I live in a small (400) town in mid Missouri, about 120 miles West of St Louis. There is one other fellow in town that had bees until last year. I had a small swarm that moved into honey supers that I was cleaning out on 9/10/19. I treated them twice with OAV near Christmas. They are doing OK (5) frames. I talked to his wife a few weeks ago and she mentioned that he didn't have any hives left. I asked if he was treating with anything for varroa and she said no.
I have a friend who lives 60 miles or so from me who kept bees until 1990 when varroa wiped him out. Since he ran into me a few years ago he decided to keep bees again. I just talked to him this morning and he asked me where he could get packages or nucs. He said he had 20 hives at his house and he lost them all this winter.
I only have 4 colonies at present and I have lost zero over the winters in the last 8 years. I have done oxalic treatments every winter near Christmas. I did lose 8 hives in 1918 in June and July.
It seems to me that there may be a correlation between what I did and what they did. What do you think?