Unless you are constantly sitting on top of your hives all the time, all it takes is one requeening to have mutts. In my albeit limited experience, colonies like to requeen themselves from a packaged or bought queen with one of their own at the first good opportunity. Since you have no control over what the virgin queen mates with (just whatever drones are in the area), odds are she's not going to be finding purebreed drones. Which means anything she lays is going to be hybrids, aka mutts.Any bees for more than a season are mutts???