Question: What is the main source of protein for bees, and how is it used?
Bees get their protein from pollen which they collect from flowers. By various means, worker bees then turn the pollen into food for the the developing young and queen honey bee.
When pollen is collected by foraging worker honey bees and returned to the nest or hive, it is then mixed with nectar (or honey) and made into bee bread for feeding larvae.
Thus honey bee larvae and young adults thus receive most of their protein from pollen which has been stored in the wax hexagonal cells as bee bread.
Some protein also comes from royal jelly which has been biosynthesized (see below) from flower pollen by nurse honey bees. Royal jelly is then secreted by special glands in the heads of worker nurse honey bees. It is fed to the queen honey bee and to worker and drone larvae for a short time.
Protein is therefore provided by pollen which is in effect, biosynthesized by nurse bees into royal jelly, which is the main source of protein for developing larvae and the queen (Ghosh et al 20202 citing Winston, 1987, Paoli et al., 2014).
Thus, in terms of the honey bee diet, for the raising of honey bees, ultimately flower pollen is the key source of protein for bees which is then turned into food in the form of stored bee bread or bee secretions.
So what happens if bees don't get enough protein-giving pollen? This is relevant for anyone wishing to create a bee garden, and is the reason why a range of nectar and pollen rich flowers and shrubs is vital.
Pollen is the primary source of protein, lipids, sterols, minerals, and most vitamins for bees1.
Flower pollen contains a range of amino acids, and of these it has been found that 10 amino acids are considered essential for honey bees3. These are:
Amino acids are known to be important in a number of areas of bee biology.
For example, arginine helps to enhance immunity and fitness, whilst lysine and methionine raise the size of the fat body2 which is especially important for storing energy and nutrients of overwintering honey bees.
Other amino acids found in flower pollen, considered non-essential, have nevertheless been found to be beneficial. For example, amino acid proline is used as fuel for flight and helps in increasing cold hardiness2.
Many, many flowering plants contain lots of nutrient rich pollen for bees, and far to many to mention on this page, but for examples see my list of bee-friendly flowers for starters.
A number of studies have been conducted, especially on wild flowers, but garden cultivars and relatives are often available, whilst others can easily be incorporated into lawns and flower borders.
For example, Ghosh et al2 profiled the amino acid content of 4 flowering plants, which contain all 10 essential amino acids for bees.
Of the four flowers listed above, the white clover and beach wave (tickseed) appeared to be especially nutritious for bees.
1. Carroll MJ, Brown N, Goodall C, Downs AM, Sheenan TH, Anderson KE. Honey bees preferentially consume freshly-stored pollen [published correction appears in PLoS One. 2021 Mar 25;16(3):e0249458]. PLoS One. 2017;12(4):e0175933. Published 2017 Apr 21. doi:10.1371/journal.pone.0175933
2. Ghosh, S., Jeon, H. & Jung, C. Foraging behaviour and preference of pollen sources by honey bee (Apis mellifera) relative to protein contents. j ecology environ 44, 4 (2020). https://doi.org/10.1186/s41610-020-0149-9
3. de Groot, A.P. Amino acid requirements for growth of the honeybee (Apis mellifica L.). Experientia 8, 192–194 (1952). https://doi.org/10.1007/BF02173740