After seeing 3 mites in one peak through the window, we decided it was time to treat for Varroa. A little late, but what the heck. There's not much going on in the Backyard, and it'll be a good exercise. Given the chance, the Varroa population will overtake the colony as the honeybee population drops.
Our hive has a solid bottom board, so we can't rely on a simple grease patty to promote dropoff. Any mites that fall off the bees can simply climb back on a passerby. We have to use a miticide to actually kill the mites. (We finally do have sumac berries, but still no smoker.) Scaling down the recipe recommended by Bees for Development, Spice the Mite with Nutmeg, we made a tracking strip and inserted it into the hive where the bees would be forced to walk over it. In theory, they pick up some of the grease and track it all over the place as they walk over the combs and their sisters. The mites loose their grip, and the essential oil kills them within hours.
Nutmeg EO runs over $11 for a .5 oz. bottle at the local health food store, so we used the ancient tea tree oil in our medicine cabinet. Our weather is far from Grenadian, so we left the tracking strip in twice the recommended time. When we pulled it out, there were only 4 mites on it. That's a very low count, so either the miticide didn't work or the colony is well below the "economic threshhold" (generally considered 50 in a 24hr sticky board test). We're hoping it's the former but, in case it's the latter, we took one more step.
The next day, an unseasonably warm 73°F, we placed a tracking strip on the landing board and left it there until the sun set. When the wax hardened, the tracking strip was rendered useless. There was, however, 1 dead mite; not bad for 4 hours. The stuff works! Unfortunately there was a dead drone, too, stuck wingside down in the melted/hardened miticide.
We should have started treating earlier, say in September or even October, so the tracking mix wouldn't harden and lose it's effectiveness. Our highs are only in the 50s now, but better late than never, we hope. We'll continue to monitor and, on warm days, treat again.