Nurse Bees Provide Food for Bee and for Thee
Worker bees secrete “jelly” from the hypopharyngeal glands located in their heads. Royal jelly is fed to all brood in the first few days after hatching, and then exclusively to queen larva throughout their larval stage and much of her adult life. Another secretion is “worker” jelly, which was identified as a less-nutritious (but still very good) food given to -you guessed it- worker bee brood.
Chemically, royal jelly is a blend of water, protein, carbohydrates, fats, and trace amounts of vitamins & minerals. Its exact composition varies based on the colony’s food source, with carbohydrates coming from simple sugars: fructose and glucose. The proteins and fats are more complex and are a blend of the nurse bee’s own bodily stores (which in turn are a combination of her diet and genetics). “Worker” jelly is similar in production and makeup to royal jelly, only less nutritious.
This article will review how royal jelly is made by nurse bees, the glands involved and the composition of the final product. It concludes with its commercialisation as a bee product alongside honey, pollen and propolis.
Useful acronyms:
- RJ: Royal Jelly
- MG: Mandibular Gland
- HG: Hypopharyngeal Gland
- MRJP: Major Royal Jelly Proteins
- 10-HDA: 10-Hydroxy-2-decenoic Acid (a major lipid component in RJ)
You’ll find that I switch between the abbreviation and full name throughout because I edit by hand and I’m not perfect (No AI?! *Gasp*).
How Worker Bees Produce Royal Jelly
In short, the proteinaceous royal jelly is secreted by the hypopharyngeal gland (HG) cells on the side of head, and travel down the collecting duct into the mouthparts. Here, the mandibular gland adds lipids and other compounds, producing the complete royal jelly for feeding brood and queen. Worker jelly production follows the same process, with the end product having a lower nutritional content: less 10-HDA, more dilute and more varied in composition based on the hive’s foraging diet).
More detailed: the nurse bee consumes the hive’s bee bread and honey stores (or sugar if you’re feeding them in times of dearth). The fats/proteins/carbs from the food are metabolized into the RJ precursors – Major Royal Jelly Proteins, 10-HDA, enzyme co-factors, and energy for the synthesis process itself. The egg yolk protein vitellogenin is synthesised and added to the RJ mixture (as opposed to doing its function of egg development; Amdam et al., 2003).
With the precursors prepared, the HGs are activated, secreting the MRJPs (MRJP 1-5 make up the bulk of the mixture), enzymes, peptides and water, whilst the MGs add the lipids and other trace nutrients. The two secretions are blended in the head cavity to form the final royal jelly for regurgitation into the brood cell or trophallaxis feeding to Her Majesty The Queen.
Mandibular Gland & Hypopharyngeal Gland Development
Two glands are involved in royal jelly production: the hypopharyngeal gland (HPG) in the head and the two mandibular glands (MG) at the base of each mandible (“jaw”). HPG is composed of acini, small units containing secretory cells that produce and secrete the jelly. This jelly is transported down into the mouthparts to the MG, where the lipid-based compounds (described below) are synthesised and added to the jelly mixture.
In newly-emerged bees (newbees!), the HGs are formed but not yet functional (reviewed in Ahmad et al., 2021). Around six days after emergence, they become nurse bees and at this stage the HGs are fully developed, maintaining their size until they begin middle aged bee activities (~15 days after emergence). HGs in foragers are small but still functional; studies show that they switch from RJ-secretion to carbohydrate metabolism (i.e. producing enzymes for nectar processing like α-glucosidase; Kubo et al., 1996 & amylase/glucose oxidase; Ohashi & Kubo 1999).
The mandibular glands add lipids to the RJ, and are fully formed in the third day of adult bee life (Pan et al., 2024). Pan and colleagues imaged 3-day old newbee MGs until 16 days of age, and proposed three classification categories: category one for the cell cleaning/early nurse bees (days 3-6), category two for nurse bees producing RJ in earnest (days 9-12; RJ secretion peaks between days 6-12), and category three for the middle aged bees (16 days until commencing forager duties ~21 days).
When not used for royal jelly production, the MGs secrete pheromones for colony level communication. This is the primary function of queen MGs, and workers do this too in times of swarming or defence- go read that article.
Why Nurse Bees?
Nurse bees do the brood rearing and royal jelly production as they are physiologically prepared and “socially cued” (via division of labour) to perform the task in the ~6-15 days post-emergence. They are primed with the appropriate hormonal and metabolic activity for brood care, so they begin consuming pollen and honey to produce RJ. As you’ve read above, their hypopharyngeal glands are at optimal levels, and their mandibular glands are producing fatty acids instead of pheromones.
Hormonally, the nurse bees have high vitellogenin, low juvenile hormone, and this combination stimulates nurse bee-haviour (in foragers, it is the opposite, high juvenile hormone, low vitellogenin – better for flight and foraging, not so much RJ secretions). Pheromonally, the presence of brood is a self-regulating feedback loop: the more brood around, the more worker bees are directed/prolonged into the nurse bee role (Mohammedi et al., 1996). As brood numbers decline, the nurse bees move onto their next caste: the 101 tasks of a middle aged bee.
Worker Jelly is Used in Caste Determination
If RJ is so superior, why do we have the weaker worker jelly? A strong possibility could be for the control of honey bee castes – too much royal jelly, and in too large numbers will lead to too many queens in one hive, or workers with more “queen like” characteristics. The review by Alhosin suggests that diet-driven epigenetic changes are how honey bees can produce two distinct castes (i.e. queen and worker) from the same set of DNA (Alhosin, 2023). He notes that inhibition of DNA methyltransferase enzymes (particularly DNMT3) results in worker bees with fully developed ovaries, a result identical to that of larvae reared on pure royal jelly (i.e. the queen diet).
The one of the active ingredients, 10-HDA, inhibits the enzyme histone deacetylase HDAC3, whose inhibition enables the acetylation of histone proteins and turning larvae into queens. Other biologically active ingredients also inhibit the enzymes and without getting too technical, this targeting leads to a domino effect of inhibition or activation of epigenetic-modifying enzymes, ultimately determining if a larva becomes worker or queen.
Composition of Royal Jelly
Broadly, the average RJ sample is 60-70% water, 12-15% proteins, 10-16% sugars, 3-6% lipids and the rest is found in vitamins, minerals and compounds like peptides and enzymes. These fluctuations are due to the colony’s geography, diet, and time of production (e.g. spring vs summer). In appearance, it is a white-yellow material with a slightly pungent odour and taste. It has an unhomogenized jelly-like consistency (surprise!) due to the presence of undissolved pollen granules.
90% of the sugars in RJ are fructose and glucose, a chemical composition similar to honey. What other sugars that exist are in trace quantities (<10%) and are reflective of the nectar sources gathered by the colony (e.g. ribose, erlose, maltose, and other -oses; Popescu et al., 2009). The review by Xue and colleagues examined royal jelly sugar concentrations from Europe, finding variations between samples from Italy, France, Bulgaria and even Anatolia (Xue et al., 2017). The big takeaway is that nutrient concentrations are dependent on location, with some areas having flowers that produce more of a certain sugar type which is reflected in the composition of that hive’s jelly.
Over half of royal jelly’s weight is protein, and 80% of those proteins belong to the Major Royal Jelly Protein (MRJP) family. This is a family of nine1 proteins and are named sequentially based on the order of discovery (e.g. MRJP-1, MRJP-2 and so on; Drapeau et al., 2006). MRJP-1 is the most abundant MRJP family member. Another protein family is the Jelleines (involved in antimicrobial activity, reviewed in Lima et al., 2024), with the remaining protein components being an assortment of enzymes and polypeptides (royalisin, glucose oxidase, hymenoptaecin, apidaecin etc…).
Physiologically, these proteins have various functions, from promoting/inhibiting cell division, increasing/reducing inflammation, inhibiting/promoting immune cell function, antimicrobiral effects etc… all this is to say each body part/cell line responds differently to royal jelly, with the effects being largely positive (plenty of references for this just search “Royal jelly & X cells”).
The lipid composition of royal jelly is mainly in free fatty acids,, with 10-HDA being the marker for lipid quality (and by extension, RJ; Pattamayutanon et al., 2018). Like the protein list above, the fatty acids have medicinal qualities and antimicrobial effects, along with a long list of neuro-something benefits.
Trace Elements in RJ: Amino Acids, Vitamins and VOCs
Amino acids are abundant in RJ, totalling 17 (out of the 20 known ones). Of these components, methionine and glutamine breakdown over time, and are used as a marker of a royal jelly’s quality. Other compounds present in trace quantities are the free-base nucleotides (remember A-T G-C, the building blocks of DNA? No? Then don’t worry, I’m mentioning them for completeness) and the adenosine-5’ phosphates (AMP, ADP, ATP), the primary sources of energy for our cells.
Most of the vitamins in RJ are the B-vitamins, with B5 & B3 having the highest concentrations (reviewed in Barnutiu et al., 2011). Others like Vitamin A, D E & C are present in lower qualities.
The volatile organic compound profile of RJ contribute to RJ’s flavour profile, with esters and aldehydes being highest in concentrations at 25% & 17.5% respectively. Other known VOCs are ketones, acids and alcohols.
Royal Jelly Viscosity & Acidity Enable Queen Larvae to Hang Upside Down
How is it that queen larvae are reared in vertical cells with downward-facing opening? Shouldn’t gravity cause the larva to fall out? The answer is in the acidity and viscosity (“thickness”) of RJ, which attaches the queen to the cell ceiling (Buttstedt et al., 2018). When Buttstedt and colleagues increased the pH of RJ from the native 4.0, they found decreasing viscosity that corresponds with increased larval drop rate, peaking at pH 5.9 whereby all experimental larvae dropped out of their cells (n=10).
pH is a measure of hydrogen ions in a solution, and it is not the hydrogen that is keeping larva attached, rather pH’s effects on MRJP1-apisimin complex, whose fibril network controlled RJ’s viscosity (Buttstedt et al., 2018). At pH 4, the complex forms long fibril-ous structures which give jelly its viscose nature; these fibrils split into smaller compound chains when the pH is around 5.0-7.0.
Extracting Royal Jelly for Human Consumption
Techniques for extracting royal jelly are labour intensive. Just think: the queen (or worker) cell is filled with less than a gram of jelly, and the larva must first be removed from the cell before jelly extraction. To do so, the labourer must have excellent eyesight and motor control to extract the larva without damaging it (else it contaminates the jelly) and then siphon the jelly into a sterile vessel. Suppose the process takes less than a minute… in an hour you’d have a whopping ~60 g of RJ, and ~480 g in a 8-hour workday… and you thought your output was low?
One modern technique uses plastic worker foundation to simplify the extraction process: “a plastic worker foundation with regular holes, plastic cell bottoms mounted on a bar that can be inserted into the comb to fill the holes, and into the bottomless plastic queen cups on RJ production bars” (Orsolic & Jembrek 2024 referencing Collazo et al., 2021). This is combined with selective breeding of high-RJ producing bees, frequent requeening and multi-queen colonies (see below).
China is the world’s largest supplier of RJ, followed by Eastern Europe. RJ has gained attention as a functional food that is good for this system or that body part, y’know- that whole marketing spiel of how it’ll prevent cancer, cure diabetes and suppress your uncle’s strong opinions on minorities who emigrated to the West in the past five years– that sort of stuff. The interested reader is invited to do their own research on the health benefits of RJ. This article is for bee, not for thee.
Selective Breeding of A.m. ligustica Produced a High-Royal-Jelly-Producing Bee Strain
We’ve selected bee species for gentleness, honey production and low swarming tendency (the Italian bees A.m ligustica2), and in China, they’ve taken the next step by adding high RJ production. A.m. ligustica was chosen because she produces large quantities of RJ, accepts large numbers of grafted larvae for queen rearing, has nurses with high HG activity and a low swarming tendency coupled with high brood-rearing capacity (reviewed in Cao et al., 2016 & worth reading).
Chinese beekeepers selectively bred colonies on the basis of their royal jelly content per queen cell cup, the ease of new-queen/requeening acceptance and the volume of jelly secreted by the nurse bees. Once a colony met these criteria, its brood was intensively bred through mass queen-larva-rearing, artificial insemination with quality drones, and so on.
High Royal Jelly producing bees generate over 10 kilograms of RJ per year3. In China, peak RJ production is from March to November, and the seasonal harvests are further optimised by supplemental feeding, frequent requeening and keeping multi-queen colonies (as in, two queens, one colony- possible if you know your way around a queen excluder!).
Royal Jelly in Food Processing & Preservation
Outside of direct human consumption, the antioxidant activity of RJ has found its way to preserving meat products- for example, to improve the stability of pork patties during storage over storage (Park et al. 2024 ) or to reduce the nitrate content of dry-fermented sausages (common in curing meat; Hospital et al. 2024). The authors use this in combination with propolis and wax, noting the combination had a greater effect on improving sausage shelf life. We’ve already seen propolis and wax being used to preserve other foods, now royal jelly is added to the mix.
RJ’s antimicrobial effects come from 10-HDA (the same 10-HDA used to assess its quality), along with the peptides royalisin and the jellenies family. The acidic composition of RJ and its high enzymatic activity makes it unfavourable for microbial growth (just like the acidity and enzymatic activity of honey…). The vitamins, flavonoids, and phenols give RJ free radical scavenging capacity, which reduces lipid oxidation and colour degradation in packaged foods. This makes it useful as a food coating, or a direct additive to fatty foods like the aforementioned sausages.
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Footnotes
- The ninth protein was characterised by Peiren & colleagues after analysing the protein content of honey bee venom (Peiren et al., 2005). They found three new proteins: one from the platelet-derived and vascular endothelial growth factor families (PDGF/VEGF, i.e. involved in blood vessel functionality), one matching MRJP-8 (the first catalogued occurrence of MRJP in venom?), and one similar to the MRJP family but with no known matches to it. This latter protein was thus named MRJP-9. A later study by the same authors found that these proteins are the most “ancient members” of all MRJPs, suggesting that what we now know as “royal jelly” started out as a component of bee venom.
For completeness, Drapeau and colleagues describe 10 MJRPs, however the tenth protein is closer in structure to the “Yellow” protein family of Drosophila, so in effect, there are nine functional MRJPs (Drapeau et al., 2006). ↩︎ - Baitala and colleagues reported several royal jelly proteins in Africanised honey bees and suggested that they could be used for mass royal jelly production (Baitala et al., 2010 & Baitala et al., 2013) however this idea has not yet caught on in Africa & South America… go figure. Couldn’t figure it out? Here’s an article on Africanised honey bees. ↩︎
- For reference, harvesting RJ from your average A.m. ligustica queen cell cup results in less than a gram of royal jelly. ↩︎