The rusty patched bumblebee, once one of the most common bees buzzing about Minnesota’s gardens, could be on the verge of extinction and is likely to be the first of its kind to find a place on the federal endangered species list.

The U.S. Fish and Wildlife Service has proposed legal protection for the bee, named for the distinctive orange marking on its back, after an extraordinarily swift decline in its numbers over the past two decades.

Like dozens of other pollinators, the rusty patched is suffering from widespread use of chemical pesticides, an increasingly flowerless landscape, disease and climate change.

But its decline also illustrates the often unexpected consequences for insects from the way people grow their food. Along with three of its cousins, the rusty patched may be succumbing to a fungal epidemic spread by commercial bumblebees, which are bred and sold for pollination in greenhouses, cranberry bogs, blueberry fields and apple orchards.

“This is dramatic,” said Sheila Colla, an entomologist at York University in Toronto. “There aren’t many ways a species can disappear in a large landscape that rapidly.”

Once a frequent sight buzzing across much of the Upper Midwest and East Coast, only 72 rusty patched bumblebees have been seen since 2000, said Rich Hatfield, who tracks them for the Xerces Society for Invertebrate Conservation.

About a third of those sightings were in Minnesota, but that doesn’t necessarily mean the bee is doing better here. It could be that more people here are looking for it, thanks to wild bee surveys sponsored by the state Department of Natural Resources and the University of Minnesota’s Bee Lab.

In fact, it’s difficult to know just how many rusty patched or other bumblebees are around: Unlike honeybees raised by beekeepers, no one pays much attention to wild bees, said Elaine Evans, the U entomologist conducting the bee surveys.

But documenting their whereabouts is becoming increasingly vital to their survival, Evans said. Scientists need to know what conditions they like, where they spend the winter, and even where they could be collected if someday it proves that raising them in captivity is the only way to save them.

“Where they are is a big one,” Evans said.

The Xerces Society has launched a nationwide effort to track the insects through a program called Bumblebee Watch. Anyone who sees a bumblebee can take a photo and send it to the Xerces Society with the date and location. “By getting more eyes out there, maybe we will find populations that are doing well,” Colla said.

But unless unknown pockets of the rusty patched suddenly pop up, the chances for its long-term survival are grim, scientists say. Like all wild bees, it’s probably more susceptible to pesticides like neonicotinoids that have been implicated in the decline of honeybees. And wild bees rely more than commercial bees on native wildflowers, which are disappearing from the landscape with the expansion of row crops and lawns across the Upper Midwest.

Rapidly evolving weather patterns from climate change may also be a culprit — including a shift in the bloom time of early spring flowers that bumblebees rely on when they emerge from hibernation.

But scientists say the rusty patched may have suffered a killer blow that other species escaped: an epidemic spread from bumblebees used in commercial pollination.

‘Buzz pollination’

Like honeybees, bumblebees are playing a growing role in world agriculture. Millions of colonies are reared and transported around the world every year to pollinate crops such as tomatoes and apples.

They are one reason why greenhouse tomato operations like Bushel Boy Farms in Owatonna are flourishing year-round even in cold climates like Minnesota’s. Owner Keith Kersten relies on regular shipments of bumblebees in cardboard boxes to pollinate the rows and rows of tomatoes in his greenhouses, destined for Twin Cities grocery stores.

Once upon a time, tomato flowers were pollinated by hand, an expensive and time-consuming procedure. But bumblebees are uniquely qualified for the job. Their heavy vibration results in what’s called “buzz pollination,” forcing the pollen out of the flower and onto the bee.

And unlike honeybees, each bumblebee colony lives for just one season; only the queens survive the winter to reproduce the following year. That means the colonies don’t need to be shipped back when pollination is over.

In 1997, commercial bumblebee growers in California reported that their factories had been decimated by disease from a fungus called nosema. It’s common among bumblebees, said Sydney Cameron, an entomologist at the University of Illinois. But when insects are massed together in large groups, their pathogens evolve to become more lethal than they are under natural conditions, she said.

“There are so many hosts, the hosts become expendable,” she said.

And that’s the same time that the rusty patched and its relatives began disappearing. Scientists have found that wild bumblebees around greenhouses and fields using commercial bumblebees carry far more infections than those farther away.

Cameron even compared the frequency of nosema in wild bees over time by studying dead specimens contained in natural history collections. She found that after 1997, there was a huge increase in the number of wild bees that carried the fungus.

Certified disease-free?

Commercial bumblebee growers say that the connection between their bumblebees and the decline in wild bees has not been proved, and that honeybees also transmit infections to wild bees. Moreover, they say, they have a vested interest in keeping their colonies disease-free. They now screen for some diseases, and even sterilize the pollen that the bumblebees eat to make sure to minimize the infections from the honeybees that produce it.

“We are very much concerned,” said Felix Wäckers, head of research and development for Biobest, a Belgian company that pioneered the use of bumblebees for pollination.

But the Xerces Society and other researchers argue that commercial bumblebee producers need more oversight and should be held to consistent standards around the world. Wild bees are already weakened by exposure to pesticides and lack of forage, making them more vulnerable to diseases that could be spread by bees moving around the world.

“Until there is an independent agency that is certifying these bees as disease-free before they head to market, I remain very skeptical of their claims,” said Hatfield of the Xerces Society.

It’s also possible that the rusty patched could bounce back, Cameron said. The surviving bumblebees could be the ones that are resistant to the disease, and they could form the base for a new population. Winning a place on the endangered species list might help, she said, because it would come with greater protections for habitat and funding for conservation.

At least, she said, “it can’t hurt.”