thereafter, nurse bees gradually incorporate pollen and honey depending on larval age (Winston, 1987). Larvae consume pollen mainly on the 4th and 5th days of their life. Cremonez (1998) established that a larva consumes 30 mg of proteins (i.e., 125 mg of pollen) to become a worker; which means that one kilogram of pollen can potentially raise 8,000 workers.

A good protein content for drone larvae and for the first days of the adult stage allows rapid and normal sexual maturity (Szolderits and Crailsheim, 1993), and a large number of spermatozoa produced (Nguyen, 1999). These protein needs are covered by the food (a mixture of glandular secretions, pollen, and honey) that young workers give to drones aged 1 to 8 days.

A colony will therefore consume between 12 and 40 kg of pollen per year. The qualitative aspect of pollens is very important insofar as it is the amount of proteins brought to the hive that is decisive. For example, a colony that collects 3 kg of pollen at 20% protein will have the same amount of proteins available as a colony that collects 2 kg of pollen at 30% protein.

3. Amino acids

Amino acids are small nitrogen-containing molecules that bind together to form peptides (when they are few in number) or proteins (when they are more than 50). There are 20 in nature.

 

The bee is capable of synthesising 10 of them from their components (derived from proteins ingested through diet), but the other 10 cannot be synthesised and must be provided as such through diet. These are the essential amino acids (the list is given in Figure 4).

 

Some plants, such as eucalyptus, do not contain one or more essential amino acids (isoleucine in this case). If bees consume this pollen in quantity and over the long term, the induced deficiency will increase the risk of disease occurrence (Mendoza, 2013).

4. Lipids

These are important sources of energy used for the composition of reserves. It is accepted that fatty acids are necessary components of phospholipids, which play an important role in the structural integrity and function of insect cell membranes.

 

There are not many studies on lipids in apidology, but we know that:

• Pollens with a high lipid content seem to attract bees more strongly (Singh et al., 1999).
• In bee tissues, the most common lipids are sterols (Somerville, 2005).
• Cholesterol and 24-methylene cholesterol seem to increase brood rearing (Somerville, 2005).
• The role of polyols (such as glycerol) is under discussion for bees, in light of other insects that hibernate, where they have an “antifreeze” function.
• Pollen could play a health role thanks to the antagonistic action of certain fatty acids on the agents responsible for European and American foulbrood (Somerville, 2005).

5. Minerals

The proper functioning of the bee’s organism requires a supply of minerals. These are involved in many vital reactions. The main ones are given by Somerville (2005): calcium, chlorine, cobalt, copper, phosphorus, iron, magnesium, manganese, nickel, potassium, sodium, iodine, and zinc.

 

 

It should be noted, however, that mineral salts, in large quantities, increase the amount of water retained in the bee’s faeces, and therefore their volume, and require more cleansing flights for their evacuation. It is therefore necessary to ensure that wintering is not done with foods that are too rich in minerals, such as honeydews (we have also said that some honeydew sugars are toxic).

6. Water

Water is indispensable to keep minerals in solution, for many vital chemical reactions for the organism of the bee

It is also used to increase relative humidity in the brood area (70%) to allow its development. Brood is indeed sensitive to dehydration (bodily drying) and can disappear entirely from the hive if there is a water shortage. Water is also used to regulate the colony’s body temperature (through ventilation). It should be specified, however, that the bee’s metabolism does not allow the elimination of water. The bee therefore cannot regularly consume nectar, which is very moist.

 

The amount of water consumed by a colony depends greatly on brood rearing and temperature. Based on his personal experience in Spain, Antonio Pajuelo considers a consumption of 1 litre of water per colony per week during the rearing period (during or outside nectar flow). In addition, bees have a preference for water rich in mineral salts, which explains why they can be attracted to livestock effluents.

In winter, bees consume the water resulting from condensation of the ambient humidity inside the hive, due to the temperature difference between the core of the cluster (warm) and the periphery of the colony (cold).

7. Individual and collective reserves

All the body reserves of a bee are located on its back, under the 5th tergite (abdominal segment). When observing a bee, this corresponds to the 3rd visible segment. A kind of “hump” is present under the cuticle (see Figure 6), formed by a special storage tissue made up of trophocytes: cells that accumulate fat bodies and other nutrients (Paes de Oliveira, 2003).

These reserves are the bee’s individual reserves. They are mobilised when the bee is confined inside the hive without being able to go out (in winter), or to survive a period of absence of reserves in the hive and without external input. These reserves are complemented by the “collective” reserves in the hive frames. When it can, the bee replenishes its individual reserves from the hive reserves.

This accumulation phenomenon is particularly visible in winter bees, which contain large fat reserves in their trophocytes, which enlarge the abdomen until it exceeds the length of the wings (see Figure 7). This phenomenon also exists during the season, in periods of intense flowering: seeing fat bees in hives is a sign of good flowering. Conversely, during dearth periods, bees will consume their body reserves.

 

The colony’s collective reserves are therefore located on the frames:

• Honey in the upper part of brood frames and in outer frames and supers.
• Pollen forms an arc around the brood and in adjacent frames.

Attention, the colony’s reserves continue to evolve inside the hive and are perishable!

It must be taken into account that pollen, even if fermented to increase its preservation, has a “best-before date” in the hive. Somerville (2005) and Vasquez (2009) indicate that it begins to deteriorate significantly after two months. It will gradually lose components (and therefore its properties), until reaching a strong deterioration from which bees remove it from the hive. This phenomenon is very visible at the end of winter. The development of brood rearing in spring, a key step in restarting colonies, therefore occurs jointly with the arrival of fresh pollen.

Nevertheless, if there is no new pollen input, bees continue to consume old bee bread.

7.1 What about honey?

Honey reserves keep longer than pollen. The preservation of honey in the hive depends on the temperature of the storage area (White, 1964). We can consider that, for the bee, the “best-before date” of honey is 4 years.

Indeed, beyond this period, the HMF (hydroxymethylfurfural) produced present a risk of toxicity for the bee. HMF results from dehydration of sugars, particularly fructose. At room temperature, the rate of HMF formation is about 1 mg/kg of honey per month. High temperatures accelerate HMF formation, as do more acidic honeys or honeys harvested long ago.

In addition, over time there is a loss of honey’s nutritional properties corresponding to the deterioration of organic compounds, flavonoids, aromas, etc.

There is no risk of fermentation if honey moisture is correct (below 18.5%), which is mostly the case. Exceptions exist in our climates, for example during autumn nectar flows on short and humid days: bees may cap honey at about 20.5% moisture. In addition, for fermentation to occur, the temperature must be above 20 °C, which limits the phenomenon.

Bees swallow their food directly. They have a sucking-type feeding apparatus. The mandibles act as pincers and are only used to detach and amalgamate food. It is therefore very important that particles are small (maximum 0.2 mm in diameter).

Beekeepers who prepare their own feed must therefore ensure that particles are properly disintegrated or dissolved in water without lumps or excessively large particles.

Moreover, if honey crystallises in the hive reserves, it will not be consumable by the bee (except in cases where there is strong water condensation in the hive that can dissolve the crystals: very high ambient humidity and a high bee population).

 

8. Malnutrition

The effects of malnutrition in bees are known. There is an interaction between bees and the colony, and individual problems are reflected in the adult population and brood rearing, which will be reduced qualitatively and quantitatively. Cannibalism of larvae is possible and will have an effect on the next adult generation and on the colony’s capacity to build reserves (Brodschneider, 2010).

 

Bee malnutrition is expressed by visible signs (e.g.): Queen stops laying Decreased brood survival Cannibalism (bees consume larvae) Worker mortality Stop of drone rearing Small bees, with an abdomen clearly shorter than the wings Drone mortality

One effect of malnutrition is cannibalism (bees consume larvae)

 

9. Practice

9.1 Start of season (Between the end of winter and the first honey flow)

According to Antonio Pajuelo, in most cases (depending on regions), 4 litres of feeding at the start of the season (1.5 litres/week) represent the minimum necessary to “help” colonies before the first spring honey flow. About 20% of beekeepers use these doses. Feeding more than 8 litres can only be justified when producing swarms/packages/queens. With high syrup quantities (more than 10 litres), the risk of swarming and residues in honey is high! (Guler, 2014).

This stimulation feeding (light syrup (50/50)) is therefore appropriate at the start of the season, but it can also be later if a honey flow is preceded by a long period (more than one month) without flowering.

Honey feeding is theoretically ideal; however, this technique has several disadvantages: honey can be a vector of pathogens and can in particular contain American foulbrood spores. Moreover, in practice, it can encourage robbing at certain times of the year. Finally, such feeding represents a significant cost.

9.2 End of season (Between the end of honey flows and wintering)

It is important to assess the reserves of your hives well before winter, by counting the brood-chamber frames containing reserves. This estimate must be carried out during the wintering inspection, which generally takes place in our climates between 15 and 30 September.

Pouvreau (1981), taking up the data of Beldame (1942), indicates a need of 7 kg of honey per hive between early October and late February: 2 kg/month in October and February, and about 1 kg/month from November to January.

However, there are differences between authors explained by the variability of wintering conditions. Among other things, one can cite: available flora (in autumn and at the end of winter), weather, the number of bees in the hives (and the bee race, possibly).

Current climate change results in a warming trend in autumn and winter periods, which limits the broodless period (and thus implies more brood care), and increases bee activity (cluster formed for a shorter time). These phenomena increase bee activity and the consumption of energy and food. It must therefore be taken into account and winter feeding adjusted upward (compared to the references cited above).

In conclusion, we can generalise and confirm what was indicated in the “Beekeeper’s word” synthesis on wintering: a recommendation of 15 to 25 kg of reserves necessary for winter and spring, between the end of September and the beginning of May.

It is important here to distinguish colder periods from milder ones, and colony population objectives. If a beekeeper wishes to increase the bee population before winter, they can take advantage of a mild period before the autumn and winter cold by providing a light syrup (50/50), which will stimulate the queen’s egg-laying and result in more populous colonies one month later.

 

If the population in the hive is satisfactory, or if feeding is carried out late, or if the weather is uncertain, it is better to feed with a heavy syrup (60/40 or 70/30).

In general, it is better to provide mainly heavy syrup at the end of the season, which will require less work and energy for dehydration and storage.

 

9.3 And candy in all of this?

 

Beekeepers’ practices vary quite a bit with regard to candy. Overall, a majority use it (including 46% using between 2 and 5 kg).

 

Candy is the most suitable feed in the event of winter dearth because it is placed directly close to the bee cluster. Candy also has the characteristic of lowering the condensation humidity that forms inside the hive. This humidity causes the candy to dissolve, which allows its consumption by bees (as a reminder, their mouthparts are of the sucking type). We can consider an average consumption of about 1 kg of candy per month.

This reduction in humidity is particularly interesting in humid areas (rainy areas, fog, north-facing orientation, etc.) in order to improve wintering conditions. Excess humidity in winter can indeed promote the development of moulds. In addition, candy is very rarely stored in frames. It avoids any risk of adulteration of the first honey harvest (in the event of syrup overdosing and if there is syrup left in spring in brood chambers).

It is possible to do without candy, but attention must be paid to this risk of honey adulteration at the start of the season (generally low risk, but higher in the case of early honey flows, rosemary for example).

10. Supplementary feeds

Antonio Pajuelo considers a supplementary feed as insurance that the bees’ diet will contain the components provided. There are a number of references on the effects of supplementary feeds on the domestic honey bee. One can cite, in particular, work on algae (Roussel, 2015), propolis (Antunez, 2008), plant extracts (rosemary, pomegranate, cinnamon, grapefruit...).

A parallel can be drawn with insurance contracts we can take out personally. They provide support in the event of a problem.

Antonio Pajuelo reports on the situation in Spain, where supplementary feeds are frequently used to secure colony nutrition during drought periods or when there is insecurity in terms of quantity or quality of pollen inputs, as their flowering periods are generally shorter than in France.

In a mostly oceanic climate such as that of France, supplementary feeds are recommendable in situations of unfavourable flora and/or weather depending on the quality and quantity of reserves available. These supplementary feeds are mixed with syrup or protein patties.

11. Protein feeding

First of all, it is important to note that nutritional value varies greatly for pollens, depending on plant species. Pollen feeding is considered better when colonies have reserves of at least 4 or 5 different colours.

In the same way as for supplementary feeds, pollen substitutes are often used in Spain, much more than in France it seems. Spanish beekeepers use protein patties during drought periods or when pollen inputs are insufficient qualitatively and quantitatively.

In practice, a quantitative insufficiency is considered when hives have less than one frame of pollen during brood rearing. This pollen is distributed on the upper part of brood frames and on frames at the edge of the brood. Antonio Pajuelo considers a qualitative problem when there are fewer than 4 to 5 colours of pollen in the hive.

 

These will be plant-based proteins, such as freeze-dried brewer’s yeast that we commonly consume and that is available in grocery stores, or defatted soy flour found at beekeeping equipment suppliers.

 

The palatability of protein patties is an important point for their use. Our black bee consumes without problem patties containing about 5% protein. Beyond this level, palatability decreases. Moreover, care must be taken not to provide too much protein in the colony’s diet, as digestibility would be reduced.

A question has recently been raised about an increased risk of nosemosis due to protein feeding. Fleming (2015) published a study in which he inoculated Nosema spores in the laboratory into caged bees. The groups that received protein feeding developed more Nosema spores than groups fed only sugar.

According to Antonio Pajuelo, this study is open to criticism because it concerns young bees that did not benefit from correct “seeding” of their intestinal flora (absence of trophallaxis), and because protein-fed bees live longer, which increases the risk of a higher number of Nosema spores. In addition, according to his experience and Zheng (2014), the pathogenicity of nosemosis is also related to the occurrence of a stress factor (cold, hunger, intoxication). Thus, he continues to think that protein diets are of interest in many situations.

It is important to supplement colonies if the beekeeping operation is oriented toward productivity, or for the climatic and floristic reasons already mentioned (lack of pollen or poor quality or diversity of pollen). Indeed, if colonies are not prepared before nectar flows, the nectar flow will be used to produce bees, and the harvest will be very limited (or even nil).

It is important to feed with protein supplements:

• Before the first flowering to prevent meteorological risks that can harm colony population development.
• Before a major flowering if there is a lack of pollen and nectar that could cause a population drop.
• Before entering winter, to promote population renewal with the emergence of bees well supplied with reserves, which will withstand winter well and be vigorous enough to restart well the following spring.

 

12. Questions and answers

How can the real effect of feeding or products used be evaluated?

By conducting a preliminary trial. In an apiary, choose at least 20 healthy hives that are as homogeneous as possible. Record their strength in terms of number of frames of bees, brood frames, honey frames, and pollen frames. Carry out feeding on half of the hives by alternating: one hive with feed and one hive without. One month later, repeat the measurements on the colonies. In the case of testing most supplementary feeds, it is recommended to observe colonies over a longer term. If you wish to test several products, it is important to always form groups of more than 10 hives.

How important are lipids for bee immunity?

The immune system of bees relies on the production of antimicrobial peptides (chains of fewer than 50 amino acids). Amino acid and protein intake are therefore decisive for immunity. Lipids are more important in maintaining bee body temperature, and we also think they are present in lipoproteins and hormones.

Are there scientific data on the effects of probiotics on bees?

Yes, there have been publications on the subject since the late 1970s, by M. Guilliam, G. M. Loper, L. N. Standifer… and more recent ones. In 2005 was published: “The effects of probiotic supplementation on the content of intestinal microflora and chemical composition of worker honey bees (Apis mellifera)” by A. Kaznowski et al.

Under natural conditions, bees exchange food by trophallaxis. This trophallaxis (like bee bread) results in an exchange of intestinal microflora and microfauna (microbiota) from older bees to young bees (which are almost devoid of it at emergence). This study was carried out on emerging caged bees. Providing probiotics in feed allowed seeding of the intestinal microbiota in young caged bees and increased their lifespan. In a healthy colony, with good microbiotic flora, trophallaxis enables quality seeding. But not all colonies have the same intestinal microbiota, and not all have a microbiota of good quality. Thus, adding probiotics to a supplementary feed for our bees, as we do in human or animal nutrition, may be a way of securing good conditions for colonies.

Can artificial feeding with dietary supplements reduce bees’ immunity and their ability to resist problems (low temperatures or dietary deficiencies...)?

No. There are even extremely complete feeds developed to rear bees and larvae under laboratory conditions and without any contact with the outside or with other bees. These feeds have been approved by INRA (French) since 2007 to carry out tests on pesticides, immune system peptides...

Their very high cost is not profitable and makes them inaccessible to beekeepers, but this is not a problem. Indeed, in our situations, the bees in our operations are not confined animals; they go out to forage. Thus, commercial feeding products complement the classic feeding of colonies, in conditions of food shortages (which occur naturally), due to bad weather or poor diver

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See also:

• Principles of Bee Feeding
• Practical Guide: 4.2 Feeding
• Making Your Own Fondant
• Pollen Consumption and Colony Development
• January at the Apiary