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Insecticide

An insecticide is apesticide 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 the increase in agricultural productivity in the 20thcentury.[1] Nearly all insecticides have the potential to significantly alter ecosystems; many are toxic to humans; and

others are concentrated in the food chain.[citation needed]

[edit] Classes of agricultural insecticides

The classification of insecticides is done in several different ways:[citation needed]

y Systemic insecticides are incorporated by treated plants. Insects ingest theinsecticide while feeding on the plants.

y Contact insecticides are toxic to insects brought into direct contact. Efficacy isoften related to the quality of pesticide application, with small droplets (such as

aerosols) often improving performance.[2]

y Natural insecticides, such as nicotine, pyrethrum and neem extracts are madeby plants as defenses against insects. Nicotine based insecticides have been

barred in the U.S. since 2001 to prevent residues from contaminating foods.[3]

y Plant-Incorporated Protectants (PIP) are insecticidal substances produced byplants aftergenetic modification. For instance, a gene that codes for a specific

Baccilus thuringiensis biocidal protein is introduced into a crop plant's genetic

material. Then, the plant manufactures the protein. Since the biocide is

incorporated into the plant, additional applications at least of the samecompound, are not required.

y Inorganic insecticides are manufactured with metals and include arsenates,coppercompounds and fluorine compounds, which are now seldom used, and

sulfur, which is commonly used.

y Organic insecticides are synthetic chemicals which comprise the largestnumbers of pesticides available for use today.

y Mode ofactionhow the pesticide kills or inactivates a pestis another way ofclassifying insecticides. Mode of action is important in predicting whether an

insecticide will be toxic to unrelated species, such as fish, birds and mammals.

Heavy metals, e.g. arsenic have been used as insecticides; they are poisonous and very rarely used now by

farmers.[citation needed

]

[edit] Organochlorine compounds

The insecticidal properties of the best known representative of this class of insecticides, DDT, was made by the

Swiss Scientist Paul Mller. For this discovery, he was awarded theNobel Prize for Physiology or Medicine in

1948.[4] DDT was introduced on the market in 1944. With the rise of the modern chemical industry, it was possible

to make chlorinated hydrocarbons. DDT works by opening the sodium channels in the nerve cells of the insect[citation

needed].

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[edit] Organophosphates

The next large class developed was the organophosphates, which bind to acetylcholinesterase and other

cholinesterases. This results in disruption of nerve impulses, killing the insect or interfering with its ability to carry

on normal functions. Organophosphate insecticides and chemical warfare nerve agents (such as sarin, tabun, soman

and VX) work in the same way. Organophosphates have an accumulative toxic effect to wildlife, so multiple

exposures to the chemicals amplifies the toxicity.[5