Pyrethrum refers to several Old World plants of the genus Chrysanthemum (for example, C. coccineum) which are cultivated as ornamentals for their showy flower heads. It's also the name of a natural insecticide made from the dried flower heads of C. cinerariifolium and C. coccineum. Pyrethrum was used for centuries as an insecticide and as a lice remedy ("Persian Insect Powder," "Persian Pellitory") in the Middle East. It was sold worldwide under the brand Zacherlin by Austrian industrialist J. Z… (More on Pyrethrum)