When UC Davis Entomologist Robbin Thorp begins his annual scientific survey for the critically imperiled Franklin's bumblebee this spring in its narrow distribution range, he fears he may not find it.
Over the past six years, Thorp has averaged over 43 visits per year to sites in southern Oregon and northern California.
"I count all bumblebees at each locality I visit to get an idea of relative abundance of some 20-plus species of bumblebees in the area," Thorp said.
In 1998, he sighted about 100 Franklin's bumblebees.
"It was relatively common," he said. "It was within the top 10 of the 20 or so species I was searching for."
But in the last five years, he has seen the distinctive black-faced bumblebee only once. The bumblebee that Thorp so readily recognizes by its solid black abdomen and a black inverted U-shaped design on its yellow thorax may be extinct.
"The last time I saw it was in August 2006 at Mt. Ashland when I spotted a single, solitary worker." Thorp said. "It appears that Franklin's bumblebee may be extinct before it even made the endangered insects list."
Its decline, disappearance and possible demise, closely linked to the widespread decline of native pollinators in North America, should concern all facets of society, he said.
"The loss of a native pollinator could strike a devastating blow to the ecosystem, economy and food supply," said Thorp, who has researched bumblebees for 45 years. Although he retired from his 30-year career at the UC Davis Department of Entomology in 1994, he continues his research on native pollinators and pollinator decline.
Unlike honey bees, which European colonists brought to eastern North America in the 17th century, bumblebees are natives. Both are in trouble.
"The Western bumblebee, a close relative of Franklin's, was once common from Monterey County to southern British Columbia," said Thorp, a fellow of the California Academy of Sciences since 1986. "They are virtually undetectable in those areas now."
Bumblebees, commercially reared to pollinate greenhouse tomatoes, peppers and strawberries, pollinate about 15 percent of food crops, valued at $3 billion, he said. Wildlife, including birds, elk, deer and bears depend on pollination of fruits, nuts and berries for their survival.
"We're disturbing, destroying and altering the habitat where the native pollinators exist," Thorp said. "One of the main reasons the Franklin's bumblebee is at risk is because it has such a small geographical range. It has the most restricted distribution range of any bumblebee in North America and possibly the world."
The range of Franklin's bumblebee is a swath of Northern California and Southern Oregon about 190 miles long and 70 miles wide at elevations from 540 feet to 6800 feet. Its known distribution includes Jackson, Douglas and Josephine counties in Oregon and Siskiyou and Trinity counties in California.
Franklin's bumblebee (Bombus franklini), named in 1921 for Henry J. Franklin, who monographed the bumblebees of North and South America in 1912-13, frequents California poppies, lupines, vetch, wild roses, blackberries, clover, sweet peas, horsemint and mountain penny royal during its flight season, from mid-May through September. It collects pollen primarily from lupines and poppies and gathers nectar mainly from mints.
Franklin's bumblebee is currently considered a "species of concern" by the Fish and Wildlife Service, Bureau of Land Management, Oregon Department of Fish and Wildlife and the California Department of Fish and Game. It has no legal protection under the U.S. Endangered Species Act. Neither Oregon nor California allows listing of insects under their respective state endangered species statutes.
Thorp estimates 250 different species of bumblebees exist worldwide, with approximately 45 species in the United States and Canada. "California has 27 species — or we did have," he said.