re: collapses caused by high viral load from robbed honey rather than mites

I don't think so but I have no data to prove it. My opinion is based a story that Dr Meghan Milbrath told at our local bee club earlier this week. She talked about spilling a largish quantity of a concentrated pathogen (dengue fever) in the lab and simply cleaning it up with no ill effects. On the other hand, a much, much smaller quantity of the same pathogen delivered directly into the blood stream via a mosquito bite was "no fun at all".

She made the compelling point that viruses alone are not all that dangerous. They are around us all the time and our skin (and a bee's integument) is a powerful protective organ. Viruses become dangerous when a vector such as a mosquito or varroa bite allow them to bypass the host's best defenses.

So back to the hypothesis about viruses from robbing rather than mites:
If you have a hive with say 2% mite count and low virus load, it's probably true that almost all those 2% are still sick.
If you vastly increase the virus load but not the mites, the 2% with compromised integument might get more sick but it's still just that 2%.
On the other hand if you increase the mite count to 10%, even with a low virus load you've got a lot more sick bees. The viruses already in your hive will exploit the new gaps.

My suspicion is that robbing is a part of our Fall collapse problem but that it's mites hitchhiking back more than viruses being imported.

I suppose the one counter-hypothesis is virulence of different strains. If you've been lucky enough that your local virus population has evolved into a non-virulent strain and, through robbing, the bees introduced themselves to a new more virulent strain, that alone could increase the rate of colony deaths. Is there any evidence of different strains of virus across bee populations within robbing distances?

Mike Rossander



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