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 [log in to unmask]