Stinging Descent: Knoxville article on disappearing bumble bees

By Morgan Simmons
Thursday, April 10, 2008

The collapse of honeybee colonies across the U.S. appears to have a parallel among bumblebees.

In the late 1990s, researchers began noticing a dramatic decline in three of North America’s most common bumblebee species – the western bumblebee (Bombus occidentalis), yellow-banded bumblebee (Bombus terricola) and the rusty-patched bumblebee (Bombus affinis).

Of these species, the yellow-banded and rusty-patched bumblebees are found in the Eastern U.S., where they play an important role in crop and wildflower pollination.

The Xerces Society, a nonprofit organization dedicated to the conservation of
invertebrates, has launched a nationwide effort to piece together the current and former
distribution of these species.

In addition to working with scientists, the organization also is reaching out to beekeepers, gardeners and state agencies to determine the current status of these bumblebees.

Scott Black, executive director of the Xerces Society, said it’s going to take time to unravel the mystery.

“Most people aren’t even aware,” Black said. “That’s why we started this campaign.”

One of the disappearing bumblebees, the rusty-patched bumblebee, once was abundant throughout the Eastern United States, said Black.

“If you grew up in Maine down to Tennessee and across to Minnesota, you would have seen this bumblebee,” he said. “We surveyed dozens of scientists, and they’re not finding it anymore.”

Researchers aren’t sure what’s causing the decline. One theory is that wild bumblebees have been infected with a pathogen brought back by bees reared commercially in Europe for the purpose of pollinating greenhouse tomatoes and other crops.

Other factors may include habitat destruction, pesticides, invasive species, natural pest or predator population cycles and even climate change.

Researchers at the Great Smoky Mountains National Park have strong evidence of the bumblebee decline, thanks to the All Taxa Biodiversity Inventory, a research initiative aimed at collecting, identifying and cataloguing all the life forms in the park.

Adriean Mayor, curator for the museum for the park’s Twin Creeks Science and Education Center, said neither the yellow-banded bumblebee nor the rusty-patched bumblebee have been observed in the Smokies since 2002.

“When we surveyed them in the 1990s, we got a few specimens,” Mayor said. “By 2002, people who were collecting in the field told me these species had essentially disappeared from sites they had been surveying for years.”

The Smokies are home to 13 species of bumblebees.

Mayor said one of the park’s more common bumblebee species, Bombus bimaculatus, does not appear to be in trouble.

Bumblebees are active in cooler weather and lower light levels than honeybees. They’re also “buzz” pollinators, which enables them to dislodge pollen that otherwise would remain lodged in the flower’s anthers.

Tomatoes, peppers and blueberries are some of the plants that require buzz pollination.

Janet Rock, a botanist with the Smokies, said the park contains several rare plants that include bumblebees among their pollinators.

According to the Xerces Society, the economic value of insect-pollinated crops in the U.S. in 2000 was estimated at $20 billion.

Scientists say the decline in managed hives of European honeybees because of disease, pests and Colony Collapse Disorder makes the role of wild native bees as pollinators even more important.

Honeybees are not considered a native species since they did not exist in North America until European settlers brought them over.

The Smokies have 212 species of native bees. In addition to bumblebees, they include plasterer bees, cuckoo bees, leafcutter bees, yellow-faced bees, sweat bees and various species of solitary bees.

The park’s ATBI study has documented 121 species of native bees that were previously unknown to exist in the Smokies, as well as four species that are new to science – that is, previously unknown to have existed anywhere on the planet.

According to the Xerces Society, the U.S. has 4,000 species of native bees that pollinate about $3 billion worth of agriculture each year.

Scott Black of the Xerces Society said he is concerned that native pollinators in general may be declining because of a range of factors, including habitat loss from modern farming practices, as well as pesticides.

“Most native bees are small and hard for the layperson to identify,” Black said. “The reason we have a sense that bumblebees are declining is not because they’re disappearing at a faster rate than other native bees, but because they’re bigger and easier to see.

“With other native bees, there’s a paucity of knowledge.”

© 2008 Knoxville News Sentinel