And the ailments were hurting bumblebees even more than the honeybees, said a study published in the journal . "Wild populations of bumblebees appear to be in significant decline in Europe, North America, South America and in Asia," said study author Mark Brown, of the University of London.

He said his study confirmed that a major source of the decline was "the spillover of parasites and pathogens and disease" from managed honeybee hives.

Smaller studies have shown disease going back and forth between the two kinds of bees. But Brown said his was the first to look at the problem in a larger countrywide scale and included three diseases and parasites.

University of Illinois entomology professor May Berenbaum, who wasn't involved in the study, said: "What the study shows is that the spillover for bees is turning into a boilover."

Study co-author Matthias Furst, of the University of London said the research did not definitely prove the diseases went from honeybees to bumblebees. But the evidence pointed heavily in that direction because virus levels and infection rates were higher in the honeybees, he said.

Bumblebees probably picked up diseases when they went to flowers after they had been visited by infected honeybees, Furst said. And sometimes bumblebees invaded honeybee hives to steal nectar, becoming exposed to diseases that way, he added.