I ran across some studies on the use of Thymol fed to bees in syrup while perusing the web and thought it may of interest to some beekeepers. Thymol is the main active ingredient in Vicks Vapor Rub, to my knowledge.
Apidologie has a publication ahead of print in regards to studies which indicated the feeding of small amounts of Thymol extended the longevity of bees substantially (from 20 days to 24+). The levels of Nosema Ceranae spores were greatly reduced.
I have used thymol in small amounts in my high fructose corn syrup (when feeding was necessary) to prevent bacteria growth and to possibly limit Nosema infection. Randy Oliver has reported on this.
I have done this on a rather large scale, treating 4000 gallons at a time with no apparent negative effects.