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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 genetic traits to their offspring.〔PBS (2001), (Pesticide resistance ). Retrieved on September 15, 2007.〕 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'. Pesticide resistance is increasing. Farmers in the USA 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.〔grapes.msu.edu. (How pesticide resistance develops ). Excerpt from: Larry Gut, Annemiek Schilder, Rufus Isaacs and Patricia McManus. ''Fruit Crop Ecology and Management'', Chapter 2: "Managing the Community of Pests and Beneficials." Retrieved on September 15, 2007.〕 Other sources estimate the number to be around 1000 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'') became adapted to a corn-soybean crop rotation by spending the year when field is planted to soybeans in a diapause.〔Levine E, Oloumi-Sadeghi H, Fisher JR (1992) Discovery of multiyear diapause in Illinois and South Dakota Northern corn rootworm (Coleoptera: Cerambycidae) eggs and incidence of the prolonged diapause trait in Illinois. Journal of Economic Entomology 85: 262-267.〕 As of 2014 few new weed killers are near commercialization, and none with a novel, resistance-free mode of action. ==Causes== Pesticide resistance probably stems from multiple factors: Many pest species 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 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.〔Ferro DN. 1993. Potential for resistance to Bacillus thuringiensis: Colorado potato beetle (Coleoptera: Chrysomelidae) – a model system. American Entomologist 39:38-44.〕〔Bishop BA and EJ Grafius. 1996. Insecticide resistance in the Colorado potato beetle. In: P Jolivet and TH Hsiao. Chrysomelidae Biology, Volume 1. SBP Academic Publishing, Amsterdam.〕 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 allow the pest population to expand, requiring more pesticides. This is sometimes referred to as ''pesticide trap'',〔Marten, Gerry (“Non-pesticide management” for escaping the pesticide trap in Andrah Padesh, India ). ecotippingpoints.org. Retrieved on September 17, 2007.〕 or a ''pesticide treadmill'', 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 diets 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 times develop resistance more quickly than others.〔 抄文引用元・出典: フリー百科事典『 ウィキペディア（Wikipedia）』 ■ウィキペディアで「Pesticide resistance」の詳細全文を読む スポンサード リンク
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