How honeybees make ‘baby food’ for their larvae

By Stephen Beech

Honeybees make a special “baby food” that gives their larvae a better-balanced diet, reveals new research.

The pollinators also avoid “too much of a good thing” by balancing nutrients in pollen, according to the groundbreaking findings.

The Oxford University-led research shows that bees can regulate their feeding to avoid overconsuming certain essential nutrients.

Bees are known for their intelligence, but the new study has revealed a previously unknown nutritional skill: the ability to adjust how much they eat in response to the balance of essential amino acids in their food.

The newly discovered talent helps them avoid the potentially toxic effects of overconsuming certain amino acids when pollen provides a poor nutritional match for their needs.

The study shows that many pollen sources don't provide bees with an ideal balance of essential amino acids — the protein building blocks that animals are unable to make for themselves and must obtain from their diet.

Researchers say their findings, published in the journal Current Biology, have important implications for farmers, landowners, conservationists and gardeners seeking to support pollinators.

The Oxford team explained that 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.

That means its nutrient balance may not always match what bees need to grow, survive and reproduce.

The researchers compared the essential amino acid profiles of honeybee tissues with that of pollen from 99 U.K. flowering plant species across 26 plant families.

The team then created artificial diets that either replicated the amino acid profiles of different pollen sources or honeybee tissues and fed them to newly emerged worker honeybees in controlled lab experiments.

The findings showed 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 weight and consumed a more protein-rich balance of food.

The researchers suspected that the response was linked to histidine — an essential amino acid that bees need only in small amounts.

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To test their theory, the team 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 says that may reflect a "post-digestive feedback" mechanism that helps bees avoid the potential toxic effects of overconsuming particular amino acids, rather than simply eating more pollen to make up for nutritional shortfalls.

They say a similar effect has been found in other animals. For example, in rats, excess histidine can be converted into histamine, which activates brain receptors involved in controlling food intake.

Study lead author Professor Geraldine Wright said: “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.”

But she said honeybees appear to have developed a strategy to ensure their developing young obtain a balanced diet.

They collect pollen from many different flowers and store it in the hive as "bee bread" — which is then eaten by nurse bees.

The nurse bees convert nutrients from pollen into glandular secretions, including royal jelly, which are fed to larvae.

When the researchers analyzed 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.

The researchers say it suggests that pollen mixing and processing by nurse bees may help honeybee colonies overcome the nutritional limitations of individual plant pollens.

Wright said: “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 maximize growth.”

But she says not all bees have that system.

Many wild bees, including bumblebees and solitary bees, feed pollen directly to their young.

Wright said that if their environment contains only a limited range of flowering plants, 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.

Wright added: “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.”