I'd like to add my preliminary results to the stack. I've been following Dr. R. recommendation doing both the fogging and the cords. For the first month I fogged once a week and put in 4 new mop cords every 2 weeks. I check for mites using the screened bottom board and tray. At the end of the first month I was still getting a mite count averaging 50 per 24 hour period. This was down from 100 per 24 hour for the first week. I was concerned about the mite count being so high. There were 10-20 deformed drone brood and a half dozen deformed workers at the entrance every day.
For the last month I've started fogging twice a week for around 10 seconds with 6 mop cords every 2 weeks. This is a big hive with a single deep and 5 shallows (don't ask).
Here's the interesting part. This hive is going gangbusters. It is just packed with bees, brood, honey and pollen. Three weeks ago I reversed the bottom layer deep and the shallow right above it because the deep had zero brood in it. Perfectly clean. I haven't checked since due to cool weather.
The mite count continues to hover right at 50 per day. While a high number, as a percentage of the hive population it is probably decreasing as the population grows daily. I hesitate to put in Apistan because in the Pacific Northwest we are right in the middle of the Maple tree flow and the hive is doing so well.
Here are my questions:
1) Am I hurting my hive by fogging so much?
2) Are these mite count numbers out of line with what other people are seeing?
3) Are there sustainable mite levels or are am I just breeding 'super mites' that will be resistant to FGMO in the near future?