Eric Mader, University of Minnesota
Bees and other pollinators are important to our environment, providing essential services for the production of more than two-thirds of the world’s crop species. This includes products we can grow in our backyard gardens, like apples and squash, but also things like alfalfa seed— creating forage sources for America’s meat and dairy industries.
The United States alone grows more than one hundred crops that either need or benefit from pollinators. The economic value of these crops in the U.S. was estimated to be $20 billion in 2000.
But, pollinators are in trouble. While the amount of cropland requiring insect pollination is at an all-time high, the number of managed honeybee colonies in the U.S. has dropped by 50 percent since 1945. Diseases, parasitic mites and Colony Collapse Disorder have created a honeybee crisis. It may no longer be a safe assumption that bees will always be able to provide the pollination services that farmers and gardeners need.
Before the honeybee was introduced from Europe in 1622, over 4,000 species of bees were native to North America. These include a vast and colorful diversity of gentle bumble bees, mason and leafcutter bees, mining bees, sweat bees and others. Many of these bees are more efficient crop pollinators than the non-native honeybee—especially for New World fruits and vegetables like pumpkin, tomato, cranberry, and blueberry—as well as wildflowers. Even without active management these native bees are responsible for pollinating American crops worth $3 billion annually.
Unfortunately, research is also documenting declining native bee numbers across the country, including the possible extinction of some species. While our native bees are not affected by the same disease and parasite problems as honeybees, they are facing unprecedented habitat loss, pesticide threats as well as diseases.
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The decline of honeybees and our native pollinators affects us all. Fortunately, there are steps all of us can take, even in small greenspaces, to reverse this trend.
One of the challenges that bees face in agricultural landscapes is a lack of season-long food sources. Large monocultures of bee-pollinated crops like almond, canola or watermelon, may provide a few weeks of abundant food, but a lack of adjacent wild plants blooming before and after the main crop can result in a feast or famine situation that cannot support healthy pollinator numbers.
Smaller diverse garden plantings can provide the floral diversity to support resident pollinators. Bee diversity is often maximized in landscapes where 15 or more flowering plant species are present. Different bees may have different flower preferences, so provide variety. As a general rule, gardeners who want to conserve bees should provide a minimum of three plant species that bloom at any given time during the growing season; spring, summer and fall.
This season-long food supply is especially critical early and late in the year. Native bees remain dormant throughout the winter and often need immediate food sources upon emergence in the spring. Bees that over-winter as adults, like bumble bees, often need late season nectar sources to build up their energy reserves for the long winter. Similarly, honeybees spend winter inside the hive living off honey from nectar they collected over the summer months. Without enough honey, honeybees can starve over the winter resulting in the entire hive dying off.
The plants you should choose varies from region to region, but some common garden plants that support a diversity of bee species are included in Table 1.
|Bergamot (bee balm)||Monarda|
*Check your local extension office regarding suitable plants for your area.
In addition to needing season-long food, nesting locations are important. Since the majority of native bees nest in the ground, garden practices that inhibit or destroy nests, like the widespread use of plastic mulch or extensive tilling should be avoided. Woody snags and brush piles, where they can be tolerated, also support cavity-nesting bees. Often times diverse gardens with a variety of landscape features including patches of bare soil, piles of stone and clump-forming grasses can provide ample nest habitat.
One of the most significant risks to pollinators is the widespread use of insecticides. Unfortunately, many residential and garden pesticides do not include bee toxicity information on the label. Even those products that do list this threat, only mention danger to honey bees. Many native bees are much smaller than honey bees and can be affected by correspondingly smaller doses.
Even many products approved for organic gardening, such as rotenone and spinosad, are very dangerous to bees. Some researchers believe widespread use of systemic pesticides results in death or harm (such as impaired brood production) to insects like bees and butterflies when sequestered in flower nectar.
The safest course of action is to avoid pesticides entirely. If they must be used, contact with blooming plants or areas where bees are nesting should be prevented. Evening spraying when bees are less active is one way to reduce some of the harm. Morning spraying, when plants are covered with dew is less ideal, and may result in longer residual toxicity. Choosing a liquid formulation, rather than a powder, which may become trapped in a bee’s pollen collecting hairs, may also reduce some of the risk.
Various alternatives to pesticides exist. These include pest barriers like kaolin clay sprays and floating row covers. Pheromone traps may be used for some pest insects as well. An important consideration is that the same landscape features that support healthy pollinator numbers also support other beneficial insects. An abundant mixture of flowers, and a diversity of species (including pest-resistant varieties), can prevent most major pest outbreaks.
Gardeners who are committed to increasing their local pollinator numbers might consider becoming beekeepers themselves. Many cities allow residents to keep one or two honey bee hives, even in residential settings. In addition to providing pollination for the neighborhood, these backyard hives reward their caretakers with honey and wax.
Many state beekeeper’s associations, and some Universities and Cooperative Extension agencies provide workshops and training for beginning beekeepers. While the necessary space to keep a hive is small (some people even keep rooftop hives in large cities), the initial costs can be over a hundred dollars per hive. Another common challenge is dealing with unsympathetic neighbors. Proper screening (fences or shrubs) can reduce concerns about being stung, and sharing honey are a couple of ways to maintain good neighborly relations.
Some native bees can also be encouraged to take up residence in artificial nests. For example, small wooden bumble bee hives, roughly the size of a shoe box, can be constructed, although they are infrequently used.
A more successful approach of attracting native pollinators is to provide nests for cavity-nesting species like leafcutter and mason bees. These can be bundles of cut bamboo tubes, using a natural node as a terminal end, or wooden blocks drilled with a series of dead-end holes in a variety of diameters and depths. These nest materials should be hung with the tunnel cavity remaining horizontal and protected from rain, snow, and hot direct sunlight. These types of nests should be phased out every two or three years to reduce parasites and disease spores. To do this, they can be placed inside a dark container such as a wooden box with a single ½ inch emergence hole. After a single season, most of the dormant bees present in these nest materials will emerge, and exit through the escape hole, where new clean nest materials should be waiting.
Pollinator conservation represents a unique win-win proposition for gardeners—one that provides habitat for wildlife, and directly benefits humans at the same time. Additional information is available to support these efforts from a number of sources:
The Xerces Society’s Pollinator Conservation Program works with farmers, land managers, golf course staff, public agencies, and gardeners to promote the conservation of native pollinator insects and their habitat. Xerces produces many publications on how to protect, restore, and enhance habitat (including Farming for Bees, and the Pollinator Conservation Handbook). Many of these publications are available as free downloads through the Xerces website. Xerces also provides training events—including workshops, farm walks, and seminars—to provide a first hand look at specific pollinator conservation issues. http://www.xerces.org
The U of M Bee Lab, provides the latest science-based education and outreach on sustainable honey beekeeping. The Lab’s research and bee breeding programs are playing an important role in finding solutions to a number of honey bee health threats. Information on the very popular annual beginning beekeeper short course, as well as online training are available through the website. http://www.extension.umn.edu/honeybees/index.html
Befriending Bumble Bees is a first of its kind ecologically-sound guide to attracting, conserving, and rearing bumble bees. The book can be ordered online, and author Elaine Evans maintains an extensive website with links to additional bumble bee resources. http://www.befriendingbumblebees.com/