Personally, I wouldn't use any fumigant inside a hive during cold weather.


As per open during winter.  When varroa and tracheal mites were first in US, and both were being found in beehives, I did a study of varroa mite/tracheal mite/exposure to toxic heavy metals for EPA.  It was a two-year study, 48 colonies, monitored monthly for both varroa and tracheal and chemical residues - in Helena, MT, near a lead smelter, zinc extraction, and paint production complex.  Helena winters are cold, yet we had to get bees once a month.  The results were that the combo of both mites and toxic metal exposure had a cumulative effect - those were the first colonies to go.  By end of two years, only the controls were still alive.  But it wasn't cold that killed the colonies in winter - at least, not directly.  Bee colony death occurred when all three variable were at maximum levels (numbers mites, conc of lead, arsenic, cadmium).  The most severe losses occurred early in the fall, as weather turned cool.


We had no choice about opening in winter.  We avoided breaking the cluster.  We'd have one person pop the lid, another to scan the frame tops and pull what looked like a frame at the outer-most part of the cluster.  Then, a third person pulled the first frame with bees, and the 4th person sweep off a sample of the out side bees.  Everything back together as quick as possible.  We did avoid windy days.  The clusters were so cold, nothing much happened.   What we did avoid was breaking open the cluster.





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