Big study raises worries about bees trading diseases

Commercial bees in stressful, often unhygienic working conditions may spread their pathogens to wild pollinators, a large study suggests.

These are tough times for bees, both in the wild and in colonies that commercial beekeepers and farmers manage. Several small studies have already raised the possibility that the substantial number of viruses and parasites plaguing commercial honeybees and bumblebees are spreading to wild bees that visit the same flowers (SN: 8/16/08, p. 10).

Lab tests plus a bee-disease survey in Great Britain now show that pathogens from honeybees can also trouble bumblebees, says Matthias Fürst of the Institute of Science and Technology Austria in Klosterneuburg. He and his colleagues present their data in the Feb. 20 Nature.

For decades, bee parasite research has focused on honeybees, says Peter Graystock of the University of Sussex in Brighton, England. Studies including the new one show that many pathogens shouldn’t be considered just honeybee diseases, he says.  

In lab tests, deformed wing virus, known from honeybees, harmed the bumblebee Bombus terrestris. This bee, which is common as a wild pollinator in Great Britain, died on average six days sooner if infected with the virus. That’s a loss of a quarter to a third of its adult life span.

The widespread honeybee pathogen Nosema ceranae can also jump to B. terrestris , the researchers found. Although another lab had reported that N. ceranae ravages bumblebees, the new work found that bumblebees infected young didn’t die early.

Both of these pathogens showed up in wild bees collected randomly at 26 sites around Great Britain. Deformed wing virus appeared in 36 percent of honeybees and 11 percent of the multiple species of bumblebees tested. The virus samples found in bees at a single site were genetically similar to each other but less like viruses collected at other sites. This pattern suggests local bee-to-bee transmission, the researchers argue.

This study clarifies some questions left hanging by earlier work, Fürst says. He and his colleagues documented in lab tests that the bumblebees are actually catching infections instead of possibly just carrying traces of something they brushed against.

Even though the study looked at wild bees in Great Britain, the same transmission dynamics could easily show up in North America, says coauthor Mark J.F. Brown of Royal Holloway, University of London. He cautions, however, against extrapolating to the still-mysterious honeybee deaths attributed to colony collapse disorder in North America.

Bees face other threats such as exposure to pesticides as well as disease, says Sydney Cameron of the University of Illinois at Urbana-Champaign. She and her colleagues have documented deep losses in North American native bumblebee species, and she’s now studying whether pathogens spilling over from commercial bees are playing a role. But, she says, “I can’t rank disease relative to other ‘miseries’ of bees.”