" is it not a concern that by widely using drone sacrifice to control Varroa, we are inadvertently applying a selective pressure on Varroa to push their genome toward one which infests worker brood at higher than present rates "

You will get what you breed for eventually so the simple answer to your question is yes.  Eventually can be next year or 500 years from now. That leaves two questions open that can give hints as to how long a response might take.  How intense is the selection pressure?  How complex is the genetics needed to respond to that pressure?

Clearly if all drones are killed the selection pressure is very intense.  However, if only 10% of the local hobby people use drone culling and even those that do surely do not kill every drone that really would be hardly any selection pressure.  In the later case it would likely take years and years of selection pressure to have an observable impact.  Or no impact might ever be seen as the selection pressure is simply too low to be effective, particularly when new genetics are constantly migrating in from ferals and commercial queens.  Plus the higher reproductive success in drone brood is constantly selecting for reproduction in drones.

No one has any clue how complex such genetics might be.  If it just involves up or down regulating one gene, as is often the case with  pesticide resistance, even mild selection pressure can show a measurable impact in a very few generations.  On the other hand if the needed genetics are complex, say a half dozen genes or gene regulators, putting all those factors in one mite could take years even under fairly intense selection pressure.  It is even possible some required mutant does not exist in the population and then you have to wait for that mutation to happen randomly which might be hundreds of years.

My best guess is your selection pressure is mild and the needed genetics are not simple.  So, I do not think you need to worry much.  I could be 100% wrong.

A good example to think about in this respect is resistance to the insecticide DDT.  Flies happen to naturally have a gene that strips chlorine atoms off aromatic rings.  In the case of DDT such a chlorine removal renders the metabolites non toxic.  Within ten years of the commercial introduction of DDT flies could be painted white with DDT and not die.  All that needed to happen was to up regulate the non protein coding stuff in DNA that controlled how often that dechlorination gene was expressed as a protein.  This flooded the fly with the stuff that detoxified the DDT.  On the other hand mosquitoes do not happen to have that dechlorination gene.  The end result is mosquitoes are still not resistant to DDT after 70 years of continuous use in some places.  Mosquitoes have learned to avoid DDT and thus are a bit harder to kill with the stuff than they used to be.  But, they are no place close to resistant.

Dick

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