On Saturday, I finished examining Bee Glad... and found a disturbing surprise. The bottom board was covered with thousands of varroa mites. What part this played in the death of Bee Glad... is still debatable but my surprise lies in how did this occurred. I checked the hive for mites all spring and summer, did periodic drone brood frame extraction, along with sugar dusting. When the mite count became too large in August, I treated it with Thymol and the count went down significantly. I was confident going into winter that the mite load was reasonably low, but, having seen the state of the bottom board, I imagine my confidence was unfounded.
I will be publishing some photos of the bottom board later this week.