Pyrethrins

The worldwide usage of synthetic pesticides has been rapidly increasing as plant production becomes more intensive. There is a growing recognition that many synthetic pesticides display a variety of adverse effects on human health and environmental quality. On the other hand, people have observed that some plants restricted pests better than others. Ancient growers used several plant extracts and developed procedures for their extraction and use on other crops for plant protection. Botanically derived insecticides have gained favor in recent years, due in part to the perception that, because they originate from plant material, they are more safe or natural.

Pyrethrum is a naturally occurring insecticide used in various insecticidal products and organic pest control recipes. The dried flower heads of pyrethrum contain insecticidal principles collectively called ‘‘pyrethrins,’’ of which six have been isolated and chemically identified as pyrethrin-I, pyrethrin-II, cinerin-I, cinerin-II, jasmolin-I, and jasmolin-II.

The extremely low mammalian toxicity of pyrethrins has made this group of insecticides an excellent candidate as alternative to synthetic insecticides. Pyrethrins are registered for use in commercial greenhouses for control of several insects and mites, such as armyworms, aphids, cabbage loopers, Colorado potato beetles, fruit flies, cucumber beetles, flea beetles, spider mites, leafhoppers, and tomato fruitworms.

As insecticides, pyrethrins have many desirable properties, which is why they are in so many organic pest control recipes. They are extremely toxic to insects and have a remarkably wide scope of effectiveness, they have low mammalian toxicity, and insect resistance to pyrethrins is not an issue. For most pesticides, including synthetic pyrethroids, the US Environmental Protection Agency requires detailed information for registration, but pyrethrins are relieved of this requirement because of their nontoxic nature to humans and animals.

These pyrethrin compounds are rapidly degraded by the combination of sunlight and air and, therefore, represent no environmental hazards that are usually associated with other persistent insecticides. These favorable properties enable pyrethrins to compete successfully in the insecticide market. The fact that they break down in sunlight, however, has limited their use in agriculture and forestry. Because of the pyrethrins’ nonpersistent characteristics under direct sunlight, frequent applications have to be made about every seven to ten days. The extremely low residues of pyrethrins detected in soil and runoff water and their adsorption to soil organic matter poses no environmental concern.(Antonious)

Grown specifically for its insecticide, the perennial plant pyrethrum produces pyrethins in the cases of its seeds. Pyrethins work as neurotoxins, attacking the nervous system of any type of insect.  Even when Pyrethins are present in non-fatal amounts, they seem to still have a repellent effect on insects.  Pyrethins are beginning to replace organochlorides and organophosphates as the first choice of pesticide. 

The global supply of Chrysanthemum cinerariaefolium and pyrethin comes mainly from Kenya, where the flower was originally introduced to the Eastern Africa highlands in the late 1920s.  Today, 70% of the global supply of pyrethrum is produced in Kenya.  Many small-scale farmers depend on the flower as a steady source of income and cultivate a significant amount of Kenya's pyrethrum exports.  The flower provides more than 3,500 jobs in Kenya, and is a major component of the country's export income.  (Pyrethin)

As the public’s awareness of potentially harmful chemical insecticides increases, so does the number of organic gardens. Environmentally aware people are more likely to grow their own vegetables, rather than purchase produce from stores, which may be treated with potentially harmful pesticides.

To meet the growing demand for home garden pest control, there are effective natural and organic insect sprays available. Containing pyrethrin as an active ingredient, these organic bug sprays are easily broken down by nature—by sunlight and soil. By using organic insect killers, gardeners have an effective insect control solution that doesn’t harm their plants or add harmful chemicals to the environment.

Antonious, George F. "Residues and Half-Lives of Pyrethrins on Field-Grown Pepper and Tomato." Journal of Environmental Science and Health (2004): 491-503.

Pyrethrin. 20 April 2010. 26 April 2010 <http://en.wikipedia.org/wiki/Pyrethrin>.