Testing a new oxalic acid sublimation device...works from the top.
Works with butane gas, oxalic acid vapor is circulated by a small ventilator and the special hood, so the oav gets into every corner of that hive, 3 minutes per hive, doesn't need external power, ...
Still in phase of development, but promising so far. I like it. Little vapor outside the hive, a defined dosage of oxalic acid gets sublimated and is circulated through the hive. Bees are covered in tiny oxalic acid crystals, mite drop is pretty strong.