Wildflower is published quarterly by the Wildflower Center. Its content is national in scope with articles about the conservation and use of native plants as well as news from the Wildflower Center. A subscription is provided to Wildflower Center members as a benefit of membership.
All ABuzz - Spring 2013
Why should we care about bees? If their vital role in the survival of wildflowers isn't a compelling reason, consider breakfast. Without bees, we wouldn't have coffee, orange juice or berries, to name just a few of our favorites. And that's just the beginning.
One-third of the foods in our daily diet come from plants that rely on pollinators to set seeds and reproduce. According to a recent international study, 87.5 percent of the world's flowering plant species are pollinated by birds, butterflies, bees or other insects. In temperate zones, says bee biologist Mace Vaughan, roughly 90 percent of these pollinators are native bees. In addition, many bee species are "keystone" species, essential to keeping their ecosystem humming, or "indicator" species whose numbers offer clues to the relative health of a habitat.
Everyone knows that bees are in trouble. But while Colony Collapse Disorder (CCD) in honeybees has been threatening our food supply, it has focused new attention on the native bees that could help safeguard it. For example, long before honeybees were imported from Europe and Asia and trucked to orchards and fields, bumblebees were among the primary pollinators of apple, plum and alfalfa crops. Unfortunately, native bees are in trouble too.
How much trouble? With 4,000 species in the U.S. and some 25,000 worldwide, a definitive answer is elusive. "We have the most data on bumblebees, and we know they're declining at an alarming rate," says Vaughan, who is pollinator conservation program director at the Xerces Society for Invertebrate Conservation, based in Portland, Ore. "Several species that were once common have virtually disappeared from their former territory."
Theories abound, but no one can fully explain bee decline. Vaughan believes native bee populations have been reduced over some time by the combined effects of diseases and pesticides, the weather extremes of climate change and, perhaps most important, habitat loss.
Wholesale habitat clearing for industrial, residential or agricultural development is the most obvious threat to plants and pollinators, but more subtle threats can be devastating too. When the field next to a reserve becomes a golf course, not only do bees have fewer plants to sustain them, but they're subject to chemical assaults from pesticides and herbicides. If the creation of that golf course eliminates one wildflower species from the area, a bee species that feeds only on that flower may become locally extinct. Anything that threatens wildflowers threatens bees. Conversely, creating, protecting and restoring wildflower rich habitat is an important way to support the bees that remain and help to ensure that we humans can continue to enjoy our favorite foods.
Foraging habitat for bees must be pesticide-free. Organic pesticides, such as those containing pyrethrum, are as lethal to bees as synthetics. Good bee habitat provides a safe nesting area (see sidebar) and offers flowers from which to gather nectar and pollen. Nectar provides sugar primarily fuel for the adult bee while protein-rich pollen, which also contains vitamins, minerals, lipids and sterols, is carried back to the nest with some nectar to feed the next generation. As bees gather pollen in gardens or meadows, they flit from flower to flower, leaving some pollen behind, if all goes well from the plant's point of view. This results in plant fertilization.
Native plants are the best source of food for native bees which stands to reason, because the bees and the flowers that sustain them, and whose reproductive success the bees in turn ensure, evolved together. Bees are classified as specialists or generalists. "Specialist bees evolved either with specific plants or a specific genus of plants," explains Vaughan. "Generalists seem to have evolved with the plants of a particular habitat."
University of California, Berkeley, entomologist Gordon Frankie has shown that native bees are six times more likely to visit the native plants with which they have evolved than to visit alien species. Other studies also have shown that native bees show a statistical preference for native flowers.
"Flowers grown almost anywhere will be an important food source for bees," says Matthew Shepherd, communications director at Xerces. "Even a small area planted with the right flowers will be beneficial, because each patch will add to the mosaic of available habitat."
Urban gardeners have a role to play too. Think beyond the yard to roof gardens and public spaces like schoolyards and city parks. A research team led by Frankie has been studying bees in northern California residential areas since the late 1990s and offers guidance for city-dwelling bee supporters at www.helpabee.org.
"If every house had a nice plot with some good wildflowers for native bees, that would have a huge impact," says Vaughan. "This isn't a panacea," he cautions, "but it's part of the solution overall." It's a solution in which everyone can participate.
Planning a bee garden is a little different than designing according to personal preferences, but there's no reason a bee garden shouldn't be beautiful. And it doesn't have to be a meadow. Even formal designs can be adapted to bee-friendly principles, some of which many gardeners already follow.
Use clumps or drifts of individual species. "Flowers clustered into clumps of one species will attract more pollinators than individual plants scattered throughout the habitat," Shepherd advises. Vaughan recommends an area at least 2 to 3 feet in diameter. For small spaces, choose prolific bloomers.
Select diverse flower shapes. Some bee species are generalists, others feed from a small group of flower species and a few rely on a single species. Each species evolved to forage in flowers with particular shapes. So different species have different preferences, based on their own anatomical strengths and limitations and the structure of the flowers with which they evolved. Bumblebees, for example, have long tongues that can reach the nectar pools in deep or complex flowers like penstemon, lobelia and lupine. Shorter-tongued sweat bees hang out where the nectar is in easy reach, often on composites like asters. For the most bees per bloom, try a locally native mint or sunflower. "Both are phenomenal for attracting a great variety of bees," says Mace.
Plan a succession of plants that will flower from early spring through fall. Different bee species fly at different times of the year, so the longer you can offer flowers, the more bees you can help. Bumblebees, first to arrive in spring, last to die off in fall, rely heavily on early- and late-blooming flowers.
Choose colors bees like. Because of their eye structure, bees can't see red. They are most often attracted to flowers in the blue spectrum, like wild blue indigo and closed gentian, through the whole range of purples in coneflowers, liatris and asters, as well as yellows like creosote bush and goldenrod. Bees also are drawn to white flowers such as those of most native berries, from tiny ground-hugging wild strawberry to tree-size elder.
Plant for variety, and consider trees and shrubs, including those not usually featured for their flowers. Willow species are bee favorites. These and other woody plantings add complexity and structural diversity. "Specialist bees don't need variety for good nutrition, but generalists like bumblebees do," says Vaughan. "No two plant species provide the same combination of nutrients. And a diversity of plants will attract a diversity of bees." If you think groundcover to treetops, you can create a substantial and diverse foraging habitat in a small area.
Think local. Your local bees are likely to prefer a flower native to your area to a native from another region. In comparison with cultivars and exotics, native plants across the board are more resilient to environmental stressors, such as the drought much of the country experienced in 2012. "In the garden, most native plants will survive drought with even a tiny bit of water every few weeks," says Vaughan. To get it right, consult your local chapter of the Native Plant Society or the Center's Native Plant Information Network at www.wildflower.org/explore.
Is it working? If bees are buzzing your flowers, you've done it. "If you notice new species of bees you haven't seen before, you've done very well," says Vaughan. If your flowers look great but you don't see bees, try observing at different times of day, he advises. "Some plants, like tarweed on the West Coast, produce an abundance of pollen from dawn until 8 a.m. and then nothing until the next morning."
If you happen to be growing vegetables nearby, here's another way to measure your bee-habitat success: Attract bees with wildflowers and they'll make their way into the veggie garden too. Getting a bumper crop of tomatoes? It might be because you have bees.