I have used thymol crystals for varroa since it appeared here in the autumn
of 1997.  The only other treatment used has been oxalic acid (dripped) for
the first two years.

This year I have purchased 40 OMFs as I believe that they may have two
advantages (already well publicised - mites not being able to return and
better overwintering through the increased ventilation).

However, I am wondering whether the improved ventilation is likely to reduce
the effectiveness of the thymol vapour (method is given here:
http://www.stratford-upon-avon.freeserve.co.uk/PENotes/VarroaTreatment.htm).

Presumably this would apply to a number of other treatments using substances
that evaporate or are dispensed as a fog.  Does anyone have any useful
experience or sources of information?