How Oxalic Acid Kills Mites
Gerhard Brüning describes his experiences with oxalic acid as a treatment. He discovered that oxalic acid penetrates the mite through the feet. Doesn’t matter if you dribble or vaporize. He vaporizes, because it doesn’t harm the bees (unlike dribbling).
You find pictures here in one of his reports (Unfortunately, it is German):
There he describes what occurs when oxalic acid is applied to a hive. The oxalic acid builds at the adhesive parts of the mite’s leg: the paired lobes (pulvilli) where it forms a crystal. After three hours the mite is dead. The crystal then breaks down and only a small residual remains forming akin to a drop.
Here are some pictures from the mite’s adhesive lobes under a microscope:
See the lobes attached to end of the legs:
This is where the oxalic acid accumulates and forms a crystal. Mites do try to shake it off, but can’t.
The theory behind it is that the adhesive lobes need to be moist in order for the mite to stick to the bee or other surface. The moisture comes through the leg of the mite, through the hemolymph of the mite.
Through the lobes there is direct access to the mite’s hemolymph and that is how the oxalic acid penetrates the mite and kills her.
Bees are not harmed by vaporization because they have a different mechanism at their adhesive lobes.
(OA dribbling is harmful to the bees as they eat the sugary solution and the oxalic acid harms the walls of their guts.)