PYRETHRINS (Chrysanthemum cinerariifolium)

The flowers of Chrysanthemum cinerariifolium contain a natural insecticide called pyrethrin, an aromatic herb that has been used since the 1920s in the manufacture of insecticidal sprays and powders. The flowers are harvested after blooming and are dried or the oils are extracted with solvents. These compounds have been used to control human lice, mosquitoes, cockroaches, beetles and flies. They are also used to control insects in horticultural crops, grain storage and poultry pens, as well as on dogs and cats to control lice and fleas.

Pyrethrins are contact poisons that penetrate the nervous system of an insect. Synthetic chemicals are added to the pyrethrins to create more effective insect killers than the natural pyrethrins. These synthetic chemicals are called "pyrethroids" and the general name covering both pyrethrins and pyrethroids is "pyrethrum." Pyrethrums break down fairly quickly and lose effectiveness the longer they are stored. Antioxidants are often added to prolong their effectiveness.

There are no known carcinogenic effects of these pesticides. The rare danger to human health would be if inhaled; it may bring about asthematic breathing. The most severe poisoning would be for infants whose bodies cannot break down the pyrethrums effectively. Some people experience skin reactions such as irritation, itching, pricking sensations and local burning sensations. Symptoms may last two days.

Thanks to Marcia Eischen for this report on pyrethrins and to Nancy Works for presenting it at our meeting. Marcia's source was the Extension Toxicology Network, EXTOXNET.

Pyrethrums are extremely toxic to aquatic life and slightly toxic to some bird species. Toxicity increases with warmer water temperatures and acidity. Pyrethrums are toxic to bees as well.

 

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