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Crops that have been genetically modified (GM) or engineered for pest and herbicide resistance are increasingly being developed and grown.

Herbicide tolerant (HT) crops are genetically modified to withstand herbicides better than the weeds, so heavier doses of herbicides can be used. HT varieties of soybeans and cotton are now extensively used.

Pest-deterring (Bt) crops are genetically modified to repel many insect pests. Genes from the bacterium Bacillus thuringiensis that are ‘spliced’ into the plant’s DNA cause the plant to make proteins toxic to insects. Bt varieties of corn and cotton have high usage in the USA.

Recently some pests have developed resistance to Bt crops. The Cotton Bollworm (Helicoverpa armigera)—arguably the world’s worst agricultural pest—is showing resistance both to GM crops and to most chemical pesticides.

GM crops are more widely used in the United States than in most other parts of the world. Critics fear that GM crops may encourage the evolution of ‘super bugs’ with high resistance, that spliced genes may move up the food chain, and that there may be long-term livestock and human health impacts.