Bees avoid ‘too much of a good thing’ by balancing nutrients in pollen
New Oxford University-led research reveals that bees can regulate their feeding to avoid over-consuming certain essential nutrients - and that honeybees make a specialist ‘baby food’ that gives their larvae a better-balanced diet. The results have been published today in Current Biology.
Pollen is the main source of protein for bees, however the new study found that most pollen sources were a poor match for the profile of essential amino acids that bees need. Image credit: Mykhailo Hladchenko, Getty Images.
Bees are known for their intelligence, but a new study led by the University of Oxford has revealed a previously unknown nutritional skill: they can adjust how much they eat in response to the balance of essential amino acids in their food. This helps them avoid the potential toxic effects of over-consuming certain amino acids when pollen provides a poor nutritional match for their needs.
The findings show that many pollen sources do not provide bees with an ideal balance of essential amino acids: the protein building blocks that animals cannot make for themselves and must obtain from their diet. The results have important implications for farmers, landowners, conservationists and gardeners seeking to support healthy pollinator populations.
Bees feed almost exclusively on nectar and pollen from flowers. Nectar provides mainly sugar, while pollen is their main source of protein. But unlike nectar, pollen is not produced primarily as a food reward for pollinators: it is the male reproductive material of plants. This means its nutrient balance may not always match what bees need to grow, survive and reproduce.
To investigate this, the researchers compared the essential amino acid profiles of honeybee tissues with that of pollen from 99 UK flowering plant species across 26 plant families. They then created artificial diets that either replicated the amino acid profiles of different pollen sources or honeybee tissues and fed these to newly emerged worker honeybees in controlled laboratory experiments.
The study revealed that most pollen sources tested were a poor match for the essential amino acid profile of bee tissues. Bees fed diets that more closely matched their own tissue composition (rather than pollen) ate more, gained more body mass and consumed a more protein-rich balance of food.
“Although pollen is often assumed to be a near-perfect food for bees, it is the male gamete of plants and, unlike nectar, it is rarely produced solely as a reward for pollinators. This creates a conflict of interest between the plant and the pollinator.”
The researchers suspected that this response was linked to histidine, an essential amino acid that bees need only in small amounts. To test this, they fed bees artificial diets where histidine was either high or low relative to branched-chain amino acids (such as leucine and isoleucine) that are important for bee growth and development. When histidine was relatively high, the bees ate less food overall, including both protein and carbohydrate.
The team suggests this may reflect a post-digestive feedback mechanism that helps bees avoid the potential toxic effects of over-consuming particular amino acids, rather than simply eating more pollen to make up for nutritional shortfalls. A similar effect has been seen in other animals: in rats, for instance, excess histidine can be converted into histamine, which activates brain receptors involved in controlling food intake.
However, honeybees appear to have developed a strategy to ensure their developing young obtain a balanced diet. Honeybees collect pollen from many different flowers and store it in the hive as ‘bee bread’, which is then eaten by nurse bees. These nurse bees convert nutrients from pollen into glandular secretions, including royal jelly, which are fed to larvae.
When the researchers analysed bee bread, they found that its essential amino acid profile was better balanced than most single pollen sources. Royal jelly was better still, closely matching the amino acid profile of bee tissues. This suggests that pollen mixing and processing by nurse bees may help honeybee colonies overcome the nutritional limitations of individual plant pollens.
“We predict that honeybees have evolved to create glandular secretions which are the perfect food for their larvae, providing them with the ratios of essential amino acids that maximise growth.”
However, not all bees have this system. Many wild bees, including bumblebees and solitary bees, feed pollen directly to their young. If their environment contains only a limited range of flowering plants, these bees may struggle to obtain the right balance of essential amino acids for themselves and their developing larvae.
The findings suggest that pollinator-friendly planting schemes should look beyond the number of flowers provided and consider the nutritional quality and diversity of pollen sources.
“Our results suggest that planting for pollinators should not only focus on providing flowers throughout the season, but also on ensuring a diversity of pollen sources. A varied diet may be essential for bees to obtain the right balance of nutrients.”
The study also involved researchers from the University of Southampton, Lancaster University, Newcastle University and The Hebrew University of Jerusalem.
The study ‘Nutrition of honeybees is constrained by the ratios of essential amino acids in pollen protein’ has been published in Current Biology.
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