Each year $3 billion of the U.S. economy depends on pollination from native pollinators such as wild bees.
Taylor Ricketts, a conservation ecologist at the University of Vermont, tells the American Association for the Advancement of Science annual meeting that the bees are disappearing from the country’s most important farmlands – including California’s Central Valley, the Midwest’s corn belt and the Mississippi River valley.
“This study provides the first national picture of wild bees and their impacts on pollination,” says Ricketts, director of UVM’s Gund Institute for Ecological Economics.
“Wild bees are a precious natural resource we should celebrate and protect,” he says. “If managed with care, they can help us continue to produce billions of dollars in agricultural income and a wonderful diversity of nutritious food.”
Ricketts’ map identifies 139 counties in key agricultural regions of California, the Pacific Northwest, the upper Midwest and Great Plains, west Texas, and Mississippi River valley, that appear to have most worrisome mismatch between falling wild bee supply and rising crop pollination demand.
These counties tend to be places that grow specialty crops – such as almonds, blueberries and apples – that are highly dependent on pollinators. Or they are counties that grow less dependent crops, such as soybeans, canola and cotton, in very large quantities.
Of particular concern, Ricketts says some crops most dependent on pollinators – including pumpkins, watermelons, pears, peaches, plums, apples and blueberries – appeared to have the strongest pollination mismatch, growing in areas with dropping wild bee supply and increasing in pollination demand.
Pesticides, climate change and diseases threaten wild bees, but their decline may be caused by the conversion of bee habitat into cropland, the study suggests.
In 11 key states where the map shows bees in decline, the amount of land tilled to grow corn spiked by 200% in five years, replacing grasslands and pastures that once supported bee populations.
“Most people can think of one or two types of bee, but there are 4,000 species in the U.S. alone,” says Insu Koh, a UVM postdoctoral researcher who co-hosted a AAAS pollinator panel and led the study.
“When sufficient habitat exists, wild bees are already contributing the majority of pollination for some crops,” Koh says. “And even around managed pollinators, wild bees complement pollination in ways that can increase crop yields.”
A team of seven researchers from UVM, Franklin and Marshall College, University of California at Davis, and Michigan State University created the maps by first identifying 45 land-use types from two federal land databases, including croplands and natural habitats.
They then gathered detailed input from national and state bee experts about the suitability of each land-use type for providing wild bees with nesting and food resources.
Next, they built a bee habitat model that predicts the relative abundance of wild bees for every area of the contiguous U.S., based on their quality for nesting and feeding from flowers.
Finally, the team checked and validated their model against bee collections and field observations in many landscapes.
“The good news about bees is now that we know where to focus conservation efforts, paired with all we know about what bees need, habitat-wise, there is hope for preserving wild bees,” Ricketts says.