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Bumblebees Suffer Alarming Decline In The US

January 4, 2011

Four species of bumblebees that were once abundant in the United States are now close to becoming extinct, researchers said on Monday in a study confirming that the important insects are being affected globally.

The researchers documented a 96 percent downfall in the numbers of the four species, and also confirmed their range had shrunk by as much as 87 percent.

“We provide incontrovertible evidence that multiple Bombus species have experienced sharp population declines at the national level,” the researchers reported in the Proceedings of the National Academy of Sciences.

“These are one of the most important pollinators of native plants,” Sydney Cameron of the University of Illinois, Urbana, who led the study, said in a telephone interview with Reuters, adding that the team found the results “alarming.”

In recent years, experts have documented the disappearance of bees in what is widely known as colony collapse disorder (CCD), blamed on a range of factors including parasites, fungi, viruses, pesticides and stress.

But most of the studies were focused mainly on honeybees.

Bumblebees are also important pollinators, said Cameron, but they are far less studied. Bumblebees pollinate important plants such as tomatoes, blueberries and cranberries, she noted.

“The 50 species (of bumblebees) in the United States are traditionally associated with prairies and with high alpine vegetations,” Cameron added. “Just as important — they land on a flower and they have this behavior called buzz pollination that enables them to cause pollen to fly off the flower.”

Smaller bees can accomplish the same task of pollinating tomatoes as bumblebees, but only if enough cluster on a single flower.

The disappearance of bumblebees in Europe and Asia has been well-documented, but nobody has done a large national study in the Americas.

Cameron and colleagues carried out a three-year study of 382 sites in 40 US states and also looked at more than 73,000 museum records. “We show that the relative abundance of four species have declined by up to 96 percent and that their surveyed geographic ranges have contracted by 23 percent to 87 percent,” they wrote.

While crops are not in any immediate danger from the bumblebee decline, the results do show that experts need to pay very close attention to the issue, Cameron said. Pollinators such as bees often have specific tongue lengths and pollination behaviors that have evolved along with the species of plants they interact with.

Bumblebees can thrive and fly in much colder temperatures than other species, and are key pollinators of native species in the tundra and at higher elevations, said Cameron.

“This is a wake-up call that bumblebee species are declining not only in Europe, not only in Asia, but also in North America,” she said.

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