Gardening for Pollinators

—by Margot Monson

The HPC February/March newsletter’s lead article by Anne Holzman was a timely introduction to thinking about the spring season and the sweet rewards of gardening. When I ask young students what they think of when they hear the word pollination, the first answer is almost always honey bees, and frankly, it is often the same with adults.

Since most gardeners are busy planning what they will plant in a few weeks, I’d like to expand on the relationship between plants and insect pollinators and how we might fit into this relationship.

Native pollinators

There are invertebrate pollinators found in many different insect orders, including beetles, wasps, social and solitary bees, butterflies, moths, true flies, and true bugs. (Do you know why all bugs are insects but not all insects are bugs?) Pollination is intentional when an insect transfers pollen as it moves from flower to flower foraging for pollen and nectar.

Some pollination is also incidental when a well-camouflaged predatory beetle, fly, or bug moves among flowers of a particular species waiting for its prey. There are examples of many different insects with coloration so similar to that of the flowers of a particular plant species that they predictably position themselves within the flowers of the same species waiting for unsuspecting prey to arrive. If unsuccessful, they often transfer to a different plant of the same species and lie in wait again, transferring pollen as they move.

Plants evolved along with insects, and some examples of coevolution are so specific that a plant’s survival is totally dependent on a particular species of insect. For example, the endangered bearclaw poppy found in Utah is pollinated exclusively by a species of solitary bee, Perdita meconis. Yucca plants found in the southwestern U.S. are pollinated only by moths in the genus Tegiticula, by a unique mechanism of intentional pollination not known to occur in any other insect-plant relationship:
the moth collects pollen grains and forces them into the receptive stigma of the plant in order to ensure there will be seeds produced for the moth larva to feed upon as it develops within the immature yucca fruit.

This mutual dependence means that neither species can successfully reproduce without the other. Scientists are continually learning about and discovering new ecological relationships between plants and insects.

Solitary bees

There are many species of solitary bees that are important pollinators. Most are small and unnoticed by the casual observer. They nest in the ground in tunnels, in crevices in soft wood, or in the hollows found in plant stems. A common one is the orchard mason bee, Osmia lignaria, a gentle insect that is effective in pollinating apples, cherries, and other tree fruits. It is found throughout North America.

A single female solitary bee can produce thousands of bees in her short life, and there are thousands of different species of solitary bees on this continent.

Honey bees

Honey bees, Apis mellifera, are social bees native to Europe, Africa, and Western Asia, and were introduced to other continents in the 17th century. Originally found living in hollow trees, they are no longer known to be feral and are only found in hives of beekeepers.

The hive functions with a highly structured caste system that includes the queen, her unfertilized female workers, and male drones. A single healthy hive may contain 60,000 bees. Even though they are not natives here, honey bees have adapted well throughout the U.S.

However, bees are increasingly threatened, as well explained in Holzman’s article, “It’s a Honey of a Job.” The pervasive use of chemicals has a cumulative effect on bee health, not necessarily killing bees outright, but weakening them.

Food shortage for bees

In addition to their exposure to a cocktail of toxic chemicals in our environment, honey bees lack  adequate nutrition due to a lack of plant diversity. Bees can no longer easily forage on a landscape plentiful with native wild flowers, and the monocultures to which they are often transported by migratory beekeepers provide them with only a single food source. On the road, bees are fed high fructose corn syrup and "pollen" made of soybeans.

In order to thrive, honey bees, like us, need a balanced diet found in diverse plant resources, without which they are more susceptible to disease and environmental threats. This makes the necessity for us to help them and our native pollinators as much as possible by creating a landscape planted with diversity in mind.

Our non-native honey bees can be found foraging on many non-native flowering plants such as  sweet clovers, but the more we can plant natives, the more we can encourage and sustain the many other insect pollinators as well.

Bumblebees

Bumblebees are native social insects, living in a nest that functions with a division of labor similar to that of honey bees. They can be found living underground in abandoned rodent burrows, in retaining walls with small openings that allow them to reach a protected interior space, and in hummocks of thick grass. I once found a bumble bee nest in a small abandoned birdhouse.

Bumblebees are more efficient pollinators than honey bees, but have much smaller hives and populations. A typical bumble bee nest may have up to 400 bees. In recent years there have been reports of bumble bees in decline, possibly due to their use for the pollination of tomatoes grown in hothouses, for which they are transported across the country in unnatural confinement and exposed to more chemicals in the process.

Native plants as resources for pollinators

Native plants will enhance your enjoyment of observing plant- insect interactions in your garden; they are also important because they encourage greater insect diversity. Herbivores will attract predatory insect species, and many predators act as pollinators as they search for their prey among flowers. The more plant diversity you have, the more insect diversity, the more potential pollination, the greater the habitat health.

Keep in mind that many common perennials may be labeled as “natives” but have been hybridized to increase their longevity and make them more intensely or variously colored and “desirable.” As a result of this genetic manipulation, they often lose the quantity and quality in nectar and pollen resources for which the pollinators forage. They may look attractive to us, even may tempt many invertebrate visitors, but they offer fewer nutritional rewards for insects.

Once you add native plants to your garden, watch for the presence of insect visitors. You will discover that the non-native plants often have few if any foraging pollinators. Therefore, if you buy your plants from sources that breed from the pure seeds of natives, you have a much better chance of providing valuable nutritional resources for the pollinators that visit your garden.

What should you plant?

The following list is not exhaustive but will give ideas about how to add more diversity to an existing garden. Perennial native plants that provide nectar and pollen include: mallow, common yarrow (white or pinkish—those with bright colors have been hybridized or introduced), giant hyssop, cup plant, allium (wild onion, wild leek, wild garlic), pearly everlasting, wormwood, asters (though many are hybridized), paint brush, fireweed, thistle, tickseed (Coreopsis), wild carrot, rattlesnake weed, larkspur, shooting star, Rudbeckia (coneflower—many are hybridized), daisy fleabane, Joe-pye-weed, cranesbill geranium, blanket flower, prairie smoke, common, field, and false sunflowers, cow parsnip, Liatris (blazing star, gayfeather), wild lupine (many sold are hybridized), evening primrose, penstemon, white and red baneberry, purple and white prairie clovers, (red and sweet clovers non-native), sedum, goldenrods, white turtlehead (purple is non-native), and bee balm.

Some common non-natives that do provide nectar include: daisy, globe thistle, English lavender, bird’s foot trefoil, mint, basil, marjoram, poppy, rosemary, thyme, clover, nettle, and burdock. Though you may not prefer to have thistle, burdock, or nettle in your garden, when you encounter them in the wild, look for the insects that have adapted to them, such as larvae of the lovely red admiral and painted lady.

Planting for insect larvae

Providing larval host plants for some common butterflies & moths is a vital component of pollinator habitat. Examples include several species of milkweed, thistle, wild carrot, fennel, wild lupine, parsley, plantain, clover, nettle, violets, spirea, and lilac, as well as aspen, cherry, plum, apple, rose, and willow trees; various grasses and sedges are also attractive for many butterfly species, including skippers.

There are many excellent references for the identification of and sources for native plants and for the identification of the most common insects you are likely to encounter in Minnesota. These are just a few of those I have found useful and reliable.

Seed and plant sources
(all are located in Minnesota except Seed Savers Exchange)

Glacial Ridge Growers, Prior Lake,  <www.glacialridgegrowers.com>

Landscape Alternatives, St. Croix valley, south of Taylor's Falls, <www.landscapealternatives.com>

Landscape Revival: Native Plant Expo Market, June 1, 2013, Roseville,
            <www.saintpaul audubon.org/events/2012/06/landscape-revival>

Prairie Restoration, Scandia,  www.prairieresto.com/

The Vagary, Randolph, <www.thevagary.com/>

Seed Savers seeds, at Hampden Park Co-op now! Or visit Seed Savers Exchange, Decorah, Iowa,             <www.seedsavers.org/>

Native plants are available at many farmers’ markets, but be sure to quiz the farmer about the actual “nativeness” of their plants.

Recommended books

Stephen Buchmann and Gary Paul Nabhan. The Forgotten Pollinators. Washington, D.C.: Island Press, 1996.

Christopher, Thomas, Rick Darke, Toby Hemenway, and Douglas Tallamy. The New American
Landscape: Leading Voices on the Future of Sustainable Gardening.
Portland, Oregon: Timber Press, 2011.

Evans, Elaine, Ian Burns, Marla Spivak. Befriending Bumble Bees. Regents of the University of Minnesota, 2007.

Shepherd, Matthew, Stephen L. Buchmann, Mace Vaughan, and Scott Hoffman Black. Pollinator Conservation Handbook. The Xerces Society, 2003.

Tallamy, Douglas W. Bringing Nature Home. Portland, Oregon: Timber Press, 2007.

Reference guides for insects and native plants

Moyle, John B. and Evelyn W. Northland Wild Flowers: The Comprehensive Guide for the Minnesota Region, revised edition. University of Minnesota Press, 2001.

Opler, Paul A. , Amy Bartlett Wright, and Roger Tory Peterson. Peterson First Guide to Butterflies and Moths. New York: Houghton Mifflin Company, 1998.*

Peterson, Roger Tory and Margaret McKenny. A Field Guide to Wildflowers of Northeastern and NorthCentral North America. New York: Houghton Mifflin Company, 1996.

Tekiela, Stan. Wildflowers of Minnesota: Field Guide. Cambridge, Minnesota: Adventure Publications, 1999.

White, Richard E., Christopher Leahy, and Roger Tory Peterson. Peterson First Guide to Insects of North America. New York: Houghton Mifflin Company, 1987.

Wright, Amy Bartlett and Roger Tory Peterson. Peterson First Guide: Caterpillars. New York: Houghton Mifflin Company, 1998.

* The Peterson First Guides are excellent, easy-to-use references to the common insects, with illustrations and good basic information about habitats and host plants.

[Margot Monson has been a member of the co-op since its beginnings on Cleveland and Buford Avenues, across from the St. Paul campus. As an entomologist and beekeeper, she finds most insects beautiful, all fascinating, and never tires of looking at them under her microscope.]