The Buzz on Native Pollinators
As European honeybees decline, indigenous bees and other pollinating animals can provide a backup—with a little help from their human friends
WHEN ECOLOGIST Rachel Winfree set out to survey native bees in the Delaware Valley of New Jersey and Pennsylvania, she was not optimistic about her results. Not only is the region far from any known hot spots of bee diversity, such as the U.S. Southwest, “New Jersey is also the most densely populated state in the country,” says Winfree, an assistant professor in the Department of Entomology at Rutgers University. “I was worried that after getting funding and hiring a staff, the project would turn out to be a waste of time.”
Her fears were unfounded. “We found bees everywhere,” says Winfree—thousands of individuals of 46 different species. More surprising, she and her colleagues discovered that the number of flower visits by these natives was sufficient to fully pollinate the watermelon crop on 21 of 23 farms in her study region.
Gleaning such data was the goal of Winfree’s work. As European honeybees decline in a mysterious phenomenon known as Colony Collapse Disorder (CCD), “I wanted to find out whether native bees could fill in for them,” she says. While Winfree cautions against extrapolating her results too broadly to other crops in other parts of the country, “if we lost all honeybees in this region to CCD tomorrow, between 88 and 90 percent of the watermelon crop would be fine,” she says. “Native bees are providing a backup plan—for free.”
Winfree’s results, published in Ecology Letters, have generated an excited buzz among native pollinator proponents, a diverse group of scientists, conservationists, gardening enthusiasts and others who are sponsoring activities nationwide this June to celebrate the third official National Pollinator Week. Yet even as they applaud her study—and others that show wild bees contribute to the production of crops such as blueberries, cranberries, peppers, tomatoes, alfalfa and squash—they worry about the welfare of these unsung natives.
“There has been little effort to document the long-term status of pollinator populations in the United States,” says biologist May Berenbaum, chairman of the Department of Entomology at the University of Illinois at Urbana-Champaign. Yet in a 2006 National Academy of Sciences (NAS) report, a scientific committee chaired by Berenbaum found that in cases where data do exist, pollinator population trends are “demonstrably downward.”
Pollinators comprise a diversity of wild creatures, from birds and bats to butterflies, moths, beetles, flies and even the odd land mammal or reptile. But “there’s no question that bees are the most important in most ecosystems,” says Winfree, who calls the insects “the 800-pound gorillas” of the pollinator world. Unlike social honeybees, imported to North America in the 1600s, the majority of the continent’s native bees are solitary, nesting in burrows on the ground or small holes in wood rather than building hives. Worldwide, there are some 20,000 bee species, 4,000 of them found in North America.
Bees and other pollinators are essential to human survival. “Without them, you’d lose most of your plants, and ultimately everything else,” says Winfree. To produce seeds and reproduce, three-quarters of the world’s flowering plant species rely on animal pollinators. (The others use the less precise methods of wind or water to transfer pollen between male and female flower parts.) Animal-dependent plants include more than two-thirds of the world’s crop species, whose fruits and seeds provide more than 30 percent of the foods and beverages we consume. Scientists estimate that in the United States alone, native bees perform up to $3 billion worth of pollination services annually.
Natural ecosystems and their inhabitants also rely on pollinators. Many North American songbirds, for instance, feed on the fruits, seeds and berries of plants pollinated by animals. Pollinating insects themselves, especially their plump larvae, provide protein for adult songbirds and their fast-growing fledglings. Even the notoriously carnivorous grizzly bear depends more directly on pollinators than one might expect. According to wildlife ecologist Kimberly Winter, NWF’s habitat programs manager, in some places between 80 and 90 percent of the bear’s diet is made up of fruits, nuts, bulbs and roots of animal-pollinated plants. On an ecosystem level, “losing a pollinator can have a domino effect on countless other species,” she says.
To detect pollinator population trends, long-term surveys are essential. “The few hardy souls who have undertaken such studies are finding indisputable evidence of declines,” says Berenbaum. She cites the work of biologist Arthur Shapiro, a professor of evolution and ecology at the University of California–Davis who has been monitoring butterflies on fixed transects across the state for the past 37 years. Many of the several dozen species he has tracked have declined, some dramatically. “Butterflies that were once considered utterly common are going into a tailspin, and no one knows why,” says Shapiro.
In addition to butterflies, the NAS report provides evidence of decline in three other pollinator groups: hummingbirds, bats and—especially—bumblebees. A 2008 report from the Xerces Society for Invertebrate Conservation, a nonprofit based in Portland, Oregon, paints an even bleaker picture of the familiar, fuzzy insects’ fate. Compiling data from more than three dozen scientists and “citizen monitors” across the country, the report concludes that populations of three formerly common species—the rusty-patched, yellowbanded and western bumblebee—have dropped drastically over the past decade. A fourth species, Franklin’s bumblebee (restricted to coastal Oregon and Northern California), has only been seen once in the past several years.
Though the jury is still out on the cause of these declines, the most likely culprit is an exotic disease introduced by commercially reared bumblebees, says the society’s executive director, Scott Hoffman Black. Between 1992 and 1994, he explains, queens of the western bumblebee, a species commonly used to pollinate greenhouse tomatoes, were shipped to Europe to produce colonies subsequently shipped back to U.S. farms. Scientists suspect the bees picked up a fungal disease from European bees, then spread it to wild bumblebees across the country as colonies were moved among commercial growers. (All beleaguered species are closely related to those that spent time in Europe.) “Like Native Americans decimated by smallpox brought in by Europeans, our native bees have no resistance to exotic diseases,” says Hoffman Black.
Beyond disease—suspected as a major cause of CCD in honeybees—blame for pollinator declines runs the gamut: habitat loss and fragmentation, introduced species, pesticides and global warming. “But in most cases, we don’t know,” says Laurie Davies Adams, executive director of the Pollinator Partnership, a San Francisco-based nonprofit working to raise awareness about pollinators’ plight. “We simply haven’t paid enough attention.”
There are a handful of exceptions. In the U.S. Southwest, two species of nectar-feeding bats—the lesser long-nosed and Mexican long-tongued bat—have declined due to destruction of their roosting caves. Pesticides are implicated in problems facing several native insects, though given the animals’ special sensitivity to these chemicals, “pathetically few toxicity studies have been conducted, even on honeybees,” says Berenbaum.
Like virtually all living things, pollinators are also threatened by global warming. According to biologist David Inouye of the University of Maryland, some are already beginning to respond to climate change. In the Colorado Rockies, for example, he and his colleagues recently surveyed the altitudinal distribution of several bumblebee species at the Rocky Mountain Biological Laboratory (RMBL). They compared the results with those of a survey they had conducted along the same transects as graduate students more than 30 years ago—and found that at least one species has shifted its range upslope by 1,500 feet.
Pollinators are particularly at risk to indirect effects of warming—when changes in temperature or precipitation cause shifts in the distribution of plants or the timing of nectar they produce. In another study at the Colorado lab, Inouye and RMBL colleague Billy Barr found that springtime emergence of Milbert’s tortoiseshell butterfly has been getting progressively earlier since the 1970s. Yet blooming time of the region’s spring wildflowers has not kept up. The findings demonstrate that “pollinators and plants do not respond the same way to environmental changes caused by global warming,” says Inouye. “This means they may lose the synchrony they once had.” Inouye is particularly concerned about hummingbirds—important wildflower pollinators—that migrate thousands of miles between winter habitats in the Tropics and breeding grounds in North America. Research shows that tropical and temperate ecosystems are responding very differently to global warming, and there’s no way a hummingbird wintering in Colombia would be able predict what the weather is like in Colorado.
Fortunately, there’s good news as well. Thanks to the NAS report and efforts of conservationists, there has been a flowering of appreciation for native pollinators in recent years. Concern about European honeybees has also helped. CCD, first detected soon after the report’s publication, had “a silver lining,” says Hoffman Black. “Now many more people know that their food is pollinated, and that we need bees and other animals to do that.”
Davies Adams agrees that “we see more interest in pollinators than just a few years ago—and more resources to help people help pollinators.” Among her organization’s activities is the creation of a series of ecoregional planting guides to advise gardeners on planting native species for insects and other animals. Launched in 2008, the final set of 32 guides is scheduled to be completed this June. The Xerces Society has published the Pollinator Conservation Handbook as well as a series of guides for farmers and managers of parks, golf courses and other lands.
Perhaps the biggest coup scored by pollinator proponents came last year with congressional reauthorization of the Farm Bill, which for the first time has provided specific financial incentives to growers who restore habitat for pollinators and authorized $100 million for research on the animals. Winfree has applied for funding through the law to continue working with USDA’s Natural Resources Conservation Service in New Jersey on combinations of plants that attract the greatest diversity of pollinators. She suspects the reason she found so many bees in her own study is because the region’s small farms are nestled among suburban gardens and scraps of native vegetation, habitats that provide nesting sites and additional food for the insects. Similar research conducted within vast monocultures of California’s Central Valley has so far been less encouraging.
Winfree, who launched her project in 2006, obtained equally promising results during the 2007 and 2008 growing seasons. “When it comes to human disturbances like fragmentation,” she says, “some bees may turn out to be more robust than some larger animals like birds and mammals. And that would be very good news for conservation.”
Senior Editor Laura Tangley provides food, water and nesting sites for pollinators in her own yard.
How to Plant for Pollinators
“The neat thing about pollinator conservation is that anyone, from the owner of a golf course to an apartment dweller with a window box, can do something to help,” says Scott Hoffman Black, executive director of the Xerces Society for Invertebrate Conservation. All it takes is to provide appropriate food and habitat for bees, butterflies and other pollinating species—and to avoid using the pesticides that harm them.
“Being pollinator-friendly also means you are being wildlife-friendly,” says Kimberly Winter, NWF’s habitats program manager. “And you are creating a sustainable ecosystem in your own backyard.”
Here are a few suggestions to get started:
- To provide pollinators with the best sources of food—and to prevent the spread of invasive species—choose as many plants native to your region as possible. For specific recommendations, consult the Pollinator Partnership’s free ecoregional planting guide for your area; all you need is a zip code.
- Select plants that provide a lot of nectar and pollen. Many ornamentals have been specifically bred to produce little or none of these essential foods.
- Plant a diversity of species so your yard will provide bees, butterflies and other animals with nectar and pollen from spring through fall. To attract bats and nocturnal moths, consider night-blooming plants in addition to day-bloomers.
- Be a “messy” gardener: Leave some patches of unmulched soil and brush piles that bees, birds and other animals can use to construct nests. Consider building or purchasing a bee house for wood-nesting wasps and bees.
- During hot, dry periods, provide water in shallow birdbaths or pools where pollinators can easily alight. Some wasps and bees need mud to build their nests, and butterflies like to gather in muddy puddles.
- Do not use pesticides, and encourage your neighbors to reduce their reliance on these chemicals. According to Winter, more pesticides are used in urban areas today than in agricultural regions of the United States.
For more tips, check out these sites: www.nwf.org/gardenforwildlife and www.xerces.org.
NWF Priority: Protecting Native Pollinators
Through its Certified Wildlife Habitat™ program, NWF encourages the creation of habitat suitable for bees, birds, butterflies and other pollinators, and educates landowners about appropriate host plants as well as the risks of using pesticides. The program also offers all the information needed to make your own yard welcoming to pollinators and other native animals.