Insecticides arepesticides used to killinsects.[1] They include ovicides andlarvicides used against insecteggs andlarvae, respectively. The major use of insecticides is inagriculture, but they are also used in home and garden settings, industrial buildings, forvector control, and control of insectparasites of animals and humans.
Acaricides, which killmites andticks, are not strictly insecticides, but are usually classified together with insecticides. Some insecticides (including common bug sprays) are effective against other non-insectarthropods as well, such asscorpions,spiders, etc. Insecticides are distinct frominsect repellents, which repel but do not kill.
In 2016 insecticides were estimated to account for 18% of worldwide pesticide sales.[2] 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.[3]
Insecticides are most usefully categorised according to theirmodes of action. Theinsecticide resistance action committee (IRAC) lists 30 modes of action plus unknowns. There can be severalchemical classes of insecticide with the same mode or action. IRAC lists 56 chemical classes plus unknowns.[4]
Themode of action describes how the insecticide kills or inactivates a pest.
Insecticides with systemic activity against sucking pests, which are safe topollinators, are sought after,[5][6][7] particularly in view of the partial bans onneonicotinoids. Revised 2023 guidance by registration authorities describes the bee testing that is required for new insecticides to be approved for commercial use.[8][9][10][11]
Insecticides may be systemic or non-systemic (contact insecticides).[2][12][13] Systemic insecticides penetrate into the plant and move (translocate) inside the plant. Translocation may be upward in thexylem, or downward in thephloem or both. Systemicity is a prerequisite for the pesticide to be used as aseed-treatment. Contact insecticides (non-systemic insecticides) remain on the leaf surface and act through direct contact with the insect.
Insects feed from various compartments in the plant. Most of the major pests are either chewing insects or sucking insects.[14] Chewing insects, such as caterpillars, eat whole pieces of leaf. Sucking insects use feeding tubes to feed from phloem (e.g. aphids, leafhoppers, scales and whiteflies), or to suck cell contents (e.g. thrips and mites). An insecticide is more effective if it is in the compartment the insect feeds from. The physicochemical properties of the insecticide determine how it is distributed throughout the plant.[12][13]
Organophosphates are another large class of contact insecticides. These also target the insect's nervous system. Organophosphates interfere with theenzymesacetylcholinesterase and othercholinesterases, causing an increase in synapticacetylcholine and overstimulation of theparasympathetic nervous system,[19] killing or disabling the insect. Organophosphate insecticides andchemical warfarenerve agents (such assarin,tabun,soman, andVX) have the same mechanism of action. Organophosphates have a cumulative toxic effect to wildlife, so multiple exposures to the chemicals amplifies the toxicity.[20] In the US, organophosphate use declined with the rise of substitutes.[21] Many of these insecticides, first developed in the mid 20th century, are very poisonous.[22] Manyorganophosphates do not persist in the environment.
Pyrethroid insecticides mimic the insecticidal activity of the natural compoundpyrethrin, thebiopesticide found inPyrethrum (NowChrysanthemum andTanacetum) 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 oftenapplied against household pests.[23] Some synthetic pyrethroids are toxic to the nervous system.[24]
Neonicotinoids are a class of neuro-active insecticides chemically similar tonicotine.(with much lower acute mammalian toxicity and greater field persistence). These chemicals areacetylcholine receptoragonists. They are broad-spectrum systemic insecticides, with rapid action (minutes-hours). They are applied as sprays, drenches, seed andsoil treatments. Treated insects exhibit leg tremors, rapid wing motion,stylet withdrawal (aphids), disoriented movement, paralysis and death.[25]Imidacloprid, of the neonicotinoid family, is the most widely used insecticide in the world.[26] In the late 1990s neonicotinoids came under increasing scrutiny over their environmental impact and were linked in a range of studies to adverse ecological effects, includinghoney-beecolony collapse disorder (CCD) and loss of birds due to a reduction in insect populations. In 2013, theEuropean Union and a few non EU countries restricted the use of certain neonicotinoids.[27][28][29][30][31][32][33][34] and its potential to increase the susceptibility of rice toplanthopper attacks.[35]
Diamides selectively activate insectryanodine receptors (RyR), which are largecalcium release channels present in cardiac and skeletal muscle,[36] leading to the loss of calcium crucial for biological processes. This causes insects to act lethargic, stop feeding, and eventually die.[37] The first insecticide from this class to be registered wasflubendiamide.[37]
The EU defines biopesticides as "a form of pesticide based on micro-organisms or natural products".[38] TheUS EPA defines biopesticides as “certain types of pesticides derived from such natural materials as animals, plants, bacteria, and certain minerals”.[39] Microorganisms that control pests may also be categorised asbiological pest control agents together with larger organisms such as parasitic insects,entomopathic nematodes etc.Natural products may also be categorised as chemical insecticides.
The US EPA describes three types of biopesticide.[39] Biochemical pesticides (meaning bio-derived chemicals), which are naturally occurring substances that control pests by non-toxic mechanisms. Microbial pesticides consisting of a microorganism (e.g., abacterium,fungus,virus orprotozoan) as the active ingredient. Plant-Incorporated-Protectants (PIPs) are pesticidal substances that plants produce from genetic material that has been added to the plant (thus producingtransgenic crops).
The global bio-insecticide market was estimated to be less than 10% of the total insecticide market.[40] The bio-insecticide market is dominated by microbials.[41] The bio-insecticide market is growing more that 10% yearly, which is a higher growth than the total insecticide market, mainly due to the increase inorganic farming andIPM, and also due to benevolent government policies.[40]
Biopesticides are regarded by the US and European authorities as posing fewer risks of environmental and mammalian toxicity.[39] Biopesticides are more than 10 x (often 100 x) cheaper and 3 x faster to register than synthetic pesticides.[40]
There is a wide variety of biological insecticides with differing attributes, but in general the following has been described.[42][43]
They are easier, faster and cheaper to register, usually with lower mammalian toxicity. They are more specific, and thus preserve beneficial insects and biodiversity in general. This makes them compatible with IPM regimes. They degrade rapidly cause less impact on the environment. They have a shorter withholding period.[citation needed]
The spectrum of control is narrow. They are less effective and prone to adverse ambient conditions. They degrade rapidly and are thus less persistent. They are slower to act. They are more expensive, have a shorter shelf-life, and are more difficult to source. They require more specialised knowledge to use.[citation needed]
Most or all plants producechemical insecticides to stop insects eating them. Extracts and purified chemicals from thousands of plants have been shown to be insecticidal, however only a few are used in agriculture.[44] In the USA 13 are registered for use, in the EU 6. In Korea, where it is easier to register botanical pesticides, 38 are used. Most used areneem oil,chenopodium,pyrethrins, andazadirachtin.[44] Many botanical insecticides used in past decades (e.g.rotenone,nicotine,ryanodine) have been banned because of their toxicity.[44]
The firsttransgenic crop, which incorporated an insecticidal PIP, contained agene for theCRY toxin fromBacillus thuringiensis (B.t.) and was introduced in 1997.[45] For the next ca 25 years the only insecticidal agents used inGMOs were the CRY and VIP toxins from various strains of B.t, which control a wide number of insect types. These are widely used with > 100 million hectares planted with B.t. modified crops in 2019.[45] Since 2020 several novel agents have been engineered into plants and approved. ipd072Aa fromPseudomonas chlororaphis, ipd079Ea fromOphioglossum pendulum, and mpp75Aa1.1 fromBrevibacillus laterosporus code for protein toxins.[45][46] The trait dvsnf7 is anRNAi agent consisting of a double-stranded RNA transcript containing a 240 bp fragment of the WCR Snf7 gene of thewestern corn rootworm (Diabrotica virgifera virgifera).[46][47]
RNA interference (RNAi) uses segments of RNA to fatallysilence crucialinsect genes.[48] In 2024 two uses of RNAi have been registered by the authorities for use: Genetic modification of a crop to introduce a gene coding for an RNAi fragment, and spraying double stranded RNA fragments onto a field.[47]Monsanto introduced the trait DvSnf7 which expresses a double-stranded RNA transcript containing a 240 bp fragment of the WCR Snf7 gene of theWestern Corn Rootworm.[46] GreenLight Biosciences introduced Ledprona, a formulation of double stranded RNA as a spray for potato fields. It targets the essential gene forproteasome subunit beta type-5 (PSMB5) in theColorado potato beetle.[47]
Spider venoms contain many, often hundreds, of insecticidally activetoxins. Many areproteins that attack the nervous system of the insect.[49] Vestaron introduced for agricultural use a spray formulation of GS-omega/kappa-Hxtx-Hv1a (HXTX), derived from the venom of the Australian blue mountain funnel web spider (Hadronyche versuta).[49] HXTX acts by allosterically (site II) modifying thenicotinic acetylcholine receptor (IRAC group 32).[50]
Entomopathic fungi have been used since 1965 for agricultural use. Hundreds of strains are now in use. They often kill a broad range of insect species. Most strains are fromBeauveria,Metarhizium,Cordyceps andAkanthomyces species.[51]
Of the many types of entomopathic viruses, onlybaculaviruses are used commercially, and are each specific for their target insect. They have to be grown on insects, so their production is labour-intensive.[52]
When an insect population is exposed to pesticide concentrations that are sublethal, surviving individuals may experience a variety of sublethal effects (symptoms). These effects can influence its biology, behavior, and long-term population dynamics. Documented sublethal responses include reduced or increased reproductive capacity, shortened or lengthened lifespan, altered developmental timing or deformities, disrupted feeding activity, and changes inforaging or movement patterns. Over time, these physiological and behavioral changes can slow population growth, disrupt ecological interactions, or in some cases, lead to compensatory increases in reproduction as a stress response. Sublethal exposure can lead topesticide resistance. Insects that survive may carry genetic traits that enable tolerance, and when these individuals reproduce, resistance can spread through the population and result in decreased long-term pesticide effectiveness. Understanding sublethal effects is critical forintegrated pest management strategies and for evaluating the ecological risk of pesticide use in agricultural and natural ecosystems.[53]
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.[20] Sprayed insecticide may drift from the area to which it is applied and into wildlife areas, especially when it is sprayed aerially.[20]
Persistence in the environment and accumulation in the food chain
DDT was the first organic insecticide. It was introduced duringWW2, and was widely used. One use wasvector control and it was sprayed on open water. It degrades slowly in the environment, and it islipophilic (fat soluble). It became the firstglobal pollutant, and the first pollutant toaccumulate[54] andmagnify in thefood chain.[55][56] During the 1950s and 1960s these very undesirable side effects were recognized, and after some oftencontentious discussion, DDT was banned in many countries in the 1960s and 1970s. Finally in 2001 DDT and all otherpersistent insecticides were banned via theStockholm Convention.[57][58] Since many decades the authorities require new insecticides to degrade in the environment and not to bioaccumulate.[59]
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.[60] 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.
Both number of insects and number of insect species havedeclined dramatically and continuously over past decades, causing much concern.[61][62][63] Many causes are proposed to contribute to this decline, the most agreed upon areloss of habitat, intensification of farming practices, and insecticide usage.Domestic bees weredeclining some years ago[64] but population and number of colonies have now risen both in the USA[65] and worldwide.[66] Wild species of bees are still declining.
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.[67]
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.[68] Some of them are:
Breeding crops resistant, or at least less susceptible, to pest attacks.[69]
^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.S2CID95713100.
^Soderlund D (2010). "Chapter 77 – Toxicology and Mode of Action of Pyrethroid Insecticides". In Kreiger R (ed.).Hayes' Handbook of Pesticide Toxicology (3rd ed.). Academic Press. pp. 1665–1686.ISBN978-0-12-374367-1.OCLC918401061.
^Yamamoto I (1999). "Nicotine to Nicotinoids: 1962 to 1997". In Yamamoto I,Casida J (eds.).Nicotinoid Insecticides and the Nicotinic Acetylcholine Receptor. Tokyo: Springer-Verlag. pp. 3–27.ISBN978-4-431-70213-9.OCLC468555571.
^abcBarry, Jennifer K.; Simmons, Carl R.; Nelson, Mark E (2023). "Chapter Five - Beyond Bacillus thuringiensis: New insecticidal proteins with potential applications in agriculture". In Jurat-Fuentes, Juan Luis (ed.).Advances in Insect Physiology Volume 65. Elsevier. pp. 185–233.doi:10.1016/bs.aiip.2023.09.004.ISBN9780323954662.
^abcVélez, Ana M.; Narva, Ken; Darlington, Molly; Mishra, Swati; Hellmann, Christoph; Rodrigues, Thais B.; Duman-Scheel, Molly; Palli, Subba Reddy; Jurat-Fuentes, Juan Luis (2023). "Chapter One - Insecticidal proteins and RNAi in the control of insects". In Jurat-Fuentes, Juan Luis (ed.).Advances in Insect Physiology. Vol. 65. Academic Press. pp. 1–54.doi:10.1016/bs.aiip.2023.09.007.ISBN9780323954662.
^Pesticide Usage in the United States: History, Benefits, Risks, and Trends; Bulletin 1121, November 2000, K.S. Delaplane, Cooperative Extension Service, The University of Georgia College of Agricultural and Environmental Sciences"Pesticide Usage in the United States: History, Benefits, Risks, and Trends"(PDF). Archived fromthe original(PDF) on 2010-06-13. Retrieved2012-11-10.
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.doi:10.3098/ah.2008.82.4.468.PMID19266680.
