Bees eat less when pollen protein is wrong, which changes what pollinator planting has to solve

A University of Oxford team reports in Current Biology that honeybees adjust how much they eat according to the balance of essential amino acids in their food, apparently to avoid taking in harmful excesses of particular ones ^[1][2]. The same work found that many pollens contain essential amino acids in proportions that do not closely match what bees need ^[3], which turns pollinator provisioning from a question of floral abundance into a question of protein composition.

The comparison was not narrow. The researchers matched the essential amino acid composition of honeybee tissues against pollen collected from 99 UK flowering plant species spanning 26 plant families ^[4], an average of under four species per family ^[5]. Most of those pollen samples were a relatively poor match for bee tissue ^[6]. That is less surprising once you note what pollen is: the male reproductive material of plants, and, unlike nectar, rarely produced solely as a reward for pollinators, which according to lead author Professor Geraldine Wright creates a conflict of interest between plant and pollinator ^[7][8]. Nectar supplies mostly sugar; pollen is the primary protein source ^[9].

The behavioural half of the study used artificial diets built to mimic either the amino acid profile of various pollens or the profile of honeybee tissue, fed to newly emerged workers in the laboratory ^[10]. Bees on the tissue-like diets ate more, gained more body mass, and selected a higher proportion of protein ^[11]. The researchers then isolated histidine, an essential amino acid that bees need only in small quantities ^[12]. When diets carried a high level of histidine relative to branched-chain amino acids such as leucine and isoleucine, the bees cut total intake: less protein and less carbohydrate ^[13].

That is the operationally important detail. The compensating response to an unbalanced food is not to eat more until the scarce nutrient is covered, but to stop eating. The researchers attribute this to a possible post-digestive feedback mechanism that limits intake of potentially harmful amino acid quantities ^[14], and note a parallel in rats, where excess histidine can be converted to histamine, which activates brain receptors involved in controlling food intake ^[15]. If that holds in the field, a forage patch that is abundant but badly proportioned does not merely underfeed a colony, it suppresses appetite for the carbohydrate on offer as well.

Colonies do have a buffer. Workers store mixed pollen in the hive as bee bread, and nurse bees process it into glandular secretions including royal jelly that are fed to larvae ^[16]. The researchers report that bee bread had a more balanced essential amino acid composition, consistent with the hive converting mismatched raw material into better larval food ^[17][18].

What to watch: whether anyone converts this into a planting list. The material published so far does not name which of the 99 species scored well or badly, so the practical instruction for farmers, landowners, conservationists and gardeners that the team says its work could inform ^[19] is still missing its central table. Also worth watching is whether the histidine effect replicates outside artificial diets and beyond honeybees, since the intake experiments used synthetic foods and newly emerged workers under laboratory conditions ^[10]. Seed mix vendors will reach for the mismatch finding quickly; the number to ask them for is an amino acid profile, not a species count.