Collapse Of Honeybee Colonies Could Be Due To Unique Virus-Fungus Combination
A paper on their findings was published online on 6 October in the journal PLoS ONE.
First author Dr Jerry Bromenshenk, a bee expert and biology research professor, at the University of Montana (UM) Division of Biological Sciences in Missoula, said in a statement that they don't know for sure if the two pathogens, a fungus called Nosema ceranae and a virus called insect iridescent virus (IIV), cause Colony Collapse Disorder (CCD), or whether the colonies with CCD are more susceptible to them.
"It's a work in progress, but it may be the most important advance in the search for the cause of CCD in the previous three years," said Bromenshenk.
IIV infects the abdomen of bees and is called iridescent because affected tissue appears bluish-green or purple. It is similar to a virus first reported in India 20 years ago and another found in moths, said the researchers.
Once the spores are ingested, Nosema ceranae spreads in the gut of the bee. It was first described in 1996 and identified as a disease of honeybees in 2004 in Spain.
Either the virus or the fungus can make the bees sick, but the researchers suspect that it is when the two come together that the colony collapses.
Co-author Dr Robert Cramer, a fungal pathologist at Montana State University (MSU) in Bozeman, said their data suggests a link between the two pathogens and their thinking is that "the bee gets an infection from one or the other, and this causes the bees to become stressed, which then allows the second infection to come in and more effectively cause disease".
The term Colony Collapse Disorder or CCD was coined after the drastic rise in the disappearance of honeybee colonies in North America in late 2006. In 2010, CCD again devastated honeybee colonies in the US, suggesting the problem has not been resolved and is not going away.
Bromenshenk said most other researchers in the US and other parts of the world have been focusing on RNA viruses associated with honeybees to find what causes CCD: but IIV is a DNA virus, and this "fundamental difference" points CCD research in a "whole new direction" he said.
For the study, the Montana researchers sent samples of ground up dead honeybees to a US Army-backed lab at the Aberdeen Proving Grounds in Maryland, called the Edgewood Chemical Biological Center.
At Edgewood they used a liquid-chromatograph proteomics mass-spectrometer to identify and count around 30,000 proteins in each sample.
It was from this massive collection of data that they eventually spotted the coincidence of IIV and Nosema ceranae in all the CCD samples but not in uninfected controls.
The researchers concluded that:
"These findings implicate co-infection by IIV and Nosema with honey bee colony decline, giving credence to older research pointing to IIV, interacting with Nosema and mites, as probable cause of bee losses in the USA, Europe, and Asia."
"We next need to characterize the IIV and Nosema that we detected and develop management practices to reduce honey bee losses," they added.
Meanshile, what can beekeepers to to protect their bees?
Co-author Dr Colin Henderson, who did the statistical analysis on the data, and is a faculty member at the UM College of Technology, said that the safest way, until an effective treatment is available, is to destroy infected colonies, and stick to standard quarantine routines such as disinfecting equipment and testing imported bees before adding them to colonies.
The researchers said some beekeepers notice that CCD outbreaks seem to follow long periods of cool and damp weather, and more problems seem to occur in areas with frequent fog or in hills where the weather is slightly cooler.
Bromenshenk said placing colonies in warm and sunny spots appears to help prevent CCD outbreaks.
Even if it turns out that it is not this particular pathogen duo that causes CCD, the discovery of IIV in North American bees is important, said Bromenshenk:
"It warrants additional investigation, as it's a whole different category of viruses than anyone has looked at before. It's a unique discovery."
The full team of researchers on the project included the bee specialists at UM, the fungal pathologists at MSU, insect virus specialists at Texas Tech University in Lubbock, and the Instituto de Ecologia, AC, at Xalapa, Veracruz, in Mexico.
Bromenshenk and colleagues also did a lot of the work at a Missoula-based company Bee Alert Technology, which they set up to license honeybee technologies discovered at UM.
"Iridovirus and Microsporidian Linked to Honey Bee Colony Decline."
Bromenshenk JJ, Henderson CB, Wick CH, Stanford MF, Zulich AW, et al. 2010 .
PLoS ONE 5(10): e13181.
Sources: University of Montana, wikipedia.
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