This is an oxalic acid (OA) vaporizer made by Biovet and is rated as one of the best. Choose onsite pickup and we will ship it free. It is very effective on varroa mites typically killing about 97%. It has been used in Europe for many years. It is has little or no adverse effect on queens, brood, and worker bees. Use 1 gram of OA per deep hive body. Follow all safety precautions as with any product.