Several people in my club have asked this question recently…”shouldn’t I wait to use the oxalic acid vaporizer until it is colder?” I wanted to vaporize while it was warmer, and this is a good chance to learn to think about bees.  Here are the facts we know, and some questions:

The bees started making brood after the solstice,  ( I can tell you this is true because I see them in my observation hive.

The more brood there is, the more mites will be protected from the vapor.

The phoretic mites will be on the bees nearest the brood, in the center of the cluster.  Will the vapor really get in well if the cluster is tight?

Bees are paralyzed by cold, will the vapor be so disturbing that the bees will uncluster and be unable to get back?

My instinct tells me that I need to vaporize while the bees are in the hive, but not clustered tightly, and it is warm enough that they can move around a little to groom and still get back in the cluster, and before there is any more capped brood where mites can hide.  It took a while to find someone with an answer, but David Baker from To Bee or Not To Bee had one.  He says what he has read is the OA vaporization should be done between 30 and 50 degrees.  40 was the number I had in mind, since that is the temp at which bees can move inside the hive to access honey stores.  Adding together the facts we know about bee behavior is a good way to come to a conclusion about how we should react to what we see in our hives.   What do you think, did I miss anything?  T