Well, HP, I have to agree it's impossible to know for certain what precipitated the cleanup of mite-infested pupae. After all, even people don't ever completely know what's going on with their own health, despite diagnostics and communication.
Those pics were taken under a full, non-feral TBH. Bee volume in there varies from a few to 20+ bars, at which point they go swarmy. That colony is split up now.
Yes, I'm an optimist, and I do hope the girls are good mite-biters. Seven weeks after, post-brood break & hive splits, there are just a few mites on sticky papers under the SBBs. But I used to see none, over the last 2 years...although dropped mites could've been eaten by lizards or ants.
Now, I'm no longer seeing red varroa mites on plant leaves in the garden as I did last month. Actually I'd never seen any varroa away from bees, until the ferals got here.
I didn't cull drones. I did do powdered-sugar puffs on inspection days (~10 days because of time of year, but not always breaking open brood nest). And there's loads of good forage, good variety, good propolis resources.
Today the temp was good to check all the brood. Everything's beautiful, none of the Qs are laying drones right now, and they're busy making more bees. And they lived happily ever after, I hope.