DAVIS —When University of California, Davis entomologist Robbin Thorp begins his annual scientific survey for the critically imperiled Franklin’s bumblebee this spring in its narrow distribution range of southern Oregon and northern California, he fears he may not find it.

He’s seen the distinctive black-faced bumblebee, splashed with yellow markings on its thorax and atop its head, only once in the last five years.

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.

“I’ve seen Franklin’s bumblebee only once in the last five years,” Thorp said. “I didn’t find it in 2007. I didn’t find it in 2004 or 2005. The last time I saw it was in August 2006 at Mt. Ashland when I spotted a single, solitary worker.”

“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, a 45-year researcher of bumblebees. Although he retired from a 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 our 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,” he said, “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. Its range is about 190 miles north to south and 70 miles east to west in a narrow stretch between southern Oregon and northern California between the coast and Sierra-Cascade ranges.”

Its known distribution includes Jackson, Douglas and Josephine counties in Oregon and Siskiyou and Trinity counties in California. It lives at elevations ranging from 540 feet in the north to 6800 feet in the south.

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, Thorp said. Neither Oregon nor California allows listing of insects under their respective state endangered species statutes.

Over the past six years, Thorp has averaged over 43 visits per year to sites in southern Oregon and northern California. He visits both historic and non-historic sites.

“Each year since 1998, I’ve made about 3-5 trips of several days each in search of Franklin’s bumblebee,” he said. “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.”

In 1998, he sighted 100 of the Franklin namesake. “It was relatively common,” he said. “It was within the top 10 of the 20 or so species I was searching for.”

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.

It’s not just Franklin’s bumblebee that’s at risk. Populations of the Western bumblebee (Bombus occidentalis) and two close relatives in the east, the Rusty-patched bumblebee (B. affinis) and the Yellow-banded bumblebee (B. terricola) are rapidly dwindling, too, Thorp said.

Thorp theorizes that commercialization of bumblebees sparked the spread of diseases that has contributed to their steep decline. “In the early 1990s, USDA/APHIS (Animal and Plant Health Inspection Service of the U.S. Department of Agriculture) allowed export of two species of North American bumblebee queens to Europe to rear colonies to pollinate our greenhouse crops,” he said. “When the colonies were shipped back to us, I suspect they may have picked up diseases from European bumblebees. Western and Franklin bumblebees began declining at the same time while other bumblebees were thriving in the same area.”

Circumstantial evidence points to a species of the single-celled fungus, Nosema, that’s known to affect bumblebees but not honey bees, he said. “It’s likely that the Nosema outbreak in commercial bumblebee production facilities in North America reported in 1998 is also responsible for the severe declines seen in Franklin’s bumblebee and the Western bumblebee and their two close relatives in the east.”

The bumblebee, a third larger than the honey bee, lives underground, often in abandoned rodent burrows. Their colonies die by autumn and are started anew the following spring by queens that hibernated over the winter. The bumblebees produce only enough honey for their small colony, usually numbering less than several hundred, while honey bees live in 50,000-member hives and store honey throughout the year.

Although bumblebees differ greatly within and between species, especially in size and tongue length, generally bumblebees are considered more efficient and effective pollinators than the honey bee, Thorp said. Their larger and more furry bodies allow them to catch more pollen; the longer tongues of some species enable them to dip inside long-tubed flowers, such as larkspurs and columbine; they visit a broader range of flowers; and they generate their own body heat, enabling them to forage earlier in the day and on overcast days when honey bees stay in their hives.

Bumblebees are especially suited for tomato flowers. “Tomato flowers require buzz pollination,” Thorp said. The anthers (part of the stamen that contains the pollen) have to be vibrated or buzzed to release the pollen to enable pollination. Bumblebees are very effective at this.”

Thorp estimated that bumblebees pollinate 42 percent of families of flowering plants in California. “They fly farther between stops and are more likely to move from plant to plant, rather than just from flower to flower on a single plant or tree, which is important for cross pollination.”

A 2006 National Academy of Sciences study reported that many pollinators are at risk in North America, and that many species are disappearing from local areas. “We don’t have lot of good background monitoring data,” Thorp said. “We’re beginning to find that museum collections give us good baseline data.”

One third of food we eat comes from crops that require pollination, said Thorp, who also teaches bee courses for the American Museum of Natural History of New York at their field station in Arizona and chairs the Advisory Committee for the Jepson Prairie Reserve, a vernal pool ecosystem located near Dixon.

Bumblebee and other pollinators, such as the blue orchard bee, could reduce the overdependence on the honey bee and relieve concerns about food security and agricultural sustainability. Thorp noted that California’s 600,000 acres of almonds require two beehives per acre or 1.2 million colonies for pollination from mid-February to mid-March. About half of the commercial bees in the United States are moved to California during that period.

To protect the bumblebees, Thorp advocates that we prevent the spread of diseases from commercially reared and managed bumblebee colonies to native populations. “Companies in Europe, Israel and Canada have adapted bumblebees for commercial use. We need to ensure that stocks of bees and all that we export and import around the world for breeding are free of diseases.”

And, Thorp said, we need to learn more about the virulence and cross-infectivity of strains of disease organisms, such as Nosema bombi, between commercially reared bumblebees and bumblebee species in the wild.

Urbanization and the extensive use of pesticides are other crucial concerns. To continue to survive, bumblebees need a habitat providing pollen and nectar resources, abandoned rodent burrows for their nests, and queen hibernation sites.

"We are delighted to have an internationally recognized expert in native bees of the caliber of Robbin Thorp as part of our team to rebuild the bee biology program at UC Davis," said Walter Leal, professor and chair of the UC Davis Department of Entomology. "More and more it is becoming clear that the solution for the current pollination crisis is a multi-faceted approach in which native bees will play a pivotal role."