The Pyrethrum reference article from the English Wikipedia on 24-Jul-2004
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Pyrethrum

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Pyrethrum (Chrysanthemum cinerariaefolium, Family Asteraceae) is a perennial African plant with a daisy-like appearance and white, pink or red flowers. The same species is also known as Pyrethrum roseum, Chrysanthemum coccineum, Tanacetum coccineum, or simply, the Painted Daisy.

The flower is good for use as a long-lasting cut flower. The plant will re-bloom in late summer if pruned.

The plant is economically important as a natural source of insecticide. The flowers are pulverized and the active components, a group of esters called pyrethrins (C21H28O3, or C22H28O5) 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 a 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.

Kenya produced 90% (over 6,000 tons) of the world's pyrethrum in 1998, but production in Tasmania is now increasing.

Pyrethroids are synthetic insecticides based on natural pyrethrum: an example of one is permethrin. 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

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