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Superfood for Honeybees

Posted August 7, 2024

Introduction

A variety of insects can produce honey — bumblebees, stingless bees, even honey wasps — but only honeybees (Apis species) produce enough to stock grocery store shelves. This ability didn’t happen overnight; it was millions of years in the making. Bees made the split from wasps around 120 million years ago, during a surge in the evolution and spread of flowering plants. This floral diversity — along with a shift in bee behavior of feeding pollen, rather than insects, to bee larvae — spurred the evolution of the approximately 20,000 bee species known today.

Although nectar is consumed, primarily as a supplemental food, by a broad range of insects spanning at least five orders, it is processed and stored by only a small number of species, most of which are bees and wasps in the superfamily Apoidea. Within this group, Apis mellifera has evolved remarkable adaptations facilitating nectar processing and storage; in doing so, this species utilizes the end product, honey, for diverse functions with few if any equivalents in other phytophagous (feeding on plants) insects. Honey and its phytochemical (plant) constituents, some of which likely derive from propolis, have functional significance in protecting honeybees against microbial pathogens, toxins, and cold stress, as well as in regulating development and adult longevity. The distinctive properties of A. mellifera honey appear to have arisen in multiple ways, including genome modification; partnerships with microbial symbionts; and evolution of specialized behaviors, including foraging for substances other than nectar. That honey making by A. mellifera involves incorporation of exogenous (external) material other than nectar, as well as endogenous (internal) products such as antimicrobial peptides and royal jelly, suggests that regarding honey as little more than a source of carbohydrates for bees especially compared to the popular management practice of sugar feeding is a concept in need of revision.

Biologically active constituents of honey, beyond sugars, appear to contribute substantively to bee health in diverse contexts that, by virtue of the unique nature of perennial eusociality (overlapping brood care) and associated food processing and storage, have no equivalent in conventional herbivores or even in other florivorous (flower-feeding) hymenopterans.

Nectar

Nectar is a plant tissue with no known function other than to reward mutualists; as such, it has long been regarded in the literature as chemically innocuous (harmless), attractive to the broadest range of consumers among floral rewards. Lacking appreciable protein, floral nectar is not constituted by plants to serve as a complete source of nutrition for mutualists (mutual benefit), and there are no known nectar-feeding animals that do not also consume other protein- or lipid-rich materials during their life cycle. Pollen is often the principal protein source for nectarivores, but alternate protein sources include plant tissues, fungi, other arthropods (particularly during larval stages), and vertebrate blood during adult stages.

As a highly digestible source of carbohydrate energy, nectar is vulnerable to theft by inappropriate floral visitors that consume nectar without performing pollination services or by microbes that preempt its use by pollinators by degrading its quality. Honeybees, for example, avoid nectar containing certain bacterial communities. Many nectar phytochemicals, particularly phenolics and alkaloids, are antimicrobial and may protect against microbial alterations in quality. In addition, alkaloids, phenolics, and other phytochemicals can defend nectar against inappropriate animal visitors by acting as feeding deterrents. Beyond repelling nectar thieves or robbers, limiting meal size of even effective pollinators can benefit the plant in some cases by inducing them to depart and to resume foraging on other conspecific flowers, increasing cross-fertilization opportunities.

Pollen

Bees are confronting several environmental challenges, including the intermingled effects of malnutrition and disease. Intuitively, pollen is the healthiest nutritional choice, however, commercial substitutes are widely used in beekeeping. Interestingly, feeding natural and artificial diets shapes transcription (DNA segment copying into RNA molecules) in the abdomen of the honeybee. Nutritional stress may be exacerbated in the presence of pesticides which upregulates detoxification genes increasing the energy cost of detoxification. Additionally, nutrient quality can influence xenobiotic (chemical) toxicity. Dietary protein quality and quantity are particularly important; pesticide sensitivity of adult bees depends at least in part on the quality of pollen consumed. Studies also support that a balanced, natural pollen diet allows bees to maintain a healthy metabolism and, in case of disease, provides individuals with a better fitness to mitigate the pathologic stress. Thus, a balanced, natural diet is essential to individuals and, by extension to overall bee colony health.

Floral Diversity

It cannot be overstated the importance of diversity in floral nutrition sources to sustain healthy honeybee populations by strengthening the natural mutualistic relationships. Recent fluctuations seen in honeybee populations have been attributed to habitat degradation, chemical intensive agriculture, pests and pathogens. Even as the demand for pollination services continues to grow, the ecological impacts of modern agriculture, including the elimination of remnants of native prairies and wildflower patches, are leading to a distinct drop in the diversity of the pollen/nectar diet of bees, compromising their health and physiological abilities. Adult bees need continuous access to carbohydrate, protein, lipids and other floral compounds to meet their energy needs and the nutrients in pollen and nectar play a vital role in meeting these needs and improving the ability of bees to cope with stress.

The relationships between flowering plants and their pollinators have an extensive co-evolutionary history. Embedded within this long-standing plant-pollinator mutualism, is the nutritional benefit for pollinators in return for the pollination services. Honeybees are among the most efficient pollinators, and the floral nectar and pollen they collect offer an assortment of proteins, lipids, carbohydrates, as well as micronutrients such as vitamins and phytochemicals. These primary constituents of nectar and pollen are essential for larval, and adult nutrition. While macronutrients derived from floral rewards play an integral role in the life history stages of honeybees, the role of phytochemicals is only now being explored. Understanding the impact of dietary phytochemicals is necessary to enhance reproduction, development, and foraging activities in honeybees which will pave the way towards maintaining healthy colonies and sustainable populations. Adequate nutrition is essential for normal honeybee colony growth and productivity. Individual bees with adequate and balanced nutrition are better equipped to resist biotic (living) and abiotic (nonliving) stressors and contribute effectively to improving colony food storage and performance.

The complex mutualistic interactions are highly suggestive of the functional significance of phytochemicals leading to profound implications for honeybee health and colony management practices. Extending the worker bee lifespan increases the overall foraging time allowing the colony to rapidly collect and store greater amounts of nectar and pollen. The increase in longevity and pathogen tolerance also has positive implications for colony productivity. Supplemental feeding of honeybee colonies is common practice among beekeepers to promote colony growth and overall health. It is clear that supplementation with sugar is not equivalent of bees consuming honey which is a mixture of extremely important polyfloral nectar and phytochemicals therein.

Honey

Creation of honey by A. mellifera as a storage form for nectar circumvents or minimizes the problems of unpredictability, ephemerality (transient), susceptibility to microbial contamination, and phytochemical variability and having access when needed to these chemicals for the health of the adult bees and brood. Several distinctive behaviors, some of which may be unique to Apis species, have evolved that facilitate the transformation of nectar (and other carbohydrate-rich foods) into honey. As a eusocial (social structure) species, A. mellifera utilizes a workforce of highly mobile adults to collect nectar as it becomes available across the landscape, utilizing sophisticated communication to inform nestmates about the location and quality of nectar sources. Individuals typically begin foraging two to three weeks postemergence, primarily for pollen and nectar.

Returning foragers transport nectar from the field in their crop (honey stomach), during which time enzymatic processing begins within them, and, when they return to the hive, they discharge the contents to waiting nestmates. A cadre of nest workers (nectar-receiver or food-storer bees) continues nectar processing by promoting water removal, each individual sucking up and regurgitating nectar onto her proboscis, thereby increasing its surface area and expediting evaporation. Other workers further promote evaporation by wing-fanning to increase circulation within the hive.

Active evaporation reduces the water content of nectar from approximately 80–90% to 50–60%; this more concentrated solution is then placed in cells and moved intermittently, dehydrating passively until a final concentration of 18–25% is reached, whereupon the cell is capped. The high sugar concentration renders ripe honey hygroscopic (readily absorbing moisture), and as a supersaturated sugar solution, it is inimical (adverse) to microbial growth. Among Apis species, average honey moisture content is characteristically somewhat lower for A. mellifera than for its sympatric congeners (similar group). Similarly, honey of stingless bees (Meliponini) is generally found to have higher moisture content than honey made by sympatric A. mellifera.

Beyond behavior, biochemical processing of nectar into honey involves a distinctive suite of enzymes. As they concentrate nectar, bees add enzymes to metabolize nectar components. Sucrase activity—cleavage of the disaccharide sucrose into its component monosaccharides glucose and fructose—allows bees to produce a supersaturated solution by increasing the number of solutes (parts) per liquid volume. This in turn increases honey’s osmolarity (solute concentration) and its microbial toxicity; microbes that are not osmotolerant (grow while stressed by the sugar concentration) can die from plasmolysis (shrinkage) and exosmosis (transfer through the membrane). Also involved in processing nectar into honey is glucose oxidase (GOX), which, by oxidizing glucose to produce gluconic acid and hydrogen peroxide, protects honey from microbial degradation by lowering pH and sterilizing the medium via free hydroxyl radical production and subsequent oxidation of bacterial DNA, membrane lipids, and proteins.

Because nectars, and thus honeys, can contain substantial quantities of potentially toxic phytochemicals, enzyme-mediated detoxification of phytochemicals is a prerequisite for utilizing nectar-based food. In A. mellifera, the principal Phase 1 enzymes involved in xenobiotic (external/foreign) detoxification are the cytochrome P450 monooxygenases (P450). Some detoxification, however, may occur passively. As honey ripens in the hive, it is exposed to hive temperatures maintained in the range of 35°C/95°F; the phenolic content of nectar of Aloe littoralis (a succulent native to arid regions in South Tropical Africa and Southern Africa ) is significantly reduced from 0.65% to 0.49% after exposure within an Apis cerana hive to these temperatures for 24 hours, suggesting that Apis species may have some capacity to “cook” honey to render it less chemically challenging.

Water and plant resins are also involved in honey production and utilization. A subset of foragers collect water and store it temporarily for multiple uses, including not only evaporative cooling but also honey dilution; due to its high viscosity, honey generally must be diluted by nurse bees to be fed to larvae and adults, particularly in winter. As for resins, some foragers collect them for processing into propolis, an antimicrobial mixture that, in wild colonies, lines and seals virtually all interior surfaces in the nest (forming a antimicrobial propolis envelope). Although plant resin sources vary widely, honeybees display distinct preferences for particular plant species (and even chemotypes within species). Propolis has long been regarded as a structural agent, providing strength to cell walls, as well as an antimicrobial agent, but the chemical selectivity of resin foragers suggests that bees critically differentiate among resin sources based on their biological activity.

Among the main phytochemicals reported in honey in northern latitudes—pinobanksin, pinocembrin, quercetin, chrysin, and galangin—few if any occur in floral nectars, but all occur widely in propolis. Resins do not appear to be consumed directly but resin phytochemicals may be available for consumption by virtue of the ability of honey, particularly in early stages of ripening in cells while still dilute, to absorb them. Aqueous extracts of propolis typically contain many phenolic acids, including cinnamic acid derivatives, that occur broadly in honeys.

Processing food prior to storage to prolong its shelf life is exceptionally unusual among animals. Humans are perhaps unique in engaging in diverse food-processing behaviors that increase food suitability and consistency for consumption, ensure its availability during periods of scarcity, remove toxins, facilitate transport and distribution, and deactivate spoilage microbes. These functions all have, to some degree, parallels in the lives of honey-making bees. Although honey has enormous nutritional significance as the principal energy source for flight, thermoregulation, and wax production, its phytochemicals, with their diverse biological properties, including but not limited to antimicrobial activity, make it well-suited to serve as a functional food and self-administered medicinal source.

Honey Storage

Honey proteins are essential bee nutrients and antimicrobials that protect honey from microbial spoilage. The majority of the honey proteome (protein complement) includes bee-secreted peptides and proteins, produced in specialized glands; however, bees need to forage actively for nitrogen sources and other basic elements of protein synthesis. Nectar and pollen of different origins can vary significantly in their nutritional composition and other compounds such as plant secondary metabolites. Worker bees producing and ripening honey from nectar might therefore need to adjust protein secretions depending on the quality and specific contents of the starting material.

Though some studies have not determined a difference in these qualities between foraged nectar and sugar solution it is clear the bees themselves do introduce additional basic elements such as royal jelly protein which can only be produced by the bees themselves. These unique bee-specific proteins make honey a specialized and beneficial superfood product for both the adult and developing bees especially during times of need when nectar of specific qualities can’t be consumed as an energy source.

Sugar solution-based honey-like products include exclusively bee-specific proteins. This is in accordance with previous studies. The investment of worker honeybees adding proteins based on the individuals’ reserves is not without purpose: storing bee-produced proteins in honey(-like products) prevents or at least strongly decelerates protein degradation and therefore provides an alternative protein storage strategy compared to direct storage in secreting gland tissue (even by overwintering bees) or haemolymph (internal fluid). Long-term experiments have shown that honey protein content decreases by 46.7% after 6 months, independent of the botanical origin. However, under natural conditions, honey might not be stored for longer than 6 months in the hive, as honeybees produce and consume their own honey stores regularly, depending upon the brood status, number of individuals and flowering season. The general energy requirements of the colony for processes such as temperature regulation are also a critical factor influencing honey storage duration. Furthermore, the storage of honey in wax cells and finally cell capping may significantly contribute to counteracting—and/or the retardation of—the decay of proteins and other honey compounds.

Honey as Functional Food

The capacity to store food provides the honeybees with an opportunity to selectively choose among the variety of stored products in an adaptive way dependent on their own or the colony’s health status. Honeybees, however, do more than just store food—bees process both nectar and pollen extensively before storing them.

Functional foods are defined as those that provide essential nutrients often beyond quantities necessary for normal maintenance, growth and development and/or other biologically active components that impart health benefits or desirable physiological effects.

In view of the exceptional capacity of the honeybee colony to store foraged plant products over extended periods of time”, it provides a theoretical framework for understanding effects of honey on bee health that are not readily explained by its nutritional content, much as the terms self-medication, pharmacophagy, and pharmacophory have been variously used to describe the medicinal use of nonfood plant material as a response to parasitic infection or other diseases.

As a functional food, honey differs from plant material consumed only in response to specific stresses in that it is a regular diet item that promotes health due to its content of nutraceuticals, a term coined in 1989 to describe a “food, or parts of a food, that provide medical or health benefits, including the prevention and treatment of disease”. Nutraceuticals are regarded as a toolbox for the prevention of disease or as food products to be taken as part of the usual diet in order to have beneficial effects that go beyond basic nutritional function. Ironically, it’s been recognized that honey is a functional food and source of nutraceuticals for humans long before its multifarious roles in honeybee health were suspected. Many of the same functional properties of honey that are operative in humans may well have evolved in the context of enhancing bee health.

The most well‐known functional properties of honey are its antioxidant and antimicrobial activities. The bioactive components of honey are affected by the flora from which it is produced and by geographical variations. Phenolic compounds promote, among other activities, high antioxidant action, being capable of minimizing intracellular oxidative damage associated with cellular aging, apoptosis and neurodegenerative diseases. A living cell system would provide a better platform for determining antioxidant activity, since the bioactive honey compounds can act modulating antioxidant defense gene expression. Indeed, phenolic compounds, amino acids and reducing sugars are among the substances responsible for honey antioxidant activity. Most of phenolic compounds also exert antimicrobial activity against a number of pathogens and spoilage microorganisms. The antimicrobial activity of honey is also due to the action of enzymes. In addition, honey was found to contain lactic acid bacteria (LAB), which itself produce a myriad of active compounds that remain in variable amounts in mature honey. In addition, these antioxidant compounds might play a key role as prebiotic, protecting and stimulating growth of probiotic bacteria. Oligosaccharides present in honey are well‐known prebiotic substances stimulating growth, activity and protecting probiotic bacteria during passage through the gastrointestinal tract and during storage of the products.

Toxin Tolerance and Detoxification

Honey consumption by bees has been demonstrated to enhance tolerance of ingested natural and synthetic toxins. Relative to consuming high-fructose corn syrup or sucrose, consuming honey enhanced survival of adult bees in the presence of aflatoxin B1, a mycotoxin produced by Aspergillus. Ingestion of extracts of honey, pollen, or propolis upregulated CYP6AS genes encoding enzymes that metabolize quercetin and CYP9Q genes encoding enzymes that metabolize quercetin, the acaricides coumaphos and bifenthrin, and neonicotinoid insecticides.

Relative to most other insect genomes, the western honeybee Apis mellifera has a deficit of detoxification genes spanning Phase I (functionalization), II (conjugation) and III (excretion) gene families. Although honeybees do not display across-the-board greater sensitivity to pesticides, this deficit may render them vulnerable to synergistic interactions among xenobiotics. Diet quality, in terms of protein and phytochemical content, has a pronounced influence on tolerance of toxic compounds. Detoxification gene inventory reduction may reflect an evolutionary history of consuming relatively chemically benign nectar and pollen, as other apoid pollinators display comparable levels of cytochrome P450 gene reduction. Enzymatic detoxification in the eusocial A. mellifera may be complemented by behaviors comprising a ‘social detoxification system,’ including forager discrimination, dilution by pollen mixing, and colony food processing via microbial fermentation, that reduces the number or quantity of ingested chemicals requiring detoxification. Genome-level deficits in detoxification and immunity relative to other insects may also be an evolutionary eusociality. In terms of immunity, bees display cooperative behavioral defenses against parasites and pathogens, including ‘social fever’ to kill temperature-sensitive bacteria, collection of antimicrobial plant resins for propolis, and removal of diseased brood, that collectively comprise a ‘social immunity’ system.

Alternative Food Sources

Severe declines in honeybee populations have made it imperative to understand key factors impacting honeybee health. Of major concern is nutrition, as malnutrition in honeybees is associated with immune system impairment and increased pesticide susceptibility. Beekeepers often feed high fructose corn syrup (HFCS) or sucrose after harvesting honey or during periods of nectar dearth. Relative to honey, chronic feeding of either of these two alternative carbohydrate sources elicited hundreds of differences in gene expression in the fat body, a peripheral nutrient-sensing tissue analogous to vertebrate liver and adipose tissues. These expression differences included genes involved in protein metabolism and oxidation-reduction, including some involved in tyrosine and phenylalanine metabolism. Differences between HFCS and sucrose diets were much more subtle and included a few genes involved in carbohydrate and lipid metabolism. This suggests that bees receive nutritional components from honey that are not provided by alternative food sources widely used in apiculture.

A honey diet elicited a transcriptional profile distinct from sucrose and HFCS diets. These differences were present in honeybee colonies, with vastly different viral loads, indicating the impact of honey on fat body gene expression is robust. These results suggest that constituents in honey differentially regulate physiological processes and that sucrose and HFCS may not be equivalent nutritional substitutes to honey.

Research has shown that honey – but not sucrose or HFCS – upregulates genes associated with protein metabolism and oxidation reduction indicative that honey elicits health-related physiological differences. Previous research has already identified honey constituents that upregulate detoxification pathways in the gut and now it’s been shown that honey also induces gene expression changes on a more global scale. These changes may have toxicological relevance under natural conditions in contemporary agroecosystems, where bees are routinely exposed to toxins and pesticides.

Overwintering

Stored honey is essential to the survival of overwintering honeybees in temperate climates, and there is some evidence that honey constituents other than carbohydrates promote cold tolerance. Supplemental ABA increases both the innate immune response and overwintering survival of honeybee colonies at cold temperatures (25° C/77° F) that otherwise reduce survival by almost half relative to standard temperatures (34° C/93° F). Supplemental ABA also accelerated development in larvae experiencing cold stress, possibly by elevating transcription of Hex7b, as well as vitellogenin (vg) and heat shock protein 70 (hsp70), both of which are cold stress–responsive. This research suggests that ABA coordinates stress responses, including cold exposure and wounding, through the Toll pathway.

Conclusion

Based on the nature of the honey they produce, honeybees are unique among animals in their ability to process nectar and package it for long-term storage. That said, identifying a genomic signature of honey making remains an elusive goal, as does understanding the evolution of the distinctive behaviors and physiological adaptations associated with the process. Moreover, much of the received wisdom about honey is not well supported by an abundance of literature. An evaluation of bee genomes indicates that activity historically attributed to invertase in honey making may actually be produced by α-glucosidase and that to some extent acid phosphatase and catalase activity might be due to endogenous (internal), rather than exogenous (external), enzymes. Moreover, although honey constituents can have striking impacts on individual bee behaviors, including learning and memory, colony-level impacts of such behavioral effects are rarely assessed, and mechanisms underlying short-term behavioral responses are not easily elucidated with genomic tools.

A limitation of the honey chemistry literature is that it is dominated by efforts to identify unique constituents for authenticating floral origin and by attempts to characterize individual constituents responsible for a particular type of biological activity. Thus, little attention has been paid to interactions among the hundreds of honey constituents already identified and to potential synergistic or antagonistic effects among constituents, which may derive not only from flowers but also from the bees themselves, from plant-derived resins in propolis, and possibly from bee-associated microbiomes. The diversity of the biological activities of honey depends not only on the diversity of the phytochemicals that bees collect from the environment, but also on the interactions among those phytochemicals and chemicals of non-plant origin, and virtually no studies have tested for interactions among these hundreds of co-occurring substances.

Understanding how phytochemical diversity affects the beneficial effects of honeys on the health of both individual bees and the colony as a whole has implications for the future of apiculture. Due to intensification of agricultural monocultures, urbanization, and other forms of habitat degradation, honeybees are often unable to find sufficient plant resources to thrive and, when pressed, will collect and consume a variety of human-produced substances that differ dramatically in composition from their natural foods. Moreover, beekeeping practices that substitute sucrose or high-fructose corn syrup for honey in times of nectar dearth may affect bee health by altering expression patterns of multiple genes involved in protein metabolism and oxidation reduction relative to honey. Even if sugars are similar between natural and human foods, the absence of a honey phytochemical profile may have consequences with respect to maintaining immunity, detoxification, and thermoregulatory capabilities. Because resin collection is limited to a narrower range of plant sources than is nectar, the absence of suitable sources can also lead to potentially maladaptive behavior, including collecting asphalt to incorporate into propolis; the effects of the presence of asphalt constituents and the absence of resin constituents that normally are incorporated into honey have not yet been assessed.

In summary, honey is integrated into virtually all aspects of the lives of honeybees; more importantly, its composition has the potential to influence or ameliorate the most persistent problems that have afflicted contemporary apiculture for the past three decades—namely, pesticides, pathogens, parasites, and poor nutrition. Understanding how honeybees utilize honey as a functional superfood can have significant dividends in improving honeybee health and provide new insights into the importance of food storage in social evolution.

Referenced Materials

Robbing Stress

Harbo Assay, Varroa Sensitive Hygiene Testing

Mold, should I be concerned?

STOP PRETENDING.

START BEE-TENDING.

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