CATCH THE BUZZ - New Demons Found...The Trail Gets Warmer

CATCH THE BUZZ

New Demons Found. The CCD Trail Gets Much Warmer.

In 2007a team* was formed to search for the cause of Colony Collapse Disorder. Using mass spectrometry-based proteomics, a technique modified by the military for screening samples for pathogens, they found a fungus and an unusual virus associated with samples from colonies with CCD symptoms.

An insect iridescent virus (IIV) in bees from CCD colonies is new to the U.S. It shows similarities to an IIV first reported in India 20 years ago, as well as to an IIV found in moths. The method of its introduction to bees in North America remains a mystery but it probably arrived in infected bees, or it crossed over to bees from another insect.

 

All animals, ranging from lowly bacteria to humans have DNA as their genetic material. Viruses, however, have either DNA or RNA as their genetic material. RNA is a chemical variant of DNA.

 

The viruses thus far associated with honey bees in colonies with colony collapse disorder symptoms have been of the RNA type. The insect iridescent virus the research team correlated with CCD is a DNA virus, however.  That is a fundamental difference and takes CCD research in a whole new direction. This was when the team brought in RNA virus experts.

 

The DNA in these viruses is something to behold. Their size and shape, and the way they are stacked inside the cells they infect fundamentally alters light in such a way that it causes iridescence. Viruses and infected host tissue may have a bluish green or purplish hue. Insect iridescent viruses have also been shown to contain a protein that causes host cells to self destruct in a process called apoptosis, which can be a viral attack mechanism or a host defense strategy.

 

Additionally there is a significant statistical link between CCD, the iridescent virus and a fungal parasite of the genus Nosema. It remains unknown if these two pathogens in concert cause CCD, or, are CCD colonies more likely to succumb to these two pathogens?  

 

Currently, the team is trying to isolate the specific strain of iridescent virus in U.S. bees so that they can characterize it alone and in combination with Nosema. The work is ongoing but it may be the most important advance in the previous three years.

There are more than two dozen known insect iridescent viruses. As a general rule, the impact of these viruses ranges from covert infections with relatively minor effects, to highly virulent and lethal infections. This lethality is one reason that this group of viruses has been scrutinized as a potential biopesticide, for applications such as mosquito control. This is not good news for beekeepers. In India, an iridescent virus, called IIV-24, has been implicated in high losses of honey bee colonies.

It is known that in an Asian honey bee, Apis cerana, a combination of parasites and pathogens co-exist, including: (1) a Nosema parasite called Nosema ceranae, (2) an iridescent virus, (3) parasitic and predacious mites, and (4) two other RNA-type viruses, Kashmir bee virus and a Sacbrood virus.

Both Kashmir bee virus and Nosema ceranae have been in North America for a decade or more. How similar is the CCD strain of iridescent virus to the IIV-24 from A. cerana? Is it possible that US bees acquired IIV from the Asian bee along with Nosema ceranae and Kashmir bee virus? 

This IIV also seems to be closely related to an IIV virus called IIV-6 that occurs in other insect species. So this may be a variant of this virus that managed to transmit to a new host – bees.

Knowing exactly what IIV species is involved will be important so that it can be tracked and monitored to develop a control strategy. There is not a means of controlling the virus, although there are simple ways of monitoring Nosema, which can be seen under a microscope, and some options are available to beekeepers for reducing Nosema levels.

Once the strain of IIV in CCD colonies is identified, and assuming that the IIV link with CCD can be confirmed, the potential exists to use IIV presence as an indicator of CCD. It should be very easy to develop a PCR assay or even to use simple serological tests like ELISA to rapidly detect IIV. Until then, proteomics will be used to screen samples. Proteomics is an excellent screening method, but it takes more time and analysis costs are higher than for PCR or ELISA.

With an inexpensive and rapid assay, the ability to screen all colonies in an area for IIV exists. Until an effective treatment can be developed, eliminating infected colonies may be an option, as well as screening before new colonies are allowed to enter.

Standard quarantine practices such as testing imported bees before they are added to colonies, and disinfecting equipment would likely help. We can do a better job if we know the exact identity of the culprit(s).

In the short term, the possibility of developing treatments against the IIV seems remote. Some possible treatments include antiviral drugs or heat treatment of hives. Most IIVs replicate at about 21 degrees C and do not replicate above 30-32 degrees C. Higher temperature may suppress the virus by halting replication, whereas cool weather and damp conditions may speed up replication of both IIV and Nosema. Many instances of CCD have occurred following extended periods of cool, damp weather, with more problems with bees in areas with frequent fog or in hill areas where the weather is cooler bein g reported. Placing bees in warm, sunny locations appears to help.

Finally, in a bee collapse that occurred in the northeastern part of the U.S. some years ago, an IIV was seen in varroa mites that prey on bees. Varroa may act as a vector for the dispersal of the virus among bee colonies, just as mosquitoes transmit West Nile virus or malaria to humans. Varroa is known to increase damage caused by other viruses, and beekeepers who fail to control varroa levels are likely to sustain high colony losses.

In all cases, management practices that reduce Nosema and mite loads and try to reduce long term exposures to cool, damp environmental conditions are likely to reduce colony susceptibility to IIV.

The entire paper is published in the online Journal Plos One. Find it at http://www.plosone.org/home.action

*The team includes bee specialists at The University of Montana in Missoula, fungal pathologists at Montana State University, and a group of virologists and chemists at the US Army Edgewood Chemical Biological Center (ECBC). Later, after they received the initial results, they added specialists in insect viruses from Texas Tech University and the Instituto de Ecologia AC in Mexico. Team members include Dr. Jerry Bromenshenk, Univ. Mt, Colin Henderson, Univ. Mt., Charles H. Wick, U. S. Army, Robert A. Cramer, Univ. MT., Shan Bilimoria, Texas Tech, and Trevor Williams, Instituto de Ecologia AC in Mexico and several others listed on the research paper.

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