February 20, 2014
Managed Honeybees Infecting Wild Bumblebees With Disease
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redOrbit Staff & Wire Reports - Your Universe OnlineWild bumblebees are in decline throughout the world because they are likely contracting deadly diseases from ailing domesticated honeybees, researchers reported Wednesday in the journal Nature.
The study helps answer something scientists have been struggling with for some time – understanding why the world’s bee populations, both wild and captive, are in decline.
Although bumblebees aren’t moved from farm to farm like honeybees, whose pollination is critical for farmers, they nevertheless provide a significant portion of the world’s pollination of flowers and food, particularly greenhouse tomatoes, the researchers noted.
"Wild and managed bees are in decline at national and global scales. 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,” said lead researcher Dr. Matthias Fürst from the Royal Holloway University of London.
Dr. Fürst and colleagues assessed common honeybee diseases to determine if they could pass from honeybees to bumblebees, and found that the deformed wing virus (DWV) and the fungal parasite Nosema ceranae – both of which have major negative impacts on honeybee health – can infect worker bumblebees and, in the case of DWV, reduce their lifespan.
The researchers then collected honeybees and bumblebees from 26 sites across the UK and screened for the presence of the parasites. The results revealed that both parasites were widespread.
"One of the novel aspects of our study 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,” Dr. Fürst explained.
The researchers also examined how diseases spread, and studied genetic similarities between DWV in different pollinator populations.
They found three factors that suggest honeybees are spreading the parasites into wild bumblebees – honeybees have higher background levels of the virus and the fungus than bumblebees, bumblebee infection is predicted by patterns of honeybee infection, and honeybees and bumblebees at the same sites share genetic strains of DWV.
"We have known for a long time that parasites are behind declines in honeybees," said study co-author Professor Mark Brown, also of the Royal Holloway University of London.
"What our data show is that these same pathogens are circulating widely across our wild and managed pollinators. Infected honeybees can leave traces of disease, like a fungal spore or virus particle, on the flowers that they visit and these may then infect wild bees."
Although recent studies have provided anecdotal reports of the presence of honeybee parasites in other pollinators, the current study is the first to determine the epidemiology of these parasites across the landscape. The results suggest an urgent need for management recommendations to reduce the threat of emerging diseases to our wild and managed bees, the researchers said.
"National societies and agencies, both in the UK and globally, currently manage so-called honeybee diseases on the basis that they are a threat only to honeybees. While they are doing great work, our research shows that this premise is not true, and that the picture is much more complex,” Brown said.
“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.”
Brown noted that the latest research shows that bumblebees are more negatively affected by disease compared with honeybees. The average wild bumblebee lives 21 days, while the infected ones live just 15 days, he said. Furthermore, while honeybee hives have tens of thousands of workers, bumblebee hives have just hundreds, at most, and are therefore more vulnerable if losses are sustained.