1. The importance of pollen

The true start of the beekeeping season depends not only on lengthening days, which can modestly restart laying, but above all on fresh pollen supply. Pollen is the colony's staple food, providing amino acids, proteins, lipids, minerals, and vitamins.

Converted into bee bread with the help of commensal microbiota, it supplies bees with compounds they cannot produce themselves. This nutrition makes vitellogenin production possible in the fat bodies, an essential step for the synthesis of royal jelly by the hypopharyngeal glands.

In young bees, vitellogenin production rises rapidly after emergence and peaks at the nurse bee stage. This dynamic corresponds to the period during which the colony must produce large quantities of royal jelly, required by larvae but also by adults, particularly foragers.

2. The central role of vitellogenin

Vitellogenin circulates in the haemolymph and can be stored in the fat bodies and ovaries when not in use. In the honey bee, this glycoprotein does not serve a purely reproductive function: it also influences physiology, behaviour, longevity, and immune function.

It is present in several key compartments of the bee, notably the haemolymph, the fat bodies, the hypopharyngeal glands, and the brain. It is involved in transport, storage, resistance to oxidative stress, synthesis, metabolisation, secretion, and trophallaxis.

Vitellogenin acts in interaction with juvenile hormone. A high titre inhibits the transition to foraging tasks, while a decline in vitellogenin and a rise in juvenile hormone favour the shift to foraging. Its level also influences the orientation of foraging activity: high concentrations favour later foraging with a greater focus on pollen collection, whereas lower concentrations are associated with earlier foraging oriented more towards nectar.

By reducing oxidative stress, vitellogenin also contributes to extending the lifespan of workers and the queen. This helps explain the longevity of winter bees, which accumulate substantial reserves in their fat bodies.

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3. Resumption of brood and colony development

In spring, the resumption of laying and the presence of larvae — which emit brood pheromone — mobilise the vitellogenin stored in the fat bodies. This mobilisation enables bees to feed the brood and prompts available bees to collect pollen. The result is a resumption of laying and a general mobilisation of the colony.

The first bees to emerge then have the time needed to assimilate pollen, develop their hypopharyngeal glands, and allow their flight muscles to mature. Once capable of producing royal jelly, they progressively replace the winter bees and take over brood feeding, which further accelerates colony development.

The new generations push the older nurse bees towards the periphery, while a cohort of middle-aged bees remains available to perform various tasks as needed. Many of them receive nectar from the foragers. When nectar can no longer find space above the brood nest, it is held in the honey stomach, which triggers the development of the wax glands and wax production. This is the moment when the frame lugs turn white, a sign of insufficient space.

In this context of abundance, drone brood can also develop. Drones too require large amounts of royal jelly, both at the larval stage and for the maturation of their flight and reproductive capacities.

4. Social organisation and task regulation

The article emphasises that bees do not automatically become foragers at a set age. They take on these external tasks only when the colony requires it. A forager produces a pheromone — ethyl oleate — in her honey stomach, which inhibits the transition of middle-aged bees to foraging.

This pheromone is transmitted by trophallaxis during nectar transfer. When foragers are numerous, the inhibitory signal is strong and the number of middle-aged bees increases. Together with other stimuli — such as brood area or vitellogenin level — this mechanism regulates task allocation and maintains a reserve of deployable bees in the event of sudden forager losses.

If colony development continues normally, the population becomes very large and the queen's pheromone is no longer sufficient to prevent the construction of queen cells: the swarming impulse may then be triggered. During the main season, the average lifespan of a worker bee remains short, which obliges the colony to maintain extensive brood rearing to preserve its demographic balance.

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5. End of season and formation of winter bees

The transition from summer bees to winter bees is explained not primarily by the season itself, but by the absence of open brood. The presence of open brood inhibits the storage of vitellogenin in the fat bodies — storage that is indispensable for acquiring winter bee status.

The laying cycle depends on genetics but also on pollen availability. When pollen supply ceases, the queen stops laying, which leads to a broodless period and allows the production of winter bees. The greater the area of open brood, the stronger the inhibitory effect.

Summer bees placed in overwintering conditions without having built up such reserves have virtually no chance of survival, in contrast to bees that have been able to accumulate these resources. The article thus invites reflection on the value of certain ground cover plants that provide pollen late in the season, as they may maintain a late brood.

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6. Dearth, abundance, and colony plasticity

In the event of a pollen shortage, nurse bees first draw on proteins from their internal reserves. If the shortage persists, they cannibalise the drone brood, then the eggs, and then the young worker brood.

As a last resort, they convert the remaining proteins into reserves stored in their fat bodies, as with winter bees, allowing the colony to wait for better conditions.

During a heavy nectar flow, the situation reverses. Foragers are numerous outside, which weakens the inhibitory effect and drives middle-aged bees to become foragers. Nectar is then stored throughout the brood nest, which reduces the queen's laying opportunities. With the decline in brood, nurse bees can transition to an intermediate stage and then join the foragers in turn.

This mechanism allows the colony to deploy a large proportion of its workforce to foraging during the few genuinely favourable days of the season. However, after an intense nectar flow the colony emerges weakened, as many foragers die rapidly. It then needs time to recover its balance.

7. Colony decline and weakening factors

Vitellogenin is also involved in immune mechanisms and is more abundant in strong colonies than in weak ones. When nurse bees or middle-aged bees are affected by certain chemical substances or bacteria, they deploy their vitellogenin for defence. Their juvenile hormone level then rises, which drives young bees to prematurely take on foraging tasks.

This premature task displacement causes accelerated ageing, reduces brood-rearing quality, and shortens bee lifespan. If this phenomenon coincides with pollen deficits, the situation can rapidly lead to colony death. In winter bees, the effect is expressed primarily as a reduction in their longevity.

The article also mentions the possible role of deficient brood thermoregulation, which may prolong the capping period and reduce the quality of the bees produced. Taken together, this shows that colony decline results from complex mechanisms, far beyond a simple forager loss following an isolated poisoning event.

In conclusion, these findings underscore the importance of adequate protein nutrition and sufficient thermoregulation for proper colony functioning.

 

►Download article: The Keys to the Colony

 

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See also:

• Pollen consumption and colony development
• Winter survival of honey bee colonies
• Pheromones as drivers of behavioural plasticity
• Downward spiral: chronicle of a foretold death

 

References

Amdam, G., Norberg, K., Hagen, A., & Omholt, S. (2003). Social exploitation of vitellogenin. Proceedings of the National Academy of Sciences of the United States of America, 100(4), 1799-1802.

Crailsheim, K. (1991). Interadult feeding of jelly in honeybee (Apis mellifera L.) colonies. Journal of Comparative Physiology B, 161, 55-60.

Schmickl, T., & Crailsheim, K. (2004). Inner nest homeostasis in a changing environment with special emphasis on honey bee brood nursing and pollen supply. Apidologie, 35, 249-263.

Li, Z., Zhang, S., Zhang, J., Liu, M., & Liu, Z. (2009). Vitellogenin is a cidal factor capable of killing bacteria via interaction with lipopolysaccharide and lipoteichoic acid. Molecular Immunology, 46, 3232-3239.

Münch, D., & Amdam, G. (2010). The curious case of aging plasticity in honey bees. FEBS Letters, 584(12), 2496-2503.

Nelson, C. M., Ihle, K. E., Fondrk, M. K., Page, R. E. Jr, & Amdam, G. V. (2007). The gene vitellogenin has multiple coordinating effects on social organization. PLoS Biology, 5(3), e62.

Visscher, P. K., & Dukas, R. (1997). Survivorship of foraging honey bees. Insectes Sociaux, 44, 1-5.

Leoncini, I., Le Conte, Y., Costagliola, G., Plettner, E., Toth, A. L., et al. (2004). Regulation of behavioral maturation by a primer pheromone produced by adult worker honey bees. Proceedings of the National Academy of Sciences of the United States of America, 101, 17559-17564.

Harris, J. L. (2008). Development of honey bee colonies initiated from package bees on the northern Great Plains of North America. Journal of Apicultural Research and Bee World, 47(2), 141-150.

Smedal, B., Brynem, M., Kreibich, C. D., & Amdam, G. V. (2009). Brood pheromone suppresses physiology of extreme longevity in honeybees (Apis mellifera). The Journal of Experimental Biology, 212, 3795-3801.

Mattila, H. R., & Otis, G. W. (2007). Dwindling pollen resources trigger the transition to broodless populations of long-lived honeybees each autumn. Ecological Entomology, 32(5), 496-505.

Di Prisco, G., Zhang, X., Pennacchio, F., Caprio, E., Li, J., Evans, J., DeGrandi-Hoffman, G., Hamilton, M., & Chen, Y. (2011). Dynamics of persistent and acute deformed wing virus infections in honey bees, Apis mellifera. Viruses, 3(12), 2425-2441.

Khoury, D., Myerscough, M., & Barron, A. (2011). A quantitative model of honey bee colony population dynamics. PLoS ONE, 6(4), e18491.