Sources of Pyrethrum
Pyrethrum is a pyrethrins-containing insecticide product derived from certain Old World chrysanthemum flowers (Asteraceae Family), including the Chrysanthemum cinerariaefolium (Dalmatian Chrysanthemum) and the Chrysanthemum coccineum or Tanacetum coccineum (Pyrethrum Daisy or Painted Daisy). These flowers contain insect-killing chemicals called pyrethrins. The active ingredients are particularly found in the seed coats.
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Pyrethrins
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There are two pyrethrins, pyrethrin I and pyrethrin II, useful for insecticidal purposes, both being degradable. It may be for that reason that they do not linger and build up, and that subsequent insect tolerance has not developed. Both pyrethrins are destroyed upon exposure to light and oxygen. One of the difficulties of pyrethrins is that they destroy not only so-called undesirable "bugs", but useful insects such as bees as well. in addition, they can also pose some health risks for pets and humans.
Other Insecticides in Pyrethrum
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In addition to the pyrethrins, there are two other groups of insecticides found in pyrethrum, namely cinerin I, cinerin II, jasmolin I, and jasmolin II. Interestingly, all six of the pesticide components of the relevant chrysanthemums contains a cyclopropane ring as part of their structure. The insecticides attack the nervous system of the insects; at lower levels, they are found to serve also as insect repellents.
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Sources of Pyrethrum
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Although pyrethrum is historically associated with Dalmatia and Persia, dating back hundreds of years, today the overwhelming leader in world supply is Kenya and the highlands of East Africa.
Use in the Garden
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Gardeners sometimes plant pyrethrum chrysanthemums as companion plants to reduce insect infestation.
Pyrethroids
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Chrysanthemic acids have been chemically modified to form pyrethroids, which in some areas are not considered low-impact pesticides. They are designed to persist longer in the environment before degradation occurs; chrysanthemic acids may also be paired with so-called synergists, such as piperonyl butoxide, which are designed to overcome the natural detoxifying mechanisms of insects.
Complete Synthesis of Chrysanthemic Acid
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Although current sources of pyrethrum are flower-based rather than man-made, a total synthesis of chrysanthemic acid has been accomplished, and is described in the "Journal of Organic Chemistry"(see reference below). Schematically, the chemistry involved may be seen at the University of Wisconsin's Department of Chemistry website.
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References
Resources
- Photo Credit Pyrethrin I - Public Domain; Wikimedia Commons
