1. Honey consumption

Plant nectar and, to a lesser extent, honeydew associated with insect exudations are the main sources of carbohydrates for the honey 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 preferentially exploit 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 through the incorporation of digestive enzymes from their saliva. When the transformed product 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. Its low water content and high sugar concentration allow:

• long-term preservation, including a reduced risk of fermentation
• high nutritional value for the bee
• higher digestibility of honey compared with nectar

Highly diluted substances such as nectar require a high 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 will consume 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 a substantial share of bee nutrition and are mainly used for energy expenditure. The main uses can be mentioned below (in decreasing order of energetic cost):

• Thermoregulation (ventilation, heat production). This activity depends on outside temperature: during the season, brood must be maintained at 35 +/- 2 °C. When outside temperature is low, bees produce heat (see our summary Parole d’apiculteur, “How do your bees get through winter?” from January 2015). Thermogenesis (heat production) is the most energy-demanding activity for the bee. When temperatures are 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) entail high energy consumption.
• Construction activities (wax production).
• Brood feeding (royal jelly production).

Carbohydrates can also be converted 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 (the bee cuticle) are derivatives of glucose.

The sugars usually present in honeys are assimilated by bees. The most common are also 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 two 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 more complex sugars have no energetic value for the bee. Some are poisons at low concentration (galactose, arabinose, xylose, melibiose, mannose, raffinose, stachyose, and lactose). Pectin and many gums are also toxic to the bee. Thus, certain honeydews (containing, among other things, raffinose and gums) can cause problems.

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

The bee must hydrolyze sucrose into glucose and fructose, then glucose into fructose, in order to break it down and use it (for energy production or the 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 bee organism will not stop synthesizing them. Moreover, these enzymes are not “lost” after use: each has an active site that, in the presence of sugars, carries out hydrolysis and becomes available again after the reaction—although, of course, there are losses of enzymes 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 eliminate air bubbles in the cells when it is stored.

The introduced bacteria will enable:

• optimization of digestibility, notably through the breakdown of pollen grain walls and the digestion of carbohydrates
• an increased presence of enzymes useful for pollen maturation
• the 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 intestines of young bees with these bacteria (and thus acquisition of their benefits for digestion and vitamin synthesis).

The composition of bee bread is broadly close to that of fresh pollen, but the latter contains more compounds of interest, bacteria, enzymes, and molds (Guilliam, 1997). Its biological value is therefore higher.

Bee bread provides proteins, amino acids, fibers, lipids, vitamins, and minerals to the colony. It thus helps to balance the bees’ diet so as to prevent deficiencies (in particular in vitamins and minerals).

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

 

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

 

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

• it is the predominant amino acid in hemolymph proteins,
• it is an essential amino acid (see figure 4 - next page) that can only be supplied by diet.

 

 

In the first days after emergence, the adult bee requires a protein-rich diet, a large share of which is used for the development of the 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 stabilizes at 20% of the initial needs from 15 days after emergence (Crailsheim, 1986). Often, nurse bees ensure through 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 (likewise during heavy Varroa infestation), their hypopharyngeal glands do not develop fully and their production of royal jelly does not allow normal brood development and/or adequate feeding of the queen. The latter’s egg-laying is reduced as a result. Secretions from the hypopharyngeal glands 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 plays a role 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 progressively incorporate pollen and honey depending on larval age (Winston, 1987). Larvae mainly consume pollen on the 4th and 5th days of their life. Cremonez (1998) established that a larva consumes 30 mg of protein (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 the production of a large number of spermatozoa (Nguyen, 1999). These protein needs are covered by food (a mixture of glandular secretions, pollen, and honey) provided by young workers 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 protein supplied 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 available protein as a colony that collects 2 kg of pollen at 30% protein.

3. Amino acids

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

 

The bee is able to synthesize 10 of them from their components (derived from proteins ingested through diet), but the other 10 cannot be synthesized and must be supplied 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 building 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 el, 1999).
• in bee tissues, the most frequent 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 the bee, in light of other insects that hibernate, where they have an “antifreeze” function.
• pollen may have a health role thanks to the antagonistic action of certain fatty acids against the agents responsible for European and American foulbrood (Somerville, 2005).

5. Minerals

Proper functioning of the bee 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 feces, and therefore their volume, and require more cleansing flights for evacuation. Care must therefore be taken not to overwinter with feeds that are too rich in minerals, such as honeydews (we also noted that certain honeydew sugars are toxic).

6. Water

Water is essential to keep minerals in solution and for many vital chemical reactions in the bee organism

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

 

The quantity 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 liter of water per colony per week during brood-rearing periods (during or outside nectar flow periods). In addition, bees have a preference for waters rich in mineral salts, which explains why they can be attracted by livestock effluents.

In winter, bees consume the water resulting from condensation of ambient hive humidity, 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 of a bee’s body reserves 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 consisting of trophocytes: cells that accumulate fat bodies and other nutrients (Paes de Oliveira 2003).

These reserves are the bee’s individual reserves. They are mobilized when the bee is confined in the hive without being able to fly out (in winter), or to survive a period without reserves in the hive and without external input. These reserves are supplemented by “collective” reserves in the hive frames. When possible, 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, causing the abdomen to swell to the point of exceeding wing length (see figure 7). This phenomenon also exists during the season, during periods of intense flowering: seeing fat bees in hives is a sign of good blooms. Conversely, during dearth periods, bees consume their body reserves.

 

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

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

Warning, 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 improve its preservation, has an “optimal best-before date” in the hive. Somerville (2005) and Vasquez (2009) indicate that it begins to deteriorate significantly after two months. It progressively loses components (and thus its properties), up to a point of marked deterioration after 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 colony restart, therefore occurs jointly with the arrival of fresh pollen.

Nevertheless, if there is no input of new pollen, 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 “optimal best-before date” of honey is 4 years.

Indeed, beyond this period, the HMF (hydroxymethylfurfural) produced presents a risk of toxicity for the bee. HMF results from the dehydration of sugars, in particular 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 honey harvested long ago.

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

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

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

Beekeepers who make their own feeds must therefore ensure that particles are properly disintegrated or dissolved in water without lumps or overly large particles.

In addition, if honey crystallizes 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 bee malnutrition are known. There is an interaction between individual bees and the colony, and individual problems affect the adult population and brood rearing, which will be reduced both qualitatively and quantitatively. Cannibalism of larvae is possible and will affect the next adult generation and the colony’s capacity to build reserves (Brodschneider, 2010).

 

Bee malnutrition manifests itself through visible signs (e.g.): Queen stops laying Decreased brood survival Cannibalism (bees consume larvae) Worker mortality Cessation 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 the season (Between end of winter and the first nectar flow)

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

This stimulatory feeding (light syrup (50/50)) is therefore adequate at the start of the season, but it may also be so later if a nectar flow is preceded by a long period (more than one month) without flowering.

Honey feeding is theoretically ideal; however, this technique has several drawbacks: honey can be a vector for pathogens and may in particular contain spores of American foulbrood. Moreover, in practical terms, it can promote robbing at certain times of the year. Finally, such feeding represents a non-negligible cost.

9.2 End of the season (Between the end of nectar flows and overwintering)

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

Pouvreau (1981), drawing on data from 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 variability in overwintering conditions. These include, among others: available flora (in autumn and at the end of winter), weather, the number of bees in hives (and possibly the bee strain).

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

In conclusion, we can generalize and confirm what had been indicated in the Parole d’apiculteur summary on overwintering: a recommendation of 15 to 25 kg of reserves needed for winter and spring, i.e., between the end of September and the beginning of May.

It is important here to distinguish colder periods from milder ones, and to consider objectives regarding colony population size. If a beekeeper wishes to increase the bee population before winter, they can take advantage of a mild spell before the autumn and winter cold by providing a light syrup (50/50), which will stimulate the queen to lay 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 preferable to provide predominantly heavy syrup at the end of the season, which will require less work and energy for dehydration and storage.

 

9.3 And what about fondant in all this?

 

Beekeepers’ practices vary quite widely with respect to fondant. Overall, a majority use it (including 46% between 2 and 5 kg).

 

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

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

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

10. Complementary feeds

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

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

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

In a predominantly oceanic climate such as that of France, complementary feeds are advisable when flora and/or weather are unfavorable, depending on the quality and quantity of available reserves. These complementary feeds are mixed into syrup or protein patties.

11. Protein feeding

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

In the same way as for complementary feeds, pollen substitutes are often used in Spain, apparently much more than in France. Spanish beekeepers use protein patties during drought periods or when pollen inputs are insufficient in quality and quantity.

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

 

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

 

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

A question was recently raised regarding an increased risk of nosemosis due to protein feeding. Fleming (2015) published a study in which he inoculated laboratory cages of bees with Nosema spores. Groups receiving a protein diet 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 proper “seeding” of their intestinal flora (absence of trophallaxis), and because bees fed with proteins live longer, which increases the risk of a higher number of Nosema spores. In addition, based on his experience and Zheng (2014), the pathogenicity of nosemosis also depends on the appearance 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 pollen quality or diversity). 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 may harm colony population development.
• Before a major flowering, if there is a lack of pollen and nectar that could cause a population decline.
• Before winter entry, to promote population renewal with the emergence of bees well supplied with reserves, which will withstand winter well and be sufficiently vigorous to restart effectively the following spring.

 

12. Questions and answers

How can the actual effect of feeding or the products used be assessed?

By carrying out a prior trial. In an apiary, choose at least 20 healthy hives that are as homogeneous as possible. Record their strength in terms of the 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. For testing most complementary feeds, it is recommended to observe colonies over the longer term. If you wish to test several products, it is important always to 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 inputs are therefore decisive for immunity. Lipids are more important in maintaining the bee’s 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 this subject since the end of the 1970s, by M. Guilliam, G. M. Loper, L. N. Standifer… and more recent ones. In 2005, the following 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 their food through trophallaxis. This trophallaxis (as well as bee bread) results in an exchange of intestinal microflora and microfauna (microbiota) from older bees to young bees (which are almost devoid of it upon emergence). This study was carried out on newly emerged bees in cages. Providing probiotics in the diet enabled seeding of the intestinal microbiota in young caged bees and increased their lifespan. In a healthy colony with a good microbial flora, trophallaxis allows high-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 dietary supplement for our bees, as we do in human or animal nutrition, may be a way to secure good conditions for colonies.

Can artificial feeding with dietary supplements reduce bees’ immunity and their capacity to withstand problems (low temperatures or nutritional 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 (France) 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 supplement the colonies’ usual diet under conditions of nutritional deficiencies (which occur naturally), due to bad weather or poor diver