See Where Wild Bees Are Disappearing Across the U.S.

A first-of-its-kind study shows the decline of pollinator populations is bad news for California and other agricultural states.
(Photo: Brendan McDermid/Reuters)
Jan 13, 2016· 2 MIN READ
John R. Platt covers the environment, wildlife, and technology and for TakePart, Scientific American, Audubon, and other publications.

America’s wild bees are in decline, and that could cause major problems for some of the nation’s most important agricultural states.

Scientists already knew that the insects were in trouble, but a new study finds that wild bee populations fell in 23 percent of the continental United States between 2008 and 2013. Another 9 percent of the country experienced likely but as-yet-unquantified bee population declines. According to the study, the pollinators are now at risk in 139 counties across the country, many of which are in key agricultural areas such as California’s Central Valley and the Midwest’s corn belt.

Lead author Insu Koh, a postdoctoral associate at the University of Vermont, said the study offers the first coast-to-coast snapshot of the die-off. It also reveals a previously unquantified risk. “The most surprising aspect of our findings was that the wild bee declines are most likely in so many key agricultural areas, which need pollinators the most,” he said.

The study found what Koh called a “mismatch” between the crops most in need of pollinators and the areas that have experienced the greatest wild pollinator losses. According to the study, 39 percent of U.S. croplands that rely on pollination now face a potential bee shortage. Crops that could suffer because of the lack of wild pollinators include apples, peaches, blueberries, watermelons, pumpkins, and almonds. Managed pollination with commercially raised honeybees can pick up some of the slack but not all of it, because the supply of honeybees, whose populations have also plummeted, has not kept up with rising demand, according to the study.

(Map: Courtesy the University of Vermont)

The researchers also found bee declines around many crops that are less dependent on pollination, such as soybeans, canola, and cotton. Those crops tend to be grown in large fields that replace essential habitats for wild bees.

Other than conversion of habitat into agricultural land, the study didn’t examine the specific causes of wild bee declines, although those are wide and varied. “More research is also needed to understand the dynamics of how climate change, pesticides, and habitat loss impact different species of bees across different areas,” Koh said.

RELATED: Wild Bees Could Save Our Crops—If We Save Them

(Map: Courtesy the University of Vermont)

The study based its conclusions on several factors, including changes in land use over the five-year period, trends in total wild bee abundance, and trends in the demand for commercial pollination services. More than a dozen experts provided assessments of habitat conditions and bee populations around the country.

The researchers didn’t try to determine the health of each of the estimated 4,000 U.S. wild bee species, many of which are at risk or endangered, and instead focused on estimating the total number of wild bees in each county, regardless of species. Determining exactly which species are at risk “would be interesting and important to explore in the future, now that we have an initial national portrait,” Koh said.

In addition to the need to look at individual bee species, Koh said the study shows where new information is needed. “Our research can help direct future bee surveys and monitoring to places and crops where the least amount of good data exists,” he said.

More important, however, it provides a road map both for conservation and for preserving the country’s agricultural economy. “We hope these findings can help direct habitat restoration efforts to areas where they will most benefit bees and farmers,” Koh said.