It matters little if they do, they quickly loose it when not challenged by a particular pesticide. Just rotate treatments say three years Apivar followed by three years with Apistan. Pesticide resistance in varroa is energetically expensive and non resistant mites will soon outnumber the resistant ones once there is no more pesticide applied (this is why no longer than 6 weeks with strips is important).....and even if you have a few left the Dec/Jan oxalic acid dribble/vape should take care of most of those.