Pyrethrin is a class of organic compounds derived from the pyrethrum plant, commonly used as an insecticide. It is obtained from Dalmatian or Persian chrysanthemum and is a neurotoxin that causes paralysis in insects. Pyrethrins are relatively nontoxic to mammals but are highly toxic to fish and moderately toxic to birds and bees.
Pyrethrin refers to a class of organic compounds collectively known as pyrethrins that are derived from the parent chemical, pyrethrum. While there are six main types, the most common are a pair of esters distinct from each other as pyrethrin I and II. Both possess a basic molecular structure cyclopropane. However, type I has one less oxygenated carbon molecule than type II.
In general, pyrethrin is the active constituent of the flowers of the pyrethrum plant, better known as chrysanthemum. A member of the daisy family, several related species are grown as perennial ornamentals. However, the compound is obtained from Dalmatian chrysanthemum (Chrysanthemum cinerariaefolium) or Persian chrysanthemum (C. coccineum), also known as Painted Daisy. These two species are grown commercially to produce pyrethrin for use as an insecticide. While other chrysanthemums also have insecticidal properties, they are not as effective.
Pyrethrin is produced from the plant’s flowers by one of two methods. The flowers are dried and ground into pyrethrum powder, or are subjected to solvents to extract the volatile oils to produce a resin. The compound is sold under various trade names.
The species from which pyrethrin is obtained are considered excellent insect deterrents even in their natural state. This is because they exhibit protective effects on nearby plants and protect them from infestation. In fact, these plants are often featured in companion planting, a natural pest control method used by organic gardeners.
Pyrethrin is classified as a neurotoxin. It rapidly permeates the insect’s shell or skin and causes immediate paralysis. However, where a large area or large number of insects are being treated, it may only be effective as a “knockdown” measure. Indeed, the protective enzymes of the insect degrade the insecticide and allow its recovery. For this reason, pyrethrin can be given in combination with organophosphates or carbamates to discourage enzyme activity and ensure a lethal dose.
In general, pyrethrins are considered relatively nontoxic to mammals, including humans. However, Type I is considered a “restricted use pesticide” by the United States Environmental Protection Agency and its availability and use is limited to certified applicators. This may be because pyrethrins are highly toxic to fish and moderately toxic to birds and bees. The compounds do not persist in the environment as they biodegrade easily when exposed to oxygen, moisture and sunlight.
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