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Pyrethrins are natural insecticides
produced by certain species of the
chrysanthemum plant. The flowers of the plant are harvested shortly
after
blooming and are either dried and powdered or the oils within the
flowers
are extracted with solvents. The resulting pyrethrin containing
dusts
and extracts usually have an active ingredient content of about
30%.
These active insecticide components are collectively known as
pyrethrins.
Two pyrethrins are most prominent, pyrethrin-I and pyrethrin-II. |
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The pyrethrins have another four different active
ingredients, Cinerin I and II
and Jasmolin I and II. Pyrethrin compounds have been used primarily
to control human lice, mosquitoes, cockroaches, beetles and flies.
Some pyrethrin dusts, used to control insects in
horticultural crops, are only 0.3% to 0.5% pyrethrins, and are
used at rates of up to 50 lb/A.
Other pyrethrin compounds may be used in grain storage and in poultry
pens and on dogs and
cats to control lice and fleas. |
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The natural pyrethrins are contact poisons which
quickly penetrate the nerve system of the insect. A few minutes
after application, the insect cannot move or fly away. But, a knockdown
dose does not mean a killing dose. The natural pyrethrins are swiftly
detoxified by enzymes in the insect. Thus, some pests will recover.
To delay the enzyme action so a lethal dose is assured, organophosphate's,
carbamates, or synergists may be added to the pyrethrins.
Excerpt from a paper contained in the Pesticide Information Project
of Cooperative Extension
Offices at Cornell University, Michigan State University, Oregon
State University, and University
of California at Davis. |
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