# Is it mites, or the viruses they carry that kill a hive?



## ruthiesbees (Aug 27, 2013)

the mites feeding on the brood and adult bees creates holes in the exoskeleton. A bee's exoskeleton does not "heal" like our skin does, so it leaves a "hole" where viruses can enter the bee and weaken it.

The rats didn't cause the Bubonic plague, but they were the vector that allowed it to spread so widely. I'd say it's the same with the varroa mite. Control the mite and you can control how much affect a virus can have on a bee. No hole in the exoskeleton, no way for it to get in.


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## fatshark (Jun 17, 2009)

Deformed wing virus (DWV), which is arguably the most important _Varroa_-transmitted virus, replicates in the mite and is transferred when the mite feeds on a developing pupa. Other viruses are transmitted in a similar way. Without question the viruses are what kills the hive ... but remember that in many cases the viruses are already there, being transmitted between bees during feeding (a route that the bees can cope with perfectly well). It's only when the mite directly injects the virus, bypassing the normal defence systems of the bees, that you get disease.

In the laboratory you can reproduce the effect _Varroa_ has by directly injecting honey bee pupae ... these bees get sick, whereas they don't get sick if the virus is fed to them. There is also some evidence that the mite may suppress the immune response of the bee - it's ability to defend itself against the virus. However, formally, no-one has tested whether virus-free mites (there aren't any!) do this as well.

Control the mites and you'll control spread of the pathogenic strains of the virus.


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## kilocharlie (Dec 27, 2010)

Some of the studies that investigated "CCD" concluded that multiple stressors was the most common cause of colonies dying out, but noted that the presence of varroa destructor, and the associated viruses, was a large contributing factor.

If your bees are not known to have mite tolerating behaviors, an IPM program is likely the best interim approach, while importing in mite-fighting genetics over the long term. Many a neophyte beekeeper hears (and gets sucked in by) opinions about "treatment-free" bees and marches off to sacrifice his wimp bees to the ferocious mites.

In what little research I have read, Randy Oliver has posted his findings and told his conclusions better than most. He recommends implementing an IPM strategy while the search goes on for a sustainable practice. Check out his website, www.scientificbeekeeping.com, the section of articles about Varroa Management.


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## FlowerPlanter (Aug 3, 2011)

This goes with what fatshark is saying. Viruses spread by mites, more mites bee become infected. This study shows a "thresholds of between 2000 and 3500 mites" It's the viruses that do the damage. 

http://onlinelibrary.wiley.com/doi/10.1111/j.1365-2656.2004.00776.x/full


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## Adrian Quiney WI (Sep 14, 2007)

Some work has taken place with "superinfection exclusion" in the UK. As I understand it, the hypothesis is that at the DNA level there is only so much space that can be occupied by viruses. 
A beekeeper in the UK has been keeping bees for 19 years without chemicals and thought that his bees were surviving because of grooming behaviors, and his selection for them. It appears he was wrong. The evidence appears to show that his bees are infested with mites, but are not dying because the viruses in his bees are not fatal to the bees - he has no DFW.
This is a link to the study.
http://www.nature.com/ismej/journal/vaop/ncurrent/full/ismej2015186a.html
For those who would rather watch a 10 minute BBC segment on video here is an alternative.
https://www.youtube.com/watch?v=DUFDXl8VGvs


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## A'sPOPPY (Oct 13, 2010)

Following


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## fatshark (Jun 17, 2009)

Adrian Quiney WI said:


> Some work has taken place with "superinfection exclusion" in the UK. As I understand it, the hypothesis is that at the DNA level there is only so much space that can be occupied by viruses.
> A beekeeper in the UK has been keeping bees for 19 years without chemicals and thought that his bees were surviving because of grooming behaviors, and his selection for them. It appears he was wrong. The evidence appears to show that his bees are infested with mites, but are not dying because the viruses in his bees are not fatal to the bees - he has no DFW.
> This is a link to the study.
> http://www.nature.com/ismej/journal/vaop/ncurrent/full/ismej2015186a.html
> ...


Superinfection exclusion doesn't work quite as described. Generally one virus that's already present prevents the infection by a second virus - for example, the first virus might inhibit the expression on the cell surface of a protein that is required by the second virus to bind and infect that cell. There are other mechanisms that explain this as well. There are also alternative explanations for the observations of a single predominant apathogenic strain of DWV in those colonies, but it's certainly intriguing.

A key question would be what happens to a pupa/bee infected with the "blocking" virus when it is deliberately and specifically infected with a virulent strain. This hasn't been done, but needs to be to conclude that it's superinfection exclusion. 

There are other isolated populations of bees - some mentioned in the paper referred to above - which show a similar phenotype. If tested, these should also show the predominant 'blocking' virus presumably ...


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## philip.devos (Aug 10, 2013)

@Adrian Quiney & Fatshark: The side-discussion you have included in this thread is quite intriguing. Obviously if an innoculation of a benign "blocking" virus could be introduced, in my opinion that COULD be more acceptable than the use of chemicals.


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## Adrian Quiney WI (Sep 14, 2007)

fatshark, thanks. Philip, I agree. I am glad the scientist was looking at this man's apiary. I hope that this generates a different line of research that leads to something helpful.


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## fatshark (Jun 17, 2009)

philip.devos said:


> @Adrian Quiney & Fatshark: The side-discussion you have included in this thread is quite intriguing. Obviously if an innoculation of a benign "blocking" virus could be introduced, in my opinion that COULD be more acceptable than the use of chemicals.


There's a long way to go ... and two very big hurdles that need to be overcome. The first is open mating of queens. DWV is transmitted vertically (from the Q via eggs and via drone semen) and horizontally (through feeding). Therefore you'd need to hope that the 'blocking' virus was competitive in such an open mating scenario. Secondly, DWV is a virus with an RNA genome. These types of viruses exhibit two methods (mutation and recombination) of rapid genetic change. Therefore, you'd also have to hope (or ensure somehow, though goodness knows how) that the 'blocking' virus didn't either alter through mutation or recombine with another less desirable virus.

Until then - and I'm a beekeeper who treats - we have to continue doing whatever we do to minimise mite levels in colonies.

Finally, remember that this blocking only applies to DWV ... and _Varroa_ is known to transmit a bunch of there RNA viruses. The problems some beekeepers have with some of the related bee paralysis viruses will not be stopped, and might even get more pronounced if we stop controlling mite levels (because we don't need to as we've cracked the DWV problem). Sorry there's not more good news.


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## kilocharlie (Dec 27, 2010)

Either answer, the mite or the virus (the chicken or the egg?), a couple of drone combs placed in the hive and pulled right after capping, then given a good hard freezing helps keep the mitey mites down.

Bees that bite mites help. Bees that uncap infected cells help. Keeping the queens young and fresh helps. A good strong mite treatment on August 15th helps. Breedinging queens with VSH helps. Good beekeeping practices help.

Neglect does not help much.


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