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One Picture


Pollination
Plan Bee
While the honeybee’s collapse—and its potentially devastating impact on our food supply—has been making news, scientists are quietly doing groundbreaking fieldwork that shows native bees can step into the breach. First, though, they need a little help from us.

 

Threading through dewy watermelon vines in the cool pre-dawn hours, ecologist Rachael Winfree slips bags made of bridal veil over flowers on the verge of bloom. There is some urgency to the work because when the sun comes up over this New Jersey farm, the blossoms will open for just a single day. Winfree wants to know which of the roughly 350 species of bees found in the area visit the watermelons and help pollinate the crop. The first step is beating the bees to the blossoms.

Soon rumbling bumblebees, sweat bees, and occasionally leafcutter bees are buzzing among the nectar-rich flowers. The handmade bags use bridal veil because it is the perfect gauge of mesh to keep blooms untouched by even tiny, iridescent green bees.

What Winfree is doing is actually a meticulous accounting exercise. When a veil is removed, the uncovered flower is allowed a visit from a single bee. The species group is noted. Then the flower is covered again and sent to Winfree’s lab at Princeton University, where the postdoctoral fellow at the University of California-Berkeley is a visiting researcher. There the grains of pollen are counted under a microscope. In this test, long-horned bees delivered 118 grains per visit; honeybees, 41; and bumblebees, 53. On some visits a bee may arrive drenched in pollen from another flower; on other visits it may be carrying none. Therefore it can take anywhere from 10 to 60 visits to a single flower to deliver the roughly 1,400 grains of pollen needed to produce a full-sized melon.

Twenty-three farms, 46 species of native bees, 15,000 flowers, and hundreds of hours of pollen counting later, a clear picture emerges from the hubbub among the watermelon vines. Native bees collectively provided the full pollination needed for a marketable watermelon crop at about 90 percent of the farms Winfree studied in New Jersey and Pennsylvania. Honeybees alone would have provided the necessary full pollination on 78 percent of the farms. Taken together, the honeybees and the natives would have fully pollinated all of the farms in 2005 and 71 percent in 2007.

For the past year the honeybee’s free fall nationwide and its impact on our food supply have been making headlines. “It has become clear now that relying on the honeybees alone is risky business,” says Claire Kremen, an ecologist at the University of California-Berkeley who worked with Winfree on the bee research in New Jersey and Pennsylvania. “This is a weak link in our agricultural chain.” What is beginning to receive more attention is the encouraging news that she and Winfree confirmed in those New Jersey and Pennsylvania fields: Native bees may be capable of substituting for beleaguered honeybees.

Indeed, in many of these small watermelon fields, natives provided all the pollination required. That doesn’t necessarily mean they could replace managed honeybees in other situations. Watermelon flowers are particularly attractive to a variety of bee species, and the fields where the research was done were about four acres each or less, which is on the small end for commercial growing. But it does suggest that native bees provide more pollination backup for honeybees than is generally thought. “This is an insurance policy that farmers may not know they have,” says Winfree. The key is habitat, either close to or even within agricultural lands (between fields, for example, or alongside irrigation ditches). Providing this habitat can safeguard the diversity of native bees while at the same time supporting the nation’s food and our farmers.

No native bee species live in large perennial hives or gather extensive stores of honey the way honeybees do (though without the communal home and honey to protect, native bees win points for stinging less). Rather they tend to be solitary, tunneling narrow burrows in the ground or the soft pith of twigs or nesting in preexisting cavities in trees or rotting wood. Natives are already major pollinators for some crops, including blueberries, blackberries, raspberries, cranberries, peppers, alfalfa, squash, and certain kinds of tomatoes. In some cases they’re better at jobs honeybees are routinely used to perform. Blue orchard bees, for example, are much more efficient almond pollinators than honeybees on a bee-per-bee basis. What honeybees have going for them—and what makes it easy to overlook their relative inefficiency—is that they can be managed and moved from place to place in massive numbers.

“Honeybees are in effect six-legged livestock,” reported University of Illinois entomologist May Berenbaum when she testified before Congress last year about a potential pollinator crisis in this country. Honeybees, which have been managed for thousands of years, were brought to North America some 400 years ago from Europe. In recent decades, however, they have been beset by a growing number of maladies, from bacterial and viral diseases to mites and other parasites. The varroa mite, for instance, may be responsible for the near total disappearance of wild honeybee hives.

The number of managed hives has dropped by almost half, from 4 million in the 1980s to 2.4 million in 2007, and even that number required extraordinary efforts by beekeepers after as many as 30 percent of all hives were lost during the winter of 2006–2007. Up to half of those losses were due to a phenomenon called colony collapse disorder. Potential causes include a newly discovered pathogen, stress from poor nutrition, the constant relocation from field to field through the year—or the cumulative effect of all the other stresses. Exposure to pesticides may also be partly to blame.

Fortunately, since diseases tend not to jump species, the plagues on honeybees aren’t affecting wild bees. The primary threat to many of the 4,000 bee species native to the United States—and the estimated 30,000 species worldwide—is habitat loss, specifically fewer places to forage and nest. Given that three-quarters of the flowering plant species on the planet rely on pollinators and that there are reports of pollinator declines on four continents, concern about a pollination crisis is well founded.

Pollination—the reproductive process by which pollen with the male genetic information is carried to the plant’s female parts—happens in a variety of ways. Water carries pollen to some aquatic plants. Cereals such as rice, wheat, and corn are wind-pollinated. Some plants, including peanuts and lettuce, with male and female organs on the same flower, are self-pollinating. Others, such as melons, have separate male and female flowers. Many fruits, vegetables, and nuts depend on pollinators. Beetles, birds, bats, and butterflies are important contributors, as are ants, moths, and wasps. Even lizards, monkeys, and bears can get into the act. But in the end, bees do most of the pollinating.

After nine years spent working on the role of native pollinators in agricultural areas as an academic adviser, collaborator, and leading researcher, Kremen has become a point person in the field. “Not all plants rely on pollinators to the same degree,” she says, “so it is hard to come up with a single number. But we can say up to 35 percent of our food benefits from pollinators to some degree, including about 75 percent of our fruits and vegetables. It isn’t just how many calories but also what food—some of it is food we like and a lot of it is food that has important micronutrients, vitamins in particular.

Native bees, of course, are important in the larger scheme of things. As Berenbaum pointed out in her testimony to Congress, native bees “serve as keystone species in most terrestrial ecosystems in that the services they provide allow most plants to reproduce and maintain genetic diversity. These plants in turn provide food and shelter for animals; fruits and seeds produced by insect pollination are a major part of the diet of approximately 25 percent of birds and mammals ranging from red-backed voles to grizzly bears.”

 

The eastern farms where Winfree works tend to be knitted into a patchwork landscape of forested, developed, and agricultural plots that are home to a variety of crops. That polyculture makes it easier for bees, because flowers bloom at different times, yielding a steady and varied food source for them to supplement what’s available in adjacent native habitat.

Kremen has been working at the opposite extreme, parts of which may be the least hospitable agricultural habitat for native bees. In the summer heat and dry ground of California’s Yolo County, vast fields spread west to the pale foothills that separate the Central Valley’s farming communities from the San Francisco Bay Area, about an hour away. There are almond, walnut, and stone fruit orchards here as well as fields of tomatoes, sunflowers, melons, rice, and alfalfa. Only instead of plots of a few acres, the fields can be planted in quarter sections (160 acres) or sometimes even full sections (640 acres, or a square mile). This is food production on a massive scale, a place where neat rows of a single crop fill the entire field and often grow to within feet of the road.

When irrigation was brought to the region, it meant the end for many of the dry grasslands and forests of valley oaks that were once common here. The reengineering has helped create one of the country’s most agriculturally productive regions. Not unlike a factory floor, anything that could gum up the works around the fields has been cleared out. In a practice known as clean farming, the banks of irrigation canals and the ribbons of space between crop and pavement are nothing more than bare ground. (“If it isn’t a crop, you spray it or disc it,” one farmer says.)

Unfortunately, massive monocultures, without even weedy patches along their borders, are about as friendly to wild bees as a parking lot. This is a big problem, because bees need food for their entire active period, which for some Central Valley species can be 10 months a year. “Pollinators are key rivets in the ecosystem,” Winfree explains. “If you lose the rivets, the machine falls apart.” Adds Kremen, “It used to be that farmers didn’t manage pollinators at all because all of the pollination was from native pollinators. That has changed because agriculture has changed.” Now fields far from any natural habitat have few if any wild bees, and honeybee hives are trucked into agricultural areas across the country to service blooming fields and orchards.

The most expensive crop to pollinate is almonds, which have such a brief but simultaneous bloom that 1.3 million honeybee hives are trucked into California from around the country. As recently as 2000, this cost about $40 a hive. Today, as honeybees struggle and almond cultivation expands, the price has jumped to about $140 a hive. Considering the scale of this effort, even a small contribution by native pollinators would be economically significant.

Honeybees, road-tripping from state to state, with overly busy schedules and an overreliance on the imbalanced nutrition available from monocrops, are having an increasingly hard time keeping up. “What we’re seeing with pollinators is just another indicator on the nonsustainability of this type of agriculture,” Kremen says. “We need to slowly bring back sustainable elements that make economic sense for the farmers.”

 

Driving through Yolo County, it’s hard to miss the egg-size tomatoes speckling the sides of the highways, where they have been spilled by open tandem-trailer trucks bouncing out of fields and onto county roads. This is where the so-called processing tomatoes—varieties with names like AB 2, Heinz 9780, Peto Hypeel 303, Campbell CXD 179—that go into ketchup, soup, and salsa come from. They have been bred to withstand harvesting by a machine that looks like a cross between an amusement park ride and a rolling factory. The Dr. Seussian contraption hoovers its way through the densely planted rows of heavily laden tomato plants and leaves behind a bare field. Inside, paddles, controlled by electronic eyes, slap away green tomatoes and pass red ones onto a conveyor belt. The belt runs between a team of workers who stand on a platform, inspecting the tomatoes as the whole production roars through the field, harvesting up to 60 tons an hour. During high season this carnival ride runs 24 hours a day on some farms.

The ingenuity and scale of such an industrial approach makes it easy to forget that tomatoes are part of a natural system. One plus for processing tomatoes is that they’re often self-pollinated, but other kinds—cherry varieties—have a different flower morphology that makes them less productive without pollinators. And here’s where the unique abilities of some native bees really shine.

Sarah Greenleaf, an ecologist at Sacramento State University who works with Kremen, zooms her focus from the outsized scale of the tomato harvest onto the bell of an individual cherry tomato blossom. Each flower has a fused tubelike anther that holds the pollen and surrounds a pistil, which must be fertilized. To release the pollen, bees do something called buzz pollination, Greenleaf says. “What they do is land on the flower and grab it really tight. Then they beat their wings. They don’t fly anywhere but they vibrate like crazy, and that gets the pollen out of the flower.” For her research Greenleaf, too, had to buzz-pollinate the flowers in her own way. “Without vibrating the flower you can’t get the pollen. The only way to get it out is to vibrate the flower with a frequency of about middle C. If you take a tuning fork and get it vibrating, then hold it up against the flower, you will see a little stream of pollen come shooting out.”

She’s illustrating the native bee’s specialized skill. “Honeybees can’t buzz-pollinate,” says Greenleaf. “They can’t get the pollen. Tomato flowers don’t have nectar. There is no reason for honeybees to visit tomatoes, and they don’t. If you put honeybee hives out to pollinate your tomatoes, you get absolutely no benefit, so farmers don’t do it,” she says.

“Because honeybees are the only bee that most farmers manage for row-crop pollination, they assume tomatoes don’t need bees,” she continues. “But there are all these other bees that can and do visit tomatoes that aren’t managed.” All tomato varieties can produce some fruit in the absence of pollinators, but Greenleaf has found that native pollinators can significantly improve cherry tomato crops, potentially by providing more complete pollination. If a cucumber is less than fully pollinated, it will be curved, not straight; a partially pollinated apple can have a flat side or a tilt. When buzz pollinators are present, 45 percent more flowers produce tomatoes and the weight of the tomatoes nearly doubles.

Greenleaf’s research with hybrid sunflowers revealed yet another example of the value of native pollinators. Honeybees can be so focused on collecting pollen for the hive that they go only to male flowers. By neglecting the female flowers, of course, there’s no pollination. She discovered that honeybees are five times more productive as sunflower pollinators when native bees are present. “Wild bees aren’t doing much pollination themselves,” she says. “They are much more important by disrupting the honeybees.”

The upshot of these scientific studies, Greenleaf says, is that “there are more wild bees in fields that are closer to natural habitat.” Some wild bees are able to forage only a few hundred yards from their nest, so to increase the number of native pollinators, there has to be more habitat. Luckily, bees don’t necessarily have to have pristine land; in fact, fragmented, mixed-use landscapes seem to work well for many species. “One thing farmers can do,” says Greenleaf, “is plant native plants on their farms, and retain patches of natural habitat in places that can’t be farmed, like along streams and ditches.”

 

Bruce Rominger walks beside an irrigation slough, on a bank recently replanted with native grasses, shrubs, and trees. The fifth-generation Yolo County farmer and his brother work 3,000 acres of grapes, tomatoes, sunflowers, and other crops, some organic, some conventional. He is collaborating with Audubon California on several habitat-restoration projects on the farm. At the edge of a field, Rominger points to a “bee condo”—a post topped with a block of wood drilled with rows of holes of various sizes. It was set out only a few weeks ago, he says, but already most of the holes are filled with various species of wood-nesting native bees.

Vance Russell, director of Audubon California’s Landowner Stewardship Program, says, “Farmers are usually very busy and concerned about their bottom line. They often don’t have the time, technical expertise, or the funding to do restoration or conservation projects, so that is where we come in.”

For the past nine years the Audubon program has been assisting farmers and ranchers to restore habitat on their land.  “The project has evolved from working with a handful of farmers scattered all over to working with groups of contiguous landowners and entire watersheds trying to get at greater habitat connectivity over a much larger area,” Russell says. Since 2003 Audubon and the farmers have been collaborating with the Xerces Society, tapping its expertise in invertebrate conservation to make sure the restoration work benefits pollinators, too.

Large tracts of land are important for many conservation purposes, but for insects even small patches can make a difference. Kremen explains how focusing on pollinators allows a different approach. “If you want to deliver pollination services into an agricultural landscape,” she says, “you need to have a lot of fingers, narrow areas, like riparian corridors, even fragments, which is pretty much the opposite of all tenets of conservation biology, where you are trying to avoid edge effects with larger chunks of habitat.”

In July 2007 Audubon California purchased the 6,800-acre Bobcat Ranch in western Yolo County. Some of the ranch is actively grazed by cattle. Much of it is blue-oak woodlands. The aim here is to demonstrate the economic viability of integrating ranching and conservation practices so that the ranch could be an anchor for a much larger swath of protected uplands.

Such projects please Kremen. “Places like the Bobcat Ranch are really great sources of strong, diverse bee populations,” she says. Perhaps the ranch can become the palm of a hand whose fingers, formed by hedgerows on adjoining land and by restored streams and irrigation canals, spread out of the hills across the valley floor. With those corridors, she says, “you are making that environment much more of a friendly place for bees, but also for other species, too, like birds, that might use some of those resources as they are moving between bigger conservation areas.”

Like the Romingers, Frank Muller and his brothers grow both organic and conventional crops in Yolo County, including walnuts, wine grapes, tomatoes, and sunflowers. Four years ago, encouraged by one of their farm managers, the Mullers planted native flowers and shrubs along the border of a field to attract insects that fight crop pests in hopes of reducing the need to spray. “You start a project trying to benefit yourself in one area and it turns out to have multiple benefits. That’s the nature of how these things are: Not only do they attract beneficial insects. They attract pollinators, and they’re habitat for birds and wildlife,” Muller says. “It was the edge of a field. The soils weren’t that great and sometimes it flooded in the winter, so we really don’t feel like we lost anything by taking it out of production.”

The Mullers, with the help of Audubon California and the Xerces Society, have supplemented their conserved area each year, adding a more complete suite of blooming plants. They have now created five acres of habitat, including a two-acre island in a slough. Muller has noticed the pollinators concentrated in these set-asides. “As time goes on and they build up nesting sites, you start to see more and more of them.” Muller adds, “There are all sorts of bugs that I’ve never seen before.” Along with the insects may come birds that were not common before the conservation efforts: golden-crowned sparrows, lazuli buntings, blue grosbeaks, house and purple finches, Lincoln’s sparrows, and California quail.

For Muller it is a different way to appreciate his land. “We firmly believe in this. We spend a lot of time on the farm, not just working but living. My wife and I go out there. It’s incredible: No matter what time of year it is, there’s something flowering.”

For years farmers have been able to find ample advice about managing honeybees: where to rent hives, how many hives are needed for this crop in this size field, and other technical matters. Now, as honeybee populations plummet and our pollination problems become ever clearer, we need a similar plan—call it Plan B—with native bees at its center. It should piece together various parts—what crop is being pollinated, what kind of habitat will attract the most beneficial species, what farming practices best promote native bee populations—into a coherent and actionable whole. Wild bees may not be able to replace their imported cousins, but it’s become increasingly clear—through the work of Kremen, Winfree, Greenleaf, and others in watermelon, tomato, sunflower, canola, blueberry, and cranberry fields across the country—that providing habitat for native pollinators around farmland, where economics and shorter-term pragmatism dictate decisions, may actually be the kind of conservation that pays.

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Ted O’Callahan is a Connecticut-based freelance writer.

WHAT YOU CAN DO

In 2003 the Xerces Society launched the California Agricultural Pollinator Project in collaboration with scientists from the University of California-Berkeley, the Center for Land-Based Learning, and Audubon California. Xerces, whose mission is the conservation of invertebrate biodiversity, including native pollinators and their habitat, offers a wealth of information on this issue. California Audubon also offers information for farmers and gardeners looking to attract native pollinators. The USDA’s Natural Resources Conservation Service has a lot of useful information as well.

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