>In my experience, placing any product that depends upon evaporation (formic, thymol, other essential oils) under the lid is unreliable. Better to place in the center of the brood nest, where the temperature is constant, and where it is more difficult for the bees to simply fan the fumes away from where they might do some good. I have used only thymol crystals since we found varroa here in 1997. Based on a paper by Higes, I place 8g of crystals on an old honey jar lid (Petri dish substitute!) placed on the excluder directly above the cluster; this is repeated weekly for 3 weeks (rather than Higes original 4 weeks). An eke raises the crown board to provide an air space. This has served me well for 16 years. With a single brood box on most of my colonies, it is difficult to see how I could get closer to the centre of the brood nest. Best wishes Peter 52°14'44.44"N, 1°50'35"W *********************************************** The BEE-L mailing list is powered by L-Soft's renowned LISTSERV(R) list management software. For more information, go to: http://www.lsoft.com/LISTSERV-powered.html