Honeybees raised by humans for their honey or for agricultural pollination may be spreading diseases to their wild counterparts in the U.K., according to new research that could provide one more clue to the phenomenon of colony collapse disorder.
The study, published Feb. 19 in the journal Nature, links the diseases found in "managed" or livestock honeybees with wild bumblebees that lived near each other at 26 sites in the United Kingdom. The wild bumblebees contracted diseases that were common within the managed population.
"Wild and managed bees are in decline at national and global scales," lead researcher Matthias Fürst from Royal Holloway, University of London, said in a news release. "Given their central role in pollinating wildflowers and crops, it is essential that we understand what lies behind these declines. Our results suggest that emerging diseases, spread from managed bees, may be an important cause of wild bee decline."
The researchers tested the bees at the 26 sites for two diseases that are common in managed populations: deformed wing virus and a fungal parasite called Nosema ceranae. Both diseases showed up in the wild bumblebees. The deformed wing virus alone can reduce bumblebee lifespans from 21 days to 15 days.
"One of the novel aspects of our study," Fürst said, "is that we show that deformed wing virus, which is one of the main causes of honeybee deaths worldwide, is not only broadly present in bumblebees, but is actually replicating inside them. This means that it is acting as a real disease; they are not just carriers."
The researchers theorize that the managed honeybees leave traces of their pathogens on flowers; the bumblebees then land on the flowers, allowing the diseases or fungi to transfer to the wild populations. Their study does not conclusively prove this transfer or that the diseases actually are making the journey from honeybee to bumblebee (or vice-versa), but Fürst did tell the Associated Press that the honeybees had higher virus levels and infection rates.
Fellow researcher Mark Brown told the AP that the disease could have a bigger impact on wild bumblebees, which live in smaller colonies than managed populations and have less ability to withstand high mortality rates.
In the news release, Brown noted that current efforts to understand and manage colony collapse disorder may be too focused on livestock populations. "National societies and agencies, both in the U.K. and globally, currently manage so-called honeybee diseases on the basis that they are a threat only to honeybees." He praised that work, but suggested that "the picture is much more complex. Policies to manage these diseases need to take into account threats to wild pollinators and be designed to reduce the impact of these diseases not just on managed honeybees, but on our wild bumblebees too."
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