Ben,I don't think the hive was robbing out one that was failing in the area, non of the other hives in the yard had such a heavy mite load. If there was robbing going on I would expect to see a heavy mite population in all the hives in the yard.
My take on it is that #3 hive had such a heavy infestation that the matriarchal mite population wasn't getting knocked down till I went to a four day treatment regime. One thing that I didn't include on the graph was a large brood die off near the end of the 4 day treatment period. My notes showed that most of the dead brood out in front of the hive had deformed wings.
I'm not saying that a robbing situation with a mite bomb hive couldn't happen, hive #3 would of been a perfect example of it if the hive had failed. Just in this instance the hive came into my yard in the spring as a nuc with a heavy mite load, I didn't treat and ended up with the classic heavy mite infestation by the end of the year. Surprisingly hive #3 survived despite all that happened to it and was a good producer this year.
So far this year's count has been iffy because of the heavy rain I'm getting over the last few days. Most of the mite drop counts have been below 50 with some counts under 20 mites in 24 hours. I did the second set of treatments today and will keep up with the daily mite drop counts.
More to come ;)