Insecticide

For other uses, see Insecticide (disambiguation).
For a broader coverage related to this topic, see Pesticide.
FLIT manual spray pump for insecticides from 1928

An insecticide is a substance used to kill insects.[1] They include ovicides and larvicides used against insect eggs and larvae, respectively. Insecticides are used in agriculture, medicine, industry and by consumers. Insecticides are claimed to be a major factor behind the increase in agricultural 20th century's productivity.[2] Nearly all insecticides have the potential to significantly alter ecosystems; many are toxic to humans; some concentrate along the food chain.

Insecticides can be classified in two major groups: systemic insecticides, which have residual or long term activity; and contact insecticides, which have no residual activity.

Furthermore, one can distinguish three types of insecticide. 1. Natural insecticides, such as nicotine, pyrethrum and neem extracts, made by plants as defenses against insects. 2. Inorganic insecticides, which are metals. 3. Organic insecticides, which are organic chemical compounds, mostly working by contact.

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

Insecticides are distinct from insect repellents, which do not kill.

Type of activity

Systemic insecticides become incorporated and distributed systemically throughout the whole plant. When insects feed on the plant, they ingest the insecticide. Systemic insecticides produced by transgenic plants are called plant-incorporated protectants (PIPs). For instance, a gene that codes for a specific Bacillus thuringiensis biocidal protein was introduced into corn and other species. The plant manufactures the protein, which kills the insect when consumed.[3]

Contact insecticides are toxic to insects upon direct contact. These can be inorganic insecticides, which are metals and include arsenates, copper and fluorine compounds, which are less commonly used, and the commonly used sulfur. Contact insecticides can be organic insecticides, i.e. organic chemical compounds, synthetically produced, and comprising the largest numbers of pesticides used today. Or they can be natural compounds like pyrethrum, neem oil etc. Contact insecticides usually have no residual activity.

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

Biological pesticides

Main article: Biopesticide

Many organic compounds are produced by plants for the purpose of defending the host plant from predation. A trivial case is tree rosin, which is a natural insecticide. Specific, the production of oleoresin by conifer species is a component of the defense response against insect attack and fungal pathogen infection.[5] Many fragrances, e.g. oil of wintergreen, are in fact antifeedants.

Four extracts of plants are in commercial use: pyrethrum, rotenone, neem oil, and various essential oils[6]

Other biological approaches

Plant-incorporated protectants

Transgenic crops that act as insecticides began in 1996 with a genetically modified potato that produced the Cry protein, derived from the bacterium Bacillus thuringiensis, which is toxic to beetle larvae such as the Colorado potato beetle. The technique has been expanded to include the use of RNA interference RNAi that fatally silences crucial insect genes. RNAi likely evolved as a defense against viruses. Midgut cells in many larvae take up the molecules and help spread the signal. The technology can target only insects that have the silenced sequence, as was demonstrated when a particular RNAi affected only one of four fruit fly species. The technique is expected to replace many other insecticides, which are losing effectiveness due to the spread of pesticide resistance.[7]

Enzymes

Many plants exude substances to repel insects. Premier examples are substances activated by the enzyme myrosinase. This enzyme converts glucosinolates to various compounds that are toxic to herbivorous insects. One product of this enzyme is allyl isothiocyanate, the pungent ingredient in horseradish sauces.

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.[8]

Bacterial

Bacillus thuringiensis is a bacterial disease that affects Lepidopterans and some other insects. Toxins produced by strains of this bacterium are used as a larvicide against caterpillars, beetles, and mosquitoes. Toxins from Saccharopolyspora spinosa are isolated from fermentations and sold as Spinosad. Because these toxins have little effect on other organisms, they are 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., Beauveria bassiana, Metarhizium anisopliae), nematodes (e.g., Steinernema feltiae) and viruses (e.g., Cydia pomonella granulovirus).

Synthetic insecticide

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 completely alien to nature.

Organochlorides

The best known organochloride, DDT, was created by Swiss scientist Paul Müller. For this discovery, he was awarded the 1948 Nobel Prize for Physiology or Medicine.[9] DDT was introduced in 1944. It functions by opening sodium channels in the insect's nerve cells.[10] The contemporaneous rise of the chemical industry facilitated large-scale production of DDT and related chlorinated hydrocarbons.

Organophosphates and carbamates

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, disrupting nerve impulses and killing or disabling the insect. Organophosphate insecticides and chemical warfare nerve agents (such as sarin, tabun, soman, and VX) work in the same way. Organophosphates have a cumulative toxic effect to wildlife, so multiple exposures to the chemicals amplifies the toxicity.[11] In the US, organophosphate use declined with the rise of substitutes.[12]

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

Pyrethroids

Pyrethroid pesticides mimic the insecticidal activity of the natural compound pyrethrum, the biopesticide found in pyrethrins. 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.[13]

Neonicotinoids

Neonicotinoids are synthetic analogues of the natural insecticide nicotine (with much lower acute mammalian toxicity and greater field persistence). These chemicals are acetylcholine receptor agonists. They are broad-spectrum systemic insecticides, with rapid action (minutes-hours). They are applied as sprays, drenches, seed and soil treatments. Treated insects exhibit leg tremors, rapid wing motion, stylet withdrawal (aphids), disoriented movement, paralysis and death.[14] Imidacloprid may be the most common. It has recently come under scrutiny for allegedly pernicious effects on honeybees[15] and its potential to increase the susceptibility of rice to planthopper attacks.[16]

Ryanoids

Ryanoids are synthetic analogues with the same mode of action as ryanodine, a naturally occurring insecticide extracted from Ryania speciosa (Flacourtiaceae). They bind to calcium channels in cardiac and skeletal muscle, blocking nerve transmission. Only one such insecticide is currently registered, Rynaxypyr, generic name chlorantraniliprole.[17]

Insect growth regulators

Insect growth regulator (IGR) is a term coined to include insect hormone mimics and an earlier class of chemicals, the benzoylphenyl ureas, which inhibit chitin(exoskeleton) biosynthesis in insects. Diflubenzuron is a member of the latter class, used primarily to control caterpillars that are pests. The most successful insecticides in this class are the juvenoids (juvenile hormone analogues). Of these, methoprene is most widely used. It has no observable acute toxicity in rats and is approved by World Health Organization (WHO) for use in drinking water cisterns to combat malaria. Most of its uses are to combat insects where the adult is the pest, including mosquitoes, several fly species, and fleas. Two very similar products, hydroprene and kinoprene, are used for controlling species such as cockroaches and 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.

Environmental Effects

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.[11]

Sprayed insecticide may drift from the area to which it is applied and into wildlife areas, especially when it is sprayed aerially.[11]

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.[18]

DDT was brought to public attention by Rachel Carson's book Silent Spring. One side-effect of DDT is to reduce the thickness of shells on the eggs of predatory birds. The shells sometimes become too thin to be viable, reducing bird populations. This occurs with DDT and 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 organochlorine pesticides have been banned from most uses worldwide. Globally they are controlled via the Stockholm Convention on persistent organic pollutants. These include: aldrin, chlordane, DDT, dieldrin, endrin, heptachlor, mirex and toxaphene.

Pollinator decline

Insecticides can kill bees and may be a cause of pollinator decline, the loss of bees that pollinate plants, and colony collapse disorder (CCD),[19] in which worker bees from a beehive or Western honey bee colony abruptly disappear. Loss of pollinators means a reduction in crop yields.[19] Sublethal doses of insecticides (i.e. imidacloprid and other neonicotinoids) affect bee foraging behavior.[20] However, research into the causes of CCD was inconclusive as of June 2007.[21]

Examples

Pyrethroids

Neonicotinoids

Ryanoids

Insect growth regulators

Plant-derived

Biologicals

Other

See also

References

  1. ↑ IUPAC (2006). "GLOSSARY OF TERMS RELATING TO PESTICIDES" (PDF). IUPAC. p. 2123. Retrieved January 2014. Check date values in: |access-date= (help)
  2. ↑ van Emden, H.F.; Peakall, David B. (30 June 1996). Beyond Silent Spring. Springer. ISBN 978-0-412-72800-6.
  3. ↑
  4. ↑ "dropdata.org". dropdata.org. Retrieved 2011-01-05.
  5. ↑ Trapp, S.; Croteau, R. (2001). "Defensive Biosynthesis of Resin in Conifers". Annual Review of Plant Physiology and Plant Molecular Biology. 52 (1): 689–724. doi:10.1146/annurev.arplant.52.1.689. PMID 11337413.
  6. ↑ Murray B. Isman "Botanical Insecticides, Deterrents, And Repellents In Modern Agriculture And An Increasingly Regulated World" Annual Review Of Entomology Volume 51, pp. 45-66. doi:10.1146/annurev.ento.51.110104.151146
  7. ↑ Kupferschmidt, K. (2013). "A Lethal Dose of RNA". Science. 341 (6147): 732–3. doi:10.1126/science.341.6147.732. PMID 23950525.
  8. ↑ Cole Rosemary A (1976). "Isothiocyanates, nitriles and thiocyanates as products of autolysis of glucosinolates in Cruciferae". Phytochemutry. 15: 759–762. doi:10.1016/S0031-9422(00)94437-6.
  9. ↑ Karl Grandin, ed. (1948). "Paul Müller Biography". Les Prix Nobel. The Nobel Foundation. Retrieved 2008-07-24.
  10. ↑ Vijverberg; et al. (1982). "Similar mode of action of pyrethroids and DDT on sodium channel gating in myelinated nerves". Nature. 295 (5850): 601–603. Bibcode:1982Natur.295..601V. doi:10.1038/295601a0. Retrieved 2012-04-28.
  11. 1 2 3 Palmer, WE, Bromley, PT, and Brandenburg, RL. Wildlife & pesticides - Peanuts. North Carolina Cooperative Extension Service. Retrieved on 14 October 2007.
  12. ↑ "Infographic: Pesticide Planet". Science. 341 (6147): 730–731. 2013. doi:10.1126/science.341.6147.730. PMID 23950524.
  13. ↑ Class, Thomas J.; Kintrup, J. (1991). "Pyrethroids as household insecticides: analysis, indoor exposure and persistence". Fresenius' Journal of Analytical Chemistry. 340 (7): 446–453. doi:10.1007/BF00322420. Retrieved 2012-04-28.
  14. ↑ Fishel,F.M. 2009. Pesticide Toxicity Profile: Neonicotinoid Pesticides IFAS Publication #PI-80
  15. ↑ Insecticides taking toll on honeybees
  16. ↑ Yao, Cheng; Shi, Zhao-Peng; Jiang, Li-Ben; Ge, Lin-Quan; Wu, Jin-Cai; Jahn, Gary C. (20 January 2012). "Possible connection between imidacloprid-induced changes in rice gene transcription profiles and susceptibility to the brown plant hopper Nilaparvata lugens Stål (Hemiptera: Delphacidae)". Pesticide Biochemistry and Physiology. 102 (3): 213–219. doi:10.1016/j.pestbp.2012.01.003. ISSN 0048-3575. PMC 3334832Freely accessible. PMID 22544984.
  17. ↑ "Pesticide Fact Sheet- chlorantraniliprole" (PDF). http://www.epa.gov/opprd001/factsheets/chloran.pdf. Retrieved 2011-09-14. External link in |publisher= (help)
  18. ↑ Metcalf, Robert L. (2002). "Ullmann's Encyclopedia of Industrial Chemistry". Ullmann’s Encyclopedia of Industrial Chemistry. Wiley-VCH. doi:10.1002/14356007.a14_263. ISBN 3527306730. |chapter= ignored (help)
  19. 1 2 Wells M (March 11, 2007). "Vanishing bees threaten US crops". www.bbc.co.uk. BBC News. Retrieved 19 September 2007.
  20. ↑ Colin, M. E.; Bonmatin, J. M.; Moineau, I.; et al. (2004). "A method to quantify and analyze the foraging activity of honey bees: Relevance to the sublethal effects induced by systemic insecticides". Archives of Environmental Contamination and Toxicology. 47 (3): 387–395. doi:10.1007/s00244-004-3052-y. PMID 15386133.
  21. ↑ Oldroyd, B.P. (2007). "What's Killing American Honey Bees?". PLoS Biology. 5 (6): e168. doi:10.1371/journal.pbio.0050168. PMC 1892840Freely accessible. PMID 17564497.
  22. 1 2 3 4 "Cinnamon Oil Kills Mosquitoes". www.sciencedaily.com. Retrieved 5 August 2008.
  23. ↑ "Cornelia Dick-Pfaff: Wohlriechender Mückentod, 19.07.2004".
  24. ↑ "Oregano Oil Works As Well As Synthetic Insecticides To Tackle Common Beetle Pest". www.sciencedaily.com. Retrieved 23 May 2008.
  25. ↑ "Almond farmers seek healthy bees". BBC News. 2006-03-08. Retrieved 2010-01-05.

Further reading

External links

Look up insecticide in Wiktionary, the free dictionary.
Wikisource has the text of the 1920 Encyclopedia Americana article Insecticide.


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