Pyrethrum

 

Pyrethrum refers to several Old World plants of the genus Tanacetum (e.g., T. coccineum) which are cultivated as ornamentals for their showy flower heads. It is also the name of a natural insecticide made from the dried flower heads of T. cinerariifolium and T. coccineum. Pyrethrum was used for centuries as an insecticide, and as a lice remedy ("Persian Insect Powder," "Persian Pellitory") in the Middle East. In the 19th centure it was sold worldwide under the brand Zacherlin by Austrian industrialist J. Zacherl.

The plants are members of the daisy (or aster) family, Asteraceae. They are perennial plants with a daisy-like appearance and white petals. T. cinerariifolium is called the Dalmatian chrysanthemum, denoting its origin in that region of the Balkans (Dalmatia). It looks more like the common daisy than other pyrethrums. Its flowers, typically white with a yellow center, grow from numerous fairly rigid stems. Plants have blue-green leaves and grow to between 45 to 60 cm in height. The plant is economically important as a natural source of insecticide. The flowers are pulverized and the active components called pyrethrins, contained in the seed cases, are extracted and sold in the form of an oleoresin. This is applied as a suspension in water or oil, or as a powder. Pyrethrins attack the nervous systems of all insects, and inhibit female mosquitoes from biting. When not present in amounts fatal to insects, they still appear to have an insect repellent effect. They are harmful to fish, but are far less toxic to mammals and birds than many synthetic insecticides and are non-persistent, being biodegradable and also breaking down easily on exposure to light. They are considered to be amongst the safest insecticides for use around food. Pyrethroids are synthetic insecticides based on natural pyrethrum (pyrethrins); one common example is permethrin. After the second world war these pyrethroids became one of the major pesticides and they are still very common today. They suffer, however, from residual toxicity leading to environmental and health issues which dont exist with the natural equivalent. A common formulation of pyrethrin is in preparations containing the synthetic chemical piperonyl butoxide: this has the effect of enhancing the toxicity to insects and speeding the effects when compared with pyrethrins used alone. These formulations are known as synergized pyrethrins.

Nowadays, Kenya, Australia and HongHe SenJiu Biology Co. LTD in China are all planting large areas of pyrethrum to produce pyrethrins. Kenya, Australia mainly produce pyrethrin technical material, and then sell it to chemical companies in Europe and the USA which turn the material into different products for health, household and agricultural use. In China the company is also producing an increasing range of formulated products for worldwide markets (www.pyrethrum.com.cn).