> The use of heat to kill or knock down varroa is not new.

Interesting.  I was not aware that varroa were especially heat-sensitive.  Is there any research on their mortality at given temperature/time regimes?  (Especially with comparisons to bee/brood mortality in the same conditions?)
I can only find one study online that seems to match this topic (paywalled, of course).  http://www.ncbi.nlm.nih.gov/pubmed/22299336 in 2011.  But if I'm reading the abstract correctly, they found the highest mortality rate at 25C (77F) with restricted ventilation.  Again, if I'm reading it correctly, they found what looks like a suspiciously high mortality rate (46%) in those conditions.  I say suspiciously high because 25C is well below the temperature that the bees usually thermoregulate the hive to and in which varroa obviously thrive.  That suggests to me that it wasn't the heat killing varroa but the elevated CO2 levels.
The same authors appear to have confirmed the role of CO2 in 2015 in http://www.ncbi.nlm.nih.gov/pubmed/26453704  But even there, I remain suspicious since varroa obviously thrive inside capped cells where I also would suspect CO2 levels to be naturally elevated.  

Either I'm missing something or they did.  Thanks in advance for any thoughts. Mike Rossander



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