> Good points Pete,  but extremely antiquated and as I see, it not relevant data. 

If you could kill a hive 100 years ago by opening it in the dead of winter, you can still do it. Bees have not gotten hardier, probably the opposite. 

The following paper collected everything that was known at the time (2006) about the use of oxalic on bees, which has been used in Europe for decades. 

> This review presents and evaluates current knowledge about oxalic acid with regard to its applicability as a control for V. destructor. In addition to the scientific literature, we have included articles from practical beekeeping journals, because many studies were only published there.

> Trials were conducted in Southern, Central and Northern Europe as well as North America when outside temperature ranged from 3 to 13 °C. ... Oxalic acid was applied at an outside temperature ranging from 2 to 16 °C. ... using oxalic acid tablets (1 g oxalic acid dihydrate/tablet) in the Varrox evaporator ... application should be conducted during the broodless period at an outside temperature of > 2 °C

Eva Rademacher, Marika Harz. Oxalic acid for the control of varroosis in honey bee colonies - a review. Apidologie, Springer Verlag, 2006, 37 (1), pp.98-120. <hal-00892183>

Really, this is all I am saying: it should be done when the temperature is above freezing for several days. It's been shown that it may take that long for the colony to re-cluster. Anyway, I don't care if people gas their bees in winter. 

PLB

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