Long-term population trends for the honeybee, the most important managed pollinator in North America, are demonstrably downward, a National Research Council report warned.
Of the multitude of ways humans could be harming the planet, the report said, one that has largely been ignored is the "pollinator crisis" - the global decline in the number and viability of species that are involved in the reproduction of flowering plants.
"Ironically, despite its apparent lack of marquee appeal, pollinator decline is one form of global change that actually does have credible potential to alter the shape and structure of the terrestrial world," the report said.
"Over the past decade, the public has begun to take notice and ask whether a pollinator crisis is brewing and, if so, what can be done to avert it."
Among the various pollinator groups, evidence for decline in North America is most compelling for the honeybee, Apis mellifera, which enable the production of 90 commercially grown crops, the report said.
"Research indicates that shortages of pollinators for agriculture already exist and that decreases in wild pollinator populations could disrupt ecosystems in the future," Committee on the Status of Pollinators in North America chairman May Berenbaum said in releasing the report.
The committee that wrote the report said there is little or no population data for many pollinators and called for stepped-up efforts to monitor the pollinators and improve understanding of their basic ecology.
"Nevertheless, there was sufficient evidence for the committee to conclude that some North American species are in decline, especially the honeybee," the report said.
"Honeybees are crucial to agriculture, pollinating more than 90 commercially grown crops; for example, it takes about 1.4 million colonies of honeybees to pollinate 550,000 acres of almond trees in California."
The report said studies showed that U.S. honeybee populations have dropped since the 1980s when the Varroa destructor mite was introduced, although the full extent of the decline is unclear because of problems with the way the federal government collects statistics on the beekeeping industry.
The report said the shortage of bees was significant enough that they had to be imported from outside North America last year for the first time since 1922, when the Honeybee Act banned such imports for fear they would introduce non-native pests.
Such fears are still justified, the committee warned, recommending that USDA and relevant agencies in Canada and Mexico take steps to prevent the introduction of new pests, parasites, and pathogens if bees are imported.
Antibiotic-resistant pathogens and encroachment by Africanized honeybees also are hurting North American honeybee levels, the committee noted in recommending the USDA support research to improve pest-management and bee-breeding practices.
Long-term trends for several wild bee species - especially bumblebees - as well as some butterflies, bats, and hummingbirds also show population drops, the committee found.
"The causes of decline in wild pollinators vary by species and are difficult to determine," the report says. "Like the honeybee, the bumblebee has been hurt by the introduction of a non-native parasite."
It urged USDA and other federal agencies to support research aimed at the sustainable management of these populations. In the meantime, it said, landowners can take simple and relatively inexpensive steps to make habitats more "pollinator friendly," for instance by growing native plants.
"Many simple and relatively low-cost practices that would promote pollinator conservation are known and available," it said. "Land managers and landowners, including farmers and homeowners, should be encouraged to adopt `pollinator-friendly' practices, many of which incur little expense.
"Farmers and ranchers can be offered economic incentives to adopt such practices. Landowners such as homeowners and businesses could contribute to the conservation of pollinators by planting wildflowers to provide floral resources for resident and migratory adult pollinators and by providing nesting sites for females."
The USDA should expand its efforts to encourage innovative approaches to protecting honey bee health by developing sustainable pest and resistance management programs for Varroa mites, including identifying additional least-toxic alternative pesticides and non-chemical cultural bee management practices.
The department should also improve genetic stocks of honey bees by refining methods for breeding, selecting, maintaining, and improving stocks with disease and pest resistance, moderated temperament, and improved honey production. The report also proposed refining methods for producing high-quality queen production from selected stocks including controlling mating to ensure expression of desired traits in colonies.