I did not use menthol and although I treated the hives for varroa, I have not done a good job of monitoring. I probably got what I deserved and the poor bees I am supposed to be caretaking suffered the consequences.
I'm turning over a new leaf and doing a better job when I get my new bees. You may be very correct on the tracheal mites. The bees seemed to be doing fine going into the winter even after I treated them so I don't think it was the treatment.
When I cleaned the hives out, it looked like one of the hives might have died early. The bees were pretty dried up and there didn't seem to be a lot of them. The others looked like they might have just died. There were quite a lot of bees with their tail ends sticking out of cells There was no bad smell in the hives, no sign of moth destruction or anything else that looked like
The fellow that I am getting the nucs from is a former state bee inspector and requires that he inspect the hive bodies and frames you bring to pick up the nucs. Hopefully he won't find anything bad that way.
In what months are you putting on menthol? Do you keep grease patties on at all times (something I have done before but did not do this year)?