By Brian DeVore
It's a crisp October morning at a cafe in St. Paul's Swede Hollow neighborhood, and the insects are here for the lunch special: all the nectar they can eat. Entomologist John Luhman scans a flower and vegetable garden adjacent to the cafe patio as bees, wasps, and hover flies pay their bill by transporting a few grains of pollen from plant to plant.
At one point, a common eastern bumblebee (Bombus impatiens) plunges into the depths of a snapdragon. And then, like a car backing out of a leafy garage, it slowly withdraws, its hairy legs dusty with protein gold. The bee will carry some of the pollen back to its nest -- a hole in the ground, such as an abandoned rodent den. As the bee continues to collect pollen along the way, some of the pollen will rub off on the next snapdragon it visits. Thus, by being forced to do some tricky navigation, the bee pollinates the flowers, forging a key link in the plant's chain of reproduction.
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Plants play such tricks in the pollination game for good reason: It's the basis of their survival. Pollinators -- wild insects and domesticated honeybees -- help 70 percent of the world's wild and cultivated flowering plants reproduce. Every third bite of our food is a result, directly or indirectly, of an insect transporting pollen. Without pollinators we would have to say goodbye to (or do with a lot less of) an array of fruits, vegetables, legumes, and alfalfa, as well as many wildflowers.
Bees purposefully collect pollen to feed on its rich protein, but a variety of creatures participate in the pollination parade. Butterflies, moths, wasps, flies, ants, bats, hummingbirds, and yes, mosquitoes, play a role in plant pollination, though they do not feed on pollen.
"Pollinators are really a keystone group that other organisms rely on," says Eric Mader, assistant professor of extension at the University of Minnesota and the national pollinator outreach coordinator at the Xerces Society for Invertebrate Conservation. "Pollination is almost as essential to life as water and oxygen."
Some pollinators are gasping. Scientists, farmers, beekeepers, and conservationists are alarmed at recent pollinator declines around the world, including Minnesota. The National Academy of Sciences reported in 2007 that long-term population trends for North American wild pollinators are "demonstrably downward." At least four dozen species of wild bees in this country are on the Xerces Society's "red list" of at-risk pollinators. Though multiple causes could lead to population declines, many wild bees are suffering from the loss of natural habitat.
Because wild bees are integral to a healthy ecosystem, any conservation initiatives that help them could have a positive effect on other parts of the environment. And because these denizens of field and forest play such a crucial role in food production, people have compelling reasons to conserve and propagate wild pollinator habitat not only in natural areas but also on farms, along roads, even in back yards.
Bumblebees are among the most efficient pollinators present in Minnesota, and three species appear to be declining. The yellow-banded bumblebee (Bombus terricola) and the rusty-patched bumblebee (Bombus affinis) haven't been officially sighted here since 1999 and 2003, respectively, according to the Xerces Society. The American bumblebee (Bombus pensylvanicus) may also be in trouble. "When you think about three bumblebees declining in a state where you have 12 to 13 bumblebee species overall, that's major," says Mader. The waning of these species could adversely affect crops of cranberries, alfalfa seed, blueberries, apples, melons, tomatoes, and wildflowers, among other plants.
The decline of wild bees comes at a time when their domestic cousins are also struggling. Domesticated honeybees, imported from Europe in the 1600s, provide the majority of managed pollination to cultivated crops in this country. A few years ago, beekeepers began losing honeybees to a condition called Colony Collapse Disorder, or CCD. Nationwide, they lost a third of their honeybees between 2007 and 2008, with many of these losses due to CCD. Fortunately beekeepers were able to make up most of these losses, but the threat of CCD persists. University of Minnesota entomologist Marla Spivak says CCD is likely brought on by numerous factors -- disease, parasites, pesticides, lack of good foraging areas leading to poor nutrition, and increased workload -- which all add up and stress out these apian workhorses.
One way to reduce stress on honeybees is to tap into help from the wild, says Spivak. Of the estimated $20 billion in services pollinators provide U.S. crops annually, around 15 percent comes from wild insects. In the upper Midwest, the potential for native species to transport pollen is huge. Together, Minnesota, Wisconsin, and Michigan have more than 500 species of native bees.
In many ways, native bees are superior pollinators to domesticated honeybees. Bumblebees will fly in bad weather when their domestic cousins are holed up. As few as 250 orchard mason bees (Osmia lignaria) -- native metallic-tinted bees present throughout the country, including Minnesota -- can pollinate an acre of apples, a job that could require 40,000 honeybees. A bumblebee can cling to inverted flowers such as blueberries and efficiently buzz pollinate -- shake pollen off by vibrating its wings. On vegetable farms in New Jersey and Pennsylvania, wild bees visited flowers more frequently than did honeybees in three out of four crops studied, according to the Journal of Applied Ecology.
To help pollinators, experts say: Plant flowers. But a monoculture of mums won't fly. Bees need a succession of plants blooming from April until frost. Goldenrod and asters blooming in September are gold mines for pollinators looking for high-energy food before winter.
Though native bees can help pollinate cultivated crops, they need regular access to natural foraging and nesting areas. In southern and western Minnesota, they need prairies, wildflower meadows, and brushy fencerows. Brushlands and shrubby areas harbor pollinators in the northern region. Manicured lawns and pine plantations may be green, but without blooming plants they might as well be concrete as far as pollinators are concerned.
As diverse natural habitats have declined, so have pollinators, say entomologists. "Rather than look at individual insects that are threatened, just look at their habitat," says Luhman, a biological control expert with the Minnesota Department of Agriculture. "If the habitat is in trouble, chances are the insects that like that habitat are in trouble."
The synergistic relationships between pollinators and natural habitat are becoming increasingly clear, says Minnesota Department of Natural Resources botanist Welby Smith. In the United Kingdom, a decline in bee diversity has resulted in the diminished distribution of 75 species of wild plants that require insects for pollination, according to the journal Science.
"Native pollinators pretty much evolved in association with these diverse wild plant communities, and so their presence can tell us a lot about a habitat's overall health," says Smith. "In order to protect the habitat of the wild plants, we need to protect the wild pollinators."
All pollinators, wild and domesticated alike, require a seasonal succession of blooming plants to get through spring, summer, and fall -- and prepare for winter. Colonies of wild pollinators such as bumblebees are annual, meaning they are formed when a solitary queen emerges in May or June. Throughout the season, colonies must collect large amounts of pollen (a source of protein) and nectar (carbohydrates) to produce new queens. Bumblebees can be seen as late as October clinging to sunflowers, attempting to glean the last bit of sustenance from the plants before the season shuts down. Plants that bloom early in spring and late in fall are critical to pollinator populations.
Pollinators also need a habitat free of chemicals. Pesticides can be particularly dangerous to bees as they forage in sprayed areas, collecting and storing chemical-saturated pollen. A Penn State University study released in August 2008 showed honeybee hives across the country had low levels of over 70 pesticides.
Minnesota farms have the potential to provide more pollinator habitat. The Natural Resources Conservation Service has started training staff to help farmers establish and maintain pollinator-friendly habitats. Native wildflowers can provide excellent foraging for pollinators. So can cover crops that are allowed to flower. Reducing tillage causes less disruption of nesting habitat, because two-thirds of bees nest underground. Leaving logs, stumps, snags, and clumps of grass will provide nesting sites for the rest. Fencerows with willow, dogwood, or other flowering plants provide foraging habitat on working farmland without disrupting the agronomic productivity. For producers raising pollinator-dependent crops such as apples, blueberries, pumpkins, canola, or sunflowers, there's an added bonus: "Growers will have a way of creating a healthy population of their own pollinators, reducing dependency on rented hives," says Mader.
Current NRCS guidelines in many states recommend at least one to two acres of pollinator habitat for every 25 acres of pollination-dependent cropland. And it needs to be relatively close: Bumblebees will range up to a mile from their nest to forage, while for tiny solitary bees (some species are small enough to ride on a bumblebee's antenna), a flight of 200 yards would be a major undertaking.
Roadsides, ditches, and buffer strips can also serve as wild pollinator habitat. Over twice as many total number of wild bees and almost 50 percent more bee species were found along highways planted to native prairie when compared with weedy byways, according to a 2008 University of Kansas study.
During the past two decades the DNR Roadsides for Wildlife program has promoted the establishment and protection of natural vegetation along roads. "Even the narrowest strip of wildflowers will help bees, especially if you have native wildflowers blooming throughout the growing season," says Carmelita Nelson, DNR Roadsides for Wildlife coordinator. Nelson estimates that the southern two-thirds of Minnesota has 525,000 roadside acres that could be planted with native wildflowers to provide prime pollinator habitat.
Botanists and entomologists say even a few square yards of native flowering plants in a yard, garden, or vacant lot can make a difference. This kind of ecological restoration can truly be a win-win, says Spivak of the University of Minnesota.
"It would give the wild pollinators nesting and feeding sites. It would help the domestic bees. It would help everything," Spivak says, hesitating for a moment before adding one more benefit: "Isn't there a theory that when you plant flowers, there's less crime?"
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