not for long, the perlite won't kill them. There just won't be any food in there so that would be a problem for them because they would eventually starve
Perhaps I'm missing something here.. I assume you're talking about perlite that is supporting active growth? They'd simply have to move up a bit for a feast lol.. I always found spider mites to be nice and cozy living on the plant they're destroying.. Getting all they need from sucking the life blood of our girls.. I don't think the substrate would make any difference..? They can live out their entire life cycle on a host plant - be it eatting, breeding or egg laying.. Please correct me if I'm wrong..