OA sublimated on 11th December - temp climbed up to around 7C locally and that loosened up the cluster thus making OA treatment more effective. My 2 colonies were treated, 2 colonies belonging to one friend, 8 belonging to another plus a few others. No mite fall from one of my hives so far - no doubt someone will tell me that means I didn't need to treat - and the other colony produced a grand total of 32 dead mites over the course of 7 days.