The honey bee diet requires many amino acids
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).
So much pollen, so little nutrition
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
Mononculture 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 no one type of pollen does what a variety of pollens can do. Honey bees evolved on diverse vegetation and that is still what serves them best.
In a natural environment, monocultures aren’t much of a problem. A bee would seldom—if ever—run into an endless monoculture of dandelions, so they don’t cause an issue. But bees plunked down in the middle of acres and acres of a single crop will have trouble nourishing the next generation. And even if the young bees survive and mature, their immunity to diseases, parasites, and even pesticides may be compromised. Just like any other animal, bees need healthy immune systems to survive, and adequate immunity depends on proper nutrition.9
Invasive species make a poor honey bee diet
Many beekeepers welcome the vast acreages of invasive plants that are swallowing the landscape. The reason is nectar. Some of the invasive plants, including star thistle, Japanese knotweed, Chinese tallow, and kudzu are excellent honey producers that fill the supers and pay the bills. But although they are a bonus for the beekeeper, they can be hard on the bees.
Invasive species are simply another form of monoculture. Like the planted crop, the invasive weed reduces biodiversity. Instead of having a vast array of flowers to choose from, the bees have one main entree. Instead of forty different types of pollen, each with a unique amino acid profile, the bees are left with one. Instead of a kaleidoscope of flowers blooming one after the other across the seasons, there is one ginormous bloom followed by dearth.
The main difference between a planted crop and an invasive weed is that invasives don’t stop at the edge of the farmer’s field. Instead, they creep into neighborhoods, wildlands, median strips, and abandoned properties. Some patches stretch as far as you can see, smothering everything beneath them and restricting the selection of nectar and pollen for uncounted species of bees, butterflies, and beneficial insects.
Whenever the diversity of plant life is compromised, all those that depend on it are weakened as well. After foraging on invasive plants, managed honey bees may require pollen supplements to keep them healthy. But the others—the native bees, beneficial insects, and other random invertebrates—are simply out of luck. And when the insects disappear, the birds, frogs, and mammals that ate them go hungry as well. In any biological system, nothing is as toxic as uniformity.
Use of herbicides
Herbicides hurt bees in multiple ways. Although the direct effect of herbicides on honey bees is inconclusive, some research has shown that the ingestion of glyphosate is linked to a reduced ability to navigate.10 Perhaps more problematic is the fact that herbicides kill natural bee forage, such as flowering weeds, while simultaneously promoting the spread of invasive plants.
Roadsides, croplands, cityscapes, and playgrounds that are stripped of natural vegetation are magnets for invasive species. Just as farmers prepare the soil for their monoculture crops by spraying the weeds, other users of herbicides prepare the soil by spraying the native vegetation, thus making it more attractive to invasive weeds. It seems a shame to spray roadside vegetation with herbicides and then feed soybean meal to our bees.
Although we don’t know much about the long-term effects of climate change, a few disturbing papers have suggested subtle problems. One recent study examined the protein content of goldenrod pollen in comparison to goldenrod pollen obtained from herbarium collections where the plants were collected years ago. The scientists found that the amount of protein in goldenrod pollen dropped by about one-third between 1842 and 2014.11
Similar studies have shown that the protein content of grains used for human food has also dropped during this period, and the drop is believed to be due to higher carbon dioxide levels in the atmosphere. Apparently, an abundance of carbon dioxide causes plants to grow faster and bigger, but the increased growth in the vegetative parts reduces the amount of protein stored in seeds and pollen.
Warmer spring temperatures are also causing some plants to bloom out of sync with the native bees that pollinate them. This occurs when the plants bloom earlier in the year, while the bees emerge at the regular time. In monolectic relationships where one bee species pollinates one plant species, both bee and plant can go extinct.12
What can beekeepers do?
Beekeepers can no longer ignore the protein needs of their colonies. Instead, we must keep in mind that, depending on location, the pollen supply may not be as plentiful, as diverse, or as nutritious as it was in the past. We shouldn’t hesitate to use pollen supplements if there is a chance our bees might need them. Especially when we see disease, poor overwintering, or lackluster performance, we need to remember that well-fed colonies will outperform their malnourished counterparts.
Looking at the larger picture, planting a diverse assortment of flowers and flowering trees may be our best long-term solution. Some groups have worked to alter the spraying regimens in their local communities—simply changing the timing of maintenance can make a big difference. Others are working to build community awareness by planting pollinator gardens, utility easements, median strips, and parks with bee-friendly flowering species. Planting flowers may seem like a small thing, but if enough people understand the consequences of a diversity-starved environment, perhaps we could make a difference.
Honey Bee Suite
- Snodgrss RE, Erickson EH, Fahrbach SE. 2007. The Anatomy of the Honey Bee. In JM Graham (Ed) The Hive and the Honey Bee (pp. 111-165). Hamilton, Illinois: Dadant & Sons, Inc.
- De Mardo RJ, Farina WM. 2003. Trophallaxis in forager honeybees (Apis mellifera): resource uncertainly enhances begging contacts. Journal of Comparative Physiology. 189(2):125-34.
- Corby-Harris V, Snyder L, Meador C, Ayotte T. 2018. Honey bee (Apis mellifera) nurses do not consume pollens based on their nutritional quality. PLOS: January 11, 2018. https://doi.org/10.1371/journal.pone.0191050
- Papanikolaou AD, Kuhn I, Frenzel M, Kuhlmann M, Poschlod P, Potts SG, Roberts SPM, Schweiger O. 2017. Wild bee and floral diversity co-vary in response to the direct and indirect impacts of land use. Ecosphere 8(11):e02008. 1002/ecs2.2008
- Galetto L, Kevan PG. 2007. The Production of Nectar and Pollen. In JM Graham (Ed) The Hive and the Honey Bee (pp. 345-368). Hamilton, Illinois: Dadant & Sons, Inc.
- Levin MD, Haydak MH. 1957. Comparative value of different pollens in the nutrition of Osmia lignaria. Bee World 38: 221-226.
- Loper GM, Berdel RL. 1980. The effects of nine pollen diets on brood rearing of honeybees. Apidologie 11: 351-359.
- Genissel A, Aupinel P, Bressac C, Tasei JN, Chevrier C. 2002. Influence of pollen origin on performance of Bombus terrestris micro-colonies. Entomologia Experimentalis et Applicata 104:329-336.
- Alaux C, Ducloz F, Crauser D, Le Conte Y. 2010. Diet effects on honeybee immunocompetence. Biology Letters 6: 562-5.
- Sol Balbuena M, Tison L, Hahn ML, Greggers U, Menzel R, Farina WM. 2015. Effects of sublethal doses of glyphosate on honeybee navigation. Journal of Experimental Biology 218: 2799-2805.
- Ziska L H, Pettis J S, Edwards J, Hancock JE, Tomecek MB, Clark A, Polley HW. 2016. Rising atmospheric CO2 is reducing the protein concentration of a floral pollen source essential for North American bees. Proceedings of the Royal Society B: Biological Sciences 283: 1828, 20160414. http://doi.org/10.1098/rspb.2016.0414
- Thomson JD. 2010. Flowering phenology, fruiting success and progressive deterioration of pollination in an early-flowering geophyte. Philosophical Transactions of the Royal Society B: Biological Sciences 365: 3187-3199.