Surface area will have a very large impact on the rate of sublimation or evaporation as would any air movement.  My guess is that the gel formulation is to promote "evaporation".   In thinking about the mode of action of thymol, I wonder if it is more repellent than deadly, or if it lessens the ability of riding mites to determine when to jump off into a cell.  As to removal, I would think that either solid or powdered thymol would be very difficult for the bees to physically remove, assuming the carry it out in their mandibles... 

             ***********************************************
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