With the recent decline of the European honey bee, it is more important than ever to encourage the activity of other native pollinators to keep your flowers beautiful and your grains and produce plentiful. In Attracting Native Pollinators, you’ll find ideas for building nesting structures and creating a welcoming habitat for an array of diverse pollinators that includes not only bees, but butterflies, moths, and more. Take action and protect North America’s food supply for the future, while at the same time enjoying a happily bustling landscape.
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About the Author
The Xerces Society is a nonprofit organization based in Portland, Oregon, that protects wildlife through the conservation of invertebrates and their habitat. Established in 1971, the Society is at the forefront of invertebrate protection worldwide, harnessing the knowledge of scientists and the enthusiasm of citizens to implement conservation programs. They are the authors of 100 Plants to Feed the Bees, Farming with Native Beneficial Insects, and Attracting Native Pollinators.
Marla Spivak, PhD, is Distinguished McKnight Professor of Apiculture and Social Insects at the University of Minnesota. She was a 2010 MacArthur Fellow.
Read an Excerpt
Why Care About Pollinators?
CONSIDER FOR A MOMENT that insect-pollinated fruits and vegetables provide most of the vitamins and minerals we need, and they diversify our diet beyond meat and wind-pollinated grains. The United States and Canada alone grow more than a hundred different crop plants that need pollinators. Without bees, there would be no apples, pumpkins, strawberries, or many other fruits and vegetables.
The economic value of insect-pollinated crops in the United States in 2003 was estimated to be between $18 and $27 billion. If this calculation is expanded to include indirect products, such as the milk and beef from cattle fed alfalfa, pollinators may be responsible for more than twice this amount. Scientists at the Xerces Society and Cornell University have estimated that approximately 15 percent of this value comes from native bees living in the landscape on and around farms.
In the Pacific Northwest, for example, pollinator-dependent crops are a mainstay of the agricultural economy. In both Oregon and Washington, these crops are concentrated in three agricultural sectors: fruits and berries, alfalfa seed, and vegetable and flower seed. Oregon ranks first in the United States for harvest of blackberries, loganberries, black raspberries, boysenberries, and youngberries. Washington ranks first in the United States for apples, sweet cherries, and pears. Both states also produce substantial crops of vegetable and flower seed that depend on good pollination, and both are major producers of alfalfa seed, whose production requires bee pollination. In 2008, the combined value of pollinator-dependent crops from these two states alone was nearly $3 billion.
Similar examples exist across the country. Maine's 60,000 acres of low-bush blueberries make that state the largest blueberry producer in the United States, with a crop valued at $75 million a year. In New Hampshire and Vermont, the combined 10,000 acres of apple production are valued at more than $30 million a year.
In the Upper Midwest, Wisconsin's cranberry industry contributes $350 million annually to the state's economy and employs more than 7,000 people. With 18,000 acres of cranberry bogs, Wisconsin is the nation's largest cranberry producer. To meet growing export demand, the state is expected to add another 5,000 acres of production within the next decade, all of it requiring bee pollination.
Pollinators also are directly or indirectly responsible for many beverages (such as apple and cranberry juice), fibers (especially cotton and flax), and oil crops such as canola and sunflower, which are increasingly being used for biofuel production. We cannot overlook that pollinators are responsible for many of the beautiful flowering plants and trees in our gardens, which can provide us with spiritual inspiration, better mental health, and improved learning. Research suggests that spending time outside can improve concentration, help the behavior of children with attention disorders, and improve test scores. In short, insect-pollinated plants are the basis for much of our food, our economic stability, and our overall well-being.
BENEFITS TO NATURAL AREAS AND ECOSYSTEMS
The work of pollinators has value beyond providing food and resources for people. Pollinators help keep plant communities healthy and productive. In many areas, pollinators are crucial for flowering plants: for example, almost all of the arid South-west's bushes and smaller trees — such as mesquite, creosote bush, and chamise — are pollinated by bees.
When the pollinators are lost, bushes and trees may continue to flower and look normal for decades. By the time someone notices that they are not reproducing, it may well be too late to reintroduce a pollinator and preserve the ecosystem.
In the case of some rare species, only by identifying and understanding the habitat needs of their pollinators can we even begin to ensure the plants' survival. Protecting the plant's habitat isn't sufficient. The endangered dwarf bear poppy (Arctomecon humilis), for example, grows only in the Virgin River basin of southern Utah. The flower's dedicated pollinator — the minuscule Mojave poppy bee (Perdita meconis) — was finally identified nearly a decade after the plant was listed under the Endangered Species Act. Only then could conservation efforts focus on all aspects essential for its survival, including providing nesting sites for its pollinator.
Supporting Plants and Animals
Pollinators are not only essential to plant reproduction, but they help plants in other ways as well. The larvae of some flower-visiting beetles bore holes in dead or weakened trees, thereby initiating decay and returning the nutrients locked away in the tree back into the soil to be used by other plants.
In some areas, pollinators support plant communities that in turn stabilize the soil, thus preventing erosion and helping to keep creeks clean for fish, mussels, and other aquatic life. Willow shrubs and trees, for example, are important for the stabilization of stream and river banks. Because there are separate male and female plants, insects transfer much of the pollen from the male to the female willow flowers. Goldenrods, another example, are important colonizers of disturbed habitat. They too depend upon insects to produce their abundant seed.
Mammals, ranging from red-backed voles to grizzly bears, depend on insect-pollinated fruits and seeds. In the late summer, fruits can account for more than 60 percent of a grizzly bear's diet. About a quarter of all birds consume, as a major part of their diets, the fruits and seeds that result from animal pollination. Pollinating insects themselves are food for birds, lizards, and spiders, and as such are a central part of the food web. More than 90 percent of birds rely on insects during at least one stage in their life. Studies have demonstrated that diverse plant communities along stream banks, such as those that support pollinators, also support more diverse and abundant communities of insects that fall into the adjacent streams and become food for fish.
Managing Habitat for Pollinators
Considering the central role that pollinating insects and their habitat play in functioning ecosystems, it's easy to see how pollinator conservation can provide a framework for habitat management that helps other plants and animals. Until recently, however, habitat management has not considered pollinator habitat. In the Midwest, for example, restored prairie is maintained with burning or mowing. This site maintenance traditionally has focused squarely on the plant communities, with little thought to impacts on pollinators such as bees and butterflies. Supporting pollinators, on the other hand, requires limiting mowing or burning to a third or less of the site at any one time so that there is no year where all floral resources are unavailable. This results in more of a mosaic environment that allows for colonization of disturbed sites from the nontreated areas and a more diverse habitat.
BENEFITS TO PEST MANAGEMENT
Many insects that visit flowers as adults to feed on nectar or pollen also provide pest control for plants. For example, the larvae of many syrphid flies eat aphids. The adult fly fuels itself by eating sugary nectar. It then searches for plants with aphids where it lays eggs. The maggot that hatches from the egg patrols the plant looking for aphids, which it grabs onto and sucks dry, leaving behind a trail of shriveled bodies. An abundance of small flowers, such as those found on yarrow, fennel, or alyssum, increases the number of eggs an adult syrphid can lay over her lifetime. So, while the fly may provide some pollination, it also provides plants with protection from the pests that would harm them.
Still other pollinators are parasitoids that lay their eggs inside plant-eating aphids and caterpillars. Some of the most common parasitoids are tachinid flies and braconid and ichnuemonid wasps. When parasitoid eggs hatch, the larvae slowly feed on their host. During this period, the host typically is less active than it would be otherwise, doing less damage to the plant where it is feeding. Then, when the parasitoid larvae have completed their feeding and development, they kill their host, pupate, and emerge as adults.
Given the importance of pollinators, scientists have been documenting with particular alarm the dramatic declines in populations of bees and other pollinating insects in recent decades. In the mid-1990s, the yellow-banded bumble bee (Bombus terricola) was the most abundant bumble bee in Wisconsin. Ten years later, it made up less than 1 percent of the state's bumble bees. Across the continent, a similar fate has befallen the western bumble bee (B. occidentalis). Once one of the most abundant bumble bees on the West Coast, its numbers have crashed since the early 1990s and it is rarely seen now.
It gets worse. Franklin's bumble bee (B. franklini), restricted to a small area along the Oregon-California border, may have gone extinct during the same period. The most likely cause of these sudden declines is the spread of disease from commercially reared bumble bee colonies.
"Oh, a few bees," you may think. "Why worry?" Bees are the preeminent pollinators in North America. Pollinators are a keystone species group; the survival of a large number of other species depends upon them. As mentioned, they are essential to the reproductive cycles of most flowering plants, supporting plant populations that animals and birds rely on for food and shelter. Pollinators are also indicator species, meaning that the viability and health of pollinator populations provide a snapshot of the health of the ecosystem. As the insects that many plants require for adequate pollination disappear, the effect on the health and viability of crops and native plant communities can be disastrous.
In California, the endangered Antioch Dunes evening primrose (Oenothera deltoides ssp. howellii) survives on only a few acres of degraded sand dunes; it lacks pollinators and thus produces only a fraction of its potential seed crop. The rare white fringed orchid (Platanthera praeclara), scattered across grasslands of the midwestern United States, is now visited by a species of moth that is not native to the habitat. This moth fails to pollinate the flowers because its long tongue can reach the nectar without its head and body touching the pollen. Furthermore, it drinks nectar that might otherwise attract hawk moths with shorter tongues, which are the orchid's legitimate pollinators.
Each spring in Maine, more than 60,000 honey bee hives are unloaded from semitrailers into the state's expansive low-bush blueberry farms. Each hive contains more than 20,000 bees that have made the overnight journey from Florida or the Carolinas. They are there, in the blueberries, because modern industrial-scale agriculture has reduced the area of habitat available to support the more than 270 bee species that are native to the state. And when the blueberry bloom is over, the lack of forage means that the bees will be moved to other crops in other states. The native bees are in fact far superior pollinators of blueberry than the nonnative honey bee, having evolved with the wild blueberry plants in Maine's pine barrens over thousands of years. What these native bees lack is habitat: food available from spring to fall.
In China's Sichuan Province, one of the largest apple-producing regions in the world, farmers perch on ladders in mountainside orchards to pollinate the blossoms by hand. The farmers have adopted this practice because wild bees are now absent in their area, and honey beekeepers refuse to bring in their hives due to excessive pesticide use in the orchards.
Four factors — the loss and fragmentation of habitat, the degradation of remaining habitat, pesticide poisoning, and the spread of diseases and parasites — account for most of the declines in populations of bees and other pollinators. These factors have complex political, economic, and social origins that are not easily addressed. At the local level, however, the solutions to many of these problems are simple and straightforward. Many insects are fairly resilient, and there are actions we can take in our own backyards and neighborhoods, on farms and ranches, and in city parks and wild areas, to help strengthen and support pollinator populations.
The imperative behind this book is the fact that, as with most wild creatures, pollinator populations are declining as a result of human activity. If this trend continues, driving species of pollinators to extinction, the result will be disastrous not only for the insects but for humans as well. This book provides tools — information, understanding, and practical suggestions — that will help you begin to reverse this trend by providing and enhancing pollinator habitat and by becoming more aware of how your actions affect pollinators.
The Biology of Pollination
POLLINATION IS CENTRAL to the life cycle of flowering plants. Pollen must move from male to female parts of flowers for the plant to develop seed and reproduce. Movement of pollen within a flower or between flowers on the same plant is called self-pollination; the movement of pollen among flowers on different plants is cross-pollination. Although some plants can produce seed from self-pollination, most require cross-pollination; many plant species actually have genes that prevent their own pollen from fertilizing their ovules.
In addition, a transfer and mixing of genes occurs when pollen moves among plants. Over multiple generations, this results in more vigorous plants that constantly evolve to thrive in changing conditions.
HOW POLLINATION WORKS
Understanding pollination starts with understanding the roles of each different part of a flower. Like all organisms that rely on sexual reproduction, flowering plants have both male and female structures. Pollen grains — vessels for a plant's male gametes (sex cells) — need to move from the former to the latter to achieve fertilization. The male structure, called the androecium, is made up of the stamen, which consists of a bulbous anther on the end of a thin filament. The anther produces pollen. The female parts are collectively known as the pistil, formed of one or more carpels. Carpels contain the female gametes. Each carpel has three principal parts: a sticky or feathery tip, called the stigma; an ovary buried in the base of the carpel; and between the two, a stalklike extension called the style.
INSIDE A FLOWER
In some flowers, such as those of wild roses, apple trees, or cacti, the stamens and carpels can usually be clearly seen. The stamens form a ring at the base of the petals, surrounding the central pistil. In other plants, such as tomatoes, the stamens are fused together and surround the pistil.
The number of both stamens and carpels in a flower ranges from none to many. When the male and female parts occur together in the same flower, it is referred to as a complete or hermaphroditic flower. When a flower is lacking either stamens or carpels, it is called an incomplete flower, and will be male or female. Male and female flowers may also occur on separate male and female plants in the case of dioecious (Latin for "two houses") species, or both may be found on the same plant in the case of monoecious (Latin for "one house") species. To round out this complex mixing and matching of male, female, and combined flowers, there also are rare cases of androdioecious and gynodioecious plants where one type of plant has hermaphroditic flowers and the other type of plant has either male-only (androdioecious) or female-only (gynodioecious) flowers.
Flowers may occur singularly, as simple flowers such as lilies, or in complex clusters of flowers called an inflorescence, such as the spike of flowers on the lupines. Sunflowers and other daisies are an extreme example of an inflorescence; what appears as a single flower head is, in fact, hundreds of tiny individual flowers.
Excerpted from "Attracting Native Pollinators"
Copyright © 2011 The Xerces Society.
Excerpted by permission of Storey Publishing.
All rights reserved. No part of this excerpt may be reproduced or reprinted without permission in writing from the publisher.
Excerpts are provided by Dial-A-Book Inc. solely for the personal use of visitors to this web site.
Table of Contents
Preface: A New World
Part 1: Pollinators and Pollination
1. Why Care About Pollinators?
2. The Biology of Pollination
3. Meet the Pollinators
4. Threats to Pollinators
Part 2: Taking Action
5. Strategies to Help Pollinators
6. Providing Foraging Habitat
7. Reducing Impact of Land Management Practices on Pollinators
8. Nesting and Egg-Laying Sites for Pollinators
9. Pupation and Overwintering Sites
10. Home, School, and Community Gardens
11. Pollinator Conservation on Farms
12. Pollinator Conservation in Natural Areas
13. Urban Greenspaces, Parks, and Golf Courses
14. Special Considerations for Other Landscapes
15. Grassroots Action
Part 3: Bees of North America
Bees are Everywhere
The Name Game
Watching Bees and Other Flower Visitors
Part 4: Creating a Pollinator-Friendly Landscape
Recommended Pollinator and Butterfly Host Plants
About the Authors
About the Xerces Society Invertebrate Conservation