Hi:
 
Blair is correct about C02 and bees.  EPA's bioassays for pesticides and
honey bees call for the use of C02.  However, too much C02 or repeated
doses can induce mortality.  As per Atkins, we gas them once with just
enought to knock them out for less than two minutes.  Much longer and you
can expect to see mortality in the controls.
 
Just a guess, but I assume bees are probably not greatly affected by
gradual chilling - after all, it happens every night in some of our more
northern climates.  Even if the cluster is warm in the center, the bees
on the outside get chilly until rolled into the center where it is
warmer.  Whether there is a seasonal difference in ability to sustain
cold without much harm is another matter.
 
As per mites, I don't know about varroa, but we found tracheal mites
alive after 3-5 days at -80 C!!!  Look for our paper...  Granted, most
aren't that tough, but some are.
 
Cheers
 
Jerry J. Bromenshenk
The University of Montana
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