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Pesticide resistance describes the decreased susceptibility of a pest population to a
pesticide Pesticides are substances that are meant to control pests. This includes herbicide, insecticide, nematicide, molluscicide, piscicide, avicide, rodenticide, bactericide, insect repellent, animal repellent, microbicide, fungicide, and lampri ...
that was previously effective at controlling the pest. Pest species evolve pesticide resistance via
natural selection Natural selection is the differential survival and reproduction of individuals due to differences in phenotype. It is a key mechanism of evolution, the change in the heritable traits characteristic of a population over generations. Charl ...
: the most resistant specimens survive and pass on their acquired heritable changes traits to their offspring.PBS (2001)
Pesticide resistance
Retrieved on September 15, 2007.
If a pest has ''resistance'' then the pesticide lacks ''efficacy'' efficacy and resistance are inversely related. Cases of resistance have been reported in all classes of
pests PESTS was an anonymous American activist group formed in 1986 to critique racism Racism is the belief that groups of humans possess different behavioral traits corresponding to inherited attributes and can be divided based on the superiority ...
(''i.e.'' crop diseases, weeds, rodents, ''etc.''), with 'crises' in insect control occurring early-on after the introduction of pesticide use in the 20th century. The
Insecticide Resistance Action Committee The Insecticide Resistance Action Committee (IRAC) was formed in 1984 and works as a specialist technical group of the industry association CropLife to be able to provide a coordinated industry response to prevent or delay the development of insec ...
(IRAC) definition of
insecticide Insecticides are substances used to kill insects. 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 ...
resistance is ''a heritable change in the sensitivity of a pest population that is reflected in the repeated failure of a product to achieve the expected level of control when used according to the label recommendation for that pest species''. Pesticide resistance is increasing. Farmers in the US lost 7% of their crops to pests in the 1940s; over the 1980s and 1990s, the loss was 13%, even though more pesticides were being used. Over 500 species of pests have evolved a resistance to a pesticide. Other sources estimate the number to be around 1,000 species since 1945.Miller GT (2004), ''Sustaining the Earth'', 6th edition. Thompson Learning, Inc. Pacific Grove, California. Chapter 9, Pages 211-216. Although the evolution of pesticide resistance is usually discussed as a result of pesticide use, it is important to keep in mind that pest populations can also adapt to non-chemical methods of control. For example, the northern corn rootworm (''
Diabrotica barberi ''Diabrotica barberi'', the northern corn rootworm, is a species of skeletonizing leaf beetle in the family Chrysomelidae. It is found in North America. Adults feed on corn, and, when corn is unavailable, goldenrod Goldenrod is a common name ...
'') became adapted to a corn-soybean
crop rotation Crop rotation is the practice of growing a series of different types of crops in the same area across a sequence of growing seasons. It reduces reliance on one set of nutrients, pest and weed pressure, and the probability of developing resistant ...
by spending the year when the field is planted with soybeans in a
diapause In animal dormancy, diapause is the delay in development in response to regular and recurring periods of adverse environmental conditions.Tauber, M.J., Tauber, C.A., Masaki, S. (1986) ''Seasonal Adaptations of Insects''. Oxford University Press It ...
. , few new
weed killer A weed is a plant considered undesirable in a particular situation, "a plant in the wrong place", or a plant growing where it is not wanted.Harlan, J. R., & deWet, J. M. (1965). Some thoughts about weeds. ''Economic botany'', ''19''(1), 16-24. ...
s are near commercialization, and none with a novel, resistance-free mode of action. Similarly, discovery of new
insecticide Insecticides are substances used to kill insects. 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 ...
s is more expensive and difficult than ever.


Causes

Pesticide resistance probably stems from multiple factors: * Many pest species produce large numbers of offspring, for example insect pests produce large broods. This increases the probability of mutations and ensures the rapid expansion of resistant populations. * Pest species had been exposed to natural toxins long before agriculture began. For example, many plants produce
phytotoxins Phytotoxins are substances that are poisonous or toxic to the growth of plants. Phytotoxic substances may result from human activity, as with herbicides, or they may be produced by plants, by microorganisms, or by naturally occurring chemical react ...
to protect them from herbivores. As a result, coevolution of herbivores and their host plants required development of the physiological capability to detoxify or tolerate poisons. .
AGRIS AGRIS (International System for Agricultural Science and Technology) is a global public domain database with more than 12 million structured bibliographical records on agricultural science and technology. It became operational in 1975 and the data ...
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* Humans often rely almost exclusively on pesticides for pest control. This increases selection pressure towards resistance. Pesticides that fail to break down quickly contribute to selection for resistant strains even after they are no longer being applied.Daly H, Doyen JT, and Purcell AH III (1998), ''Introduction to insect biology and diversity'', 2nd edition. Oxford University Press. New York, New York. Chapter 14, Pages 279-300. * In response to resistance, managers may increase pesticide quantities/frequency, which exacerbates the problem. In addition, some pesticides are toxic toward species that feed on or compete with pests. This can paradoxically allow the pest population to expand, requiring more pesticides. This is sometimes referred to as ''the pesticide trap'', or a ', since farmers progressively pay more for less benefit. * Insect predators and parasites generally have smaller populations and are less likely to evolve resistance than are pesticides' primary targets, such as mosquitoes and those that feed on plants. Weakening them allows the pests to flourish. Alternatively, resistant predators can be bred in laboratories. * Pests with limited viable range (such as insects with a specific diet of a few related crop plants) are more likely to evolve resistance, because they are exposed to higher pesticide concentrations and has less opportunity to breed with unexposed populations. * Pests with shorter
generation time In population biology and demography, generation time is the average time between two consecutive generations in the lineages of a population. In human populations, generation time typically ranges from 22 to 33 years. Historians sometimes use thi ...
s develop resistance more quickly than others. * The social dynamics of farmers: Farmers following the common practices of their peers is sometimes problematic in this case. Overrelying on pesticides is a popular mistake and becomes increasingly popular as farmers conform to the practices around them. * Unfamiliarity with variation in
regulatory enforcement Enforcement is the proper execution of the process of ensuring compliance with laws, regulations, rules, standards, and Norm (social), social norms. Governments attempt to effectuate successful implementation of policies by enforcing laws and r ...
can hamper policy makers' ability to produce real change in the course of resistance evolution.


Examples

Resistance has evolved in multiple species: resistance to
insecticide Insecticides are substances used to kill insects. 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 ...
s was first documented by A. L. Melander in 1914 when scale insects demonstrated resistance to an inorganic insecticide. Between 1914 and 1946, 11 additional cases were recorded. The development of organic insecticides, such as
DDT Dichlorodiphenyltrichloroethane, commonly known as DDT, is a colorless, tasteless, and almost odorless crystalline chemical compound, an organochloride. Originally developed as an insecticide, it became infamous for its environmental impacts. ...
, gave hope that insecticide resistance was a dead issue. However, by 1947
housefly The housefly (''Musca domestica'') is a fly of the suborder Cyclorrhapha. It is believed to have evolved in the Cenozoic Era, possibly in the Middle East, and has spread all over the world as a commensal of humans. It is the most common fly ...
resistance to DDT had evolved. With the introduction of every new insecticide class –
cyclodiene Hexachlorocyclopentadiene (HCCPD), also known as C-56, Graphlox, and HRS 1655, is an organochlorine compound with the formula C5Cl6. It is a precursor to pesticides, flame retardants, and dyes. It is a colourless liquid, although commercial samples ...
s, carbamates, formamidines,
organophosphates In organic chemistry, organophosphates (also known as phosphate esters, or OPEs) are a class of organophosphorus compounds with the general structure , a central phosphate molecule with alkyl or aromatic substituents. They can be considered a ...
,
pyrethroids A pyrethroid is an organic compound similar to the natural pyrethrins, which are produced by the flowers of pyrethrums (''Chrysanthemum cinerariaefolium'' and '' C. coccineum''). Pyrethroids are used as commercial and household insecticides. I ...
, even ''
Bacillus thuringiensis ''Bacillus thuringiensis'' (or Bt) is a gram-positive, soil-dwelling bacterium, the most commonly used biological pesticide worldwide. ''B. thuringiensis'' also occurs naturally in the gut of caterpillars of various types of moths and butterflie ...
'' – cases of resistance surfaced within two to 20 years. * Studies in America have shown that
fruit flies Fruit fly may refer to: Organisms * Drosophilidae, a family of small flies, including: ** ''Drosophila'', the genus of small fruit flies and vinegar flies ** ''Drosophila melanogaster'' or common fruit fly ** '' Drosophila suzukii'' or Asian fruit ...
that infest orange groves were becoming resistant to
malathion Malathion is an organophosphate insecticide which acts as an acetylcholinesterase inhibitor. In the USSR, it was known as carbophos, in New Zealand and Australia as maldison and in South Africa as mercaptothion. Pesticide use Malathion is a pes ...
. * In
Hawaii Hawaii ( ; haw, Hawaii or ) is a U.S. state, state in the Western United States, Western United States, located in the Pacific Ocean about from the U.S. mainland. It is the only U.S. state outside North America, the only state that is ...
,
Japan Japan ( ja, 日本, or , and formally , ''Nihonkoku'') is an island country in East Asia. It is situated in the northwest Pacific Ocean, and is bordered on the west by the Sea of Japan, while extending from the Sea of Okhotsk in the north ...
and
Tennessee Tennessee ( , ), officially the State of Tennessee, is a landlocked state in the Southeastern region of the United States. Tennessee is the 36th-largest by area and the 15th-most populous of the 50 states. It is bordered by Kentucky to t ...
, the
diamondback moth The diamondback moth (''Plutella xylostella''), sometimes called the cabbage moth, is a moth species of the family Plutellidae and genus '' Plutella''. The small, grayish-brown moth sometimes has a cream-colored band that forms a diamond along ...
evolved a resistance to ''
Bacillus thuringiensis ''Bacillus thuringiensis'' (or Bt) is a gram-positive, soil-dwelling bacterium, the most commonly used biological pesticide worldwide. ''B. thuringiensis'' also occurs naturally in the gut of caterpillars of various types of moths and butterflie ...
'' about three years after it began to be used heavily. * In England, rats in certain areas have evolved resistance that allows them to consume up to five times as much
rat poison Rodenticides are chemicals made and sold for the purpose of killing rodents. While commonly referred to as "rat poison", rodenticides are also used to kill mice, squirrels, woodchucks, chipmunks, porcupines, nutria, beavers, and voles. Despite ...
as normal rats without dying. * DDT is no longer effective in preventing
malaria Malaria is a Mosquito-borne disease, mosquito-borne infectious disease that affects humans and other animals. Malaria causes Signs and symptoms, symptoms that typically include fever, fatigue (medical), tiredness, vomiting, and headaches. In se ...
in some places. Resistance developed slowly in the 1960s due to agricultural use. This pattern was especially noted and synthesized by Mouchet 1988. * In the southern United States, ''
Amaranthus palmeri ''Amaranthus palmeri'' is a species of edible flowering plant in the amaranth genus. It has several common names, including carelessweed, dioecious amaranth, Palmer's amaranth, Palmer amaranth, and Palmer's pigweed. It is native to most of the s ...
'', which interferes with cotton production, has evolved resistance to the herbicide
glyphosate Glyphosate (IUPAC name: ''N''-(phosphonomethyl)glycine) is a broad-spectrum systemic herbicide and crop desiccant. It is an organophosphorus compound, specifically a phosphonate, which acts by inhibiting the plant enzyme 5-enolpyruvylshik ...
and overall has resistance to five sites of action in the southern US . * The
Colorado potato beetle The Colorado potato beetle (''Leptinotarsa decemlineata''), also known as the Colorado beetle, the ten-striped spearman, the ten-lined potato beetle, or the potato bug, is a major pest of potato crops. It is about long, with a bright yellow/o ...
has evolved resistance to 52 different compounds belonging to all major insecticide classes. Resistance levels vary across populations and between
beetle Beetles are insects that form the order Coleoptera (), in the superorder Endopterygota. Their front pair of wings are hardened into wing-cases, elytra, distinguishing them from most other insects. The Coleoptera, with about 400,000 describ ...
life stages, but in some cases can be very high (up to 2,000-fold). * The
cabbage looper The cabbage looper (''Trichoplusia ni'') is a medium-sized moth in the family Noctuidae, a family commonly referred to as owlet moths. Its common name comes from its preferred host plants and distinctive crawling behavior. Cruciferous vegetable ...
is an agricultural pest that is becoming increasingly problematic due to its increasing resistance to ''Bacillus thuringiensis,'' as demonstrated in Canadian greenhouses. Further research found a genetic component to Bt resistance. * The widespread introduction of ''
Rattus norvegicus ''Rattus'' is a genus of muroid rodents, all typically called rats. However, the term rat can also be applied to rodent species outside of this genus. Species and description The best-known ''Rattus'' species are the black rat (''R. rattus'' ...
'' combined with the widespread use of anticoagulent rodenticides such as
warfarin Warfarin, sold under the brand name Coumadin among others, is a medication that is used as an anticoagulant (blood thinner). It is commonly used to prevent blood clots such as deep vein thrombosis and pulmonary embolism, and to prevent str ...
has produced almost equally widespread resistance to vitamin K antagonist rodenticides around the world.


Consequences

Insecticides are widely used across the world to increase agricultural productivity and quality in
vegetable Vegetables are parts of plants that are consumed by humans or other animals as food. The original meaning is still commonly used and is applied to plants collectively to refer to all edible plant matter, including the flowers, fruits, stems, ...
s and
grain A grain is a small, hard, dry fruit (caryopsis) – with or without an attached hull layer – harvested for human or animal consumption. A grain crop is a grain-producing plant. The two main types of commercial grain crops are cereals and legume ...
s (and to a lesser degree the use for
vector control Vector control is any method to limit or eradicate the mammals, birds, insects or other arthropods (here collectively called " vectors") which transmit disease pathogens. The most frequent type of vector control is mosquito control using a vari ...
for livestock). The resulting resistance has reduced function for those very purposes, and in vector control for humans.


Multiple and cross-resistance

* Multiple-resistance pests are resistant to more than one class of pesticide. This can happen when pesticides are used in sequence, with a new class replacing one to which pests display resistance with another. *
Cross-resistance Cross-resistance is when something develops resistance to several substances that have a similar mechanism of action. For example, if a certain type of bacteria develops resistance to one antibiotic, that bacteria will also have resistance to sev ...
, a related phenomenon, occurs when the genetic mutation that made the pest resistant to one pesticide also makes it resistant to others, often those with a similar
mechanism of action In pharmacology, the term mechanism of action (MOA) refers to the specific biochemical interaction through which a drug substance produces its pharmacological effect. A mechanism of action usually includes mention of the specific molecular targ ...
.


Adaptation

Pests becomes resistant by evolving physiological changes that protect them from the chemical. One protection mechanism is to increase the number of copies of a
gene In biology, the word gene (from , ; "...Wilhelm Johannsen coined the word gene to describe the Mendelian units of heredity..." meaning ''generation'' or ''birth'' or ''gender'') can have several different meanings. The Mendelian gene is a ba ...
, allowing the organism to produce more of a protective
enzyme Enzymes () are proteins that act as biological catalysts by accelerating chemical reactions. The molecules upon which enzymes may act are called substrates, and the enzyme converts the substrates into different molecules known as products. ...
that breaks the pesticide into less toxic chemicals. Such enzymes include
esterase An esterase is a hydrolase enzyme that splits esters into an acid and an alcohol in a chemical reaction with water called hydrolysis. A wide range of different esterases exist that differ in their substrate specificity, their protein structure, ...
s,
glutathione transferase Glutathione ''S''-transferases (GSTs), previously known as ligandins, are a family of eukaryotic and prokaryotic phase II metabolic isozymes best known for their ability to catalyze the conjugation of the reduced form of glutathione (GSH) to ...
s, and mixed
microsomal In cell biology, microsomes are heterogeneous vesicle-like artifacts (~20-200 nm diameter) re-formed from pieces of the endoplasmic reticulum (ER) when eukaryotic cells are broken-up in the laboratory; microsomes are not present in healthy, livin ...
oxidase In biochemistry, an oxidase is an enzyme that catalyzes oxidation-reduction reactions, especially one involving dioxygen (O2) as the electron acceptor. In reactions involving donation of a hydrogen atom, oxygen is reduced to water (H2O) or hydroge ...
s. Alternatively, the number and/or sensitivity of
biochemical receptor In biochemistry and pharmacology, receptors are chemical structures, composed of protein, that receive and transduce signals that may be integrated into biological systems. These signals are typically chemical messengers which bind to a recept ...
s that bind to the pesticide may be reduced. Behavioral resistance has been described for some chemicals. For example, some ''
Anopheles ''Anopheles'' () is a genus of mosquito first described and named by J. W. Meigen in 1818. About 460 species are recognised; while over 100 can transmit human malaria, only 30–40 commonly transmit parasites of the genus ''Plasmodium'', which c ...
''
mosquitoes Mosquitoes (or mosquitos) are members of a group of almost 3,600 species of small flies within the family Culicidae (from the Latin ''culex'' meaning " gnat"). The word "mosquito" (formed by ''mosca'' and diminutive ''-ito'') is Spanish for "lit ...
evolved a preference for resting outside that kept them away from pesticide sprayed on interior walls. Resistance may involve rapid excretion of toxins, secretion of them within the body away from vulnerable tissues and decreased penetration through the body wall. . Mutation in only a single gene can lead to the evolution of a resistant organism. In other cases, multiple genes are involved. Resistant genes are usually autosomal. This means that they are located on
autosomes An autosome is any chromosome that is not a sex chromosome. The members of an autosome pair in a diploid cell have the same morphology, unlike those in allosomal (sex chromosome) pairs, which may have different structures. The DNA in autosomes ...
(as opposed to
allosome A sex chromosome (also referred to as an allosome, heterotypical chromosome, gonosome, heterochromosome, or idiochromosome) is a chromosome that differs from an ordinary autosome in form, size, and behavior. The human sex chromosomes, a typical ...
s, also known as sex chromosomes). As a result, resistance is inherited similarly in males and females. Also, resistance is usually inherited as an incompletely dominant trait. When a resistant individual mates with a susceptible individual, their progeny generally has a level of resistance intermediate between the parents. Adaptation to pesticides comes with an evolutionary cost, usually decreasing relative fitness of organisms in the absence of pesticides. Resistant individuals often have reduced reproductive output, life expectancy, mobility, etc. Non-resistant individuals sometimes grow in frequency in the absence of pesticides - but not always - so this is one way that is being tried to combat resistance. Blowfly maggots produce an enzyme that confers resistance to
organochloride An organochloride, organochlorine compound, chlorocarbon, or chlorinated hydrocarbon is an organic compound containing at least one covalently bonded atom of chlorine. The chloroalkane class (alkanes with one or more hydrogens substituted by chlor ...
insecticides. Scientists have researched ways to use this enzyme to break down pesticides in the environment, which would detoxify them and prevent harmful environmental effects. A similar enzyme produced by soil bacteria that also breaks down organochlorides works faster and remains stable in a variety of conditions.Marino M. (August 2007)
Blowies inspire pesticide attack: Blowfly maggots and dog-wash play starring roles in the story of a remarkable environmental clean-up technology
. ''Solve'', Issue 12. CSIRO Enquiries. Retrieved on 2007-10-03.
Resistance to
gene drive A gene drive is a natural process and technology of genetic engineering that propagates a particular suite of genes throughout a population by altering the probability that a specific allele will be transmitted to offspring (instead of the Mende ...
forms of population control is expected to occur and methods of slowing its development are being studied. The molecular mechanisms of insecticide resistance only became comprehensible in 1997. Guerrero et al 1997 used the newest methods of the time to find mutations producing pyrethroid resistance in dipterans. Even so, these adaptations to pesticides were unusually rapid and may not necessarily represent the norm in wild populations, under wild conditions. Natural adaptation processes take much longer and almost always happen in response to gentler pressures.


Management

In order to remediate the problem it first must be ascertained what is really wrong. Assaying of suspected pesticide resistance - and not merely field observation and experience - is necessary because it may be mistaken for failure to
apply In mathematics and computer science, apply is a function that applies a function to arguments. It is central to programming languages derived from lambda calculus, such as LISP and Scheme, and also in functional languages. It has a role in th ...
the pesticide as directed, or microbial degradation of the pesticide. The
United Nations The United Nations (UN) is an intergovernmental organization whose stated purposes are to maintain international peace and security, develop friendly relations among nations, achieve international cooperation, and be a centre for harmonizi ...
'
World Health Organization The World Health Organization (WHO) is a specialized agency of the United Nations responsible for international public health. The WHO Constitution states its main objective as "the attainment by all peoples of the highest possible level of h ...
established the Worldwide Insecticide resistance Network in March 2016, due to increasing need and increasing recognition, including the radical decline in function against pests of vegetables.


Integrated pest management

The Integrated pest management (IPM) approach provides a balanced approach to minimizing resistance. Resistance can be managed by reducing use of a pesticide. This allows non-resistant organisms to out-compete resistant strains. They can later be killed by returning to use of the pesticide. A complementary approach is to site untreated refuges near treated croplands where susceptible pests can survive. When pesticides are the sole or predominant method of pest control, resistance is commonly managed through pesticide rotation. This involves switching among pesticide classes with different modes of action to delay or mitigate pest resistance.Graeme Murphy (December 1, 2005)
Resistance Management - Pesticide Rotation
. Ontario Ministry of Agriculture, Food and Rural Affairs. Retrieved on September 15, 2007
The Resistance Action Committees monitor resistance across the world, and in order to do that, each maintains a list of modes of action and pesticides that fall into those categories: the
Fungicide Resistance Action Committee Fungicides are biocidal chemical compounds or biological organisms used to kill parasitic fungi or their spores. A fungistatic inhibits their growth. Fungi can cause serious damage in agriculture, resulting in critical losses of yield, quality, ...
, the
Weed Science Society of America The Weed Science Society of America (WSSA) is a nonprofit, learned society focused on weed science. It was founded in 1956. The organization promotes research, education, and extension outreach, provides science-based information to the public an ...
(the
Herbicide Resistance Action Committee CropLife International is an international trade association of agrochemical companies founded in 2001. It was previously known as ''Global Crop Protection Federation'' and started out as ''International Group of National Associations of Manufactu ...
no longer has its own scheme, and is contributing to WSSA's from now on), and the
Insecticide Resistance Action Committee The Insecticide Resistance Action Committee (IRAC) was formed in 1984 and works as a specialist technical group of the industry association CropLife to be able to provide a coordinated industry response to prevent or delay the development of insec ...
. The
U.S. Environmental Protection Agency The Environmental Protection Agency (EPA) is an independent executive agency of the United States federal government tasked with environmental protection matters. President Richard Nixon proposed the establishment of EPA on July 9, 1970; it be ...
(EPA) also uses those classification schemes. Manufacturers may recommend no more than a specified number of consecutive applications of a pesticide class be made before moving to a different pesticide class. Two or more pesticides with different modes of action can be tankmixed on the farm to improve results and delay or mitigate existing pest resistance.Chris Boerboom (March 2001)
Glyphosate resistant weeds
Weed Science - University of Wisconsin. Retrieved on September 15, 2007


Status


Glyphosate

Glyphosate Glyphosate (IUPAC name: ''N''-(phosphonomethyl)glycine) is a broad-spectrum systemic herbicide and crop desiccant. It is an organophosphorus compound, specifically a phosphonate, which acts by inhibiting the plant enzyme 5-enolpyruvylshik ...
-resistant weeds are now present in the vast majority of
soybean The soybean, soy bean, or soya bean (''Glycine max'') is a species of legume native to East Asia, widely grown for its edible bean, which has numerous uses. Traditional unfermented food uses of soybeans include soy milk, from which tofu an ...
, cotton, and
corn Maize ( ; ''Zea mays'' subsp. ''mays'', from es, maíz after tnq, mahiz), also known as corn (North American and Australian English), is a cereal grain first domesticated by indigenous peoples in southern Mexico about 10,000 years ago. The ...
farms in some U.S. states. Weeds resistant to multiple herbicide modes of action are also on the rise. Before glyphosate, most herbicides would kill a limited number of weed species, forcing farmers to continually rotate their crops and herbicides to prevent resistance. Glyphosate disrupts the ability of most plants to construct new proteins. Glyphosate-tolerant
transgenic crops Genetically modified crops (GM crops) are plants used in agriculture, the DNA of which has been modified using genetic engineering methods. Plant genomes can be engineered by physical methods or by use of ''Agrobacterium'' for the delivery of s ...
are not affected. A weed family that includes waterhemp ('' Amaranthus rudis'') has developed glyphosate-resistant strains. A 2008 to 2009 survey of 144 populations of waterhemp in 41 Missouri counties revealed glyphosate resistance in 69%. Weed surveys from some 500 sites throughout Iowa in 2011 and 2012 revealed glyphosate resistance in approximately 64% of waterhemp samples. In response to the rise in glyphosate resistance, farmers turned to other herbicides—applying several in a single season. In the United States, most midwestern and southern farmers continue to use glyphosate because it still controls most weed species, applying other herbicides, known as residuals, to deal with resistance. The use of multiple herbicides appears to have slowed the spread of glyphosate resistance. From 2005 through 2010 researchers discovered 13 different weed species that had developed resistance to glyphosate. From 2010-2014 only two more were discovered. A 2013 Missouri survey showed that multiply-resistant weeds had spread. 43% of the sampled weed populations were resistant to two different herbicides, 6% to three and 0.5% to four. In Iowa a survey revealed dual resistance in 89% of waterhemp populations, 25% resistant to three and 10% resistant to five. Resistance increases pesticide costs. For southern cotton, herbicide costs climbed from between a few years ago to about in 2014. In the South, resistance contributed to the shift that reduced cotton planting by 70% in Arkansas and 60% in Tennessee. For soybeans in Illinois, costs rose from about .


''Bacillus thuringiensis''

During 2009 and 2010, some Iowa fields showed severe injury to corn producing Bt toxin
Cry3Bb1 Delta endotoxins (δ-endotoxins) are pore-forming toxins produced by ''Bacillus thuringiensis'' species of bacteria. They are useful for their insecticidal action and are the primary toxin produced by Bt maize/corn. During spore formation t ...
by
western corn rootworm The Western corn rootworm, ''Diabrotica virgifera virgifera'', is one of the most devastating corn rootworm species in North America, especially in the midwestern corn-growing areas such as Iowa. A related species, the Northern corn rootworm, ...
. During 2011, mCry3A corn also displayed insect damage, including
cross-resistance Cross-resistance is when something develops resistance to several substances that have a similar mechanism of action. For example, if a certain type of bacteria develops resistance to one antibiotic, that bacteria will also have resistance to sev ...
between these toxins. Resistance persisted and spread in Iowa. Bt corn that targets western corn rootworm does not produce a high dose of Bt toxin, and displays less resistance than that seen in a high-dose Bt crop. Products such as Capture LFR (containing the pyrethroid
bifenthrin Bifenthrin is a pyrethroid insecticide. It is widely used against ant infestations. It is not a restricted chemical in the United States and is commonly sold in hardware stores to control pests in homes. Chemical properties Bifenthrin is poorly ...
) and SmartChoice (containing a
pyrethroid A pyrethroid is an organic compound similar to the natural pyrethrins, which are produced by the flowers of pyrethrums (''Chrysanthemum cinerariaefolium'' and '' C. coccineum''). Pyrethroids are used as commercial and household insecticides. In ...
and an
organophosphate In organic chemistry, organophosphates (also known as phosphate esters, or OPEs) are a class of organophosphorus compounds with the general structure , a central phosphate molecule with alkyl or aromatic substituents. They can be considered ...
) have been increasingly used to complement Bt crops that farmers find alone to be unable to prevent insect-driven injury. Multiple studies have found the practice to be either ineffective or to accelerate the development of resistant strains.


See also

*
Antibiotic resistance Antimicrobial resistance (AMR) occurs when microbes evolve mechanisms that protect them from the effects of antimicrobials. All classes of microbes can evolve resistance. Fungi evolve antifungal resistance. Viruses evolve antiviral resistance. ...
*
Male accessory gland Male accessory glands (MAG) in humans are the seminal vesicles, prostate gland, and the bulbourethral glands (also called Cowper's glands). In insects, male accessory glands produce products that mix with the sperm to protect and preserve them, i ...
*
Persistent organic pollutant Persistent organic pollutants (POPs), sometimes known as "forever chemicals", are organic compounds that are resistant to environmental degradation through chemical, biological, and photolytic processes. They are toxic chemicals that adversely ...
*
Stockholm Convention on Persistent Organic Pollutants Stockholm Convention on Persistent Organic Pollutants is an international environmental treaty, signed on 22 May 2001 in Stockholm and effective from 17 May 2004, that aims to eliminate or restrict the production and use of persistent organic ...
*
Vavilovian mimicry In plant biology, Vavilovian mimicry (also crop mimicry or weed mimicry) is a form of mimicry in plants where a weed evolves to share one or more characteristics with a domesticated plant through generations of artificial selection. It is name ...


References


Further reading

*


External links


Overview of insecticide resistanceIRAC, Insecticide Resistance Action CommitteeRRAC, Rodenticide Resistance Action Committee HRAC, Herbicide Resistance Action CommitteeUK Resistance Action groupsArthropod Pesticide Resistance Database
* * EPPO's efficacy testing site: {{pesticides Pesticides Pests (organism) Garden pests