Study Says Bumblebees Experiencing Large Population Drop

Some bumblebee populations in the United States are dropping at an alarming rate, and University of Illinois researchers are investigating the potential causes.

There are 50 species of bumblebees in North America. Researchers examined eight of them, and discovered that in the last 20 years, half of the species declined in relative abundance by as much as 96 percent and experienced a reduction in geographic range by as much as 87 percent.

The researchers compared historical data from 73,000 museum records dating back to the late 1800s with recent U.S. national surveys of more than 16,000 specimens from about 400 sites.

U of I entomologist Sydney Cameron, the lead author of the three-year study, said the rate of decline marks an important finding because bumble bees play important roles in the country's food production.

"That certainly could impact the efficiency of our food production for many crops, such as cranberries, blueberries, tomatoes," Cameron said. "Bumble bees are especially good pollinators of these types of crops."

Cameron said the bumblebees with significant population declines have a lower genetic diversity than bumblebees with healthier populations. She also said it has been hypothesized that North American queen bees may have brought a parasite, known as Nosema bombi, back to the United States from Europe after being raised in the rearing facilities of native bumble bees. However, she said it is unknown if these factors contributed to some species dying out.

"No one's pointing a finger at anyone," she said. "We're just trying to figure out where the Nosema that we're finding in our North American bees came from."

Scientists last year looked at another phenomenon affecting honeybees called "colony collapse" in which large numbers of a hive's worker bees disappear. Research suggests a fungus and virus may be to blame.

The reason for the population decline among the honeybees is still being determined. It may have something to do with climate change, disease, or even low genetic diversity, according to some researchers. But Cameron noted that it is too early to jump to any conclusions.

The report was published in the Proceedings of the National Academy of Sciences.

(Photo courtesy of Johanna James-Heinz)