Guys. You do not understand about evolution nothing
Varroa evolution is so that it is pest of Apis cerana. In that host it is harmless because it lives only in drone brood.
It is actually a parasite - and they do not want to kill their hosts. Varroa destructor doesnt belong on our honeybees, it kills them.
But anyhow, the theory of evolution, NATURAL selection. Lets pretend for a second that we didnt drone sacrifice, but for some reason any varroa which entered the european honeybee drone cell died.
What would happen with varroa in europe? Would it die out?
HOW does varroa choose to enter drone brood? WHY does some varroa go into worker brood? It doesnt think, "oh well I have been on this nurse bee for a week now, no sign of any drone brood, what the heck lets jump into this worker brood - I know it has a shorter brood cycle but beggars cant be choosers"? No, there is a natural instinct for a varroa to enter a cell.
If there is a genetic difference which determines that choice (just like a genetic difference which meant a small proportion of varroa were resistant to pyrethroids), then by killing varroa in drone brood ONLY, we are breeding varroa which prefer worker brood. If we all do that, then drone sacrifice becomes useless as a control method for varroa (just like pyrethroids are now).
Unless you, or anyone else KNOWS there is no
genetic reason why varroa prefer (or identify) drone brood, then wholescale drone sacrifice
COULD breed varroa which prefer worker brood.
In other words, for drone sacrifice to be effective we WANT varroa which prefer drone brood. If we kill all those off, it wont be effective any more.
Also, should be as a matter of course, be killing all (most of) our drones all through the season?!