By Sue Smith-Heavenrich
I spent 10 minutes one morning last summer watching the bees in my blooming asparagus – the bumblebees, honeybees and a number of smaller bees I couldn’t immediately identify. They were incredibly busy, moving from one flower to the next. In the squash and pumpkin blossoms, small bumblebees were vibrating, making quite a racket and dusting themselves liberally with pollen. The weedy pathways were busy with tiny sweat bees. (Don’t let anyone tell you they can’t sting!)
By now most of us are aware that honeybee populations are declining due to mites, parasites and disease. In the last five years, 30% of managed colonies have been damaged, and many state apiculturists predict that between 75 and 90% of feral honeybees have died as well. As honeybee populations decrease, farmers and gardeners are looking to native bee populations to take up the slack.
Of all the land in the United States devoted to insect-pollinated crops, about two-thirds of those fields are not supplied with managed bee colonies. In 1996, University of Arizona researcher Jim Donovan reported an increase in activity by native bees in squashes and pumpkins. The native squash bee, Peponapis, was four to eight times more active than the honeybees, and was working the fields an hour earlier than its domesticated cousins. According to a recent study from Auburn University, in Alabama, 11 species of native bees accounted for 91% of the pollination of June-flowering squashes.
In Maine, squash and berry farmers depend heavily upon native bees to pollinate their crops. A study of nine Maine farms showed that bumblebees (Bombus spp.) were the most common bee visiting pumpkins and squashes. Blueberries and cranberries depend upon the pollination services of Bombus and other natives. At least eight species of Osmia (Megachilidae) help transfer pollen between blueberry flowers. Unfortunately, notes Dr. Connie Stubbs of the University of Maine at Orono, the local populations of native bees in many Maine fields are below levels needed to pollinate crops adequately without reliance on honeybees.
About one-third of our food depends upon native insect pollinators. Seven crops (worth about $1.25 billion annually in the United States) are pollinated primarily by wild insects: cashews, squash, mangos, cardamom, chocolate, cranberries and highbush blueberries. The production of 18 other major crops depends to some extent on wild pollinators. A recent survey found that at least 800 cultivated plant species rely on wild bees and other insects for pollination. Strawberry yields increase 28% when pollinated by wild insects, and blueberries, apples, pears, plums and cherries can form fruits only after insect pollination.
Some plants, such as tomatoes, eggplants and peppers, will set fruit without the help of insect pollinators. But with the help of insects, especially bumblebees, the crops yield more. Substantial literature shows the value of bumblebees to commercial crops, especially in areas with colder or wetter summers, or at higher elevations. Bumblebees are increasingly being used in glasshouse production of tomatoes in the Netherlands.
Meet the Natives
More than 3500 species of bees are native to North America, and they are as diverse in appearance and lifestyles as they are numerous. The smallest is the size of a fruit fly, about 2 mm, and the largest is about 80 mm in length (That’s over 3 inches!). Some are solitary, some social. Some nest in existing holes, while others drill their own nests in wood or soil. Because they produce little or no commercial honey or wax products, are hard to identify, and their nests are difficult to find, these bees are not well known. A typical backyard garden in the Northeastern United States hosts about 30 species of bees. In Maine, you should get to know five groups of native pollinators: leafcutting bees, mason bees, sand bees (also known as mining bees), sweat bees and bumblebees.
Bumblebees (Bombus spp.) are probably the most easily recognized bees after honeybees. They are larger, furrier, and very “bee-like,” which makes sense when you realize they’re in the same family as the honeybees. Of 46 species of bumblebees in North America, 12 are found in Maine crops and wildflowers. Bumblebees are primitively social bees, and nest underground in old mouse nests or other cavities. Colonies are usually small, about 100 to 400 bees. They are important pollinators in cold climates. Bumblebees are buzz-pollinators and are effective at pollinating tomatoes, eggplants, peppers, melons, blueberries and cranberries.
Leaf-cutting bees (Megachile spp.) are solitary, usually grayish bees. Active in midsummer, 120 species are native to North America. As their name suggests, leaf-cutters snip pieces of leaves to line their nests. They nest in ready-made cavities, hollow plant stems, in crevices, and will use drilled wood nesting blocks. They collect pollen on the scopa (brush of hair) on the underside of their abdomen. Recent USDA trials show leafcutters to be efficient pollinators of carrots in screened enclosures. Only 150 leafcutter bees were needed to do the work that would normally require 3,000 honeybees. Because they are gentle, even when in confined spaces, they are an ideal candidate for vegetable production in greenhouses. (To learn more about using leafcutter bees, call Vincent Tepedino at the USDA Bee Biology Lab in Logan, Utah, at (801) 797-2559.)
Mason bees (Osmia spp.) are small, solitary, blue or green bees related to the leafcutters. About 140 species are native to this continent. The majority nest in existing cavities, such as empty snail shells, but a few dig nests in the ground. They construct cells of mud, dung, plant resin, twigs, pebbles – thus their name “mason” bee. The blue orchard bee, Osmia lignaria, is the most widespread species in Maine and the United States. Studies in apple orchards show that only three to four females are needed to pollinate a full-sized apple tree, a job that would require over 100 honeybees. On a good day an orchard bee will visit 1600 to 2400 flowers, pollinating 95 percent of them. Maximum apple pollination can be achieved with as few as 250 female Osmia lignaria per acre.
Sand bees (Andrena) are perhaps the most common mining bee, with over 500 species native to North America. Several species appear early in the spring, in March and April, and pollinate a variety of fruit crops, trees and wildflowers. They are drab, solitary, and rarely noticed, yet these bees may be the most abundant wild pollinators in our fields. These bees excavate nests in the ground, leaving tell-tale mounds of soil. They often hide their nest entrances beneath leaf litter or in the grass.
Sweat bees (halictids) are small, measuring about 4 mm, and usually dark colored, though some are bright green. Some species are solitary, some are primitively social. Most nest underground, digging their own burrows, and you will often find many nests in one area. Unlike other mining bees, halictid females mate before hibernating for the winter, so they can begin nesting earlier in the spring. About 500 species are native to North America.
Advantages of Native Bees
Native bees have a number of advantages over honeybees as pollinators. Many are active early in the spring, before honeybee colonies reach large size. Native bees prefer fruit flowers, so they tend to stay in a crop rather than fly between crops, providing more efficient pollination. Because they fly rapidly (up to 15 mph), native bees can pollinate more plants. In leafcutter and mason bees, the pollen is carried loosely under the abdomen, so it is easily brushed onto the stigma of the next flower. Unlike honeybees, the males also pollinate the crop. Native bees are usually gentle, with a mild sting, and do not get disoriented in greenhouses.
Unfortunately, native bee populations are in decline. In 1995, some regions of the United States suffered a shortage of pumpkins and squashes due to the scarcity of native bee pollinators. European studies show that the decrease in bumblebee population in England is due to changes in land use – primarily the removal of hedgerows – and the increasing use of herbicides and other pesticides. In turning hedgerow to cropland, farmers eliminate wild forage plants and destroy nesting sites for many species of native bees. Ground nesting bees, including mining bees and bumblebees, are especially vulnerable to agricultural practices such as clean cultivation, irrigation, and use of chemicals. Studies in Poland demonstrate an inverse relationship between field size and bee diversity.
Habitat Management for Native Bee Populations
“It is time to protect our native beneficial bees through habitat conservation and sustainable agriculture,” says Suzanne Batra, a USDA bee researcher in Beltsville, Maryland. The best way to preserve them and continue to gain from their pollination services is to preserve wildland. In addition, gardeners and farmers can help preserve and increase native pollinator populations.
The easiest and least expensive way to preserve native bee populations and attract these busy pollinators to your own crops is to manage your garden habitat by providing nesting materials and flowers for pollen. Most bees love sun and prefer to nest in dry places. For ground nesting bees, this means a patch of undisturbed soil in a sunny spot. For wood- and stem-nesting bees this means piles of branches, bamboo sections, hollow reeds, or nesting blocks made out of untreated wood. Mason bees need a source of water and mud, and many kinds of bees are attracted to weedy, untended hedgerows.
You can create domiciles for native pollinators using inexpensive materials. Pack old-fashioned paper straws into a milk carton or coffee can (with both ends opened) and glue them in. Attach these domiciles securely to tree branches for leafcutter and mason bees. Or you can drill nesting holes 1/4″ in diameter and 4 to 6″ long into blocks of wood, and attach these (facing east) to fence posts or beneath your garage eaves. Connie Stubbs attaches her bee domiciles to 3-foot strips of ceiling lath and puts them right out in the fields.
Bumblebees, squash bees, and many other kinds of bees nest in the ground. Bumblebees are attracted to clay pots left upside down (the kind with the hole on the bottom). They also like wood and brush piles, and compost piles. Female squash bees need moist, undisturbed soil to dig their burrows; protect these habitats from tilling and plant squash every year to keep the populations of these important pollinators intact. If you find tiny 1/2-inch-wide holes in your lawn, with tiny dirt piles, these are the homes of nesting bees. Let that area of your lawn go wild for the season.
Raymond Williams, a beekeeper in upstate New York for 50 years, has been trapping and raising native bee pollinators for the past five years. “Whatever else you do,” he says, “make sure you fasten the domiciles securely and protect the bees from pests. ”Woodpeckers and mice tend to be problems. Ray protects his pollinators by putting 1-1/4″ trellis or netting around the domiciles after the bees have hatched. In the fall he takes the domiciles into his barn or garage to store, wrapping hardware cloth around each one to keep the mice out. Next spring, when his fruit trees are just about ready to bloom, he’ll put them out in the orchard, secured to stakes or tree limbs.
Native bees need food when their preferred crop plants aren’t in bloom, so you’ll need to plant a variety of annuals, perennials, and flowering trees and shrubs. Some plants that serve pollinators will also attract beneficial insects, as well as contribute to the aesthetics of your garden. You might consider planting a border of mixed wildflowers around your garden. (See sidebar for list of flowers native bees love. )
All bees are chemically sensitive, so DO NOT use pesticides. Herbicides and insecticides will kill them. If you must spray for pest control, choose an organic soap or spray and spray after sunset, when the pollinators are in their nests.
For nice illustrations of some native bees, check out “Not Just Honeybees Do It: The Other Pollinators,” by Amy Bartlett Wright. National Gardening May/June 1997: 33-37 & 74.
Batra, Suzanne W. , 1997. Unsung Heroines of Pollination. Natural History, May 1997.
— , 1994. “Diversify with Pollen Bees.” American Bee Journal 134 (9): 591-593.
Buchmann, Stephen L. & Gary Paul Nabhan, 1996. The Forgotten Pollinators. Island Press/Shearwater Books.
Forgotten Pollinators Campaign, 1996. “Rescued Harvest: How wild, native pollinators have filled in for decimated honeybees to service fruit and vegetable crops.” A report for the Forgotten Pollinators Campaign on 1996 field trials across the United States. (Forgotten Pollinators Campaign, 2021 N. Kinney Rd, Tucson, AZ 85743)
Hubbell, Sue. 1997. “Trouble with Honeybees.” Natural History, May 1997.
La Salle, John & Ian D. Gauld, eds. Hymenoptera and Biodiversity. 1993. C.A.B. International (UK)
O’Toole, Christopher & Anthony Raw. Bees of the World. 1991. Facts on File, NY.
Stubbs, Connie, et al., 1992. Alternative forage plants for native (wild) bees associated with the lowbush blueberry, Vaccinium spp. in Maine. Technical Bulletin 148 (Feb 1992) from the Maine Ag. Experiment Station, U. of Maine, Orono, 14469.
Torchio, Philip F. , 1987. “Use of non-honey bee species as pollinators of crops.” Proc. Ent. Soc. Ont. 118: 111-124.
See also Jim Tabor’s article, “Solitary Bees to the Rescue?” in the Sept-Nov. 1996 issue of The Maine Organic Farmer & Gardener.
About the author: Sue lives in Candor, N.Y., with her husband and two children.
Buzz-pollination: the bee vibrates inside the flower, shaking pollen all over its body.
Domicile: material modified to serve as nest site for bees, such as holes drilled in wood.
Nectar: secretion in flowers containing sugars, amino acids and other compounds. Bees prefer nectar with 30 to 50% sugar.
Pollination: moving pollen from the anthers (male part) of one flower to the stigma (female part) of another.
Scopa: a brush of specialized hairs with which bees transport pollen to their nest.
Social bees: live together in a communal nest and share foraging and nest duties. Honeybees are social bees; bumblebees and sweat bees are to a smaller degree.
Solitary bees: each female constructs and provisions a nest, lays eggs, raises young. Usually generations do not overlap.
Where to Get Advice & Bees
Dr. Connie Stubbs, 5722 Deering Hall, Dept. of Biological Science, University of Maine, Orono, ME 04469. (207) 581-2754. She is researching native pollinators in cranberry and other crops.
Raymond Williams, P.O. Box 1943, Binghamton, NY 13902-1943. (607) 775-3369. He has lots of practical know-how and advice for anyone who wants to begin raising native bees for pollination.
Dr. Suzanne Batra, Bee Research Lab, Bldg. 476, USDA, Beltsville, MD 20705. She can offer literature, advice, and may have some bees (in small quantities) available for folks who want to try raising them. She also has a list of people who raise pollen bees for sale.
Custom Paper Tubes offers “The Garden Pollinator,” a nest tube filled with 30 dormant blue orchard bees (approx. $50.00 for tube & bees). Custom Paper Tubes, P.O. Box 44187, Cleveland, OH 44144-0187 (800) 343-8823. They will have their “Garden Pollinator” offered through gardening catalogs.
Suggested Plants for Native Bees
Native bees, unlike honeybees, do not fly great distances from their nests to forage. Plantings for native bees should be within 200 yards of your garden. Flowers can often be included within the gardens, and those marked with (*) not only provide pollen for native bees, but attract other beneficial insects.
Flowers & Herbs:
bee balm *
calendula (single varieties)
Shrubs & Trees:
fruit trees (apple, cherry, plum)