It's not just honeybees that are in trouble. Wild bees are disappearing from much of the nation's farmland — especially in Minnesota and much of the Upper Midwest.

Overall, wild bees declined across nearly one-fourth of the country between 2008 and 2013. But some areas are now so inhospitable to wild bees that the nation's crops, including soybeans in western Minnesota, are probably not getting the pollination they need for peak production, researchers at the University of Vermont found in the first nationwide study to map the abundance of wild bees.

"Those farmers are going to be looking at inconsistent yields," said Taylor Ricketts, a professor at the University of Vermont, and one of the lead researchers on the study.

Wild bees provide $3 billion worth of pollination services to the nation's food system. Some crops, like almonds, blueberries and other fruits, are totally reliant on either domesticated honeybees that are trucked at a high cost, or wild insects that live around the fields. The researchers found that 39 percent of the croplands that need insects face a threatening mismatch between rising demand for pollination and a dwindling supply of wild bees.

In all, there are 139 counties with an imbalance, including Roseau and Otter Tail counties in Minnesota.

Hot spots are areas of the country growing the crops that need insects the most — central California, northwest Washington, Michigan and a vast stretch from western Minnesota through Iowa and the Dakotas. Minnesota alone accounted for nearly 13 percent of the overall decline, said Insu Koh, another author and researcher at the University of Vermont.

Where wild bees are in most trouble

Source: University of Vermont. Map by C.J. Sinner

In Minnesota, apple trees and soybeans, which need both wind and insects for peak production, are the primary crops that need pollinators.

Ricketts said that the decline is driven by the conversion of natural land into intensely managed row crops. In 11 key states where the study showed bees in precipitous decline, the amount of land tilled for corn spiked 200 percent in five years, the researchers found.

In California, global demand for nuts has created vast monocultures of orchards. In Minnesota and the rest of the Corn Belt, the federal biofuels mandate that drives ethanol production has eaten up millions of acres of prairies and pastures, he said.

"It reinforces what others have found," he said. "Corn is on the rise, and bees are declining."

The researchers used federal data to track changes between 2008 and 2013 on 45 different types of landscapes — including prairies, wetlands, forests and cropland. They then used detailed estimates from more than a dozen scientists to score how hospitable each type of land is for bees. Prairies, for example, provide ample nesting grounds and plenty of flowers for food. Cornfields, in contrast, provide no food or nesting sites, and insects are vulnerable to pesticides.

In all, they estimated that wild bees have declined on 23 percent of landscape, and 60 percent of that drop occurred in just 11 states, including Minnesota and the Dakotas.

Minnesota surveys bees

The Minnesota Department of Natural Resources is conducting a survey of the 400 wild bees that are native to the state, but the results are not in yet, said Crystal Boyd, a DNR entomologist. Still, the University of Vermont study fits with what's she's seeing on the landscape, she said. For example, surveyors have found only one yellow banded bumblebee, which is a species that should be pretty common, she said.

"It emphasizes the need for long-term monitoring to get a handle on population trends," she said.

Ricketts said that the research was designed to help figure out where conservation funds should be focused to protect and revive struggling insect populations.

"It's not really a mystery how to help pollinators." he said. "They need flowers, nesting sites, undisturbed soils and trees. And they need not to be poisoned by chemicals."

Earlier this year the White House released a pollinator protection plan that calls for bringing back 7 million acres of land as pollinator habitat.

Minnesota has enacted numerous conservation projects with pollinators in mind, including on the 450 square miles of land managed by the Board of Soil and Water Resources, millions spent on research and land protection from lottery and legacy funds, and the state's long-term plan to restore native prairie along the western edge of the state.

Josephine Marcotty • 612-673-7394