pyrethrum

Pyrethrum is an insecticidal extract obtained from the dried flower heads of certain chrysanthemum species, principally Chrysanthemum cinerariifolium and Chrysanthemum coccineum (also classified as Tanacetum cinerariifolium). The flowers are harvested, dried, and processed to produce powders or concentrates that contain the active compounds known as pyrethrins.

The six closely related esters that make up pyrethrins are pyrethrin I and II, cinerin I and II, and jasmolin I and II. They act on the insect nervous system by prolonging the opening of voltage-gated sodium channels, producing rapid paralysis. Pyrethrins are relatively rapidly degraded by light and air, and have low mammalian toxicity, though they can irritate skin or eyes and may provoke allergic reactions in sensitive people. Formulations often include synergists to boost effectiveness.

Pyrethrum production involves cultivation of suitable cultivars, hand-harvesting of flower heads, drying, and extraction of pyrethrins using solvents or mechanical means. The resulting products are used as natural insecticides in agriculture, home gardens, and some public health applications. Major producers include Kenya, Ethiopia, and Tanzania, with historical roots in the Dalmatian region of Croatia.

Safety and environmental notes: Pyrethrins degrade rapidly in sunlight and have low persistence in the environment, but can be toxic to aquatic organisms and some beneficial insects if misused. They are generally considered compatible with organic farming when used as directed. Synthetic pyrethroids—stable, petrochemical-derived analogs—are related but distinct classes used widely in modern pest control.