>Probably the queen in your split mates with commercial stock, too.

Yes, bound to happen unless you have the luxury of an isolated mating station, but there are steps that we can take to mitigate the situation.

We try to mate as many queens as possible in the home apiary which we try to flood with 'desirable' drones.
We regularly bring what we consider to be good genetic material back to the home apiary.
We graft from desirable stock, but also employ opportunistic techniques such as making up a nuc from a colony with one or two supersedure cells where we have a desirable queen.
We cull mis-matings due to outside influence.
We use good 'production quality' queens that do not meet all our criteria in distant out-apiaries.

We have always given minimal varroa treatment (and only with thymol) in order to expose colonies to varroa in the hope that they will ultimately develop resistance.  We are now down to one treatment just after the crop is removed and we see very little evidence of varroa damage.  Last winter we lost zero colonies out of 107.  The weather is now our worst problem.

Seems to me that opportunistic is now the way to go.  The days of being able to make detailed plans have disappeared - if they ever really existed - so flexibility and lateral thinking (remember that?) pays off.

Best wishes

Peter 
52°14'44.44"N, 1°50'35"W

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