The pyrethrins are a class of organic compounds normally derived from Chrysanthemum cinerariifolium that have potent insecticidal activity by targeting the nervous systems of insects. Pyrethrin is synthetically made by industrial methods, but it also naturally occurs in chrysanthemum flowers, thus is often considered an organic insecticide, or at least when is not combined with piperonyl butoxide or other synthetic adjuvants. Their insecticidal and insect-repellent properties have been known and used for thousands of years.