Pyrethrin
Encyclopedia
The pyrethrins are a pair of natural organic compound
Organic compound
An organic compound is any member of a large class of gaseous, liquid, or solid chemical compounds whose molecules contain carbon. For historical reasons discussed below, a few types of carbon-containing compounds such as carbides, carbonates, simple oxides of carbon, and cyanides, as well as the...

s that have potent insecticidal activity. Pyrethrins are neurotoxin
Neurotoxin
A neurotoxin is a toxin that acts specifically on nerve cells , usually by interacting with membrane proteins such as ion channels. Some sources are more general, and define the effect of neurotoxins as occurring at nerve tissue...

s that attack the nervous systems of all insect
Insect
Insects are a class of living creatures within the arthropods that have a chitinous exoskeleton, a three-part body , three pairs of jointed legs, compound eyes, and two antennae...

s. When present in amounts not fatal to insects, they still appear to have an insect repellent
Insect repellent
An insect repellent is a substance applied to skin, clothing, or other surfaces which discourages insects from landing or climbing on that surface. There are also insect repellent products available based on sound production, particularly ultrasound...

 effect. Pyrethrins are gradually replacing organophosphate
Organophosphate
An organophosphate is the general name for esters of phosphoric acid. Phosphates are probably the most pervasive organophosphorus compounds. Many of the most important biochemicals are organophosphates, including DNA and RNA as well as many cofactors that are essential for life...

s and organochloride
Organochloride
An organochloride, organochlorine, chlorocarbon, chlorinated hydrocarbon, or chlorinated solvent is an organic compound containing at least one covalently bonded chlorine atom. Their wide structural variety and divergent chemical properties lead to a broad range of applications...

s as the pesticide of first choice. They are non-persistent, being biodegradable, and break down on exposure to light or oxygen. The chemical structure of pyrethrins inspired the production of a variety of synthetic insecticides called pyrethroid
Pyrethroid
A pyrethroid is an organic compound similar to the natural pyrethrins produced by the flowers of pyrethrums . Pyrethroids now constitute a major commercial household insecticides...

s such as bifenthrin
Bifenthrin
Bifenthrin is a pyrethroid insecticide that affects the nervous system of insects.It was discovered and developed by FMC Corporation. Products containing bifenthrin include Talstar, Maxxthor, Capture, Brigade, Bifenthrine, Ortho Home Defense Max, Bifen IT, Bifen L/P, and Scotts LawnPro Step...

, permethrin
Permethrin
Permethrin is a common synthetic chemical, widely used as an insecticide, acaricide, and insect repellent. It belongs to the family of synthetic chemicals called pyrethroids and functions as a neurotoxin, affecting neuron membranes by prolonging sodium channel activation. It is not known to...

, and cypermethrin
Cypermethrin
Cypermethrin is a synthetic pyrethroid used as an insecticide in large-scale commercial agricultural applications as well as in consumer products for domestic purposes. It behaves as a fast-acting neurotoxin in insects. It is easily degraded on soil and plants but can be effective for weeks when...

.

History and biosynthesis

The pyrethrins occur in the seed cases of the perennial plant
Perennial plant
A perennial plant or simply perennial is a plant that lives for more than two years. The term is often used to differentiate a plant from shorter lived annuals and biennials. The term is sometimes misused by commercial gardeners or horticulturalists to describe only herbaceous perennials...

 pyrethrum
Pyrethrum
Pyrethrum refers to several Old World plants of the genus Chrysanthemum which are cultivated as ornamentals for their showy flower heads. Pyrethrum is also the name of a natural insecticide made from the dried flower heads of C. cinerariifolium and C...

 (Chrysanthemum
Chrysanthemum
Chrysanthemums, often called mums or chrysanths, are of the genus constituting approximately 30 species of perennial flowering plants in the family Asteraceae which is native to Asia and northeastern Europe.-Etymology:...

 cinerariaefolium
), which has long been grown commercially to supply the insecticide
Insecticide
An insecticide is a pesticide used against insects. They include ovicides and larvicides used against the eggs and larvae of insects respectively. Insecticides are used in agriculture, medicine, industry and the household. The use of insecticides is believed to be one of the major factors behind...

.

Well after their use as insecticides, their chemical structure were determined by Hermann Staudinger
Hermann Staudinger
- External links :* Staudinger's * Staudinger's Nobel Lecture *....

 and Lavoslav Ružička
Lavoslav Ružicka
Lavoslav Ružička FRS born as Lavoslav Ružička was a Croatian scientist and winner of the 1939 Nobel Prize in Chemistry who worked most of his life in Switzerland...

 in 1924.Pyrethrin I
Pyrethrin I
Pyrethrin I is one of the two pyrethrins, natural organic compounds with potent insecticidal activity. It is an ester of -trans-chrysanthemic acid with --pyrethrolone.- Total synthesis:...

 and pyrethrin II
Pyrethrin II
Pyrethrin II is an organic compound that is a potent insecticide. It is one of the two pyrethrins, the other being pyrethrin I. Thousands of tons this mixture are produced annually from chrysanthemum plants, which are cultivated in warm climates...

 are structurally related esters with a cyclopropane
Cyclopropane
Cyclopropane is a cycloalkane molecule with the molecular formula C3H6, consisting of three carbon atoms linked to each other to form a ring, with each carbon atom bearing two hydrogen atoms...

 core. Pyrethrin I is a derivative of (+)-trans-chrysanthemic acid
Chrysanthemic acid
Chrysanthemic acid is an organic compound that is related to a variety of natural and synthetic insecticides. It is related to the pyrethrin I and II, as well as the pyrethroids...

. Pyrethrin II is closely related but one methyl group is oxidized to a carboxymethyl group, the resulting core being called pyrethric acid. Knowledge of their structures opened the way for the production of synthetic analogues, which are called pyrethroid
Pyrethroid
A pyrethroid is an organic compound similar to the natural pyrethrins produced by the flowers of pyrethrums . Pyrethroids now constitute a major commercial household insecticides...

s. In terms of their biosynthesis
Biosynthesis
Biosynthesis is an enzyme-catalyzed process in cells of living organisms by which substrates are converted to more complex products. The biosynthesis process often consists of several enzymatic steps in which the product of one step is used as substrate in the following step...

, pyrethrins are classified as terpenoid
Terpenoid
The terpenoids , sometimes called isoprenoids, are a large and diverse class of naturally occurring organic chemicals similar to terpenes, derived from five-carbon isoprene units assembled and modified in thousands of ways. Most are multicyclic structures that differ from one another not only in...

s, being derived from dimethylallyl pyrophosphate
Dimethylallyl pyrophosphate
Dimethylallyl pyrophosphate is an intermediate product of both mevalonic acid pathway and DOXP/MEP pathway. It is an isomer of isopentenyl pyrophosphate and exists in virtually all life forms...

, which combine by the action of the enzyme chrysanthemyl diphosphate synthase
Chrysanthemyl diphosphate synthase
In enzymology, a chrysanthemyl diphosphate synthase is an enzyme involved in the biosynthesis of terpenoids. This enzyme is also known as CPPase. It catalyzes the chemical reaction shown below :...

.

Production

The majority of the world's supply of pyrethrin and Chrysanthemum cinerariaefolium comes from Kenya
Kenya
Kenya , officially known as the Republic of Kenya, is a country in East Africa that lies on the equator, with the Indian Ocean to its south-east...

, which produces the most potent flowers. Other countries include Dalmatia and Japan. The flower was first introduced into Kenya and the highlands of Eastern Africa during the late 1920s. Now, Kenya produces as much as 70% of the world's supply of pyrethrum. A substantial amount of the flowers are cultivated by small-scale farmers who depend on it as a source of income. It is a major source of export income for Kenya and source of over 3,500 additional jobs. About 23,000 ton/y were harvested in 1975. The active ingredients are extracted with organic solvents to give a concentrate containing pyrethrin I and II, cinerin I and II, and jasmolin I and II. Supercritical carbon dioxide
Supercritical carbon dioxide
Supercritical carbon dioxide is a fluid state of carbon dioxide where it is held at or above its critical temperature and critical pressure.Carbon dioxide usually behaves as a gas in air at STP or as a solid called dry ice when frozen...

 has also been used as an extractants.

As an insecticide

Pyrethrins are used in many varieties of insecticide, fogging products and in some pet products and have been used as an insecticide
Insecticide
An insecticide is a pesticide used against insects. They include ovicides and larvicides used against the eggs and larvae of insects respectively. Insecticides are used in agriculture, medicine, industry and the household. The use of insecticides is believed to be one of the major factors behind...

 for over 100 years. In the 1800s, it was known as "Persian Insect Powder," "Persian Pellitory", and "Zacherlin". They affect the flow of sodium out of the nerve cells in insects, resulting in repeated and extended firings of the nerves, causing the insects to die. Piperonyl butoxide
Piperonyl butoxide
Piperonyl butoxide is an organic compound used as pesticide synergist, especially for pyrethroids and rotenone. It does not by itself have pesticidal properties. However, when added to insecticide mixtures, typically pyrethrin, pyrethroid, and carbamate insecticides, their potency is increased...

, a synergist, is often used in combination with pyrethrin, making the mixture more effective by not allowing the insect's system to detoxify the pyrethrin. Although pyrethrin is a potent insecticide, it also is a insect repellent
Insect repellent
An insect repellent is a substance applied to skin, clothing, or other surfaces which discourages insects from landing or climbing on that surface. There are also insect repellent products available based on sound production, particularly ultrasound...

 at lower concentrations. Observations in food establishments demonstrate that flies are not immediately killed but are found more often on windowsills or near doorways. This suggests that, due to the low dosage applied, insects are driven to leave the area before dying. Pyrethrin and the synergists are biodegradable and rapidly disintegrate in sunlight and air, thus assuring that there will be no excessive build-up of insecticides dispensed in the area being treated.

Toxicity

The United States Department of Agriculture
United States Department of Agriculture
The United States Department of Agriculture is the United States federal executive department responsible for developing and executing U.S. federal government policy on farming, agriculture, and food...

 has stated that synergized pyrethrum " is probably the safest of all insecticides for use in food plants " and that " a pyrethrum formulation is approved for use around foodstuffs." All pyrethrins are easily hydrolyzed and degraded by stomach acids in mammals, so toxicity following ingestion by pets is very low. However, pyrethrins are dangerous for fish. Toxicity is usually associated with applying much more of the product than directed. Care should be taken to observe direction labels when using this substance around humans and animals. Overdose and toxicity can result in a variety of symptoms, especially in pets, including drooling, lethargy, muscle tremors, vomiting, seizures and death. Toxicity symptoms in humans include asthmatic breathing, sneezing, nasal stuffiness, headache, nausea, incoordination, tremors, convulsions, facial flushing and swelling, and burning and itching sensation. Permethrin
Permethrin
Permethrin is a common synthetic chemical, widely used as an insecticide, acaricide, and insect repellent. It belongs to the family of synthetic chemicals called pyrethroids and functions as a neurotoxin, affecting neuron membranes by prolonging sodium channel activation. It is not known to...

 and other pyrethroids are synthetic
Chemical synthesis
In chemistry, chemical synthesis is purposeful execution of chemical reactions to get a product, or several products. This happens by physical and chemical manipulations usually involving one or more reactions...

 versions of pyrethrin which have much greater potential for causing toxicity. The latest information regarding toxicity of piperonyl butoxide
Piperonyl butoxide
Piperonyl butoxide is an organic compound used as pesticide synergist, especially for pyrethroids and rotenone. It does not by itself have pesticidal properties. However, when added to insecticide mixtures, typically pyrethrin, pyrethroid, and carbamate insecticides, their potency is increased...

 has determined that it can pose a distinct health risk when it becomes airborne and pregnant women are exposed during the third trimester. This leads to delayed mental development in young children. A 2011 study found a significant association between piperonyl butoxide (PBO), a common additive in pyrethroid formulations, measured in personal air collected during the third trimester of pregnancy, and delayed mental development at 36 months. Children who were more highly exposed in personal air samples (≥4.34 ng/m3) scored 3.9 points lower on the Mental Developmental Index than those with lower exposures. The lead researcher stated, "This drop in IQ points is similar to that observed in lead exposure. While perhaps not impacting an individual's overall function, it is educationally meaningful and could shift the distribution of children in the society who would be in need of early intervention services."

See also

  • Persian powder
    Persian powder
    Persian powder is a Plant toxin insecticide powder, also called "Persian Pellitory" and Insect powder.-Biological pest control:Persian powder is a green pesticide that has been used for centuries for the biological pest extermination of household insects, garden pests, and agricultural pests...

  • Pyrethroid
    Pyrethroid
    A pyrethroid is an organic compound similar to the natural pyrethrins produced by the flowers of pyrethrums . Pyrethroids now constitute a major commercial household insecticides...


Category: Plant toxin insecticides

External links

The source of this article is wikipedia, the free encyclopedia.  The text of this article is licensed under the GFDL.
 
x
OK