2 lb, synergized python dust II, is the only dust to contain 2 novel active ingredients for maximum efficacy against all major livestock ectoparasites, zetacypermethrin is a 4th generation pyrethroid insecticide with enhanced potency against resistant horn fly strains, the photostable form of piperonyl butoxide is a mixed function oxidase inhibitor that reduces metabolic resistance in insects thus synergizing the pyrethroid for maximum efficacy & residual activity, shaker canister.