I am not informed in this area but am coming to the conclusion that 
mites can develop a tolerance to OA and other organic acids. I certainly 
welcome those who are better informed to correct my assumption.

The reason I assume this is that OA needs to be kept weak enough to not 
hurt the bee but strong enough to kill the mite. This is the classic 
senario for tolerance to develop. My guess is we will have a ten year 
window where the treatment will be effective, and possibly longer, but 
eventually resistance will be evident. Another observation is the less 
than 100% kill of mites with an OA application, even if the colony is 
broodless. So selection may be taking place.

In olden days, some in power would take small amounts of poison (arsenic 
for example) to develop a tolerance for it. Granted, arsenic is an 
inorganic acid, so there may be some other things at work.

The only reason for this post is that some have said that the organic 
acids will not lead to mite resistance. My guess is they will. This is 
one of those times that I will love to be proved wrong.

Bill Truesdell
Bath, Maine

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