Hi Mark, looks like you've had no response so I'll give it a try. 3 bees in a hundred would give you a 3% varroa population, during the spring often the deciding point is around 4% but we are in fall and it's best to treat so that you have the absolute minimum mite load going into the winter. The decision and method is up to you and it's a moot point if you are queenless. With no eggs larvae or brood (I think you said that) then you are likely queenless and the hive won't survive. It's pretty much to late to add a queen at this point in the year if you could even find one and haveing any chance of survival over the winter would be slim indeed. I would say chalk this year up to a learning process and start again in the spring with another Nuc or capture a swarm.
It's been a rough year in Central OR for beekeeping. I started 2020 with 3 hives, I caught a swarm and went up to 4, neglected testing for mites in June/July as I had treated in may and my hives suffered from my stupidity. I am now back to 3 hives as I joined my 2 weakest hives a few weeks ago but now it looks like that hive is now queenless so it won't survive... rough year.
So, treat if you want to but you are probably queenless so it's a moot point. Use the resources that you have (hive equipment/pulled comb [worth it's weight in gold]) to jump start next years bee keeping efforts.
