A new review on honey bee nutrition is forthcoming in the Annual Review of Entomology, some highlights (excerpted for review purpose only):

Pollen collection is regulated according to a honey bee colony’s needs, but on average, colonies
maintain about 1 kg of stored pollen. Brodschneider & Crailsheim estimated that a single ten frame
colony needs between 13 and 18 kg of pollen per year. Nectar collection is regulated
according to floral nectar availability, with great daily and seasonal fluctuations, with storage
reaching tens of kilograms.

The collection of powdery pollen by honey bees involves moistening
the grains with nectar or honey and salivary secretions before packing in the corbiculae. As a result,
sugar levels in bee-collected pollen can be up to 50% of dry mass, but usually, the proportion is not
known. This leads to underestimation of protein and other nutrients compared to fresh pollen.
Some researchers present general analyses of pollen composition, but typically, the
focus has been on the protein component, which varies from 10% to 60% dry mass in angiosperms.

Apart from crude protein levels, the other common measure of pollen quality is its amino acid
composition. The quantity of protein is actually less important than the amounts of essential amino
acids relative to bee requirements. As in nectar, the proportion of nonessential amino acids,
including proline, is high compared to essential amino acids, and some deficiencies in essential
amino acids have been identified (e.g., very low or nonexistent quantities of isoleucine in eucalypt
pollens or histidine in maize pollen).

The nurse caste of honey bee worker feeds all the other colony members. This is done either
by directly feeding them honey and bee bread or by feeding them with glandular secretions (e.g.,
royal jelly) produced after the nurse bees themselves have consumed honey and bee bread. Pollen
consumption by young nurse honey bees stimulates the development of their mandibular and
hypopharyngeal glands

When bees are fed with pollen substitutes, they digest only
25% of the protein in the diet, but this may be due to the use of protein sources such as soy flour;
they also have greater levels of infection with Nosema. 

Pollen digestion in adult honey bees can be assessed by comparing the proportion of empty pollen grains
in pollen and feces to give the extraction efficiency. A direct method is to compare the
protein content of food and feces. Gut microbes of honey bees may be involved in
degradation of structural carbohydrates in pollen, but given the speed that pollen progresses
through the bee gut, this is unlikely.

Supplementary feeding is widely used to support and build up honey bee colonies, but
the nutritional basis of protein supplements is poorly understood. At present, true substitutes
for pollen do not exist. A more rational approach based on honey bee ecology and physiology is needed.

Nutritional Physiology and Ecology of Honey Bees
Geraldine A. Wright, Susan W. Nicolson, and Sharoni Shafir

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