FatherMichael, I can't help with Varroa. The problem here is attracting a swarm. They've stopped feeding her and stopped her laying to slim down for the flight anyhoo.
Dr. Tom Seeley has a lot of good science concerning swarms. From my experience, they don't worry about the trap being full of combs. The scouts will start looking when things are warm enough. I have had one swarm, though I would guess they absconded, on March 1st. We were still getting frost at that time.
https://www.youtube.com/watch?v=JnnjY823e-wThey will start looking up and down all the branches of trees around, and will mark promising cavities. If you use Lemon Grass Oil, or the very expensive Swarm Commander, it will tell the scouts there is something interesting here. LGO has two compounds, Geraniol, and Citral, that are found in the Nasanov's gland. This is what bees mark food sources, interesting things, and you will see them fanning to send this scent when they want the rest of the colony to come home. These compounds say, "It's here!"
Using too much of this is as bad as not using it at all. But I've seen bees get all excited over a cotton pad saturated with the stuff, and hang out in the bait hives like they were going to swarm. Once they know the hive is there, you don't need to keep marking it as "here." You can tell, because there will be a half dozen bees that will hang around it for weeks at a time. They will go back to the colony and tell the other bees that there's "a really cool" place, come look at it. Then things will go into a contest the other workers will vote on. Every swarm trap isn't going to be accepted, even if everything is done right.
They don't like other bugs. I've had them hanging around, then come back a few days later to check, only to see the trap abandoned. Taking it down, I find ants have taken over, or wasps. They sure don't like a spider that's brown and has the same shape as a black widow here in the deep south. Sometimes I actually see black widows in the traps. I have yet to do any more testing, my hypothesis is the higher I hang the trap, the further from the usual range of these invaders they'll be.
For the ants, I make a bait of jelly, and borax, or peanut butter and borax. I am diabetic, so I take the needles off the spent syringes, and fill them with this stuff, the protein for the wood ants, the jelly for the others. 1/8 inch opening cut into the cap that they come with. It seems to work.
It takes a little practice to tell the difference between scout bees looking things over, and a swarm. I still get fooled. Scouts will fly out the entrance, circle around the outside of the trap, then go back in. A swarm moved in will have the bees go straight in and out.
I tend to go out to "tick country," looking for the toughest bees I can find. I can't say how successful I've been at getting them, because these "gansta" city bees have accosted my pretty wood bees, and kept me from getting things done for some years here.
