That's an interesting paper, thanks; here is the link to the freely accessible version: https://www.ncbi.nlm.nih.gov/pmc/articles/PMC6852581/ https://www.ncbi.n

That's an interesting paper, thanks; here is the link to the freely accessible version: https://www.ncbi.nlm.nih.gov/pmc/articles/PMC6852581/ https://www.ncbi.nlm.nih.gov/pmc/articles/PMC6852581/ But I'm not sure whether this is really the cause of my observation; everything looked normal in April and May, but suddenly by end of May the bumblebees vanished. I still see some from time to time (one or two a day, compared to dozens in normal years). I also found a few exhausted ones on the ground that could no longer fly, but there were no mites on those.