There is still an evolutionary pressure for bees to adapt to varroa when they are treated for it - this seems to be forgotten by many.
Its certainly forgotten by me.
Colonies that thrive better over summer, when supers are on and treatment is not happening are more likely to swarm or be split into several colonies, hence furthering their genes.
This is all off-topic - this thread is for discussion of the capture and early handling of swarms that may be feral thrivers. However:
Your bees wouldn't be in that position if they hadn't been treated earlier in the year, or last year, or at any point in their treatment-dependent lives. They would not exist, and they wouldn't be passing their genes anywhere.
[...]
For any given pathogen, where a treatment is available, it's likely there is an optimal level of treatment for development of resistance.
No treatment is the optimal level. The more treatment or other 'help' the more such development will be slowed
For example, and using extreme numbers for clarity. Bear in mind resistance is not an all-or-nothing property. If a pathogen wipes out 99.99% of its host without treatment...
Things are rarely that extreme, and each mated queen holds a huge amount of variation due to her multiple matings. On a small island yes, maybe. Otherwise, no.
What is more the _evidence_ demonstrates clearly that development of resistance occurs naturally wherever there is no treatment, and not at all where treatment is widespread.
All this is well known and well documented in the literature. I.e.
https://www.naturalbeekeepingtrust.org/darwinian-beekeeping
or:
"In the case of Varroa, which is a worldwide menace to beekeeping, we believe
apicultural
practices are responsible for maintaining virulent forms of the pathogen. In areas where the parasite has been established
for several decades in honey bee populations, without being controlled by beekeepers, the parasite no longer is lethal to infested
colonies. This is the case in South America both for Africanized bees and bees of European origin (Rosenkranz, 1999) as well as in
North Africa (Ritter, 1990). "
We can find this understanding in a great many published research papers.