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Pollination panic: honeybees are in trouble. can native pollinators rebound to fill the gap?

Outside my office window as I write this article, I can see the tomato plants in our garden heavy with fat, red fruits, like strings of big Christmas bulbs. Perhaps my favorite part of gardening is its alchemical quality, the way a crop seems to come out of nothing. The transformation of dirt and air and sunlight into a perfect tomato seems no less miraculous than the transformation of lead into gold, and it always makes me feel hopeful, secure in the natural world's generosity.

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Picking up a newspaper, though, I get a very different picture of the food supply. For nearly two years now, ominous headlines have described a mysterious ailment, colony collapse disorder (CCD), that is wiping out the honeybees that pollinate many crops. Without honeybees, the story goes, fields will be sterile, economies will collapse, food will be scarce.

But what few accounts acknowledge is that what's at risk is not itself a natural state of affairs. For one thing, in the United States, where CCD was first reported and has had its greatest impacts, honeybees are not a native species. (European colonists brought the bees to the Americas in the 1600s.) And the way most commercial crops get pollinated, with enormous populations of captive honeybees (in the United States the bees are trucked to and fro), bears little resemblance to the way things happen in the garden or, indeed, in the past. Pollination in modern agriculture isn't alchemy, it's industry.

System Bee

About three-quarters of the world's flowering plant species depend on animals to help them reproduce by moving pollen grains from the male parts of one flower to the female parts of another. (Other plants rely on wind-borne pollen or self-pollination.) Animal pollinators include birds, bats, flies, beetles, butterflies, and moths, but in most parts of the world by far the largest share of pollination is accomplished by bees.

The overall picture is similar in agriculture, with about 70 percent of the world's leading crop species benefiting from animal pollination. Animal pollination adds an estimated US $112-$200 billion annually to the value of agriculture worldwide, and animal-pollinated crops account for a little over one-third of the food supply. These crops include most fruits, vegetables, and seeds, as well as forage and hay crops fed to the animals we raise for meat and dairy products. It's not likely that we would starve to death without pollinators, since most of our calories come from wind-pollinated or self-pollinated grains like wheat, rice, and corn, but our diets would be vitamin-poor and certainly dull. Some crops, such as melons, require animal pollination in order to set fruit at all. Others, like tomatoes and raspberries, can self-pollinate but produce more, larger, or better fruit with the help of pollinators--in the case of tomatoes, 45 percent more fruit compared to self-pollination alone.

Although a few crops are pollinated by other kinds of insects--certain figs are pollinated by wasps, for instance--in general animal pollination in agriculture means bees. For most of agricultural history, the various bee species native to a given place carried out much of this work invisibly, and "pollination just ... happened," as Scott Hoffman Black, executive director of the Xerces Society, an invertebrate conservation organization, puts it. But in modern industrial agricultural systems, pollinators are almost always honey-bees, kept and managed specifically for pollination.

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In the United States, commercial production of more than 100 crops, from almonds to zucchini, is said to depend on honeybees. Many growers rent honeybees from commercial bee-keepers who truck their hives from place to place to pollinate different crops. Perhaps the most dramatic example of the scale of this pollination industry is provided by the California almond crop, which requires nearly 60 billion bees to pollinate its 223,000 hectares of blooms from mid-February to mid-March each year.

The total number of hives involved in the U.S. pollination industry has been somewhere between 2.5 million and 3 million in recent years (it's difficult to pinpoint an exact number, both because of the catastrophic losses from CCD and because the U.S. Department of Agriculture doesn't keep statistics on the use of hives for pollination). These hives are ferried along three major pollination routes--West Coast, Midwest, and East Coast--with beekeepers in each region moving their hives to warm southern climates for the winter, then following the sequence of blooms throughout the growing season. University of Illinois entomologist May Berenbaum, who chaired a National Academy of Sciences panel that recently reviewed the status of managed and native pollinators in North America, has referred to honeybees as "six-legged livestock"; they are this and an insect version of migrant farm workers as well.

Colonization

Exactly how this pollination industry, built on a single imported bee species, replaced what was once a free service provided by a diverse community of native bees is not very well documented, but most ecologists agree that it is linked to agricultural intensification. In the United States, that process began around the middle of the twentieth century, as farmers began using large quantities of organophosphate insecticides, planted large-scale crop monocultures, and adopted "clean farming" practices that scrubbed native vegetation from field margins and roadsides.

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These practices killed many native bees outright--they're as vulnerable to insecticides as any agricultural pest--and made the agricultural landscape inhospitable to those that remained. Concern about these practices and their effects on pollinators isn't new--in her 1962 ecological alarm cry Silent Spring, Rachel Carson warned of a "Fruitless Fall" that could result from the disappearance of insect pollinators.

If that "Fruitless Fall" has not--yet--occurred, it may be largely thanks to the honeybee, which farmers turned to as the ability of wild pollinators to service crops declined. The honeybee has been semi-domesticated since the time of the ancient Egyptians, but it wasn't just familiarity that determined this choice: the bees' biology is in many ways suited to the kind of agricultural system that was emerging. For example, honeybee hives can be closed up and moved out of the way when pesticides are applied to a field. (That portability also enables migratory beekeeping.) The bees are generalist pollinators, so they can be used to pollinate many different crops. And although they are not the most efficient pollinator of every crop, honeybees have strength in numbers, with 20,000 to 100,000 bees living in a single hive. "Without a doubt, if there was one bee you wanted for agriculture, it would be the honeybee," says Jim Cane, of the U.S. Department of Agriculture's Bee Biology Lab in Logan, Utah.

A similar story unfolded elsewhere in the world during the latter half of the twentieth century. Although large-scale migratory beekeeping is more or less unique to the United States, in most parts of the world commercial production of many insect-pollinated crops leans heavily on the European honeybee.

The honeybee, in other words, has become a crucial cog in the modern system of industrial agriculture. That system delivers more food, and more kinds of it, to more places, more cheaply than ever before. But that system is also vulnerable, because making a farm field into the photosynthetic equivalent of a factory floor, and pollination into a series of continent-long assembly lines, also leaches out some of the resilience characteristic of natural ecosystems.

The scientists whom I spoke to in reporting this article described the near-exclusive reliance on the honeybee as "risky" and "short-sighted." Breno Freitas, an agronomist at the Universidade Federal do Ceara in Brazil, pointed out that in nature such a high degree of specialization "usually is a very dangerous game: it works well while all the rest is in equilibrium, but runs quickly to extinction at the least disbalance." In effect, by developing an agricultural system that is heavily reliant on a single pollinator species, we humans have become riskily overspecialized. And when the human-honeybee relationship is disrupted, as it has been by colony collapse disorder, the vulnerability of that agricultural system begins to become clear.

From the beginning, CCD has been a mysterious phenomenon. It was first noticed in the fall of 2006, when a number of beekeepers found their hives empty. Bees were not so much dead as gone. The adults, normally fiercely protective of the hive (that's why bees sting) seemed to have simply flown off, abandoning the queen and young.

Scientists who examined bees from stricken hives found that they were infected by a host of ills--bacteria, fungi, viruses, parasites--almost as if the insects' immune systems had collapsed. One recently discovered pathogen, Israeli acute paralysis virus (IAPV), is strongly associated with CCD, but it doesn't seem to be the only factor involved. Some beekeepers point the finger at a new and widely used class of insecticides, neonicotinoids, that are known to affect bee behavior. Others have raised concerns about the stress on hives from repeated moves each growing season. But scientists don't know how or which of these factors combine to trigger a collapse.

What they do know is that CCD is a dramatic, and widespread, problem. During the first winter after it emerged, in 2006-07, the syndrome hit up to a quarter of U.S. beekeepers, who lost between 30 percent and 90 percent of their hives. The next year, mild winter weather aided weak colonies, but even so, nationwide losses were slightly higher than they had been the year before. CCD has been reported in 36 U.S. states. It may also be affecting bees in Canada, several European countries, India, Taiwan, and Brazil, although some of these reports are poorly documented and it is not certain they all represent CCD.

Going Native

Broadly speaking, there are two approaches to freeing agriculture from dependence on a monoculture of honeybees. One is to learn how to manage additional species of bees for the pollination of specific crops. The other is to learn how to shape the agricultural landscape so that it can once again support a diverse community of wild bees.

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The former approach offers a dizzying variety of options. There are 19,200 species of bees in the world (more than the number of bird and mammal species combined), and 4,000 native to North America alone. Unlike social, hive-dwelling honeybees, most of these bees live alone. Some tunnel into the bare ground, others nest in hollow stems or abandoned insect burrows, and still others build their own homes out of clay or excavate tunnels in wood. And while most people probably think of a bee as a black-and-yellow striped thing, they can be dark brown, black, iridescent green or blue, or striped with red, white, or orange as well.

It's unlikely that any of these bees will prove as versatile and broadly useful as the honeybee, but there's ample opportunity for matching specific native bees to specific crops. Jim Cane says, "Just about every crop is visited and effectively pollinated by a native bee"--even crops that aren't themselves native. And managing wild bees within their native range has an important advantage, reducing the danger of spreading diseases to new places and new species.

In fact, a few wild bees are already being successfully managed for crop pollination. The Japanese horn-faced bee (Osmia cornifrons) takes care of pollinating apple orchards in Japan. The alkali bee is a significant pollinator of the alfalfa seed crop in the northwestern United States; farmers encourage these bees to nest on their property by providing bare patches of salt-surfaced earth. (The alfalfa crop's other pollinator, the alfalfa leafcutter bee, is also free-living, though not native to the United States.)

"The problem is trying to provide [native] bees in adequate numbers on a reliable basis in a fairly short number of years in order to service the crop," Cane says. "You're talking millions of flowers per acre in a two-to three-week time frame, or less, for a lot of crops." On the other hand, native bees can be much more efficient pollinators of certain crops than honeybees, so you don't need as many to do the job. For example, about 750 blue orchard bees (Osmia lignaria) can pollinate a hectare of apples or almonds, a task that would require roughly 50,000 to 150,000 honeybees.

"We can manage that now for pollinating small orchards of any of your tree fruits quite successfully," Cane says of the blue orchard bee. "And you get banner yields out of it." The next step is to scale up production--despite the bee's efficiency, millions of them would be needed to pollinate all the flowers in a large commercial orchard. Two small California companies are working on how to provide these larger numbers of bees at a price that is competitive with honeybees.

Scaling up production is also Cane's challenge in working with a related bee, Osmia aglaia. The showy, emerald-green insect is a promising pollinator for blackberries and raspberries on the West Coast of the United States. And Cane is also working with another cousin of these two species (Osmia ribifloris) that has the vexing habit of flying off instead of consistently nesting in the materials he provides. "If I can solve that it's a great pollinator for blueberries," he says.

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There are bee tinkerers engaged in similar work in many corners of the world. In Brazil, Breno Freitas has found that Centris tarsata, the native pollinator of wild cashew, can survive in commercial cashew orchards if growers provide a source of floral oils, such as by interplanting their cashew trees with Caribbean cherry (itself a highly valuable crop, with vitamin C-rich fruits).

Freitas is also working with the carpenter bee that is the native pollinator of passionfruit, a crop that is now painstakingly pollinated by hand. Although Freitas says that restoring patches of forest near passionfruit fields would be the best solution, he and his team have also developed a successful nesting box for carpenter bees. The box would enable growers to take bees in and out of fields, and even hire them out to neighboring farms.

Unappreciated Assets

In certain places, native bees may already be doing more than they're getting credit for. Ecologist Rachael Winfree (now at Rutgers University) recently led a team that looked at pollination of four summer crops (tomato, watermelon, peppers, and muskmelon) at 29 farms in the Delaware Valley region of New Jersey and Pennsylvania. Winfree's team identified 54 species of wild bees that visited these crops, and found that wild bees were the most important pollinators in the system: even though managed honeybees were present on many of the farms, wild bees were responsible for 62 percent of flower visits in the study. In another study focusing specifically on watermelon, Winfree and her colleagues calculated that native bees alone could provide sufficient pollination at 90 percent of the 23 farms studied. By contrast, honeybees alone could provide sufficient pollination at only 78 percent of farms.

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"The region I work in is not typical of the way most food is produced," Winfree admits. In the Delaware Valley, most farms and farm fields are relatively small, each farmer typically grows a variety of crops, and farms are interspersed with suburbs and other types of land use (which means there are opportunities for homeowners to get involved in bee conservation, too; see sidebar, p. 27). The landscape is a bee-friendly patchwork that provides a variety of nesting habitat and floral resources distributed among different kinds of crops, weedy field margins, fallow fields, suburban neighborhoods, and seminatural habitat like old woodlots, all at a relatively small scale.

"But I think what my work shows is that native bees can be sufficient in a certain type of agricultural system, "Winfree argues. And while that system is less intensive than elsewhere, it certainly isn't rarefied. New Jersey has the highest population density of all U.S. states, and New Jersey and Pennsylvania are among the top U.S. states in production of multiple bee-pollinated crops.

The picture is different in California's Central Valley, where large growers often specialize in one particular crop and it's common for farm fields to encompass more than a square mile.(260 hectares). In that system, research led by ecologist Claire Kremen of the University of California at Berkeley has revealed that only a few wild bees, and a handful of species, can be found in the largest fields.

Yet Kremen says that even in these places, native bees show remarkable resilience; "There are some bee species that are just still out there, and that has always surprised me," she says. Look closer at these apparent ecological deserts, and you find even more bees,"tucked away in the ditches between the farm fields. It's a hopeful thing that there's this sort of little reservoir [of native bees] that maybe we can build on and promote, and maybe with a change in some of the agricultural practices we could get them back out into the farm fields too."

Similar evidence is emerging elsewhere around the globe. In Costa Rica, coffee fields located within 1 kilometer of a patch of tropical forest are visited by a diverse community of unmanaged bees (mostly composed of stingless bees, but also including feral honeybees), which fully pollinate the coffee crop. Fields located farther away from forest suffer a 20 percent reduction in yield due to lack of pollination. In Poland, areas where the agricultural landscape has retained such elements as hedgerows, weedy field margins, and native riparian vegetation, there is also a thriving community of native bees. But in Germany, where such elements have disappeared from the landscape in the course of agricultural modernization, native pollinators are in steep decline.

Resiliency

"Native bees can be a component of our agricultural systems if we do the right thing," concludes Scott Hoffman Black of the Xerces Society. Leaving weeds along field margins, letting cover crops bloom, growing a variety of crops rather than large monocultures, planting patches of native wildflowers, and installing hedgerows, to name just a few measures, would all give native bees a place within the agricultural landscape.

Moreover, many of these strategies to help bees would also benefit butterflies, birds, beetles, and native plants. That's especially important because agricultural systems affect a quarter of the Earth's land surface, according to the Millenium Ecosystem Assessment. In other words, "pollinator-friendly" farming practices would not only aid pollination of agricultural crops, but also serve as a key element in the over all conservation strategy for wild pollinators, and often aid other wild species as well.

Of course, not all farmers will be able to implement all of these practices. And researchers working on alternatives to honeybees aren't suggesting that honeybees can or should be made obsolete in agriculture, or that CCD isn't a very worrisome development. Instead, they're suggesting a shift to a kind of polyglot agricultural system. For some small-scale farms, native bees may indeed be all that's needed. For larger operations, a suite of managed bees--with honeybees filling the generalist role and other, native bees pollinating specific crops--could be augmented by free pollination services from resurgent wild pollinators. In other words, they're saying, we still have an opportunity to replace a risky monoculture with something diverse, resilient, and robust.

Sarah De Weerdt is a Seattle-based science writer specializing in biology and the environment.

For more information about issues raised in this story, visit

www.worldwatch.org/ww/bees.

RELATED ARTICLE: Support Your Local Pollinators

"A lot of bees do pretty well in patchy, semi-disturbed environments," says Claire Kremen of the University of California at Berkeley. In fact, some degree of human influence on the landscape seems to benefit many species of bees. In a survey of wild bees in southern New Jersey led by Rachael Winfree, there were more bees and more kinds of them in agricultural fields, suburbs, and urban areas than in forests. And recent research in the U.K. suggests that the best home for bumblebees is a suburb.

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Bees can even adapt to city life. The most important native pollinator on New Jersey farms, the eastern bumblebee (Bombus impatiens), is also common in Manhattan. In Berlin, a patchwork of weedy spaces scattered throughout the city supports over 250 bee species.

To be sure, there are some kinds of bees that need deep forest or other pristine habitat. But overall, it seems that most species of bees don't require large swaths of undisturbed natural landscape in order to thrive. They just need patches of different resources--nesting habitat here, foraging habitat over there, overwintering habitat somewhere else--within flying distance of one another. And that means that individuals can make a meaningful contribution to conserving native bees. The Xerces Society offers a pollinator conservation handbook and detailed fact sheets aimed at homeowners at www.xerces.org.But the basic principles are pretty simple.

First, bees need food. Fortunately, what bees need is what gardeners like: a variety of plants that bloom at different times, so that something is in flower at all times during the growing season. Choose native plants where possible (though there's no need to exclude thoughtfully selected non-native species entirely). In general, heirloom varieties are best, because they have plenty of the nectar and pollen that have been bred out of many nursery strains. For region-specific planting guidelines, visit www.pollinator.org.

Second, bees need a place to call home. Many native bees nest in the ground, so give them a patch of bare soil or a small sand pile. For wood-nesting bees, provide a bee block-a piece of wood drilled with holes of varying sizes.

Finally, bees need a refuge from insecticides. "What many people do not know is that often more pesticides are used on urban landscapes than in agricultural areas," Scott Hoffman Black says. But, he says, it's rarely necessary for individual homeowners to use them.
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Author:DeWeerdt, Sarah
Publication:World Watch
Geographic Code:4EUUK
Date:Nov 1, 2008
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