Pesticide resistance
Decreased effectiveness of a pesticide on a pest / From Wikipedia, the free encyclopedia
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Pesticide resistance describes the decreased susceptibility of a pest population to a pesticide that was previously effective at controlling the pest. Pest species evolve pesticide resistance via natural selection: the most resistant specimens survive and pass on their acquired heritable changes traits to their offspring.[1] If a pest has resistance then that will reduce the pesticide's efficacy – efficacy and resistance are inversely related.[2]
Cases of resistance have been reported in all classes of pests (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 (IRAC) definition of insecticide 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'.[3]
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.[1] Over 500 species of pests have evolved a resistance to a pesticide.[4] Other sources estimate the number to be around 1,000 species since 1945.[5]
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) became adapted to a corn-soybean crop rotation by spending the year when the field is planted with soybeans in a diapause.[6]
As of 2014[update], few new weed killers are near commercialization, and none with a novel, resistance-free mode of action.[7] Similarly, as of January 2019[update] discovery of new insecticides is more expensive and difficult than ever.[8]