May 26, 2010

Microbial Link To Colony Collapse Disorder

US researchers claim to have identified a potential disease responsible for Colony Collapse Disorder (CCD) in honeybees, which is responsible for wiping out many beekeepers' entire colonies over the past few years.

Scientists from the US Department of Agriculture say the pathogens to blame are a fungus and a family of viruses.

Results of the study were presented Tuesday at the 110th General Meeting of the American Society for Microbiology in San Diego, California.

Jay Evans of the USDA Agricultural Research Service, who participated in the study, told BBC News that when the two pathogens show up together, "there is a significant correlation with colony decline."

US commercial beekeepers, many of whom have been in the business for a long time and have always had normal, healthy colonies, began losing their bees in the spring of 2007 for unknown reasons. They could find no signs of poisoning or acute mortality, and no dead bees would be found in or around the hives.

Some beekeepers lost as much as 90% of their bee populations, and every year since 2006 many have reported average losses of 30 to 35% of hives.

When the problem became evident in 2007, scientists started looking for a cause for the mysterious disease.

They collected samples, mainly from California and Florida populations, where most of the commercial pollination takes place in the US, and checked them visually for any signs of a problem.

"The most puzzling thing was that the bees [we collected] didn't show any of the pathologies or signs of disease - they looked perfectly healthy," Evans told BBC.

While researchers found a higher presence of the fungus Nosema cerenae in the infected colonies, it was not discovered until only recently that it's when bees are infected with both Nosema and with a group of RNA viruses that CCD takes place, Evans said.

To prove the theory that the two pathogens working together lead to the colony collapse, Evans and his colleagues tried to trigger a honeybee colony collapse artificially.

"We've known for some time that the viruses are not good for the bees' health, that they cause some visible symptoms like paralysis of the bees, shivering or inability to fly," explained Evans. But getting the entire colony sick was tricky, he said.

"You have to infect bees with a sort of natural level compared to what's going on in the field and then more or less wait around to see how that translates into a colony effect like a colony collapse or decline," he said.

Dr Evans believes infection spreading through pollen and flowers may be the trigger for CCD in honeybees.

Commercial beekeepers in the US usually move their bees around the country in haulers, renting them to farmers to pollinate their produce. They then bring them home, usually to some other part of the US.

When an infected bee leaves a virus on a plant, it is very likely that all other bees visiting the now infected plant will also get infected and transport the virus to their hive, elsewhere in the country.

"Once the viruses become prevalent in a colony, they spread quite rapidly both by contact among the bees and often by a parasitic Varroa mite that lives on them," said Evans, adding that his team has been able to observe the "viruses move within that mite and be transmitted from bee to bee by mite."

The fungus is transferred by the bees' excretions, he said.

"Nosema ceranae will germinate in the stomach of the bees, work its way into the rest of the body and exit when it's excreted. So when the sick bees defecate in the colony or near a colony, other bees accidentally pick up the spores of the fungus and ingest them - and that restarts the cycle," explained Evans.

Some experts, however, do not believe that the fungus and viruses are the primary cursors of CCD.

David Mendes, the president of the American Beekeeping Federation, believes that biological pathogens may be involved, but there might be something that affects the bees' immune system in the first place that would even allow the pathogens to infect them more easily.

Mendes believes there are a combination of factors working together that cause the bees to get sick and eventually get CCD. He thinks nutrition may be the key -- in particular, the bees' inability to process certain foods.

And pesticides are to blame for that, he said.

"The whole approach to controlling pests with pesticides has really shifted in the past few years; for instance, now corn seeds, before they are planted, are dipped in pesticides," Mendes told BBC News.

"There's research that says that it's not supposed to affect the pollen and the fruit - well, we've done some analysis with our citrus trees and we have found levels of the poison in the pollen that the bees are feeding to their young," Mendes added.

Whatever the cause of CCD is, Evans believes the cure is not in sight just yet.

One important thing is for beekeepers to really concentrate on the nutrition of their colony in the fall, Evans says.

"Nosema fungi respond well to improved nutrition, so supplementing the bees' diet with pollen and nectar resources in the fall will allow them to maintain more nectar as they go into the winter," he said.

Scientists warn that feeding bees more protein and using chemical treatments for fungi are only short-term solutions.

Until a cure is found, it's not just the beekeepers who are suffering -- agricultural companies and of course consumers who buy their products have been affected as well.

Commercial beekeeper Daniel Weaver says he hopes the bees will continue to fight CCD -- because without them, the world just wouldn't be the same.

"Without bees, our world would be a very dreary place to live. So many delicious fruits wouldn't be available and so many wonderful plants wouldn't be able to propagate and reproduce," he told BBC News.


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