I will assume that you are referring to Varroa Destructor and not Tracheal Mites. Some of us don't medicate at all and would not recommend it, but rather use an organic and IPM method of parasitic management. But, first and foremost, you must monitor in order to know whether they need meds. Those that medicate blindly just add to the med restistant mites.
If you choose to medicate, and with a swarm of unknown origin, it might not be a bad idea to at least quarentine them and treat right off the bat, Oxalic Acid would be a blanket treatment that would at least give them a head start on ridding them of parasites, then monitor.