Insecticide

Source: Wikipedia, the free encyclopedia.
For other uses, see Insecticide (disambiguation).
For the Nirvana compilation album, see Incesticide.
FLIT manual spray pump from 1928
Farmer spraying a cashewnut tree in Tanzania

Insecticides are

eggs and larvae, respectively. Acaricides, which kill mites and ticks, are not strictly insecticides, but are usually classified together with insecticides. The major use of Insecticides is agriculture, but they are also used in home and garden, industrial buildings, vector control and control of insect parasites of animals and humans. Insecticides are claimed to be a major factor behind the increase in the 20th-century's agricultural productivity.[2]
Nearly all insecticides have the potential to significantly alter ecosystems; many are toxic to humans and/or animals; some become concentrated as they spread along the food chain.

The mode of action describes how the pesticide kills or inactivates a pest. It provides another way of classifying insecticides. Mode of action can be important in understanding whether an insecticide will be toxic to unrelated species, such as fish, birds and mammals.

Insecticides are distinct from repellents, which repel but do not kill.

Sales

In 2016 insecticides were estimated to account for 18% of worldwide pesticide sales.[3] Worldwide sales of insecticides in 2018 were estimated as $ 18.4 billion, of which 25% were neonicotinoids, 17% were pyrethroids, 13% were diamides, and the rest were many other classes which sold for less than 10% each of the market.[4]

Systemic insecticides

Insecticides may be systemic or non-systemic (contact insecticides).[3][5][6]

Systemic insecticides penetrate into the plant and move (translocate) inside the plant. Translocation may be upward in the xylem, or downward in the phloem or both. An insecticide with a high enough concentration in phloem, is particularly effective at killing insects, such as aphids, which feed on phloem. Such insects are often termed sap-feeding insects or sucking insects. Systemicity is a prerequisite for the pesticide to be used as a seed-treatment.

Contact insecticides (non-systemic insecticides) remain on the leaf surface and act through direct contact with the insect.

Efficacy can be related to the quality of pesticide application, with small droplets, such as aerosols often improving performance.[4]

Synthetic insecticides

Further information: List of insecticides

Development

Main article:
Insecticide development

Organochlorides

The best known

cyclodiene and hexachlorocyclohexane compounds. Although commonly used in the past, many older chemicals have been removed from the market due to their health and environmental effects (e.g. DDT, chlordane, and toxaphene).[9][10]

Organophosphates

Organophosphates are another large class of contact insecticides. These also target the insect's nervous system. Organophosphates interfere with the enzymes acetylcholinesterase and other cholinesterases, causing an increase in synaptic acetylcholine and overstimulation of the parasympathetic nervous system.[11] and killing or disabling the insect. Organophosphate insecticides and chemical warfare nerve agents (such as sarin, tabun, soman, and VX) have the same mechanism of action. Organophosphates have a cumulative toxic effect to wildlife, so multiple exposures to the chemicals amplifies the toxicity.[12] In the US, organophosphate use declined with the rise of substitutes.[13] Many of these insecticides, first developed in the mid 20th century, are very poisonous.[14] Many organophosphates do not persist in the environment.

Carbamates

Carbamate insecticides have similar mechanisms to organophosphates, but have a much shorter duration of action and are somewhat less toxic.[citation needed]

Pyrethroids

Pyrethroid insecticides mimic the insecticidal activity of the natural compound pyrethrin, the biopesticide found in Pyrethrum (Now Chrysanthemum and Tanacetum) species. They have been modified to increase their stability in the environment. These compounds are nonpersistent sodium channel modulators and are less toxic than organophosphates and carbamates. Compounds in this group are often applied against household pests.[15] Some synthetic pyrethroids are toxic to the nervous system.[16]

Neonicotinoids

honey-bee colony collapse disorder (CCD) and loss of birds due to a reduction in insect populations. In 2013, the European Union and a few non EU countries restricted the use of certain neonicotinoids.[19][20][21][22][23][24][25][26] and its potential to increase the susceptibility of rice to planthopper attacks.[27]

Phenylpyrazoles

Phenylpyrazole insecticides, such as fipronil are a class of synthetic insecticides that operate by interfering with GABA receptors.[28]

Butenolides

Butenolide pesticides are a novel group of chemicals, similar to neonicotinoids in their mode of action, that have so far only one representative: flupyradifurone. They are acetylcholine receptor agonists, like neonicotinoids, but with a different pharmacophore.[29] They are broad-spectrum systemic insecticides, applied as sprays, drenches, seed and soil treatments. Although the classic risk assessment considered this insecticide group (and flupyradifurone specifically) safe for bees, novel research[30] has raised concern on their lethal and sublethal effects, alone or in combination with other chemicals or environmental factors.[31][32]

Ryanoids/diamides

Diamides are synthetic ryanoid analogues with the same mode of action as ryanodine, a naturally occurring insecticide extracted from Ryania speciosa (Salicaceae). They bind to calcium channels in cardiac and skeletal muscle, blocking nerve transmission. The first insecticide from this class to be registered was Rynaxypyr, generic name chlorantraniliprole.[33]

Insect growth regulators

white flies. Methoprene was registered with the EPA in 1975. Virtually no reports of resistance have been filed. A more recent type of IGR is the ecdysone agonist tebufenozide (MIMIC), which is used in forestry
and other applications for control of caterpillars, which are far more sensitive to its hormonal effects than other insect orders.

Biological pesticides

Main article: Biopesticide

More natural insecticides have been interesting targets of research for two main reasons, firstly because the most common chemicals are

losing effectiveness, and secondly due to their toxic effects upon the environment.[35]
Many organic compounds are already produced by plants for the purpose of defending the host plant from predation, and can be turned toward human ends.

Four extracts of plants are in commercial use: pyrethrum, rotenone, neem oil, and various essential oils[36]

A trivial case is tree

oil of wintergreen
, are in fact antifeedants.

Other biological approaches

Plant-incorporated protectants

Bacillus thuringiensis

Transgenic crops that act as insecticides began in 1996 with a

larvae such as the Colorado potato beetle.[38]

RNA interference

The technique has been expanded to include the use of RNAi insecticides which fatally

insecticide resistance.[38]

Venom

resistance question.[40]

Enzymes

Many plants exude substances to repel insects. Premier examples are substances activated by the

horseradish sauces
.

mechanism of glucosinolate hydrolysis by myrosinase
Biosynthesis of antifeedants by the action of myrosinase.

The myrosinase is released only upon crushing the flesh of horseradish. Since allyl isothiocyanate is harmful to the plant as well as the insect, it is stored in the harmless form of the glucosinolate, separate from the myrosinase enzyme.[41]

Bacterial

Bt toxin) has been incorporated directly into plants through the use of genetic engineering
.

Other

Other biological insecticides include products based on entomopathogenic fungi (e.g., Beauveria bassiana, Metarhizium anisopliae), nematodes (e.g., Steinernema feltiae) and viruses (e.g., Cydia pomonella granulovirus).[citation needed]

Synthetic insecticide and natural insecticides

A major emphasis of organic chemistry is the development of chemical tools to enhance agricultural productivity. Insecticides represent a major area of emphasis. Many of the major insecticides are inspired by biological analogues. Many others are not found in nature.

Environmental harm

Effects on nontarget species

Some 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 an insecticide granule on the ground for food and eat it.[12] Sprayed insecticide may drift from the area to which it is applied and into wildlife areas, especially when it is sprayed aerially.[12]

DDT

Main article: DDT

The development of DDT was motivated by desire to replace more dangerous or less effective alternatives. DDT was introduced to replace lead and arsenic-based compounds, which were in widespread use in the early 1940s.[42]

DDT was brought to public attention by

Stockholm Convention on persistent organic pollutants. These include: aldrin, chlordane, DDT, dieldrin, endrin, heptachlor, mirex and toxaphene.[citation needed
]

Runoff and Percolation

Solid bait and liquid insecticides, especially if improperly applied in a location, get moved by water flow. Often, this happens through nonpoint sources where runoff carries insecticides in to larger bodies of water. As snow melts and rainfall moves over and through the ground, the water picks applied insecticides and deposits them in to larger bodies of water, rivers, wetlands, underground sources of previously potable water, and percolates in to watersheds.[43] This runoff and percolation of insecticides can effect the quality of water sources, harming the natural ecology and thus, indirectly effect human populations through biomagnification and bioaccumulation.

Pollinator decline

beehive or Western honey bee colony abruptly disappear. Loss of pollinators means a reduction in crop yields.[44] Sublethal doses of insecticides (i.e. imidacloprid and other neonicotinoids) affect bee foraging behavior.[45] However, research into the causes of CCD was inconclusive as of June 2007.[46]

Bird decline

Besides the effects of direct consumption of insecticides, populations of insectivorous birds decline due to the collapse of their prey populations. Spraying of especially wheat and corn in Europe is believed to have caused an 80 per cent decline in flying insects, which in turn has reduced local bird populations by one to two thirds.[47]

Alternatives

Instead of using chemical insecticides to avoid crop damage caused by insects, there are many alternative options available now that can protect farmers from major economic losses.[48] Some of them are:

  1. Breeding crops resistant, or at least less susceptible, to pest attacks.[49]
  2. Releasing predators, parasitoids, or pathogens to control pest populations as a form of biological control.[50]
  3. Chemical control like releasing pheromones into the field to confuse the insects into not being able to find mates and reproduce.[51]
  4. Integrated Pest Management: using multiple techniques in tandem to achieve optimal results.[52]
  5. Push-pull technique: intercropping with a "push" crop that repels the pest, and planting a "pull" crop on the boundary that attracts and traps it.[53]

Examples

Source:[54]

Organochlorides

See also: Category:Organochloride insecticides

Organophosphates

See also: Category:Organophosphate insecticides

Carbamates

Pyrethroids

Neonicotinoids

Ryanoids

Insect growth regulators

Derived from plants or microbes

Biologicals

Inorganic/mineral derived insecticides

See also

References

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Further reading

  • McWilliams James E (2008). "'The Horizon Opened Up Very Greatly': Leland O. Howard and the Transition to Chemical Insecticides in the United States, 1894–1927". Agricultural History. 82 (4): 468–95.
    PMID 19266680
    .

External links

Wikisource has the text of the 1920 Encyclopedia Americana article Insecticide.
Look up insecticide in Wiktionary, the free dictionary.
Wikimedia Commons has media related to Insecticides.


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