Are you asking for migratory operations or just stationary? The bees I'm running were in the almonds. Varroa mites were not the issue. Went from 950 mid last summer to 744 good colonies sent to CA. 500 of them are still alive. Of that 500 50% are excellent, 25% are ok, and 25% need boosting. Troubles were noticed already starting 2 yrs ago when I had samples sent out for nosema spore counts. At that time there were less than 500 colonies. Last summer the nosema spore counts from the poor hives were 5-10 million spores per bee. This spring(March) samples from 15 poor colonies mixed together sent to USDA Lab Beltsville, MD showed no tracheal mite, no varroa mite, but 15.1 million spores per bee of nosema. I suggested to the owner who I run these bees for that they be fed Fumagilin last spring and it wasn't. I said they should be fed fumagilin last fall and they didn't. I told them to feed fumagilin this spring at the end of almond bloom and they didn't. Now I am fumagilin drenching them all. It sucks to do all that hard work making increases for someone to not care and just let them dwindle away because they are to cheap to pay for fumagilin.