Pollinators in urban landscapes
Most plants need pollination to reproduce and grow fruit. While some plants are wind-pollinated, many require assistance from insects, bats, hummingbirds or other animals.
Most plants need pollination to reproduce and grow fruit. While some plants are wind-pollinated, many require assistance from insects, bats, hummingbirds or other animals. Without pollinators, we would have little to no fruit, fewer vegetables and many plant species would not survive. Gardeners and farmers depend on pollinators to produce fruit and vegetable crops. In natural ecosystems, pollination is required for many types of native trees and shrubs to provide forage for birds and mammals.
For fruit and vegetable crops, honey bees, which are from Europe, are the most important pollinators because they can be brought in and out of orchards and fields easily. Honey bees have been estimated to pollinate 30 to 90% of many fruit crops, with native bee species accounting for most of the remaining pollination. The proportion of fruit pollinated by honey bees varies considerably among fruits and vegetables, and depends on whether or not hives are brought into the orchard for the pollination period, and the local population of feral honey bees.
Most honey bee colonies are kept outside city limits and are managed by commercial beekeepers, however, a growing number of small-scale beekeepers and hobbyists maintain colonies in urban landscapes. Bees can fly well over a mile to search for pollen and nectar, so colonies located within 3 miles of managed landscapes can be affected by the pesticides used.
In addition to honey bees, we have over 3,600 species of native bees in the United States, along with flies, beetles, butterflies, wasps and other insects that provide pollination services. Some of these native pollinators play important roles in crop pollination and are critical for pollinating native plants. Native bees have evolved in the region where they are found, so they tend to be well adapted to the local climate, local flowering plants and may also have developed resistance to local diseases and parasites of bees. They are sometimes called “wild” bees along with the non-native species that are not managed by beekeepers.
Native bees, butterflies and other pollinators are wildlife, deserving protection in the same way birds such as raptors and songbirds are protected. Unfortunately, honey bee health is in decline, and some native bees and butterflies are threatened. Honey bees are well studied because of their economic importance. From April 1, 2014 to April 1, 2015, the U.S. lost 42% of its honey bee colonies, and winter losses since 2006 are generally around 30% every year. Beekeepers consider annual losses of 15-20% to be acceptable, and losses greater than this make it difficult or impossible to remain profitable. The Xerces Society reports in recent years monarch populations have declined by more than 80% from the 21-year average across North America. Declines have been reported for native bee populations as well, however, for most native species we do not have adequate information on how many were here in the first place.
Read the next article in this publication series: Factors that threaten pollinator health
Or return to the beginning of this publication: How to protect and increase pollinators in your landscape