A fungus that caused widespread loss of bee colonies in Europe and Asia may be playing a crucial role in the mysterious phenomenon known as Colony Collapse Disorder that is wiping out bees across the United States, UC San Francisco researchers said Wednesday.

Researchers have been struggling for months to explain the disorder, and the new findings provide the first solid evidence pointing to a potential cause. But the results are “highly preliminary” and are from only a few hives from Le Grand in Merced County, UCSF biochemist Joe DeRisi said. “We don’t want to give anybody the impression that this thing has been solved.”

Other researchers said Wednesday that they too had found the fungus, a single-celled parasite called Nosema ceranae, in affected hives from around the country — as well as in some hives where bees had survived. Those researchers have also found two other fungi and half a dozen viruses in the dead bees.

N. ceranae is “one of many pathogens” in the bees, said entomologist Diana Cox-Foster of Pennsylvania State University. “By itself, it is probably not the culprit … but it may be one of the key players.”