I recently used formic acid (100%) to kill varroa mites. Fill an open top aluminium can (Cola can etc) with about 50ml formic acid and place into hive, cover with a mesh to prevent bees from dropping in. The effect is fantastic. However, a serious problem that I cant solve is queen tend to abscond if the colony is weak. I believe this is due strong odour that forced the queen to leave. I tried to cage the queen while placing acid but some queen died in the cage. Anyone has experience about using this chemical and what is the best solution? Maybe I should reduce formic acid to 70% or etc?
The studies I've seen say that losing queens is one of the side effects. I haven't had the problem with Oxalic acid vapor.
When you heat oxalic acid, it turns to formic acid.