>A new beek in NH told me over the phone a tricke relayed by her mentor: Pour vegetable oil (any kind) onto a napking and lay it onto the frames overnight for varoa control.
Can it really be that easy?
Most anything that makes the bees groom themselves will make some difference.
There are many oil methods. Most, because it won't turn rancid like vegatable oil, involve FGMO (Food Grade Mineral Oil). The first treatments were just painting it on the top bars. The problem is it only works for a short time and it doesnt' have knock down power. It takes keeping the bees in contact with the oil to keep the mite levels down. So Dr. Rodriguez, who started the idea, came up with several alternative methods to do this. One was to make an emoulsin of beeswax, honey and FGMO and soak cotton cords in it. This took the bees longer to get the oil out and so the treatment would last longer. Another is shop towels soaked in oil. But this doesn't take a day for the bees to get it out. Fogging with FGMO is another method to do oil. You buy an insect fogger and just use FGMO in it. If you do it every other week until late summer and every week until winter, from my experience, it works. But you can't treat once and be rid of the Varroa. You have to treat all the time from spring until winter.
Here's an idea of knockdown and efficacy:http://www.bushfarms.com/beesvarroatreatments.htm
If you look at these numbers you see that something that is 50% effective requires at least once a week treatment to be useful.http://www.bushfarms.com/beespests.htm
Here's some on all pests including Varroa in general and a section on FGMO for varroa.