In response to another thread, I'm starting this one about an application method for Formic Acid. Here's a link from the developers

http://www.wvu.edu/~agexten/varroa/FormicAcid.pdf

I've been using this method myself and it works pretty much as described, costs me something around 50 cents a treatment. I don't use the HBH, but when using the fumigator I put 1/2 drop lemongrass in the mix, which reduces queen loss right down, in my case, to zero.