It’s a warm, sunny day in April, and the California lilac (Ceanothus) bush in my San Francisco backyard is humming. Hordes of fat, fuzzy bumblebees swarm its blue blossoms, collecting a good dusting of pollen to share as they bumble from flower to flower. If I rouse myself to look around a bit, I might find a tiny solitary bee or two curled up in a checkerbloom flower, lounging after a good meal, or some leaf-cutter bees carefully excising Clarkia leaves to use as nesting material. A bright orange California poppy flower might sport an equally brilliant green sweat bee. All this bee bliss going on under my nose is a lovely harbinger of spring, but it has been carefully orchestrated: my husband, a conservation biologist and bee booster, has chosen plants specifically to attract bees to our little backyard ecosystem.

The larger world has not been so kind to bees in recent years. Last October, the National Research Council of the National Academy of Sciences (NAS), in its report “Status of Pollinators in North America,” warned that populations of bees and other pollinators, including butterflies, bats, and hummingbirds, are declining. Honeybees have suffered periodic mass die-offs from diseases and parasites, and most recently have been abandoning hives for reasons that are not understood. This phenomenon, now known as Colony Collapse Disorder (CCD), has afflicted about a fourth of all bee colonies across the country, Troy Fore, executive director of the American Beekeeping Federation, estimated in late April. “A lot of beekeepers have lost 40 to 50 percent of their hives,” he said, and some have reported losing 80 to 90 percent.

Between 1947 and 2005, the number of honey-producing commercial honeybee colonies (a colony is the population of a hive) in the United States dropped by more than 40 percent, from 5.9 million to 2.4 million, according to the NAS report. Other pollinator losses are largely undocumented, but nevertheless were reported as “demonstrably downward” for some species. The decline has been recognized since at least 1996, the year Stephen Buchmann and Gary Nabhan’s book The Forgotten Pollinators was published. The authors stated that “a pollination crisis has now become obvious in rural as well as urban settings not only in North America but on other continents as well.”

Buchmann and Nabhan also pointed out that pollination is “a process that not only keeps us fed and clothed but feeds our domesticated animals and their wild cousins as well.” Honeybees and other pollinators are essential to about three-fourths of the flowering plants in the world, some 250,000 species, including many of the fruits and vegetables that are most important to us.

But as more agricultural and wild lands disappear under pavement, less and less habitat remains for bees to forage and nest in, and what is left is often fragmented, so that it’s difficult for bees to move among habitats as different plants come into bloom. Modern agricultural practices such as monocropping--growing just one crop from fencerow to fencerow--and intensive chemical use have made large swaths of the remaining green space hostile territory for the tiny pollinators.

Honeybees’ Stressful Lives
In the 1980s, two deadly parasitic mites spread across the United States, wreaking havoc on both managed and feral honeybees. Between 1981 and 2005, the number of commercial honeybee colonies dropped by about a third, with many of the losses attributable to the mites. Other diseases and pests have also taken their toll, as has competition from aggressive Africanized bees, which have spread through several southern U.S. states, including southern California, since the early 1990s.

In fall 2006 beekeepers began reporting another calamity: they were finding many hives empty except for the queen, a few young adult bees (and then only sometimes), and the brood--eggs, larvae, and pupae. Plentiful food remained, however, and no dead bees were found either in the hives or nearby. Normally, other insects would immediately move in to take the food of a severely weakened or dying colony, but with CCD this “robbing” is delayed, suggesting that other insects were avoiding the abandoned hives.

Sporadic incidents of hive abandonment have occurred in the past, but nothing on the present scale has been reported. “This is the worst,” Fore said. So far it seems that the beekeepers suffering the heaviest losses are large-scale commercial operations that truck their hives from state to state to pollinate various crops.

Shortly after the first reports of CCD, a working group was formed to study the phenomenon, develop strategies to address it, share and disseminate information, and raise funds for research. The Colony Collapse Disorder Working Group brought together university researchers, agricultural extension educators, and state regulatory officials. Researchers are looking at several possible causes, including parasites and diseases, pathogens, poor nutrition, lack of genetic diversity of bees, increased levels of stress in adult bees, and chemical contamination.

One theory gaining ground among researchers is that a combination of causes has pushed bee colonies beyond their ability to recover. “We think this could be the ‘perfect storm’ for bees,” said Kevin Hackett, who leads the research programs on bees and pollination for the U.S. Department of Agriculture’s Agricultural Research Service (ARS). “It could be the tipping point, where the colonies just can’t fight back.”

Many commercially managed honeybees live stressful lives. Commercial beekeepers today often have thousands of hives--the biggest have as many as 60,000--and a healthy hive may house 50,000 to 60,000 adult bees in summer, at the peak of their population. During pollination season (which varies depending on the crops being served), many beekeepers pack their hives onto trucks and transport them for hundreds, sometimes thousands, of miles. “They’re never really in one spot for long,” said Rodney Gubbels, a small-scale beekeeper who has 2,000 or so hives based near Livermore, in Contra Costa County, and trucks his bees to crops in California and Oregon.

In transit bees go without food or water and may suffer from both hot and cold weather. If conditions are poor when the bees arrive--if there’s been a drought that’s reduced the floral resources, for example, or weather conditions are bad--the colonies can be further weakened by malnutrition. Added to that are the pesticides and other chemicals that bees are often subjected to, which may not kill them outright but can contaminate nectar or pollen in the hive. “Bees are always picking up something--whatever people spray,” Gubbels said. A newer class of nicotine-based pesticides is suspected of interfering with the bees’ ability to forage and navigate.

All these factors can weaken the bees’ immune systems and leave them more vulnerable to disease. Beekeepers have always lost colonies over the winter, when the bees’ populations are at their lowest and most vulnerable, according to Fore. “Bees die all the time. But 10 percent winter loss used to be bad; now 15 to 20 percent isn’t unusual.”

“The bottom line is that this shows us how fragile all pollinator systems are,” said Laurie Davies Adams, executive director of the Coevolution Institute, which promotes conserving biodiversity through land stewardship, and coordinator of the North American Pollinator Protection Campaign, a coalition of researchers, conservation and environmental groups, private industry, and state and federal agencies that works to conserve and protect pollinator populations.

Pollinators Feed People
The relationship between humans and honeybees goes back a long way. Cave paintings in Europe, Africa, Asia, and Australia show prehistoric people gathering honey. The art of beekeeping dates to at least 2400 B.C., and honey, beeswax, and propolis (bee “glue,” composed mainly of resins collected from plants and used to seal cracks in the hive) have been used medicinally since 2700 B.C. Bees and honey have figured in mythology and religion. In one Egyptian myth, the tears of the sun god Ra fell to earth as bees.

The bee everyone knows best is Apis mellifera, the Western or European honeybee, which humans have domesticated and transported around the globe. “It’s virtually everywhere humans have gone, except Antarctica,” said Robbin Thorp, professor emeritus of entomology at the University of California, Davis, who studies native bees. It’s one of only about seven species considered to be true honeybees (the exact number is disputed), among more than 20,000 known bee species worldwide. Brought to North America by settlers some 400 years ago, it is now one of the most valued species, although there are more than 4,000 native bee species on the continent, some 1,600 of which can be found in California.

Close to 100 flowering crop species in the United States rely to some degree on honeybees to reproduce. Among them are almonds, apples, avocados, peaches, strawberries, citrus, broccoli, cauliflower, carrots, and squash. A report released by the Congressional Research Service in March 2007 placed the value of these pollination services to agriculture at almost $15 billion.

California grows nearly 100 percent of the nation’s almonds and some 80 percent of the world’s. The state’s $2.3-billion almond crop, its fourth-most-valuable farm commodity in 2005, grows on 580,000 acres and depends on the services of about 1.4 million honeybee colonies, almost three-fourths of the commercial bee colonies available for pollination in the entire United States. Many colonies must be trucked to California for the bloom in February and March, some coming from as far as North Dakota. California’s almond acreage already requires the services of billions of individual honeybees, and is expected to grow by another 100,000 acres by 2010, requiring more pollinators even as the bee population declines.

Agriculture in the United States does not wholly depend upon honeybees for pollination services, but their loss would be “absolutely devastating to agriculture, no doubt about it,” Adams said. No one is suggesting that the honeybee might disappear from this continent, but “they certainly aren’t on a healthy trend.”

Return of the Natives
As the problems affecting honeybees have multiplied, scientists and farmers are realizing that it’s dangerous to rely too heavily on them for crop pollination. “There’s a lot of interest now in looking at our native bees and seeing which ones can be managed as pollinators,” said Thorp. Commercially managed native blue orchard bees, Osmia lignaria, are increasingly used for fruits and almonds. Alkali bees, which are native to North America, and alfalfa leaf-cutter bees, which were brought here in the first half of the 20th century, are used to pollinate alfalfa for seed.

Honeybees are good generalists--meaning they will pollinate a large variety of crops--but they’re not always the best pollinator for a particular crop. Bumblebees, for example--both native and non-native--typically pollinate greenhouse tomatoes because they are better than honeybees at the vibration or “buzz” pollination the plants require. Introducing exotic species of any animal or plant has potential pitfalls, however: Thorp and others fear that the virtual disappearance of two species of native bumblebee once common in western states may be due to a disease introduced by bumblebees imported from Europe for greenhouse pollination.

Although most of the U.S. Department of Agriculture’s $9-million bee research program is devoted to issues concerning honeybees, researchers at its Bee Biology and Systemics Laboratory in Logan, Utah, study other bees in North America, all but one species native--their dispersal and diseases, as well as how they can be managed for crop pollination. Entomologist James Cane helps farmers build up and manage populations of various native bees for pollination, and to improve land-management practices so as to encourage more bee visits--for example, by maintaining habitat for wild bees and guiding insecticide use with bees in mind. Right now he is looking at bees in the genus Osmia (there are about 140 species just in the United States) because many should be relatively easy to manage, and they pollinate a variety of crops. He’s found that Osmia aglaia, a cavity-nesting bee, for example, is a good, readily managed pollinator for raspberries and blackberries. He is helping two California start-ups build up to mass production of Osmia lignaria, the aforementioned blue orchard bees, for almond pollination.

Cane also works with alfalfa seed growers in the Pacific Northwest, who he says have had tremendous success managing alkali bees and alfalfa leaf-cutter bees to pollinate their crops. “There are 17 million nesting alkali bees in 60 square miles of Washington State, with some individual aggregations more populous than for any other bee on the planet,” all managed by private alfalfa growers, he said. “When you get down to ground level, you can’t even see through the bee bodies; it looks like heat waves. It’s just dizzying.”

Bee-Friendly Practices
Given the right conditions, wild bees could provide more of the pollination needed by agricultural crops. On farms that can attract a diverse and abundant population of wild bees, they can pollinate even such demanding crops as watermelon, which requires several insect visits, studies by University of California, Berkeley assistant professor Claire Kremen have shown. Now Kremen is involved in a habitat restoration effort on farms in California’s Central Valley that may help increase populations of wild native bees.

The Valley can be an inhospitable place for bees. Many of the farms there are conventional, growing one crop at a time with a lot of chemical inputs, whereas bees prefer floral variety and are highly sensitive to chemicals. Nevertheless, Kremen is optimistic that the landscape can be made more friendly to pollinators. In collaboration with Audubon California, the Xerces Society for Invertebrate Conservation, USDA’s Natural Resources Conservation Service, and the Center for Land-Based Learning, she is adding bee-friendly plants and practices--such as providing buffer strips and hedgerows around fields and planting cover crops--to riparian restoration projects on six conventional farms in Yolo County. Her research has shown that the food resources for bees on or near a farm are more important to their survival than whether or not the farmer uses pesticides. “We think we can make a pretty big difference by providing a variety of floral resources for the bees,” she said. If monitoring shows these practices are successful, the partners plan to help spread them to other farms in the Valley.

The Xerces Society and the Natural Resource Conservation Service are already working to include pollinators in programs that provide incentives for farmers to practice land stewardship and conservation. Implementing conservation projects on their land is “a lot of extra work for growers to take on,” said Mace Vaughan, Xerces’ conservation director. “We have to make sure there are as many reasons for them to do it as possible. Pollinators are one great reason.”

Meanwhile, Gretchen LeBuhn, an assistant professor of biology at San Francisco State University, is helping vineyard owners make their land more pollinator-friendly. The extensive destruction of oak woodlands to make way for vineyards in Napa and Sonoma Counties has fragmented bee habitat and meant a big loss of food resources for pollinators. But LeBuhn has found that vineyards can be made more inviting to bees by planting certain kinds of native plants in gardens or as cover crops and making sure that flowers are available to bees from spring through early fall. She also suggests tilling carefully--less often or less deeply, or leaving some areas untilled--to avoid disturbing the nests of ground-nesting bees, and putting native plants in available niches, such as along farm ponds. She has collaborated with several wine-grape growers on her research and has been invited to speak to groups of vineyard owners interested in adopting sustainable practices.

As meadows, fields, and woodlands continue to disappear, LeBuhn thinks urban parks and gardens might also be important habitat for native pollinators. “The potential is huge,” she said. Two of her graduate students have studied bee populations in San Francisco’s parks and natural areas to determine which characteristics are most important to the types and numbers of bees the parks support. One student tallied 70 species of native bees in 24 natural areas--an amazing number, considering San Francisco’s urban density, though fewer than the 87 species noted in historical records of the California Academy of Sciences.

In 2008 LeBuhn will launch “The Great Sunflower Project,” handing out sunflower seeds and seedlings to people and organizations around the San Francisco Bay Area who agree to plant them and record bee visits. “It really will contribute to our understanding of where bees are and how dense they are,” she said. “What we’re looking at [in all these projects] is how we can take lands that are being used by people and give them more resources for wildlife.

Gordon Frankie, a professor in U.C. Berkeley’s College of Natural Resources, is pursuing similar goals. He has recorded 82 species of native bees in the city of Berkeley, and has attracted at least 40 to the research garden he and his students planted. Frankie also surveys bee populations in other urban areas around the state, including Ukiah, Sacramento, San Luis Obispo, Santa Barbara, and Pasadena, where he counts the frequency of bee visits and evaluates the bee-attracting potential of various plants people choose for their gardens. “We’ve found that the same plants seem to attract the same bees all over the state,” he said.

Using this information, Frankie and his collaborators have been giving presentations at schools and museums about how to plant bee-friendly gardens, and are developing a website with extensive resources. He’s also working with Robbin Thorp and botanist Barbara Ertter on a book on gardening for bees for the natural history series of University of California Press.

Taking Bees Seriously
Meanwhile, both the Xerces Society and the North American Pollinator Protection Campaign are helping to translate researchers’ findings into user-friendly informational publications. Xerces has put out a series of fact sheets and booklets on pollinator-friendly practices for farmers, gardeners, and park and golf course managers, and produced the Pollinator Conservation Handbook. The Pollinator Protection Campaign is producing bioregional planting guides aimed at a variety of readers, with specific plant lists for 13 regions of the United States.

Both organizations also collect pollinator data from researchers and other sources--a critical task in an area where little data has been compiled. The NRC’s Committee on the Status of Pollinators found what its chair, May Berenbaum, described as an “extraordinary paucity” of information on pollinator populations--even honeybees, despite their importance to agriculture. European nations have much better information than the United States on historic populations of native bees, said Laurie Davies Adams of the Pollinator Protection Campaign, because they “have had an army of citizen naturalists since Victorian times. We didn’t have that, so it’s going to be very hard for us to know what’s been lost here.” The NRC report was a first step toward addressing this lack. It is “a baseline assessment of what we don’t know as well as what we do know,” said Adams.

“We don’t have all of the facts to really know what is happening to the majority of native bees in the United States,” agreed Xerces’ executive director Scott Hoffman Black. “But there’s more information than you’d think. For our Red List [of endangered pollinators] we reached out to scientists who work on bees and found that many of them have lots of data that just isn’t getting out there.”

Many others are also sounding the alarm about the need for better and more research. At a hearing before a subcommittee of the House Agricultural Committee in March 2007, Berenbaum joined other scientists, farmers, beekeepers, and conservationists in urging Congress to fund more research and conservation for both managed and wild bees. The 2002 Farm Bill will expire in September 2007, providing Congress the opportunity to make pollinator needs a high priority in the new legislation.

The attention now being paid to the problems of bees may be the proverbial silver lining to CCD’s storm cloud. Bees have been having a hard time of late, but it seems that a lot of people are going to bat for them now. “The good news is that people are really taking this seriously,” said Adams. “It’s long overdue.” Said Black: “People are finally getting it, that this is important.