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Honey bee nutrition is complex and unique and is not analogous to that of other livestock/animals, where nutritional needs of specific animals are well understood and appropriate diets/feed have been formulated. Honey bees are social insects, and the colony is considered a superorganism with a well-defined caste system and reproductive division of labor. Similar to their complex biology, nutrition is also complex in honey bees and can be considered at 3 levels (1) colony nutrition, (2) adult nutrition, and (3) larval nutrition.
Hence, honey bees may face significant challenges in terms of pollen diversity, quantity, and quality based on their geographic location. At present, efforts are underway across the country to improve nutrition for diversity of bees (including managed bees such as honey bees and wild bees such as many native bee species) by planting forage. A major limitation of this approach is that the target forage species are chosen predominantly based on their apparent attractiveness to bees and not based on the nutritional composition of pollen and nectar or the nutritional needs of the bees. However, beekeepers have access to supplements that exclusively provide protein but do not provide other required essential nutrients. Furthermore, there are huge gaps in knowledge regarding honey bee nutrition, and hence, to date, no optimal/balanced diet is available for honey bees.
Foraging behavior of honey bees
Foraging behavior reflects the interdependence between pollinators and plants and involves several factors from within the hive as well as from the outside environment. Diversity of available floral resources (or lack thereof) across a foraging range or across time and seasons can result in different levels and types of behavior and collected resources, which can have cascading effects on the colony’s growth, survival, and reproduction.
Factors Influencing Foraging Behavior
There are several biological factors, including the genetics and physiology of honey bees, underlying foraging behavior outside of the nutritional quality of resources. The amount of brood (developing larvae) and the levels of brood pheromone affect foraging behaviors. The larvae depend on a diet made from collected pollen, although the response may be threshold based and foragers can also revert back to nursing behavior if there are insufficient numbers of nurse bees to tend to the amount of larvae.
High levels of stored pollen can cause a negative feedback effect that inhibits pollen foraging by recruiting fewer numbers of pollen foragers, fewer trips to collect pollen, and/or smaller amounts of pollen collected during a trip.
The effects of colony-level selection on the social organization of honey bee (Apis mellifera L.) colonies: colony-level components of pollen hoarding.
Genetic variation also underlies differential foraging behavior and responses to foraging stimuli, as revealed by the selection for bees that collect and hoard high and low amounts of pollen, and the identification of regions of the genome and candidate genes associated with foraging age (the age at which young workers initiate foraging) and specialization (pollen vs nectar).
There are also factors outside of the hive that influence a bee’s foraging choices. Bumble bees have been shown to forage on pollens according to their nutritional values, whereas honey bee studies have had mixed results, with some showing bees choosing to forage on and dance for pollen resources of lower quality.
However, honey bee colonies have a complex social structure, with the superorganism having a common, centralized “stomach.” Foraging efforts may be adjusted in response to multiple factors to achieve overall optimal nutrition.
The nutritional needs of a colony change across a year as do the availability of resources, which impacts the growth of a colony. However, bees can adjust their foraging efforts and range to seek out new food patches. Relative to most other bees, honey bees have a wide foraging range with von Frisch
reporting the foraging range to be up to 13.5 km. Although many studies have reported foraging distances between 0.7 and 2.0 km, wider ranges have also been reported and have been shown to vary by month and forage type.
Environmental factors (eg, air temperature and solar radiation) can affect body temperature, but in general, the longer the distances traveled to resources, the lower the efficiency and higher the likelihood of needing to fuel their flights with more sugar for meeting the higher energy demands.
documented and described the waggle dance, a figure-eight movement of returning foragers that involves vibration of the abdomen while moving in a linear line (Video 1). The length of the dance and the angle/orientation of the vibratory movement reflect the distance and direction of resources relative to the sun.
Other bees observing the dance may be recruited to forage at the same location. This behavior continues to be studied in several contexts, including foraging preference, pollen diversity, communication, and conflict.
because of their social structure. In addition to an absence of diseases, a healthy colony must be able to sustain functioning members (workers and reproductives) capable of performing their tasks and resisting various abiotic and biotic stressors.
Consuming sufficient quantities of high-quality pollen (Fig. 1) has been shown to decrease susceptibility to the gut parasite Nosema ceranae, lower pathogen loads, improve honey bee immunity and overwintering success, improve semen quality in drones, and result in healthier honey bees that are better able to counteract pesticide stress, disease incidences, transportation stress, and parasitic pressures.
Other studies have associated nutrition with bee behavior. The physiology of the emergent spring workers may be affected by nutrition, which subsequently may alter their behavior.
Thus, optimal nutrition may be considered as the honey bee colony’s first line of defense, enabling it to better withstand both biotic and abiotic stress.
Fig. 1A frame of pollen from multiple plant sources as evident from the different colors.
As with the nutritional requirements for other animals, bee nutrients can be largely classified as macronutrients and micronutrients. As the name suggests, macronutrients are required in large quantities and are critical for the development and sustenance of honey bees. Examples include proteins, carbohydrates, and lipids. Micronutrients are equally important, even though they are required in smaller quantities. Vitamins, minerals, phytochemicals, and phytosterols are examples of the micronutrients required by honey bees. Carbohydrate-rich nectar is the primary energy source for bees and contains important phytochemicals, whereas pollen provides vital proteins, lipids, vitamins, phytosterols, and phytochemicals.
Thus, for a healthy honey bee colony to thrive, an optimal balance of all macronutrients and micronutrients is needed.
Macronutrients
Carbohydrates
Nectar and honey dew (sugar-rich liquid, secreted by some insects, such as aphids, when they feed on plant sap) are the natural sources of carbohydrates for honey bees. Foragers collect nectar and honey dew from plants and store it in their crops (honey stomachs) for transportation back to the hive. Then it is gradually converted to honey in the colony by the addition of invertase and other enzymes
As most floral nectars contain less than 50% sugar, the amount of nectar needed to support a large colony and its carbohydrate needs are thus much higher than 700 lb (∼318 kg) (of nectar) annually.
Ten amino acids in specific proportions are essential for honey bees and must be acquired through diets: arginine, histidine, isoleucine, leucine, lysine, methionine, phenylalanine, threonine, tryptophan, and valine.
A colony having 20,000 honey bees collects about 125 lb (∼57 kg) of pollen annually, and approximately 15% to 30% of the foragers are pollen foragers in a colony.
The workers further process the collected pollen that has been brought back to the hive and store it as “bee bread.” The total pollen consumptions by nurse bees within a short span of 10 days is approximately 65 mg per bee after which the consumption of pollen decreases.
Nurse bees biosynthesize proteinaceous secretions in their hypopharyngeal glands by consuming pollens, which are then progressively provisioned to the developing larvae and referred to as brood food.
The worker-destined larvae are fed worker jelly (protein-rich secretions for the first 2 days and then a mixture of protein secretions, pollen, and nectar for the next 3 days) by nurse bees, and the queen-destined larvae are fed royal jelly exclusively throughout their development.
of which essential fatty acids are a crucial component. Essential fatty acids such as linoleic and γ-linoleic acids comprise 0.4% and phospholipids comprise 1.5%
of the total lipid fraction. Apart from supporting the essential physiologic functions, fatty acids, such as oleic acid, have been shown to enhance learning and survival in bumble bees.
Sterols are a form of lipid, playing vital physiologic roles in insects, which include acting as a precursor of important molting hormones and also forming the building blocks of cellular membranes.
For honey bees, the most vital phytosterol is 24-methylenecholesterol. Studies have shown that caged honey bees fed artificial diets supplemented with 24-methylenecholesterol had longer survival and had more brood production, when compared with honey bees fed a different phytosterol in the artificial diets.
Thus, to produce ecdysteroids (makisterone-A) from sterols, honey bees exclusively depend on their diets for 24-methylenecholesterol. Recent studies have also highlighted the important physiologic impacts of 24-methylenecholesterol on honey bees, including increase in bee longevity and enhancement in head protein and abdominal lipid contents.
Of the phenolic acids and flavonols, 2 compounds are notable for their immense benefits in improving honey bee health: p-coumaric acid and quercetin. Studies have shown that phytochemical consumptions by honey bees enhance longevity, reduce Nosema infection, upregulate honey bee genes with antimicrobial properties, and counteract pesticide stress.
Beekeepers in North America generally provide protein supplements to honey bee colonies during foraging dearth (especially during fall and late fall) and spring to boost colony strength by enhancing brood rearing
(Fig. 2). Also, honey bee colonies used for crop pollination often face nutritional stress because the quality or quantity of pollen forage available to them in such agricultural landscapes can be inadequate.
Fall and late fall feeding of protein is critical, because this is the time when winter bees (diutinus) are reared in the colonies and these bees are vital for overwintering survival of colonies. However, current protein supplements available to beekeepers do not sustain long-term brood rearing in honey bee colonies. Some studies have reported that colonies fed protein supplements do not perform as well when compared with colonies receiving real pollen.
Most of the protein supplements available in the market for honey bees are either whey or soy-based products. Some of these available supplements have a small percentage of pollen added to the protein supplement. Although protein supplements are not equivalent to pollen in terms of nutrient composition, several studies have reported enhanced brood rearing and low disease susceptibility associated with the use of protein supplements.
Effects of Brood Pheromone (SuperBoost) on Consumption of Protein Supplement and Growth of Honey Bee (Hymenoptera: Apidae) Colonies During Fall in a Northern Temperate Climate.
Although it is not easy to diagnose nutritional stress in a colony, there are visual symptoms that may indicate severe nutritional stress such as larvae with low or no brood food in their respective cells (Fig. 3). The larvae reared in honey bee colonies with ample pollen stores are normally bathed in a sufficient supply of brood food provisioned by nurse bees.
Fig. 3Larvae devoid of brood food (larval starvation symptom).
Similar to protein, beekeepers also provide sugar to their colonies during times of nectar dearth (especially during fall and late fall periods) and inclement weather. Honey bee colonies are mostly fed liquid sugar syrup during spring and fall and are provided dry sugar or fondant (Fig. 4) during the winter period when bees do not prefer sugar syrup due to lower temperatures. Winter starvation can result when access to stored honey is limited, commonly seen as many inward-facing, dead honey bees in frames (Fig. 5); however, inward-facing dead honey bees in frames is not a definitive diagnosis for starvation. In spring, the concentration of sugar syrup fed to colonies is about 50%, and it is about 66% during fall or late fall. The commercial beekeepers in the Pacific Northwest report feeding their colonies between 5 and 15 L of sugar syrup in spring and 10 and 25 L in the autumn.
Even though the gut microbiota is assumed to play a role in honey bee colony health (pathogen defense) and nutrition, the specific functions of each of these dominant gut bacteria are currently unknown.
Over the past 3 years, some beekeepers have started using commercially available probiotics marketed for honey bees. These commercial probiotics claim to improve digestion and support gut health and colony health. Unfortunately, to date, there is a paucity of peer-reviewed published research regarding the benefits of these commercial probiotics to honey bees.
Supplemental Forage and Integrating Floral Diversity into Cropping Systems
Another promising option for improving bee nutrition is providing supplemental forage.
Honey bee colonies with access to supplemental forage have been reported to experience lower mortality when compared with colonies that did not have access to supplemental forage.
Over the past few years, there has been a significant emphasis on improving pollinator forage and habitat to boost bee health in the wake of colony declines, including the 2014 Presidential Memorandum for creating a federal strategy to promote the health of honey bees and other pollinators. Some nonprofit agencies such as the Project Apis m (https://www.projectapism.org/seeds-for-bees.html) have developed programs like Seeds for Bees that encourage the use of cover crops in orchards and farms to improve forage for bees. Another nonprofit organization called the Xerces Society has developed a comprehensive list of pollinator-friendly plants that are highly attractive to pollinators, including native bees and honey bees (https://xerces.org/pollinator-conservation/pollinator-friendly-plant-lists). At present, pollinator plants chosen for habitat development are based on their apparent attractiveness to bees. There is little information regarding the quality of forage (especially pollen quality) available to bees. A more scientific way to choose these plants should be based on the nutritional composition of their pollens, which vary widely in their protein, phytosterol, amino acid, and metabolite compositions.
Thus, providing diverse forage for bee pollinators is essential.
Honey bee colonies used for crop pollination often face nutritional stress, because the quality or quantity of pollen forage available to them in such agricultural landscapes can be inadequate.
Some cropping systems may put bees at risk for temporary nutritional insufficiency if the crop plant’s pollen is deficient in certain nutrients, and bees are unable to find an alternative source of these nutrients. Hence, it is imperative for beekeepers and crop producers to understand the pollen abundance and diversity that honey bees encounter during crop pollination to mitigate nutritional deficiencies by providing supplemental forage
Assessment of pollen diversity available to honey bees (Hymenoptera: Apidae) in major cropping systems during pollination in the western United States.
(Fig. 6). Furthermore, it has been documented that the honey bee colonies used for pollination in certain crops, such as blueberry, exhibit high rates of the bacterial disease European foulbrood (EFB). It is thought that poor foraging, weather, and poor availability of food resources lead to nutritional stress in colonies placed in blueberry fields due to collection of low amounts of food resources (pollen and nectar), which in turn make colonies more susceptible to EFB.
Honey bee colonies are complex and dynamic biological systems with nutritional needs that change based on internal colony conditions (eg, brood, age of adult bees) and resources that change with exterior/environmental conditions (eg, season, distance, water/drought), with needs and resources not always aligning.
Pollen and nectar are the primary food resources collected by honey bees. The honey bee colonies depend on these resources not only for colony growth but also to mitigate pathogen infection and expression of detoxification genes.
During resource (pollen and nectar) dearth, beekeepers provide nutritional supplements (protein and sugar) to their colonies. There is a significant gap in knowledge regarding nutritional needs of honey bees, especially micronutrients. Over the past few years, however, there has been renewed focus on understanding the nutrient requirements of honey bees. Many studies related to nutrition are conducted in controlled settings with limited choices for the bees to reduce extraneous variables, whereas in a natural setting, honey bees have several forage options to balance their dietary needs. Hence, there is need for more research in realistic field settings for a robust understanding of honey bee nutritional requirements.
In addition, habitat planting has also become a popular way to improve bee health, but recommendations of floral species are mostly limited to relative attractiveness rather than actual nutritional value. The lack of a current database of floral nutrient values is one challenge that researchers are working to address, but it will take time to build such a database because honey bees are generalists and visit diverse floral species. Continuing research on honey bee nutritional needs and foraging will assist in improving honey bee dietary supplements, habitat recommendations, and colony management.
Clinics care points
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Honey bee nutrition is complex and unique and is not analogous to that of other livestock/animals
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Different life stages of honey bee have different nutritional needs
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Honey bee nutrition is highly dependent on the foraging environment (floral composition of the landscape), and honey bees encounter dynamically changing floral resources in the landscape.
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Optimal nutrition can mitigate several honey bee parasites and pathogens, especially the EFB disease.
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Both the internal colony environment and external environment should be assessed to ensure the balance between need and availability.
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Beekeepers can provide supplemental nutrition (protein and sugars) to their colonies during foraging dearth.
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Caution should be exercised when feeding food resources (honey and pollen) from colonies that have died of unknown reasons or of unknown sources, because some honey bee diseases are transmissible through contaminated food.
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Planting floral habitats is another way to supplement nutrition, but more research is needed to understand the nutritional qualities of different floral resources
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At present, there is a paucity of peer-reviewed published research regarding the benefits of commercial probiotics to honey bees.
Disclosure
The authors have no conflicts of interest and no disclosures to make.
The effects of colony-level selection on the social organization of honey bee (Apis mellifera L.) colonies: colony-level components of pollen hoarding.
Effects of Brood Pheromone (SuperBoost) on Consumption of Protein Supplement and Growth of Honey Bee (Hymenoptera: Apidae) Colonies During Fall in a Northern Temperate Climate.
Assessment of pollen diversity available to honey bees (Hymenoptera: Apidae) in major cropping systems during pollination in the western United States.
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