Robbin Thorp's Mission: Saving Franklin's Bumble Bee

July 27, 2010

Bumble bee expert Robbin Thorp with a photo he took of Franklin's bumble bee. (Photo by Kathy Keatley Garvey)

(August 2011 Update: On his last trip in mid-August, Robbin Thorp didn't see Franklin's bumble bee but he did find the endangered Western bumble bee.)
DAVIS--Native pollinator specialist Robbin Thorp of the University of California, Davis, hopes that the critically imperiled Franklin’s bumble bee will soon be listed as an “endangered species” under the Endangered Species Act. “It may already be extinct, but I am hopeful that it is still out there ‘under the radar,’” said Thorp, a noted bumble bee authority and an emeritus professor of entomology at UC Davis. “I haven’t seen a Franklin’s bumble bee since August 2006 and that was a single, solitary worker at Mt. Ashland.”

In 1998 Thorp began intensive annual monitoring of Franklin’s bumble bee in its narrow distribution range of southern Oregon and northern California. That first year he counted 100.

Then the population began declining precipitously, which Thorp hypothesizes may be due to an exotic disease spread from commercial bumble bee colonies to wild bumble bee populations. His scientific surveys, conducted three to five times a year, several days each time, showed only three Franklin’s bumble bees in 2003, one in 2006, and none since then.

Franklin's bumble bee. Photo by Robbin Thorp.

He will return to the area in late July and again in mid-August for more monitoring.

“The decline of Franklin’s bumble bee is a signal that something is wrong in its environment,” said Thorp, a member of the California Academy of Sciences since 1986. “This is the canary-in-the-coal-mine measure.”

The bumble bee, mostly black, has distinctive yellow markings on the front of its thorax and top of its head. It has a solid black abdomen with just a touch of white at the tip, and an inverted U-shaped design between its wing bases.

“Franklin’s bumble bee has the smallest range of distribution of any of our 60 species of North American bumble bees, and perhaps of the 250 bumble bees in the world,” Thorp said. Its range covers about 190 miles north-south and 70 miles east-west. The known distribution includes Siskiyou and Trinity counties in California; and Jackson, Douglas and Josephine counties in Oregon.

This bumble bee is partly at risk because of its very small range of distribution,” he said. “Adverse effects within this narrow range can have a much greater effect on it than on more widespread bumble bees.”

On June 23, Thorp and The Xerces Society for Invertebrate Conservation, headquartered in Portland, Ore., petitioned the U.S. Fish and Wildlife Service to protect Franklin’s bumble bee (Bombus franklini) by listing it in the Endangered Species Act. Enacted in 1973, the Endangered Species Act seeks to protect critically imperiled plant and animal life from extinction. Secondly, it aims to recover and maintain those populations by removing or lessening threats to their survival. A species may decline due to habitat destruction or modification; disease or predation; or other reasons.

A decision on Franklin’s bumble bee is expected within 90 days.

If it’s given protective status, this could “stimulate research into the probable causes of its decline,” said Thorp, an active member of The Xerces Society. “This may not only lead to its recovery, but also help us better understand environmental threats to pollinators and how to prevent them in future. This petition also serves as a wake-up call to the importance of pollinators and the need to provide protections from the various threats to the health of their populations.”

Since the petition announcement, reaction from the public has ranged from strong approval to outright negativity: “Why do we need more bumble bees—we already have a lot of bumble bees.”

“ Yes, I am getting quite a few responses, some with photos--carpenter bees, yellow-faced bumble bees--but none of B. franklini yet,” he said. Some contacts blame the decline on “chemical gases and dust, cell phone towers and nuclear war testing,” he said.

How valuable is Franklin's bumble bee? "...in the grand scheme of our planet and its environmental values, I would say it is priceless.”--Robbin Thorp

Said Thorp: “People often ask the value of Franklin’s bumble bee. In terms of a direct contribution to the grand scale of human economies, perhaps not much, but no one has measured its contribution in those terms. However, in the grand scheme of our planet and its environmental values, I would say it is priceless.”

“Loss of a species, especially a pollinator, diminishes our global environment,” he said. “Bumble bees provide an important ecological service--pollination. This service is critical to reproduction of a huge diversity of plants that in turn provide shelter, food (seeds, fruits) to diverse wildlife. The potential cascade of effects from the removal of even one localized pollinator may affect us directly and indirectly.”

Some wonder if it’s too late to provide protection for a species that may already be extinct.

“Other species, especially plants and insects, thought to be extinct have reappeared after years of not being seen,” the UC Davis scientist said. “When populations of species are in decline, they may reach such low levels that they are not detected for several years in a row, despite intensive surveys, flying under the radar so to speak. It is my hope that this is the case with Franklin’s bumble bee.”

“One positive sign,” Thorp said, “comes from increasing finds the past two years of a related species, the Western bumble bee, which exhibited similar declines at the same time and places. If these recent sightings are a sign of recovery for the Western bumble bee, I am
hopeful that similar recovery will be found with Franklin’s bumble bee.’

Loss of habitat and the increased use of pesticides are partly to blame for the bumble bee population decline, Thorp said, but he suspects that a fungus, Nosema bombi, may be the main culprit. Other bumble bee populations in peril are the Western bumble bee and the rusty-patched bumble bee in the west, and the yellow-banded bumble bee in the northeast.

As part of a collaborative USDA grant to research his hypothesis, Thorp just returned July 5 from a two-week research trip to southern France. He and colleague Sydney Cameron of the University of Illinois and Cameron’s post-doctoral researcher, Jeff Lozier, who received his doctorate in entomology from UC Berkeley, collected Bombus terrestris for pathogen studies. They also traveled with professor Pierre Rasmont, University of Mons, Belgium, a noted authority on bumble bees of the western Palaearctic. “He showed us the collection sites for the original commercial stocks of Bombus terrestris in southern France,” Thorp said.

Known for his expertise on bumble bees, Thorp served as one of the keynote speakers at a public symposium on “The Plight of the Bumble Bee” in June 2009 at the Smithsonian Institution, Washington, D.C. His topic: “Western Bumble Bees in Peril.”

Earlier this year, The Xerces Society petitioned the USDA’s Animal and Plant Health Inspection Service (APHS) to protect wild bumble bees from the threat of diseases brought in by commercial bumble bees. Xerces seeks to “prohibit the shipment of commercial bumble bees outside of their native ranges and to regulate the interstate transport of commercial bumble bees within their native ranges by requiring permits that show that bumble bees are certified as disease-free prior to movement,” according to a recent press release. .

Like Thorp, Xerces Society officials are adamant that Franklin’s bumble bee be saved.

“It is vital that the U.S. Fish and Wildlife Service act quickly to protect this bumble bee,” said Sarina Jepsen, The Xerces Society’s endangered species program director who holds a master’s degree in entomology from UC Davis. “We hope that an Endangered Species Act listing will encourage the USDA-APHIS to protect wild bumble bees from future threats posed by nonnative commercial bumble bees.”

Scott Hoffman Black, executive director of The Xerces Society, said the decline of Franklin’s bumble bee should serve as an alarm “that we are starting to lose important pollinators. We hope that Franklin’s bumble bee will remind us to prevent pollinators across the United States from sliding toward extinction.”

The Xerces Society plans to issue more petitions to protect native bumble bees.

More About Franklin’s Bumble Bee

Franklin's bumble bee was named in 1921 for Henry J. Franklin, who monographed the bumble bees of North and South America in 1912-13.
During its flight season, from mid-May through September, Franklin’s bumble bee frequents California poppies, lupines, vetch, wild roses, blackberries, clover, sweet pea, horsemint and mountain penny royal. It collects pollen primarily from lupines and poppies, and gathers nectar mainly from mints.
Look for its known distribution: Siskiyou and Trinity counties in California; and Jackson, Douglas and Josephine counties in Oregon.
Statistics show that bumble bees pollinate about 15 percent of the U.S. field crops in an industry valued at $3 billion, according to noted bumble bee expert Robbin Thorp, emeritus professor of entomology at UC Davis. Wildlife, including birds, elk, deer and bears depend on the pollination of fruits, nut and berries for their survival. Commercial bumble bees are reared to pollinate greenhouse tomatoes, peppers and strawberries.

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--Kathy Keatley Garvey
Communications specialist
UC Davis Department of Entomology
(530) 754-6894