Dear Ivan, In our experiments with formic acid, we found that 85% formic acid may interfere with the pheromones in the bee hives and will cause increased agressive behaviour of workers against their queens. This will lead to killing up to 50% of their queens. We also found that 85% of formic acid can kill eggs and young larvae. As a result, it will be difficult for the colony to raise queens to replace the killed ones. Using the 65% formic acid is less harmful to queens and workers. It will not effect queens and drones longevity and performance as long as the acid applied at the right time of the year and within the recommended temperature range. In our studies, we also found that the formic acid will kill workers and queens infested with tracheal mites more radially than healthy ones. We have been using formic acid (65%) single application pad in spring for tracheal mite and varroa mite control in Ontario for the last 6 years with no reported queen failures or weak colonies. Best Regards. Medhat Nasr Medhat Nasr, Ph.D. Research Scientist, Ontario Beekeepers' Association Dept. Environmental Biology University of Guelph Guelph, Ontario, Canada N1G 2W1 Tel: (519) 824-4120 Fax:(519)837-0442 e-mail: [log in to unmask]