In September, I did a post called Flight of the Bumblebee. This is an update from The Campaign For Solitary Bees, who kindly sent me THIS LINK, to a wonderful article about saving bumblebees from mites. It was originally posted on UKSafari.com, one of the best wildlife sites online.
I have today (May 2018) published a review of a wonderful book from the Bumblebee Trust. If I interpret it correctly it casts doubt about mites actually being a problem. The mite commonly seen are harmless - or even beneficial - residents of their nest hitching a ride