BBC News: The beleaguered bumblebee faces a new threat, scientists say.
Researchers have found that two diseases harboured by honeybees are spilling over into wild bumblebees.
Insects infected with deformed wing virus and a fungal parasite called Nosema ceranae were found across England, Scotland and Wales.
Writing in the journal Nature, the team says that beekeepers should keep their honeybees as free from disease as possible to stop the spread.
"These pathogens are capable of infecting adult bumblebees and they seem to have quite significant impacts," said Professor Mark Brown from Royal Holloway, University of London.
Around the world, bumblebees are doing badly.
In the last few decades, many species have suffered steep declines, and some, such Cullem's bumblebee (Bombus cullumanus) in the UK, have gone extinct.
Scientists believe that the destruction of their habitats - particularly wildflower meadows - has driven much of this loss, but the latest research suggests that disease too could play a role.
The researchers looked at two pathogens commonly found in honeybees and found they can also infect adult bumblebees.
In honeybees, deformed wing virus (DWV) causes significant problems. Its severity seems to be exacerbated by the presence of another widespread parasite, the varroa mite, causing entire colonies to collapse.
Bumblebees do not carry the varroa mite, but the scientists found that those infected with DWV had a dramatically shortened lifespan. The fungal parasite has also been shown to have an impact on bumblebee longevity.
The most likely explanation is that the honeybees are acting as the source of the virus for the bumblebees” Prof Mark Brown Royal Holloway, University of London
Prof Brown said: "A significantly shorter lifespan in the field would impact on their ability to go out and collect food and look after other bees."
The researchers found the diseases were already prevalent among wild populations.
Looking at 26 sites across Great Britain and the Isle of Man, the researchers found that about 11% of bumblebees were infected with DWV and 7% were infected with the fungus. By comparison, about 35% of honeybees carried DWV and 9% had the fungus.
"A geographical patterning provides us with the information that transmission is occurring among these animals - they are sharing parasite strains," said Prof Brown.
"We cannot say it definitively, but because of the epidemiology, the most likely explanation is that the honeybees are acting as the source of the virus for the bumblebees."