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The Plight of the Bumblebee

By Douglas McInnis

With bees and other pollinators disappearing at an alarming rate, our fruits and vegetables may be in jeopardy.

EACH FALL, Hawaiian biologists from the National Tropical Botanical Garden rappel over the edge of some of the world's tallest sea cliffs. Dangling from ropes 3,000 feet above the Pacific Ocean, they carefully brush pollen onto a few trumpet-shaped flowers clinging to the cliffs.
The Hawaiian flowers are two rare species of Brighamia, of which only about 200 plants remain in the wild. Scientists believe the blossoms were once pollinated by a type of moth that is now extinct. No other pollinator has taken its place, so without the annual intervention of death defying human pollinators, the plants face extinction.
If the Hawaiian moth were the only missing pollinator, scientists might take little notice. But it is not. Habitat destruction, agricultural chemicals, and other human influences are taking a heavy toll on the world's pollinators.
In the United States, the most obvious sign of trouble is the decimation of the honeybee, the chief pollinator for commercial farms as well as backyard gardens. During the past three years' beekeepers nationwide have lost about half of their hives to a lethal combination of pesticides, two types of parasitic mites, and harsh winter weather. Wild honeybees have fared even worse; an estimated 90 percent have died.

Worldwide, losses are also mounting among many lesser known pollinators, such as monarch butterflies, wasps, flies, beetles, and vertebrate species-- including hummingbirds, flying foxes, geckos, and weasels.

Although some plants-notably grains and cereals-are pollinated by wind, the vast majority rely on insects or other animals for pollination. About 90 percent of the world's 250,000 flowering plant species, including at least 800 species that are cultivated by humans for food, need pollinators. More than 100 of these food crops including squash, cranberries, blueberries, and cashews -depend heavily on wild pollinators, whose value to agriculture has been conservatively estimated at more than $4 billion per year.
Many other plants, including carrots, can yield fruits or vegetables without pollinators but need them to produce seeds for future crops. And some important medicinal plants, including foxglove (from which the heartstimulating drug digitalis is derived), also depend on animal pollination. Without animal pollinated fruits and vegetables, our diets would be high in carbohydrates and low in vitamins, minerals, and antioxidants. "Believe me, a diet based entirely upon wind pollinated foods such as rice, barley, oats, sorghum, corn, and millet is pretty boring," says Stephen Buchmann, a U.S. Agriculture Department researcher and coauthor of The Forgotten Pollinators.
Too often, an endangered species of pollinator is nearly extinct by the time a public alarm sounds. And until recently, few scientists even noticed the larger trend."I had no way of knowing that what I saw with flying foxes in Samoa was happening in Ontario with bees," says Brigham Young University botanist Ian Cox, who has documented losses of flying foxes, a large bat that is an important pollinator of Pacific island rainforests. "We always saw-pollination as a little tidbit of natural history and never realized that it had ecosystem-wide consequences."
To understand why pollinators are so critical, it's important to know how pollination works. In a nutshell, pollination is the way plants have sex. Some plants don't need a partner; they have all the equipment for both the male and female roles, and can pollinate themselves. But most plants require a middleman to bring pollen from the male part of one plant to the female part of another.
Animals play this role inadvertently, picking up pollen as they feed on nectar, and spreading the pollen from plant to plant. The better the pollinator does the job, the more seeds are produced and the higher the yield or the better the fruit.
When one pollinator is lost, another may take its place. But the replacement may not be as effective, because the plant-pollinator interaction in many cases is like a lock and key. Some pollinators have long tongues, curved bills, or other body parts that lend themselves to working with the configurations of a particular plant.
In the United States, rabbit-eye blueberry production thrives when the southeastern blueberry bee goes to work, but plummets if the common honeybee tries. "The vaseshaped flower of the rabbit-eye blueberry is a little bit too deep for the honeybee's tongue," explains James Cane, associate professor of entomology at Aubum University. "For her to reach the nectar at the base of the flower, she's got to cram her head through the opening of the flower. Honeybees aren't happy with that kind of treatment, and they move on."

Cane says that the better adapted southeastern blueberry bee will in its lifetime, set $20 worth of fruit. "If you're a grower and you see these bees flying through your orchard, you can replace each bee with a $20 bill."

Nonetheless, some growers have unwittingly sabotaged the southeastern blueberry bee and their own prosperity. The desire to produce more blueberries prompted the growers to enlarge their fields by clearing and planting adjacent areas. In the process, they destroyed the nesting sites of the bees best suited to pollinate their crops.
But the most devastating blow to American agriculture is the growing loss of the honeybee.
Imported from Europe in the 1620s the honeybee thrived here and proved valuable for pollinating a wide variety of crops. The honeybee's communal nature makes it easy for beekeepers to manage huge colonies that can be trucked from farm to farm, although colonies of escaped honeybees can also be found in the wild.
Unfortunately, the honeybee's crosscountry travels have helped disperse two mites-a tracheal mite that suffocates the bee by attacking its respiratory system, and a bloodsucking varroa mite that attaches itself to the bee's back. Neither mite is native to the United States, which has banned bee imports since the 1920s to prevent such outbreaks, but pollination experts think the mites arrived with illegally imported bees and spread to wild honeybees.
Healthy colonies of domesticated honeybees are critical for a variety of crops. Modern farms are so huge and densely planted that wild pollinators can't possibly do the job. Pollinating California's almond crop, for example, requires about 500,000 hives filled with tiny migrant workers.

But parasites are not the only threat to bees and other pollinators. Manmade chemicals also play a role. Rachel Carson's bestselling book Silent Spring is best remembered for linking the nowbanned pesticide DDT to bird deaths more than three decades ago. But the book also gave early warning that pesticides threatened to decimate pollinators and produce "fruitless falls."

DDT has since been banned in the United States and Canada. Unfortunately, while DDT replacements may be safer for birds, some have proved far more deadly than DDT for Pollinators. "They're not a magic bullet aimed at just one organism. They're quite toxic to a broad sweep of organisms, including bees and butterflies," says Buchmann. One early case occurred in Canada's New Brunswick province when blueberry production plunged from 5.5 million pounds in 1969 to 1.5 million pounds the following year. Canadian researcher Peter Kevan traced the falling production to the use of Fenitrothion, the pesticide that replaced DDT for controlling spruce bud worms in the province's forests. Fenitrothion killed blueberry-pollinating bees along with the worms.
The problem isn't so easy to pinpoint when pollinators are killed by the slow march of development. For instance, migratory pollinators such as the monarch butterfly must contend with the shrinking number of stopover points on their annual flights from Mexico to as far north as Canada, and back again. In Hawaii, pollinators began to die when imported goats, cattle, deer, and pigs damaged forests.
In the American Midwest, development repeatedly altered the land, first when vast forests were felled for farms, and again as agriculture gave way to homes, shopping centers, and factories.
When a pollinator is lost entirely, some plants may have the ability to evolve so that they can perform both the male and female functions, scientists theorize. But such transformations take time. "I doubt enough plants could switch to self-fertilization quickly enough to solve the pollinator crisis some experts foresee," says Kent Holsinger, an associate professor of biology at the University of Connecticut.
Self-fertilizing plants may not be as healthy either. Inbreeding among animals generally produces less vigorous, less fertile offspring, and the same holds for plants.
Individuals can take steps to help pollinators survive. Backyard gardeners can attract pollinators by putting up thick wooden boards drilled with holes of different sizes; the holes are potential nest sites for bees and wasps. A milk carton packed with paper drinking straws also provides good homes for pollinators. Larger-scale efforts to conserve habitat and limit the use of agricultural chemicals are also essential.
Scientists warn that if we don't take steps to protect pollinators, we may face a tasteless future, devoid of some of the fruits and vegetables we enjoy today. "Pollination is amazing," says Cox. "It's sort of like the sun rising. We've always taken it for granted. But if you lose a species of bee, you can't get it back. I think it's safe to say we're in trouble. What we don't know is how big the trouble is."

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