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Pyrethrin (Wikipedia)
Chemical structure of some pyrethrins: pyrethrin I (R = CH3), pyrethrin II (R = CO2CH3)

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 naturally occurs in chrysanthemum flowers and is often considered an organic insecticide when it 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.

Pyrethrins are gradually replacing organophosphates and organochlorides as the pesticides of choice as the latter compounds have been shown to have significant and persistent toxic effects to humans. Because they are biodegradable pyrethrins are widely preferred to pyrethroids, which are synthetic analogues of pyrethrin that accumulate in the environment.[citation needed]

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