Pyrethrins are botanical insect repellents derived from the flowers of a species of Chrysanthemum. They’re considered one of the best vapor repellents, keeping pest flies from landing and feeding on the horse.
Permethrin is a synthetic pyrethroid with a “hot foot” action that repels and kills insect pests after they land. Permethrin lasts longer than pyrethrins alone.
Piperonyl Butoxide acts as a pesticide synergist preventing the pest flies from metabolizing the pyrethrins and permethrin, and increasing their effectiveness.