Entomologist Robbin Thorp of University of California at Davis has surveyed for the elusive creature since 1994, but hasn't spotted one since 2006, when he saw only a single bee.

The rare Franklin's bumblebee has not been seen in Southern Oregon for four years and may already be extinct, but a conservation group holding out hope for its survival has petitioned to have it listed as an endangered species.

The Xerces Society for Invertebrate Conservation Wednesday petitioned the U.S. Fish and Wildlife Service to list the bee, said Scott Hoffman Black, the group's executive director in Portland.

"We're really concerned it may be extinct, but it might not be," Black said. "We need to do some surveys and make sure its sites are protected from pesticides, off-road vehicles and excessive grazing."

Entomologist Robbin Thorp of University of California at Davis has surveyed for the elusive creature since 1994, but hasn't spotted one since 2006, when he saw only a single bee.

Thorp plans a survey of high-elevation habitats for the bee, which once "wasn't uncommon" from Roseburg to Mount Shasta, between the Cascades and Coast Range, said Black, but has "trudged down steadily" since the mid-90s.

"We still have hopes it's hiding under the radar," said Thorp. "If it's still out there, it needs protection."

The main threat to the bee is the parasitic Nosema ceranae fungus, which appears to have spread from commercial bumblebee operations a dozen years ago, said Thorp. Human activity — urbanization and use of pesticides — has compounded the problem, he said.

"We have a little bit of hope," Thorp added, because the more common Western bumblebee, also affected by the fungus, appears to have built up some resistance and has begun to reappear in its historic range.

The endangered bumblebee is a ground-dwelling "generalist," pollinating a wide variety of plants, Thorp said, adding he doesn't yet know if its decline would affect any plants that depend on pollination.

The decline in the bee's numbers and the petition for its listing as endangered "are really a wake-up call, because it's one of many pollinators in decline and it may be too late to save other pollinators also," said Black.

"The loss of one isn't going to have huge ramifications for plants," he said. There are a dozen or so varieties of bumblebees living in Southern Oregon. But if you lose two or three, when do you start seeing a change in these plant communities?"

The Xerces Society is named for a butterfly that was wiped out when the Presidio in San Francisco expanded in World War II. It tries to protect habitat by working with farmers, land owners and agencies to restore lands adjacent to farms, to modify public land management policies and to provide education on pesticide use, said Black. It resorts to legal action only in rare cases, he said.

"The loss of any species is tragic, especially pollinators," said local naturalist Pepper Trail. "Wild plants are completely dependent on pollinators and loss of one can have a cascading effect on plants. That's why we need to check on them. There's reason to fear they are extinct."

The troublesome fungus started in the 1990s when the U.S. Department of Agriculture's Animal and Plant Health Inspection Service allowed bumblebee queens to be exported to Europe to help raise colonies for pollination of greenhouse crops, said Thorp in his Web site, entomology.ucdavis.edu/news/robbinthorp.html. The drop in numbers of American bumblebees started on their return, he notes.

John Darling is a freelance writer living in Ashland. E-mail him at jdarling@jeffnet.org.