Also declining in abundance, the western bumblebee is an efficient pollinator both in the field and in greenhouses.
Photo by Stephen Ausmus, courtesy of USDA-ARS.
Regarding the challenges of the continuing decline of pollinators, Dr. Christina Grozinger said, "There is no one solution." Grozinger is a professor of entomology and director of the Center for Pollinator Research at Penn State University.
Last August, nearly 250 researchers from 15 countries attended the center's second International Conference on Pollinator Biology, Health and Policy. In her welcoming address, Grozinger noted that the impacts of stressors on multiple developmental stages and impacts on the social interactions of bees must be considered.
She said that while there are numerous pollinators, researchers have detected 137 chemical residues in surveyed honeybee colonies in the U.S. Study is complicated by the numbers; there are 4,000 bee species in this country, all of which have different physiologies, natural histories and responses to stressors. The situation is made more urgent by an increasing world population that demands nutrient-rich crops, which require pollination. "We must balance land and agrochemical use with ecosystem services provided by pollinators," Grozinger said.
This honeybee is hard at work gathering nectar from this watermelon flower.
Photo by Stephen Ausmus, courtesy of USDA-ARS.
In February, USDA Secretary Tom Vilsack announced a new $3 million program to improve pollinator health, underscoring the importance of honeybees. "Honeybee pollination supports an estimated $15 billion worth of agricultural production, including more than 130 fruits and vegetables that are the foundation of a nutritious diet," he said in a press release. "The future security of America's food supply depends on healthy honeybees."
Honeybees (Apis mellifera) came from Europe with the first settlers. Although this country has native bees, honeybees have been easier to manage on a commercial level. However, since 2006 beekeepers have been suffering honeybee colony losses averaging about 30 percent per year. The complex causes for the decline include parasites, pathogens, environmental toxins, poor nutrition and habitat loss.
If insufficiently pollinated, the flowers of a crop abort and set small, misshapen, flavorless fruit with short shelf lives. Yields - and grower profitability - are reduced. Many crops, such as cucurbits, apples and pears, have high pollination requirements.
Not unexpectedly, the cost of pollination services has risen.
The almond industry epitomizes both the costs and the importance of honeybee pollination. Gabriele Ludwig, the Almond Board of California's associate director for environmental affairs, told the pollinator conference attendees that over 6,500 almond growers span 500 miles in California's Central Valley. Almonds are the nation's top horticultural crop in export value and by far the largest user of pollinators. The industry has funded $2.2 million in pollination research since 1976.
With a total of about 870,000 acres, almond growers must rely on pollination services from mid-February through mid-March. In 2011, growers in the San Joaquin Valley spent over $280 an acre for pollination, and the cost has grown substantially since then. Unfortunately, because of Alternaria, anthracnose, brown rot, green fruit rot, hull rot, leaf blight, scab, shot hole and rust, almond growers also need to apply fungicides, some at the same time as pollination. Since the bees forage in the morning when the almond pollen is released, the orchardists apply fungicides later in the day.
An effective pollinator of commercial blueberries, this blue orchard bee is a native solitary bee.
Photo by Jack Dykinga, courtesy of USDA-ARS.
Researchers point out that combinations of pesticides often have especially adverse effects. In studying whether insecticides and fungicides act alone or in concert in honeybee hives, Penn State entomologists Dr. James Frazier and Dr. Chris Mullin have reported in the journal PLOS ONE that mixtures can have greater toxicity for honeybee larvae. The team also found that inert ingredients in pesticides enhance active ingredient toxicities. Accordingly, risk assessment should be expanded from individual pesticides to chronic and mixture toxicities that incorporate fungicides, other pesticide pollutants and their inert ingredients.
Maryann Frazier, Penn State senior extension associate, recently pointed out to growers that while fungicides are not highly toxic, they synergize with miticide treatments used by beekeepers and create considerable challenges.
Pesticides can interfere with bee navigation, learning, sperm viability, gut microflora, foraging behavior, worker productivity and pollen collection efficiency.
Bumblebees are also important pollinators. Since they are buzz pollinators, with vibrations that dislodge more pollen, they are especially efficient at pollinating the flowers of cranberries, peppers and tomatoes. They are often sought for the greenhouse tomato industry. Unlike honeybees, bumblebees are active at temperatures near 40 degrees Fahrenheit, in windy conditions, and in cloudy and rainy weather. However, as the USDA's Agricultural Research Service (ARS) points out, anecdotal evidence over the past 10 to 15 years suggests several bumblebee species are disappearing, and their range is constricting. The August 2011 issue of Agricultural Research magazine reported on the search for new pollinators by entomologist Dr. James Strange, Logan, Utah.
The western bumblebee (Bombus occidentalis) is a generalist forager that has been reared in colonies for greenhouse pollination. Since pathogens have been affecting commercial production, and it appears to be less abundant in the wild now, Strange has been researching several other native bumblebee species.
ARS scientists caution that moving bees outside their native range can lead to drastic environmental implications. They can compete with native bees for food and expose them to pathogens they're not adapted to.
Wild bees in their own range can be efficient pollinators. Presented at the Great Lakes Expo in December, research by Cornell entomologists Dr. Jessica Petersen and Dr. Brian Nault showed that wild bees maximized pumpkin fruit yield in the Finger Lakes region of New York. Fields planted with 'Gladiator' pumpkin were supplemented with rented honeybee hives at the rate of one hive for 3 acres, supplemented with eastern bumblebees at the rate of one quad for 2 acres, or not supplemented. The average fruit weight was not significantly different between the three conditions. The honeybees and bumblebees did forage on pumpkin, but also on ground cherry, clover, Queen Anne's lace, dandelion, goldenrod, English plantain and pokeweed. Interestingly, corn was 30 percent of the honeybee pollen, and nearly 50 percent of the bumblebee pollen was from solanaceous plants.
Dr. David Biddinger, tree fruit entomologist at Penn State's Fruit Research & Extension Center in Biglerville, Pa., along with others from the pollinator team, stressed the need for alternative pollinators. The blue orchard bee (Osmia lignaria) has been used in small organic orchards, but generally its numbers are inadequate for large operations. The Japanese orchard bee (O. cornifrons) is much more effective in pollinating apple trees than honeybees, which focus on nectar for honey rather than pollen.
A pair of native andrenid bees pollinating apple blossoms. They are sometimes called mining bees because they nest underground.
Photo by Nancy Lee Adamson, courtesy of Xerces Society.
Native bees can be an important pollinator, the researchers noted, as long as the landscapes in and around the farms supply forage and nest sites and the harmful effects of pesticides are reduced. Some of the largest fruit growers in Pennsylvania have relied on feral honeybees and wild pollinators with no noticeable loss in fruit quality or yields. New Jersey has about 50 native bee species that pollinate several vegetable crops. The majority of these farms have not required honeybees. Consequently, this diversity is being studied to determine if reduced-risk insecticides are conserving beneficial insects, and also to develop the management of the Japanese orchard bee.
Considering the current risks to honeybee pollination, the Integrated Crop Pollination (ICP) project's goal is to develop and deliver recommendations on how to harness the potential of native bees. The ICP combines different pollinator species, habitat augmentation and crop management practices to provide reliable and economical pollination of crops. The ICP project director, Michigan State University entomologist Dr. Rufus Isaacs, said that growers need tactics that fit into the economic reality of different regions. The project aims to provide tools to reduce risk and improve returns to growers via multiple tactics tailored to specific crops and situations. Training of growers is an important area of their extension program. "Growers don't read the Journal of Applied Ecology," Isaacs said. ICP information can be accessed at http://www.icpbees.org.
One Michigan State project under way focuses on conserving beneficial insects, determining if plantings of native Michigan wildflowers can draw abundant bees to blueberry farms. Another project models blueberry pollination to detect the most effective and economical combination of managed honeybees and bumblebees for sustainable crop pollination.
At the August conference, Mace Vaughan, Xerces Society pollinator program director, said the program's goals are to increase the population of unmanaged (wild) pollinators and support managed bees, and to increase the sustainability and profitability of agriculture. Vaughan said hedgerows enhance abundance and diversity while increasing native bees. In addition, native plants support more native bees. Cover cropping, riparian restoration, erosion control, conservation biocontrols, other wildlife conservation, forage and biomass plantings, and pesticide risk mitigation encourage pollinators.
A bee feeds on nectar in a clover field in Virginia.
Photo by Linda Richardson, courtesy of USDA-NRCS.
The Xerces Society implements conservation programs, including extensive pollinator education and outreach activities through advocacy, courses, demonstrations, publications, research, speaking engagements and a complement of resource information. The society's website (http://www.xerces.org) illustrates its programs. Habitat loss and monoculture contribute to the decline in bee numbers. To boost populations, the society encourages creating a safe haven from pesticides - particularly the systemics, such as the neonicotinoids - as well as providing nesting sites and floral diversity, which benefits both native bees and honeybees. The society also notes that many insecticides for home gardeners containing neonicotinoids can legally be applied in far greater concentrations than on farms.
Dr. Edwin Rajotte, Penn State IPM coordinator, commented that from an IPM perspective, the pollinator conference's research underscored that IPM practices, including pesticides, impact pollinators. "How crop protection is practiced could be modified to accommodate pollinators," he observed.
Grozinger said there is mounting evidence that nutrition can buffer pollinators from the effects of stressors. Plus, there is greater interest among homeowners, developers, city planners and growers in improving habitat and forage for pollinators. "Diversity in habitat can make a difference. Diverse plantings lead to habitat, which leads to diverse pollinators," she said. But the best method to restore land to support pollinator health needs to be determined. Research on which specific plantings lead to better bee nutrition is needed. Many growers agree, observing that the better the diet of bees, the greater their resilience to pathogens and pesticides.
The Center for Pollinator Research's website (http://ento.psu.edu/pollinators) features information on its beekeeping courses, events and studies, as well as the materials from the international conference.
The author is a writer/researcher specializing in agriculture.