I have played with vaporising hives and I feel that closing the hives concentrates the oxalic acid vapour within the hive and the activity of the bees spreads it through the hive so that all frame surfaces are coated. It also means you are in the apiary for a little bit longer.  In hives with high mite numbers, they started dropping after half an hour. 
 
Hobby Beekeepers in Scotland fumigate once a month (Oct - Dec).  
 
Extract from a letter from Eric MacArthur, Scotland   Mite fall is monitored continuously and if mite drop a week after the December 
oxalic treatment averages more than 1.5 mites per day the fumigation treatment is repeated. 
 
 In the past I relied on a maximum of 4 oxalic acid treatments using 1.5 g each cycle.  Oxalic acid on its own I am now convinced is not effective in preventing a rapid summer mite build up - see attached new findings by European experts.  ( He was using this as his only mite treatment and its not so effective with brood present, however there are other methods available to give a quick knock down to keep mite numbers low).
 
 
 
We often move hives fully closed hivers in cool weather, (we move them through the city partially netted) and you have about an hour before you do any damage - overheating. Did so today on a couple of hive without mesh floors at a temperature of 15C.
 
 We are having a hot, fine Christmas.  The honey flow is on.  Three days off before getting back into supering those that have already filled their supers.
 
Frank Lindsay 
Wellington
New Zealand
 
  		 	   		  
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