This discussion would be like going back to the dreaded Beesource where some of their keepers have been using OAV only as a mite treatment and have had very low winter losses and very few mites in checks made by the Virginia State inspections in the spring.  While most of the experts claimed that this was not possible as OAV is only effective in broodless colonies.  However it is difficult to claim what percentage of mites are phoretic at any one time, but can assume that there will always be phoretic mites in a colony at any time. If one takes a figure of perhaps 20% of the mite population as being phoretic, a single OAV treatment can destroy at least 90% of those mites and each treatment thereafter has a possibility of destroying another 90% of the mites that have become phoretic.  So it would seem that the only time a well dosed treatment of OAV will fail is if there are no phoretic mites which is unlikely unless the treatments are too close together.  Then there is the thought that when bees are in cluster formation that the OAV does not penetrate the cluster, now again that is a theory without any evidence to corroborate that theory.  I do treat an observation hive and observe the reaction to the treatment and have seen the bees run around in a state of panic when the vapor is first introduced and only return to normal when the vapor is no longer visible.  I will try to get them down to 40 degrees , treat and observe if they behave any differently.  It is often stated that colonies are not able to withstand many treatments of OAV without damage to the queen or colony and once again there is little evidence to confirm this either.  I have been using OAV for the past 4 to 5 years and always have over winter losses less than 10% but most of my colonies are treated with OAV around 12 times per year and as my honey is harvested in June the treatments begin in July and will end in December.  I am also of the opinion that the higher up the hive the vapor is introduced the better the crystal distribution.  Unfortunately most of the information around the treatment of OAV is anecdotal and will probably stay that way as there is little chance of research being financed.
John in north eastern VA

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