The whole food diet for bees

As I walked into Jeri Wright’s bee lab on a mid-October morning, two things were bothering me. The lab, where Wright and her team investigate bee nutrition, is in the far north of England, part of Newcastle University’s Institute of Neuroscience. The bees live on the roof and the tail end of Hurricane Ophelia was about to blow through. So would there be any bees to see, or would they be tucked up warm and safe for winter? And if there were bees still actively helping Wright’s team unravel the complexities of a bee’s diet — how to avoid being stung?

It didn’t look promising. There were no bees yet — so while we waited, the team happily shared their expert knowledge of bee stings. The trick, they said, is to choose a friendly sort of honeybee, such as the carniolan subspecies (Apis mellifera carnica) — and catch them young, before their stingers are rigid. If you must handle older bees, put them on ice until they are chilled and drowsy.

And then, bang on cue, the bees arrived. A new brood had just chewed their way out of their pupal cells inside one of the laboratory’s hives. Wright’s team leapt into action, marshalling batches of bees into see-through boxes and spooning gloopy mixtures of pollen, fats and sugars into feeders. What these mini-colonies chose to eat over the coming weeks would feed a study of how honeybees balance their diet.

Across the lab, orderly rows of slim plastic tubes stood waiting. Each would soon be occupied by a single bee, held firm, snug and ready for tests on the ability to learn which flowers offer nutrients that the bee most needs. The tubes were lovingly hand-sculpted for comfort, with a bee-sized neck rest on one side and a plunging neckline on the other to allow room for the rise and fall of a bee’s breathing body. Each tube also flew a thin pennant of duct tape: part of a bee harness.

I’d never harnessed a bee, so I was keen to learn how it’s done. You take a sleepy bee and maneuver it gently until its head and first pair of legs emerge at the top of the tube. Flip the sticky strip over its “shoulders” and secure it, then wrap a second strip over the back to prevent escape. It sounded tricky, but these experts can get 60 done in no time.

Wright’s team spends its days probing the honeybee’s gastronomic habits for good reason. Bees, both wild and domesticated, are in serious trouble and there’s an urgent need to understand what’s gone so badly wrong for them. The past few decades have seen bee populations plummet alarmingly. Some of the thousands of species of wild bees have gone extinct, while in North America and Europe, stocks of managed honeybees have fallen dramatically.

Three-quarters of all food crops — together providing a third of the world’s food supply — depend on pollination by insects, mostly bees. Their services are also crucial for maintaining the diversity of the world’s wild plants and the stability of ecosystems. The scale of bee loss has led to fears of a global pollination crisis in which crop yields begin to fall as demand for food rises, prompting international and national initiatives and a raft of research programs to tackle the issue.

What’s to blame? There is no single suspect: All the evidence points to a combination of interacting stresses — exposure to insecticides, the mysterious colony collapse disorder and infection by novel pathogens and parasites, including the aptly named destructor mite (Varroa destructor). And piling on the pressure is malnutrition — not just failure to get enough food, but also lack of the right mix of food, which bees need just as we do. Too much of one thing and not enough of another makes for unhealthy bees, more vulnerable to pests, pathogens and poisons. “It’s more and more accepted that poor nutrition is an important player in the decline of bees,” says Wright. “So it’s important to know more about what bees need.”

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Providing for the family

Most research into bee nutrition focuses on the bee species we know best, the domesticated honeybee (Apis mellifera). The basics go like this:

Bees feed on nectar and pollen collected by foragers — older worker bees with beefy flight muscles. Some foragers gather nectar, which they store in an elastic pouch in the gut known as a “honey stomach”; others collect pollen grains, packing them in “baskets” on their rear legs. Loaded to capacity, foragers return to the colony where nectar-carriers pass their load to “receiver bees” to store as honey, while pollen-bearers offload their hauls into cells to form what’s known as bee bread. “Nurse bees” draw on both to keep the colony fed, and have the job of transforming pollen into royal jelly, which they feed to larvae and to the queen, drones and older worker bees.

Today, a much fuller picture of the bee’s needs is emerging, thanks to a global network of researchers investigating what constitutes a healthy diet, how bees achieve it — and what happens when they don’t.

Basic energy requirements are met by nectar (essentially sugar water), which provides the carbohydrate bees need for activities such as flight and keeping the colony warm. Pollen provides everything else a colony needs to thrive: proteins, fats and lipids plus an assortment of micronutrients including essential sterols, vitamins and minerals. “All these nutrients are important for different reasons at different times in the growth of the colony,” says Harmen Hendriksma, a Dutch entomologist currently working in the Toth Laboratory of Integrative Insect Sociobiology at Iowa State University.

To complicate matters, bees need carbs, proteins and fats in specific but shifting proportions according to season and what’s happening in the hive. As larvae, they require more protein and fat; as adults, their wants shift towards carbohydrates. Feeding experiments show that they try to achieve the right balance by controlling what foods they collect and eat. If caged nurse bees are offered a choice of two foods (one carb-heavy, say, and another overly rich in protein), they sample both in a proportion that helps them reach an optimal ratio.

Last year Hendriksma published work showing that when a colony is suffering a dietary deficiency, forager bees try to remedy it. He and Sharoni Shafir of the Benjamin Triwaks Bee Research Center in Rehovot, Israel, allowed free-flying honeybees to forage for a week on artificial diets that lacked one of the ten essential amino acids bees need. When the week was up, the researchers offered the bees a trio of foods: one exactly the same as before, one new but still missing the vital amino acid, and one containing the missing ingredient. They assumed bees would eat from all three, picking up at least some of the amino acid in the process. Instead, foragers more often made a beeline for the food with the missing ingredient, and collected measurably more of it. “Somehow, bees know when their food isn’t up to par and show a preference for food that counters the deficiency,” Hendriksma says.

Just how they know it and how they pick the best food is the subject of considerable head-scratching. Forager bees don’t eat the food they collect, so they may be getting feedback from those that do. New evidence suggests that when a colony is suffering a nutrient deficiency, nurse bees signal their approval when foragers return with more-suitable pollen — by doing the characteristic bee waggle-dance more enthusiastically. “We don’t know much about this yet, but it’s a hot topic among bee researchers,” says Wright.

One thing they do know is what happens when bees can’t manage their diet. Malnourished bees are smaller and weaker, less fertile and shorter-lived. “If they don’t get the right nutrients, they stop producing brood and eventually the colony dies,” says Wright. Experiments suggest that malnourished bees succumb more readily to viral infections, carry more parasites and are less able to detoxify insecticides. Without the right sterols, bees can’t make the hormones responsible for molting, and if they don’t molt, they can’t grow. Deprived of omega-3 fatty acids, they can’t learn properly, a disaster for forager bees that must learn the scent or color of food flowers and provide fellow workers with precise coordinates of their location.

The impact of poor diet stretches down the generations, as honeybee ecologist Heather Mattila of Wellesley College in Massachusetts recently showed. Mattila looked at the fate of worker larvae that had been raised by pollen-starved nurse bees. The larvae grew into underweight bees that went on to become poor foragers. Some were never seen foraging at all; some managed one day’s work before dying. Those that did forage made a poor job of it: When they returned to the hive, they either failed to perform the waggle dance that points other bees to a good source of food, or gave hopeless directions.

Scratched from the menu

For many millions of years, bees satisfied their dietary needs by feeding from a variety of flowering plants, each offering nectar and pollen made to its own recipe: different types and concentrations of sugars in nectar, and in pollen, very different amounts of protein and a mixed bag of amino acids, lipids, minerals and other nutrients. But this once-extensive menu has shrunk. Land that once offered bees a smorgasbord of nectar and pollen, with a succession of new offerings from spring through fall, has been replaced by brick and concrete or crops grown in monocultures, kept free of weeds and pests with liberal applications of herbicide and insecticide. “Once, a farm would have pasture, orchards and a vegetable patch, and there would be weeds among the crops,” says Hendriksma. “All that’s disappeared.”

In the United States, around 99 percent of flower-rich prairie has vanished since European settlement, and in the last century, the United Kingdom has lost 97 percent of its flower-filled meadows. “The nutritional diversity is just not there for the bees,” says Gloria DeGrandi-Hoffman, research leader at the US Department of Agriculture’s Carl Hayden Bee Research Center in Tucson, Arizona. “For us, the more foods you have on your plate, the better balanced your diet. It’s the same for bees.”

Some crops do produce plenty of bee food, but the quality varies, the diet is monotonous and stocks usually run out after a few weeks, leaving bees at risk of starving. In the US, where provision of pollination services for agriculture is big business, beekeepers transport their colonies all over the continent to pollinate one major crop after another. “In early spring they’ll go to California for the almonds. There are almonds as far as the eye can see — and nothing else, not even weeds,” says Wright. Job done, maybe it’s off to Maine for the blueberries and then on to Florida to pollinate citrus flowers.

At each stop, there’s just one dish on the menu and often not a healthy one. “Apple orchards, for instance, produce lots of nectar and pollen,” says ecologist Bill Kunin of the University of Leeds in England. “But the pollen is nutritionally very one-sided. Of the ten essential amino acids insects need, two are present in huge amounts, one in an OK amount and seven are terrible. A bee couldn’t raise a brood just on apple pollen.”

It doesn’t take an Einstein to work out that a landscape minus its flowers equals fewer flower-feeding insects, including bees. “You pretty much don’t have to do the experiments,” says Wright. But scientists did. Last year, Kunin and colleagues in the UK showed how the long-term decline in pollinators mirrored the shrinking supply of nectar, a task that required crunching 80 years’ worth of data. As part of the UK Insect Pollinators Initiative, they measured the amount of nectar produced in a year by the vast majority of the UK’s flowering plants. Then they scrutinized national vegetation surveys carried out since the 1930s to see how the abundance and diversity of wildflowers had changed.

They found that from the 1930s to 1978 — a period of rapid agricultural change — national nectar production fell by 32 percent, then stabilized and rose again slightly. Diversity of nectar-producing flowers declined through the entire period. Today, half of all nectar in the UK is produced by just four species.

And if the shortage of wildflowers doesn’t make a foraging bee’s life difficult enough, modern agriculture exposes it to another hazard that makes it still harder to find good food. Pesticides are strongly implicated in the decline of pollinators, particularly neonicotinoids, the world’s most widely used type of insecticide. These nerve toxins find their way into nectar and pollen, and even low-level exposure interferes with bee learning and memory, disrupting their ability to forage.

There’s still much to learn about the nutritional challenges facing bees, but with each shock announcement about the disappearance of insect pollinators — October’s headline-grabber was news of a 75 percent fall in Germany’s flying insects in the past 27 years — the clamor to do something grows louder. And one way to ease the pressure on bees is to improve their diet.

Commercial beekeepers already feed their bees protein supplements when nectar and pollen are scarce. But supplements are no substitute: They lack essential compounds peculiar to pollen, and bees have trouble digesting the protein. “There’s nothing in a protein supplement diet that a bee eats naturally,” says DeGrandi-Hoffman. “And it’s difficult to build strong, healthy colonies on such diets.”

New, improved recipes that include pollen could help. “But we don’t know the minimum amount of pollen needed to make it work,” DeGrandi-Hoffman says. “The type of pollen in an artificial diet also needs to be tailored to the season. The needs of the colony are very dynamic. They are different in spring when the colony is growing than when they are preparing for winter.”

Bigger buffet, better bees

A better strategy is to add more healthy options to the bees’ menu by providing greater diversity of natural forage. There are already many initiatives to do just that: sowing wildflowers in unused patches of farmland, around field boundaries, along hedgerows, in urban backyards and other green spaces; and cutting back on mowing in parks and along roadsides to give wildflowers the chance to bloom. Thanks to so much research into the nutritional value of different sorts of pollen, such schemes may soon be able to tailor seed mixes to best meet bees’ needs. “At Newcastle, we’ve analyzed the nectar and pollen of most of the UK’s wildflowers and will soon be able to recommend what to plant to provide the best forage,” says insect physiologist Dan Stabler, a member of the Newcastle bee team.

Providing more wildflowers makes instinctive sense. But how much of an impact can such measures have? Researchers in Iowa are beginning to get a good idea. The state was once covered by flower-filled prairie. Today 90 percent of it is farmland, mostly planted with corn and soybeans. Over the last decade, each winter has seen the death of around 60 percent of Iowa’s honeybee colonies.

Since 2007, a team from Iowa State University has been measuring the benefits of planting strips of prairie vegetation amid corn and soy crops. The recently published findings are hugely encouraging. By replacing 10 percent of the cropland with prairie strips, they bumped up the number of pollinators 350 percent, and the diversity of insects 260 percent.

Now the team is testing whether honeybees living in Iowa’s soyfields can be restored to good health with a “holiday” among prairie flowers. “Once soy stops providing nectar, honeybee colonies start to lose a lot of weight, and have a slim chance of surviving winter,” says Hendriksma. “Already, we’ve seen that bees that are moved from soyfields to prairie habitat start growing into healthier bees. It was as if they had a second youth — and they have a better prospect of surviving winter.”

From a windswept lab in the north of England to Iowa’s rolling farmland, bees are sending out the same message: They need a varied and balanced diet, and that means being able to forage among the profusion of flowers that existed before humans so radically altered the landscape they live in. “We need to grow pollinator plants in the landscape, and we need to do it urgently,” DeGrandi-Hoffman says. “If we want to preserve our pollinators and keep commercial beekeeping alive, we have to act now.”