The first national study to map U.S. wild bees suggests they’re disappearing in many of the country’s most important farmlands — including California’s Central Valley, the Pacific Northwest and the upper Midwest.
If losses of these crucial pollinators continue, the new nationwide assessment indicates that farmers will face increasing costs — and that the problem may even destabilize the nation’s crop production.
The findings were published Dec. 21 in the Proceedings of the National Academy of Sciences.
A research team led by Insu Koh at the University of Vermont estimates that wild bee abundance between 2008 and 2013 declined in 23% of the contiguous U.S. The study also shows that 39% of U.S. croplands that depend on pollinators — from apple orchards to pumpkin patches — face a threatening mismatch between rising demand for pollination and a falling supply of wild bees.
The new study identifies 139 counties in key agricultural regions of California, the Pacific Northwest, the upper Midwest and Great Plains, west Texas, and the southern Mississippi River valley that have the most worrisome mismatch between falling wild bee supply and rising crop pollination demand. These counties tend to be places that grow specialty crops — like almonds, blueberries, and apples — that are highly dependent on pollinators. Or they are counties that grow less dependent crops — like soybeans, canola and cotton — in very large quantities.
Of particular concern, the study shows that some of the crops most dependent on pollinators – including pumpkins, watermelons, pears, peaches, plums, apples and blueberries – have the strongest pollination mismatch, with a simultaneous drop in wild bee supply and increase in pollination demand.
Pesticides, climate change, and diseases threaten wild bees — but the new study also shows that their decline may be caused by the conversion of bee habitat into cropland. In 11 key states where the new study 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. “These results reinforce recent evidence that increased demand for corn in biofuel production has intensified threats to natural habitats in corn-growing regions,” the new study notes.
“By highlighting regions with loss of habitat for wild bees, government agencies and private organizations can focus their efforts at the national, regional, and state scales to support these important pollinators for more sustainable agricultural and natural landscapes,” says Michigan State University’s Rufus Isaacs, one of the co-authors on the study and leader of the Integrated Crop Pollination Project, a USDA-funded effort that supported the new research.