Does the protein content of pollen play a role in honeybee decline?

Dutch summary: De voedingswaarde van stuifmeel (vooral het eiwitgehalte) beinvloedt de levensverwachting van bijen. Een te eenzijdig dieet van stuifmeel met een laag eiwitgehalte zou een rol kunnen spelen bij bijensterfte. Zie ook voor Nederlandstalige informatie over deze factor.

Pollen Power
by: Joe Traynor, February 01, 2009

Not all pollens are created equal.

All beekeepers are aware that protein is a key constituent in a healthy bee diet – honey provides the carbohydrates, pollen supplies the protein. When it comes to pollen, though, not all pollens are created equal [1,2,3].

Flower Source % Protein
Almond 25
Apple 25
Canola 24
Clover 24
Sunflower 15
Blueberry 14
Corn 15

Australia’s Graham Kleinschmidt did much of the pioneering work on the importance of protein content of pollens. Australia’s Doug Somerville made significant subsequent contributions in his classic book Fat Bees Skinny Bees[2].

Ashton[1] concludes that 'bees with very low crude protein levels, e.g., when coming off sunflowers, will run down very quickly if placed on a medium to heavy flow with average quality pollen support. Recovery of a colony after these circumstances could take as much as four months.'

It is noteworthy that the three pollens in the above list that have the lowest protein levels – sunflower, blueberry, corn – have been lurking in the background in areas where CCD has raised its ugly head. In France, where colony collapse occurred at around the time neonicotinoid pesticides were introduced, sunflowers are a major flower source. In the eastern U.S., bees that have spent a good part of the Summer on blueberries appear to be more susceptible to CCD as are bees that are on a corn pollen diet.

Before CCD hit, French beekeepers had been putting bees on sunflowers for years, with no apparent problems; the same for eastern beekeepers and blueberries, but this was before Varroa, Nosema ceranae and viruses became established, with Varroa, in particular having a negative effect on the immune system of honey bees. Malnourished bees that survived in the past may well have reached a tipping point when confronted with the combination of current pathogens and a weakened immune system. Malnourished bees in California’s central valley that had been successfully rented to almond growers for years, now succumb to CCD, or are too weak to be rented.

A 1995 study [4] divided bees into two groups: one fed solely with canola pollen, the other with sunflower pollen:

Pollen Source Life Span of Bees

Canola 51 days
Sunflower 31 days

This study was done well before the advent of CCD and the remarkable 20 day difference in life span could well cause sunflower bees that survived in past years to reach a tipping point in today’s world where they are confronted with the agents of CCD. The authors of this study concluded that their results indicated that 'growers of canola need not be concerned with the health of pollinating honey bees but that growers of sesame and especially sunflowers might take note of potential problems' and that bees on sunflowers 'will need to be provided alternate floral or nutritional supplements source to enrich their diets and maintain colony health.' (I am not aware of any similar study with blueberry pollen). There are an amazing one million acres of canola in North Dakota (N. Dakota is the bee capital of the world in the summer, as California is during February) and N. Dakota beekeepers report reasonably good colony health even though virtually all N. Dakota canola seed is treated with neonicotinoids (the material is felt to dissipate by the time canola blooms). The above data also bring up an interesting question: should growers of crops with low-quality pollen pay a premium for bee rentals?

There has been enough information on honey bee nutrition in recent years to cause most beekeepers, especially those that supply almond bees, to embark on a supplemental feeding program (see Randy Oliver for a short course on honey bee nutrition). Bees will consume a pound of supplemental feed in a week and around 16 pounds over a three-month period5. At up to $2/lb for feed (not counting labor) an intense feeding program will be a significant management expense, but some beekeepers are feeding up to 16 lbs figuring they can recoup this expense with current high almond pollination fees. Today, feeding programs often start in August-September (unless bees have access to an excellent Fall pollen source such as rabbit brush) and continue through the Fall-Winter months. Fall feeding in many cases is superior to Winter feeding – it provides younger bees with higher protein and vitellogenin levels and with more robust immune systems – longer lived bees that can maintain colony populations during the Winter. Beekeepers that fed only one or two pounds of protein supplement in past years are now feeding up to 16 or more pounds in order to get top-dollar for almond bees. Because pollen can transmit chalk brood and other harmful pathogens, beekeepers should make sure any pollen they use in supplemental feeding has been irradiated (and be aware that some methods of irradiation are more effective than others).

Beekeepers should be aware that not all supplemental feeds are alike and should look to comparative studies (and reports from the beekeeper pipeline) as to which feeds are best. Going strictly by protein content is not always a reliable indication as a 2000 study showed that a commercial feed with a 30% protein content was significantly less beneficial for bees than canola pollen and only slightly better than sunflower pollen3. All proteins contain nitrogen (N) and analysis for total N content is the usual method of determining protein content; total N is multiplied by a conversion factor – 6.25 is used in some studies2 – to obtain % crude protein. A problem with this is that non-protein materials (e.g., nitrogen fertilizers) can be added to a feed to boost its N content (but not its protein content). The recent recall of dog food products from China was due to adulteration with materials designed to increase their protein analysis.

Amino acids are what bees require in a protein supplement. All amino acids are proteins, but not all proteins are amino acids. No single pollen source contains the complete array of necessary amino acids in the proper proportion for honey bees. Bees require a mix of pollens, which is why feeding on a monoculture source of food is considered detrimental to bees. Even though an individual pollen can be an excellent source of protein (almond, apple, canola) a strict diet of one pollen will not supply bees with the full complement of required amino acids and a poor quality pollen (e.g., sunflower) can set the table for much worse. Some beekeepers mix powdered eggs (either yolks or whites or both) in patties for supplemental feeding. Although some reports indicate bees have difficulty using protein from eggs, these beekeepers report good results (all beekeepers would like to see standardized tests with egg materials as bee feed).

Pollen in feed mixes will lose its nutritional value over time3; cold, dry storage can minimize this loss. Bee-collected pollen is used in many supplemental patties, but the main protein source in patties is usually brewers yeast, because it is less expensive than pollen and has proven to be effective. Some beekeepers feel that the main benefit of pollen in patties is to make the patties more palatable so that bees will take up the protein material.

In this age of CCD, nutrition is assuming greater importance in all bee operations, large or small. The old adage 'you are what you eat' may apply more to honey bees than it does to people.

Joe Traynor is a Pollination Broker and crop specialist in Bakersfield, California.


1. David Aston, The nutritional status of bee collected pollen. The Beekeepers Quarterly, No. 28, Autumn 2004, p.29-30.

2. Doug Somerville, Fat Bees Skinny Bees RIRDC Publication 05/054 NSW Dept. of Primary Industries, 2005.

3.Stephan Pernal and R.W. Currie. Pollen quality of fresh and 1-year-old single pollen diets for worker honey bees. Apidologie 31:387-409 (2000).

4.L.S.Schmidt et al, Feeding preference and survival of young worker honey bees fed rape, sesame and sunflower pollen. J. of Econ. Entom. 88(6):1591-1595 (1995).

5. Bach, Jim, Honey Bee Research – A Vision for the Future. Western Apiculture Society (WAS) Journal, Nov. 2008, pp 8-10.


See also: Diet effects on honeybee immunocompetence