Bees have no miniature laboratory capable of instantly analysing every pollen. Faced with the flowers available, foragers combine odours, learned colours, tactile characteristics, ease of collection and information received in the hive. The colony efficiently adjusts the quantity of pollen brought back. Its capacity to select systematically the pollen offering the best nutritional value is, by contrast, much less well established.

1. Collecting a pollen does not mean knowing its full value

The energetic profitability of a nectar depends strongly on its sugar concentration and its flow rate — properties that the forager can assess directly by ingesting it. Pollen poses a different problem. Its value depends on several dimensions: proteins and the profile of essential amino acids, lipids and fatty acids, sterols, micronutrients, digestibility and possible unfavourable compounds. No single signal summarises this whole.

Moreover, pollen foragers are not its main consumers. They gather the grains on their bodies, moisten them and pack them into the corbiculae of their hind legs, but digest little of it during collection. It is mainly the young workers in the hive that consume the pollen and redistribute its nutrients to the brood. The consequences of an insufficient or inadequate pollen can therefore appear after the forager's return.

Colonies respond clearly to low stores or a weak supply by increasing the collecting effort. In an experiment where the quantity and the protein content of the stores were manipulated separately, they above all increased the total pollen income; they did not specialise in sources richer in protein (Pernal & Currie, 2001). The best-demonstrated collective competence therefore concerns the regulation of quantity, not the systematic search for the 'most nutritious' pollen.

2. Odour, touch and colour: partial cues

Identifying the signals that bees can perceive, without confusing them with a complete measurement of nutritional quality.

Experimental set-up associating colours with two pollen rewards. The study was carried out on the buff-tailed bumblebee (Bombus terrestris), not on the honey bee. © University of Exeter

Odour makes it possible to recognise a flower or a pollen already encountered. In controlled trials on the honey bee, odour dominated choices, while particle size and handling cost also influenced preference (Pernal & Currie, 2002). Such cues can make a source easy to relocate or to exploit without guaranteeing that it offers the best nutritional balance.

The antennae also carry chemosensory receptors. During proboscis extension reflex conditioning, bees distinguished pollens differing in their concentrations of amino acids or fatty acids, but not in the sterol concentrations tested (Ruedenauer et al., 2021). The experiment demonstrates a perceptual capacity under controlled conditions. It does not prove that foragers spontaneously analyse all these constituents on flowers, nor that they deduce from them the biological value for the colony as a whole.

Colour acts above all as a learned signal of the flower. Buff-tailed bumblebees learned to associate a colour with a pollen reward and changed their choice when the association was reversed (Nicholls & Hempel de Ibarra, 2014). This experiment, often presented as general proof for 'bees', did not concern Apis mellifera. It shows above all that a visual cue can lead to a known source; it does not establish that colour naturally reveals the protein content or the overall quality of the pollen.

3. Learning a source and receiving feedback from the colony

A forager learns the location, odour, colour, shape and ease of exploitation of a source. This memory favours floral constancy and reduces the time spent searching for new flowers. It can therefore produce strong fidelity to an abundant resource, even if that resource is not optimal by every nutritional criterion.

Some trials nevertheless show that the colony can correct specific imbalances. Eight colonies kept in enclosures and fed an artificial diet deficient in one essential amino acid subsequently preferred the food that made up this deficiency. Other differences between the diets, particularly in fatty acids, could not however be entirely ruled out (Hendriksma & Shafir, 2016).

Another mechanism is delayed learning. In a recent experiment, foragers did not initially avoid a pollen containing amygdalin. After this pollen had been brought into the hive, they reduced their preference for the same source over the following days (Lajad & Arenas, 2024). The colony can therefore associate the cues of a pollen with consequences that appear after its collection. The trial nevertheless used a high experimental concentration and demonstrates the learning of an unsuitable resource, not a general capacity to rank all natural pollens.

4. What the dance actually communicates

In the waggle dance, the orientation of the waggle phase indicates the direction of the source relative to the sun, while its duration gives information on the distance. The repetition and vigour of the dance influence recruitment, but they depend on the perceived profitability, on the state of the colony and on the context. Simply saying that 'the slower the dance, the further away the source' or that 'the more circuits, the more nutritious the pollen' is therefore misleading.

In trials comparing pollen mixtures, an increase in protein content neither shortened the return phase of the dance nor increased the number of circuits. The natural pollens brought back by dancers were no richer in protein than those of bees that did not dance (Beekman et al., 2016). The dance therefore does not automatically encode protein content.

A more targeted response nevertheless remains possible. After a diet deficient in omega-3 or omega-6, colonies produced faster dances for a pollen that made up the deficiency in essential fatty acids (Zarchin et al., 2017). This result shows that assessment can depend on the nutritional state of the colony. It does not allow the rhythm or the number of circuits to be converted into a general scale of 'pollen quality'.

Finally, the forager does not deposit a sample of her pellets during the dance: she unloads them into a cell. Recruits use the dance together with other information, notably the floral odours carried by the dancer or present in the hive, to find the source.

5. What the beekeeper can deduce from it

• Abundant income indicates that a source is available and heavily exploited; it does not guarantee that its pollen is balanced.
• A dominant colour may simply reflect fidelity to an attractive and abundant flowering. It does not on its own justify supplementation.
• Several colours suggest several dominant sources, but prove neither high botanical diversity nor the coverage of all requirements.
• Practical assessment must combine the continuity of income, the stores close to the brood, the development of brood rearing and the flowering plants actually accessible.
• A pollen trap removes part of the resource that the colony is seeking to regulate. Its use must therefore remain monitored, especially during a break in flowering or intensive brood rearing.
• Encouraging a diversified and continuous floral supply reduces the risk that a dominant source will lastingly impose its limitations. Diversity is an insurance, not a guarantee of balance.

The choice of pollen thus results from a combination of perception, learning, availability, collection cost and social feedback. The collective organisation is remarkable, but it does not make the colony infallible: bees can neither choose a resource absent from the landscape, nor necessarily deduce its full nutritional value before it is consumed in the hive.

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See also:

• All About Pollen
• Recognizing pollen
• Pollen consumption and colony development
• Bee dance
• The senses located in the bee’s antennae
• Dancing is something you can learn

References

• Beekman, M., Preece, K., & Schaerf, T. M. (2016). Dancing for their supper: Do honeybees adjust their recruitment dance in response to the protein content of pollen? Insectes Sociaux, 63, 117–126. https://doi.org/10.1007/s00040-015-0443-1
• Clarke, D., Whitney, H., Sutton, G., & Robert, D. (2013). Detection and learning of floral electric fields by bumblebees. Science, 340(6128), 66–69. https://doi.org/10.1126/science.1230883
• Hendriksma, H. P., & Shafir, S. (2016). Honey bee foragers balance colony nutritional deficiencies. Behavioral Ecology and Sociobiology, 70, 509–517. https://doi.org/10.1007/s00265-016-2067-5
• Lajad, R., & Arenas, A. (2024). Honey bee colonies change their foraging decisions after in-hive experiences with unsuitable pollen. Journal of Experimental Biology, 227(1), jeb246233. https://doi.org/10.1242/jeb.246233
• Nicholls, E., & Hempel de Ibarra, N. (2014). Bees associate colour cues with differences in pollen rewards. Journal of Experimental Biology, 217, 2783–2788. https://doi.org/10.1242/jeb.106120
• Nicholls, E., & Hempel de Ibarra, N. (2017). Assessment of pollen rewards by foraging bees. Functional Ecology, 31(1), 76–87. https://doi.org/10.1111/1365-2435.12778
• Pernal, S. F., & Currie, R. W. (2001). The influence of pollen quality on foraging behavior in honeybees (Apis mellifera L.). Behavioral Ecology and Sociobiology, 51, 53–68. https://doi.org/10.1007/s002650100412
• Pernal, S. F., & Currie, R. W. (2002). Discrimination and preferences for pollen-based cues by foraging honeybees, Apis mellifera L. Animal Behaviour, 63(2), 369–390. https://doi.org/10.1006/anbe.2001.1904
• Ruedenauer, F. A., Biewer, N. W., Nebauer, C. A., Scheiner, M., Spaethe, J., & Leonhardt, S. D. (2021). Honey bees can taste amino and fatty acids in pollen, but not sterols. Frontiers in Ecology and Evolution, 9, 684175. https://doi.org/10.3389/fevo.2021.684175
• Zarchin, S., Dag, A., Salomon, M., Hendriksma, H. P., & Shafir, S. (2017). Honey bees dance faster for pollen that complements colony essential fatty acid deficiency. Behavioral Ecology and Sociobiology, 71, 172. https://doi.org/10.1007/s00265-017-2394-1