Not Enough Pollinators?
Bumblebees could help
Honeycomb graphic by Ramona Kaulitzki/Shutterstock.com.
Yin-yang graphic by Nicemonkey/Shutterstock.com.
Honeybee photo by Defun/Dreamstime.com.
Bumblebee photo by Subbotina/Dreamstime.com.
Nearly every day brings news about research into the causes of the global decline of pollinators. On July 24, researchers published an article in PLOS ONE (http://bit.ly/137ip0K) reporting the discovery that exposure to common fungicides impairs the ability of commercial honeybees to fight off Nosema ceranae, a parasite of adult honeybees linked to colony collapse disorder.
The first research conducted under real-world conditions in fields from Delaware to Maine by the University of Maryland and the U.S. Department of Agriculture (USDA) found that the collected pollen contained the fungicide chlorothalonil. Bees that consumed the collected pollen were nearly three times more likely to be infected by Nosema than bees that were not exposed to the fungicide.
Researchers also confirmed what beekeepers have long known - that the miticides used to control varroa mites also harm the bees' ability to withstand parasitic infection. However, the miticides have been found to cause less damage than if the mites were left unchecked.
"We don't think of fungicides as having a negative effect on bees, because they're not designed to kill insects," said Dennis vanEngelsdorp, quoted in a Science Daily article (http://bit.ly/12kvANj). "Federal regulations restrict the use of insecticides while pollinating insects are foraging, but there are no such restrictions on fungicides, so you'll often see fungicide applications going on while bees are foraging on the crop," he explained. "This finding suggests that we have to reconsider that policy."
Losses of managed honeybee colonies from all causes nationwide for the 2012-2013 winter were 31.1 percent. These losses are slightly higher than the previous six-year average loss of 30.5 percent, but up considerably from the 21.9 percent for the warm 2011-2012 overwintering season. Data were compiled from responses from more than 6,000 U.S. beekeepers, managers of some 600,000 colonies (about 22 percent of the nation's total), who responded to a survey.
Unlike previous winters, 2012-2013 saw more colonies dwindle away rather than being lost suddenly from the onset of colony collapse disorder (CCD). The survey also found that beekeepers who later took honeybees to California to pollinate almonds had higher losses than beekeepers who did not take their bees to pollinate almonds. Almost 20 percent of the beekeepers whose colonies pollinated almonds lost 50 percent or more of their colonies. Seventy percent of all beekeepers reported losses greater than 14 percent - the level of loss that allows beekeepers to remain economically viable.
A USDA Agricultural Research Service fact sheet on bee losses is available at http://www.ars.usdahttp://.gov/is/br/beelosses/index.htm.
The need for bees
Bees pollinate over 70 of the 100 crops that provide 90 percent of the world's food. In North America, honeybees pollinate nearly 95 kinds of crops, including almonds, avocados, blueberries, cranberries and apples. Almonds currently rely almost entirely on bees as pollinators, while apples and blueberries are about 90 percent dependent on bees. High-value crops, including almonds and broccoli, rely almost entirely on pollination services provided by commercial beekeepers. At least three times as many honeybee colonies are rented for the pollination of almonds (an estimated 1.3 million to 1.5 million) as are used for apple pollination (an estimated 275,000 colonies).
While honeybees - a nonnative species formerly managed primarily for its honey - have been the preferred North American pollinator for over 100 years, they have their limitations. They are less effective or inadequate in temperatures under 59 degrees Fahrenheit or in cloudy weather. They do not work well in greenhouses or high tunnels, where they tend to fly into walls. And now they appear to be the species most affected by the conditions thought to be most responsible for CCD - a combination of disease, nutrition, habitat fragmentation, stress and pesticides.
In addition to the nonnative honeybee, at least five other bee species, all native to North America, are managed for crop pollination. Like the honeybee, some native bees are generalists, and others are specialists. Generalists collect pollen from a wide variety of flowering plants; specialists use pollen from one or two flowering plant families. Specialist pollinators include squash bees (efficient pollinators of cucurbits, including squash, pumpkin and zucchini) and blueberry bees (for the obvious). Bumblebees are also generalists. They collect pollen from a succession of plants flowering in early spring (when the queen emerges) until early fall (when the colony dies). After honeybees, bumblebees are the most widely managed bee species in the U.S.
Koppert's Quad bumblebee hives. One Quad (four separate hives shipped together) contains 1,000 bees.
Photo courtesy of Koppert Biological Systems.
Commercially managed bumblebees
Native to the U.S. east of the Rockies, Bombus impatiens (common eastern or impatient bumblebee) is the primary managed native species and has been commercially available since the mid-1980s. East of the Mississippi River, B. impatiens can be used in both fields and indoor growing situations. In states west of the Mississippi, the species can only be used indoors with a permit, except in Arizona, where there are no regulations governing either indoor or outdoor use of managed bees not native to the state, according to Ryan Hill of Koppert Biological Systems, suppliers of "nature's perfect pollinator." Federal regulations, however, do prohibit international importation of honeybees, specifically bees from Australia. In 2012, the Animal and Plant Health Inspection Service (APHIS) banned all Australian honeybees because of the potential risk that imported honeybees could introduce new pests and diseases to U.S. honeybees.
The number of B. impatiens at work in the nation's fields and greenhouses is unknown. Koppert (http://www.abetterbee.com, 800-928-8827) ships thousands of hives of B. impatiens every week. One of the company's hives contains approximately 250 bees, and hives are usually shipped in groups of four, called Quads. About 40 percent of the bees Koppert ships are used indoors, and 60 percent are used outdoors. If you're using only bumblebees, Koppert recommends using two hives (approximately 500 bumblebees) per acre, depending on the crop and environment. The exceptions are blueberries and cranberries, where three hives per acre (750 bees) are recommended. Spring (March through May) is the peak bumblebee shipping season. Bumblebees to pollinate indoor tomatoes and peppers are shipped consistently throughout the year, according to Hill.
A bumblebee queen.
Photo by llorban, CC-BY -SA-3.0, via Wikimedia Commons.
The differences between honeybees and bumblebees
Honeybees make honey, generally more than the colony itself needs to survive. Bumblebees produce honey too, although much less. This is because bumblebees do not overwinter. Except for the queen, bumblebees expire after their six to eight-week working season. The queen is the lone colony member responsible for regenerating the entire colony in the spring. To increase the potential for retaining overwintering queens, Hill advises leaving snags in and around fields to provide bumblebee habitat. Some growers make snags from old pallets and brush.
Bumblebees are much more efficient pollinators than honeybees, visiting many more blooms per minute.
Photo by Gilles Gonthier, CC-BY-2.0, via Wikimedia Commons.
Since it's not necessary to make large quantities of honey to feed the colony, bumblebees can be less selective. They tend to forage for pollen rather than nectar. Bumblebees harvest pollen from different types of flowers and can specialize in extracting it from different plant species.
With tongue extended, a female Peponapis bee sips nectar from a yellow squash flower. Squash bees are specialist pollinators.
Photo by Jim Cane, courtesy of USDA-ARS.
Bumblebees and honeybees differ in both the type and size of their colonies. Bumblebee colonies are smaller and impermanent and may be found in, on or above the ground. Honeybees live in permanent colonies that can have thousands and thousands of bees. Honeybees communicate with each other in complex ways - for example, by dancing to tell other workers where to find good supplies of pollen. Like honeybees, bumblebees also produce honey that is stored in the nest. They mark groups of flowers they have visited, but do not mark individual blooms. Koppert's bumblebees are most often used to pollinate both wild and highbush blueberries, apples, pears and cranberries.
Bumblebees are buzz pollinators, rapidly vibrating to release large amounts of pollen onto themselves.
Photo by Bob Peterson, CC-BY-SA-2.0, via Wikimedia Commons.
Some reasons for U.S. growers to consider using bumblebees include:
- Bumblebees become active at lower temperatures, near 40 degrees Fahrenheit. Honeybees do not become active until temperatures reach 60 to 65 degrees Fahrenheit.
- Bumblebees are active on cloudy, foggy and rainy days. Honeybees are less active at low light levels.
- Bumblebees will fly in winds up to 40 mph.
- Bumblebees are buzz pollinators, rapidly vibrating to release large amounts of pollen onto themselves. Buzz pollination can occur in a single bumblebee visit, whereas seven to 10 honeybee visits may be needed to fully pollinate a flower.
- Lacking the sophisticated communication of honeybees, bumblebees are less likely to leave your crop for more attractive flowers.
- Bumblebees, unlike honeybees, are attracted to flowers with narrow corollas (tubes), such as cranberries and blueberries.
- Unlike honeybees, bumblebees forage for pollen rather than nectar, transferring more pollen to the flowers' pistils with each visit. They are much more efficient pollinators than honeybees, visiting many more blooms per minute.
- Beginning earlier in the morning and ending later in the evening, bumblebees work longer days during their six to eight-week season than honeybees.
- Bumblebees do not swarm and hence are less aggressive. While only females can sting, bumblebees can sting multiple times, whereas honeybees can sting only once.
- To enhance pollination, bumblebees and honeybees can be used together.
The measure of success
"To improve crop potential, vary pollinators," says Hill. "In the end, however, the best measure of the success of pollinators is the fruit set, which, of course, depends not only on pollination and the pollinators used, but on all the other factors growers encounter daily."
Losses of managed honeybee colonies from all causes nationwide for the 2012-2013 winter were 31.1 percent.
Photo by tpsdave/pixabay.com.
Kathleen Hatt is a freelance writer and editor and a frequent contributor to Growing. She lives in Henniker, N.H.