Four species of bumblebees are in a rapid decline, possibly because of increased fungal infections and inbreeding. Researchers called the findings of the study, published in the Proceedings of the National Academy of Sciences, "disturbing" and said they were in line with findings in Europe.
"Disturbing reports of bumblebee population declines in Europe have recently spilled over into North America, fueling environmental and economic concerns of global decline," the authors wrote.
To find and count the bees, teams of researchers across the United States visited fields of flowers where hives had historically been found and gently scooped up the insects in butterfly nets.
The disappearing bees have scientists somewhat perplexed. They think a disease-causing pathogen, Nosema bombi, as well as a "lack of genetic diversity" could be plaguing the insects, but they haven't been able to prove it yet. Cameron said the Nosema bombi pathogen seems to make it difficult for queen bees to survive the winter so they can reproduce.
Honeybees in the United States are also in trouble. They are suffering from a phenomenon called "colony collapse," a disorder that seems to kill massive numbers of a hive's worker bees. Scientists aren't entirely sure what's causing the disorder, but they suspect a virus may be to blame.
"A bumblebee colony would be doing pretty good if it could simply replace itself," Delaplane told AOL News by phone today. "The study is telling us that fewer hives are able to do this, however. Colonies are becoming less and less successful at replacing themselves."
Cameron said the next step is to find out whether there's a direct link between the Nosema bombi pathogen and the decline of bees in the United States. She said scientists suspect that the disease may not be native to bees in North America and may have become a problem in the early 1990s when European beekeepers brought bees to the United States to help expand the honeybee industry.