Ted Fischer wrote: <  It just seems logical to me that resistance to Apistan
developed
> independently in this one colony

To me it seems illogical that resistance to Apistan would have developed in
only one colony, if you treated all your colonies in the same way.
Isn't it more likely that the colony in question has robbed out a heavily
infested feral colony which was on the point of collapse?
You could confirm by re-treating with Apistan and then checking for the
presence or absence of mites, rather than plunging straight into coumaphos.
Using a insert on the floor of the hive and examining daily for dead mites
would give a quick indication of whether or not significant resistance has
developed.

John Burgess, Editor Gwenynwyr Cymru/The Welsh Beekeeper
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