more than 2 mites natuaral drops in 24 hours. TREAT! Sorry to be that short. if you do not treat you will loose your hive. Hivelife from first infection to dead 3 years. And my advice don't relay on fancy treatments. If you use apistan and byvarol strictly follow the written labels. otherwise the risk will be resistant varroa.
Spring formic acid
Summer drone removement
autoumn when the hive is broodless oxalic acid