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For other uses, see Insecticide (disambiguation). 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 the increase in agricultural productivity in the 20th century[1]. Nearly all insecticides have the potential to significantly alter ecosystems; many are toxic to humans; and others are concentrated in the food chain.
[edit] Classes of agricultural insecticidesThe classification of insecticides is done in several different ways:
Heavy metals, e.g. arsenic have been used as insecticides; they are poisonous and very rarely used now by farmers. [edit] Organochlorine compoundsThe insecticidal properties of the best known representative of this class of insecticides, DDT, was made by the Swiss Scientist Paul Műller. For this discovery, he was awarded the Nobel Prize for Physiology and Medicine in 1948. 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. [edit] OrganophosphatesThe next large class developed was the organophosphates, which bind to acetylcholinesterase and other cholinesterases. This results in disruption of nervous 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 additive toxic effect to wildlife, so multiple exposures to the chemicals amplifies the toxicity.[4] [edit] CarbamatesCarbamate insecticides have similar toxic mechanisms to organophospahtes, but have a much shorter duration of action and are thus somewhat less toxic. [edit] PyrethroidsTo mimic the insecticidal activity of the natural compound pyrethrum another class of pesticides, pyrethroid pesticides, have been developed. These are nonpersistent and much less acutely toxic than organophosphates and carbamates. Compounds in this group are often applied against household pests. [edit] NeonicotinoidsNeonicotinoids are synthetic analogues of the natural insecticide nicotine (with a much lower acute mammalian toxicity and greater field persistence). Broad-spectrum – systemic insecticides with a rapid action (minutes-hours). They are applied as sprays, drenches, seed and soil treatments – often as substitutes for organophosphates and carbamates. Treated insects exhibit leg tremors, rapid wing motion, stylet withdrawal (aphids), disorientated movement, paralysis and death. [edit] Biological insecticidesRecent efforts to reduce broad spectrum toxins added to the environment have brought biological insecticides back into vogue. An example is the development and increase in use of Bacillus thuringiensis, a bacterial disease of Lepidopterans and some other insects. It is used as a larvicide against a wide variety of caterpillars. Because it has little effect on other organisms, it is considered more environmentally friendly than synthetic pesticides. The toxin from B. thuringiensis (Bt toxin) has been incorporated directly into plants through the use of genetic engineering. Other biological insecticides include products based on entomopathogenic fungi (e.g. Metarhizium anisopliae), nematodes (e.g. Steinernema feltiae) and viruses (e.g. Cydia pomonella granulovirus). [edit] AntifeedantsMany plants have evolved substances like polygodial, which prevents insects from eating, but does not kill them directly. The insect often remains nearby, where it dies of starvation. Since antifeedants are nontoxic they would be ideal as insecticides in agriculture. Much agrochemical research is devoted to make them cheap enough for commercial use. [edit] Environmental effects[edit] Effects on nontarget speciesSome insecticides kill or harm other creatures in addition to those they are intended to kill. For example, birds may be poisoned when they eat food that was recently sprayed with insecticides or when they mistake insecticide granules on the ground for food and eat it.[4] Sprayed insecticides may drift from the area to which it is applied and into wildlife areas, especially when it is sprayed aerially.[4] [edit] DDTMain article: DDT One of the bigger drivers in the development of new insecticides has been the desire to replace toxic and irksome insecticides. DDT was introduced as a safer alternative to the lead and arsenic compounds. Some insecticides have been banned due to the fact that they are persistent toxins which have adverse effects on animals and/or humans. An oft-quoted case is that of DDT, an example of a widely used (and maybe misused) pesticide, which was brought to public attention by Rachel Carson's book, Silent Spring. One of the better known impacts of DDT is to reduce the thickness of the egg shells on predatory birds. The shells sometimes become too thin to be viable, causing reductions in bird populations. This occurs with DDT and a number of related compounds due to the process of bioaccumulation, wherein the chemical, due to its stability and fat solubility, accumulates in organisms' fatty tissues. Also, DDT may biomagnify which causes progressively higher concentrations in the body fat of animals farther up the food chain. The near-worldwide ban on agricultural use of DDT and related chemicals has allowed some of these birds—such as the peregrine falcon--to recover in recent years. A number of the organochlorine pesticides have been banned from most uses worldwide and globally they are controlled via the Stockholm Convention on persistent organic pollutants. These include: aldrin, chlordane, DDT, dieldrin, endrin, heptachlor, mirex and toxaphene. [edit] Pollinator declineInsecticides can kill bees and may be a cause of pollinator decline, the loss of bees that pollinate plants, and Colony Collapse Disorder[5], in which worker bees from a beehive or Western honey bee colony abruptly disappear. Loss of pollinators will mean a reduction in crop yields.[5] Sublethal doses of insecticides (i.e. imidacloprid and other neonicotinoids) affect foraging behavior of bees.[6]. However, research into the causes of Colony Collapse Disorder remains inconclusive.[7] [edit] Individual insecticides[edit] Chlorinated hydrocarbonsSee also: :Category:Organochloride insecticides Aldrin - Chlordane - Chlordecone - DDT - Dieldrin - Endosulfan - Endrin - Heptachlor - Hexachlorobenzene - Lindane (gamma-Hexachlorocyclohexane) - Methoxychlor - Mirex - Pentachlorophenol - TDE [edit] OrganophosphatesAcephate - Azinphos-methyl - Bensulide - Chlorethoxyfos - Chlorpyrifos - Chlorpyriphos-methyl - Diazinon - Dichlorvos (DDVP) - Dicrotophos - Dimethoate - Disulfoton - Ethoprop - Fenamiphos - Fenitrothion - Fenthion - Fosthiazate - Malathion - Methamidophos - Methidathion - Mevinphos - Naled - Omethoate - Oxydemeton-methyl - Parathion - Parathion-methyl - Phorate - Phosalone - Phosmet - Phostebupirim - Phoxim - Pirimiphos-methyl - Profenofos - Terbufos - Tetrachlorvinphos - Tribufos - Trichlorfon [edit] CarbamatesAldicarb - Carbofuran - Carbaryl - Fenoxycarb - Methomyl - 2-(1-Methylpropyl)phenyl methylcarbamate [edit] Phenothiazine[edit] PyrethroidsAllethrin - Bifenthrin - Cypermethrin - Deltamethrin - Lambda-cyhalothrin - Permethrin - Resmethrin - Tetramethrin - Tralomethrin - Transfluthrin [edit] NeonicotinoidsAcetamiprid - Clothianidin - Imidacloprid - Nitenpyram - Nithiazine - Thiacloprid - Thiamethoxam [edit] Plant derived
[edit] Other[edit] See also[edit] References
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