Most of the native bees were solitary varieties: individuals that make their own nests in the soil rather than living in social hives. The most common species was Andrena carolina, a medium-size brown bee that gathers pollen only from plants in the blueberry family, including cranberry, huckleberry and azalea. Overall, though, the bulk of the bee species were generalists, collecting pollen from a wide range of plants.
A few years ago Isaacs, like Kremen, decided to find out how much wild bees contribute to blueberry pollination. Researchers have estimated the value of wild bee crop pollination in the U.S. at $3.1 billion a year; honeybee pollination is worth roughly $15 billion. Isaacs discovered that in small fields of less than an acre, wild bees took care of 82 percent of pollination. In big fields—1.5 to 16 acres—wild bees accomplished only 11 percent of pollination. Because the bulk of Michigan's blueberries are grown on large farms, Isaacs estimated that wild bees provide just 12 percent of the state's blueberry pollination. That is nowhere near enough to serve as insurance against honeybee declines, he says.
Yet if farmers had an economic incentive to add habitat—on fallow fields or in areas that are frost-prone, have poor soil or are otherwise unfit for blueberries—the story could be different. A graduate student in Isaacs's lab investigated pollination in five blueberry fields of up to 10 acres, with up to two acres planted with native Michigan wildflowers in a mix that blooms from spring until early fall. The study, not yet published or peer-reviewed, showed that booming native bee populations increased blueberry yields to such an extent that farmers could recoup the cost of establishing habitat in three to four years. Setting up habitat costs around $600 per acre, Isaacs says, but the usda's Natural Resource Conservation Service has programs that will cover between 50 and 90 percent of the expense.
Researchers continue to seek out the best ways to nurture native bees, but farmers can start improving crop pollination now. Gordon Frankie, a U.C. Berkeley bee biologist whose office sits directly above Kremen's, has spent more than a decade designing bee habitats for urban gardens, and now he has begun applying that knowledge to agriculture. “You can't have a one-size-fits-all approach,” Frankie says. “Each farm will be different, with different needs. But the idea is that we'll be able to write a prescription for any farm—you need this, this and this.” On four farms in Brentwood, Calif., about an hour outside Berkeley, he has planted a mix of shrubs and forbs near blackberry bushes and cherry trees. Frankie hopes to create a series of case studies—“an orchard cropper, a row cropper, 25 acres, 145 acres”—that he can use to reach out to similar types of farms.
Meanwhile, using data from Kremen, Williams and others, the Xerces Society has partnered with the usda's Natural Resource Conservation Service to build a “pollinator-enhancement program.” Since 2009 the group has trained more than 20,000 people—farmers, usda representatives, cooperative extension agents—in the value of native bees. It has also developed a set of concrete guidelines for farmers, explaining how to plan a meadow to attract native bees and to minimize the effect of pesticides.
A farm set up to welcome native bees could, ultimately, be better off than one reliant on honeybees. More than 20,000 species of native bees are abuzz around the world; collectively, they are exceedingly more likely to recover from disease or extreme weather than any one species of pollinator. Kremen believes the hedgerows are only a first step. The real challenge will be scaling up to 1,000-acre farms, bringing pollinators back to massive monoculture operations. She envisions a system where farms are divided into blocks that bloom at different times, so there is always food for pollinators to eat.