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I only have 1 of my 20 hives that did not swarm on me this spring. This is currently my strongest colony putting away the most amount of honey (4, 9-frame mediums drawn out fat and full). I've been popping the lids on all hives every week to check progress and add more supers if needed, and at that time I always pull my IPM boards out and clean off...

Today I pulled the board out from this strongest hive and there must have been a thousand dead varroa on the board (I don't remember seeing any previously). Either I have a real mite problem, or I have incredibly hygienic bees! However, because they did not swarm, they are also my only colony that did not experience a brood break in March... My last treatment was OA in late December, and I typically don't treat again until Formic Pro in August.

My question is what to do about a possible real mite problem in this hive right now? The colony is 7 mediums high with tons of bees and plenty of brood. I'm not sure what the current legality is with using OA vapor during honey production, but with that much space would it even be effective to do a course of OA??? Any other options out there, or just wait until I pull off the supers and deal with it then?

OA can be used with honey supers on if you have the label that says you can. That change was approved about two years ago.
https://www3.epa.gov/pesticides/chem_se ... 210430.pdf

Formic Pro/Mite Away Quick Strips can also be used with honey supers on. OAV is quicker and the bees seem to tolerate/get over the disruption of the treatment within minutes of it being applied.

What looked to be a promising year for honey has turned into frustration/more bees for me. No matter what I did (brood box reversals, checkerboarding, adding supers) hives built up in February and came out in March whenever the weather was near acceptable.

So here's what I decided to do. Rather than try to treat chemically at this stage, I instead found the queen and made a split from this hive (and another like it). This achieves four things for me:

1. Allows for a brood break to knock back the mite population
2. Reduces any swarming impulse they might sneak up and think about
3. Allows me to propagate the low swarming tendency and high honey production of these two colonies
4. Although I removed the queen, 4 frames of brood, and bees, the remaining bees will now be free to focus on honey for the rest of the flow!

Once the supers come off in late-June/early July, I will re-assess and treat for mites then.