The Beekeeper’s Companion Since 1861
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The Curious Beekeeper

So Much Pollen, So Little Nutrition

- May 1, 2018 - Rusty Burlew - (excerpt)

leafcutting bee on flower

In the back of the feed store, where pallets of fifty-pound sacks rise to the ceiling and a calico cat naps on a hanging scale, I watch two women obsess over brands of layer ration. From what I can hear, they are comparing the protein content of various brands. It makes sense. If you want healthy chickens and many eggs, your birds need a balanced diet that includes the proper type and amount of protein. It works the same way for horses, pigs, dogs, cats, and even your kids.

Although we often speak of the protein content of foods, it is the selection of amino acids that is most important. Proteins are made from strings of amino acids. When an animal needs a specific protein, it can take the amino acids it ate and string them together to build protein. Even more awesome, if an animal eats one protein, it can take it apart and re-string the amino acids to make a different protein—the one it actually needs. It’s a bit like Legos: you use single pieces (amino acids) to build the object you want (protein).

Honey bees, too, need the proper mix of amino acids to be healthy. Except for trace amounts in honey, pollen is the sole source of amino acids in the honey bee diet. And just as humans need a variety of foods to remain healthy, a honey bee colony needs a variety of pollen types.

Variety is important because not all the amino acids are found in a single type of pollen. Some have a greater assortment than others, so eating a variety of pollen types is the ticket to good colony nutrition. In nature, this would not be difficult. But in many modern settings, especially those containing a small number of flowering species, bees may come up short in one or more of the essential amino acids. A shortage can mean diminished life spans, less resistance to disease, or poor foraging ability, among other things. 

Pollen and Brood Rearing

As beekeepers, we know that pollen is necessary for brood rearing. But how does that work? It turns out that the youngest honey bee larvae do not eat pollen directly. Instead, the nurse bees eat the pollen in the form of bee bread. Such a protein-rich diet stimulates their hypopharyngeal glands to secrete royal jelly, which is then fed to the young larvae.1 After about three days, small amounts of pollen and diluted honey are mixed into the brood food of both workers and drones, while young queens continue on a diet of pure royal jelly.

Adult workers eat energy-rich honey almost exclusively. Because foragers don’t eat bee bread or pollen directly, when they do need protein, they beg the nurse bees for it.2 Although we often don’t consider it, nurse bees feed all members of the colony from time to time. 

It Looked Good at the Store

Since the foragers that collect pollen don’t eat it, they are sometimes not too picky about what they collect. Sometimes foragers will bring home other stuff—sawdust or coffee grounds, for example—that have a powdery consistency and the right particle size. This has led some researchers to believe that honey bees cannot determine the food value of pollen: if it looks like pollen, it must be good.

Although foragers sometimes collect inferior pollen or non-pollen, the nurse bees—the ones that actually have to eat the stuff—are much more selective. Think of mom coming home from the market with parsnips and rutabagas. The kids sneer: “Really? Where’s the food?” In fact, nurse bees often discard some of the treasures their sisters bring home from the field, especially things with no food value, or even that expensive pollen substitute.

But recent research shows that when it comes to actual pollen, even the nurse bees cannot determine the quality. Or, even if they recognize poor quality, they are unable to communicate that information to the foragers who are hauling it in.3 In short, since we cannot rely on the colony to adequately balance its own diet, a variety of pollen choices is the best solution.

The Need Varies with Brood Rearing

When you understand how pollen is used in the hive, you can see why a colony doesn’t need a large supply during winter. In late autumn through mid-winter, when there is little brood rearing, a colony can get by with a minimum of pollen. However, heaps of good-quality pollen are needed throughout the major brood-rearing periods, especially in late winter and early spring.

When pollen is scarce, a colony may be forced to live off protein reserves stored as vitellogenin in the workers bees’ fat bodies. But that supply is limited, so beekeepers often opt for pollen substitutes before the major flows begin. 

A Changing Environment

It is easy to fall into the trap of thinking that since our fathers, grandfathers, and great uncles never worried about bee nutrition, we shouldn’t either. Back then, the bees gathered pollen on their own and thrived. No one gave two thoughts about its source or amino acid content.

While that may be true, we have substantially changed our environment in the intervening years. No longer are urban areas separated by large swaths of natural vegetation. No longer do farms grow an impressive array of crops. And no longer do roadsides provide a sparkling display of wildflowers. No. Instead we plant vast expanses of one thing and poison the rest until the landscape is uniform and easy to manage. Bee nourishment? Who cares?

A shortage of high-quality pollen is a relatively new concern for beekeepers. Today, a bountiful and diverse supply of pollen is often lacking. Habitat loss, invasive plants, monoculture farming, and herbicides are just some of the reasons.

Biodiversity and Bee Health

One of the main indicators of a healthy environment is biodiversity. Biodiversity is simply the sum of all living things in a certain area. The area can be as large as the earth or as small as a drop of pond water.

The sum of living things in any natural system includes plants, animals, fungi, and microbes. In a pristine natural community, each of the species stays in balance with the others. They live together, fight, compete for resources, eat each other, die, and scarf up the detritus in seasonal cycles. Each species has a special function in the community, and no one species is poised to take over. From an ecological point of view, more diversity is better.

Modern farms are the antithesis of natural environments. But far from being a bad thing, modern farms are necessary to feed burgeoning populations of humans. Still, it’s important for beekeepers to understand that the agricultural environment is not great for bees. Regardless of pesticide use, the biggest hazard for bees in agriculture is a low diversity of flowering plants.4

Monoculture Crops Fall Short

For bees, pollen from flowering plants is virtually the only source of protein, lipids, vitamins, and minerals. But in modern farmlands variety is suppressed. The grower needs to minimize competition from weeds, but he also wants to protect his crop from roadside plants that might harbor disease and destructive insects.

Bee colonies that pollinate large-acreage monocultures—such as almonds—have a severe lack of variability in their diets. Just as one fruit or vegetable doesn’t satisfy all your nutritional needs, one type of pollen is not enough for bees. Pollinating these crops with honey bee colonies is fine, as long as the beekeeper understands the nutritional stress a monoculture can inflict.

Pollen from different plants varies tremendously in both the quantity and quality of protein. Researchers have found that protein content can range from about 2 to 61% by dry weight, depending on the species.5 Furthermore, depending on protein source, it may completely lack some of the amino acids necessary for proper growth and development.

An example of a mediocre pollen source is the common dandelion, Taraxacum. Bees love dandelions, and they flit from blossom to blossom in large numbers. But dandelions are missing some of the essential amino acids. Research has shown that a diet of pure dandelion pollen will hinder larval development in mason bees,6 prevent brood production in honey bees,7 and cause 100% larval rejection in bumble bees.8

Does this mean dandelions are bad for bees? Of course not. The point to remember is that ….