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Pesticide application can artificially select for resistant pests. In this diagram, the first generation happens to have an insect with a heightened resistance to a pesticide (red) After pesticide application, its descendants represent a larger proportion of the population, because sensitive pests (white) have been selectively killed.
Plants with transgenic/GM disease resistance against insect pests have been extremely successful as commercial products, especially in maize and cotton, and are planted annually on over 20 million hectares in over 20 countries worldwide [49] (see also genetically modified crops). Transgenic plant disease resistance against microbial pathogens ...
In 2013, a second issue being seen across the world, was the development of Bt resistant pests limiting the usefulness of Bt crops. [15] Main drivers for the widespread resistance in India and China included the high proportion of Bt cotton being planted, 90% and 95% respectively in 2011, [9] [16] and few refuge areas. [12] [17] [18]
The majority of these species contain genes that make them either tolerant to herbicides or resistant to insects. Other common traits include virus resistance, delayed ripening, modified flower colour or altered composition. In 2014, 28 countries grew GM crops, and 39 countries imported but did not grow them. [1]
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. [102] Over 500 species of pests have evolved a resistance to a pesticide. [105] Other sources estimate the number to be around 1,000 species since 1945. [106]
The study found that herbicide-tolerant crops have lower production costs, while for insect-resistant crops the reduced pesticide use was offset by higher seed prices, leaving overall production costs about the same. [3] [105] Yields increased 9% for herbicide tolerance and 25% for insect resistant varieties.
They have been used in companion planting as pest control in agricultural and garden situations, and in households. Certain plants have shown effectiveness as topical repellents for haematophagous insects, such as the use of lemon eucalyptus in PMD, but incomplete research and misunderstood applications can produce variable results. [1]
Viburnum lesquereuxii leaf with insect damage; Dakota Sandstone (Cretaceous) of Ellsworth County, Kansas. Scale bar is 10 mm. Knowledge of herbivory in geological time comes from three sources: fossilized plants, which may preserve evidence of defense (such as spines) or herbivory-related damage; the observation of plant debris in fossilised animal feces; and the structure of herbivore mouthparts.