Pest resistant crops

Pest resistant GM crops (primarily cotton and maize), have been genetically modified so they are toxic to certain insects. They are often called Bt crops because the introduced genes were originally identified in a bacterial species called Bacillus thuringiensis. These bacteria produce a group of toxins called Cry toxins.

Bt crops are grown widely in the USA, where an estimated 40% of GM maize is used in industrial-scale biofuels (agrofuels) subsidised by the US government. The rest of this maize is mostly used in animal feed, as is Bt maize grown in Brazil and Argentina. Some Bt maize is also grown in South Africa.

Bt maize is also grown in small quantities in Europe, mainly in Spain, where it is used in animal feed.

Bt cotton is the only GM crop authorised to be grown in India and China. It has also been grown in smaller quantities in Pakistan, Colombia, Egypt and Burkina Faso.

Because the pesticide is produced inside Bt plants, rather than sprayed on the outside, it cannot be washed off, so there are concerns that it may have adverse effects on humans, animals and wildlife if and when the crop is eaten.

Bt crops are supposed to be grown with refuges of non-GM crops and plants to reduce the likelihood of the targeted pests developing resistance (meaning that they are no longer killed by the toxin produced in the plant). Despite this, resistant pests have been found in the US and in India. In China, there have been reports of surges in other types of pest that are not effected by the toxin produced by Bt cotton.

To deal with the problem of resistant pests, one experiment in the US used releases of pests sterilised using radiation to try to reduce the population of pests in fields of Bt crops. The UK company Oxitec is developing GM insects which it hopes to be paid to release in fields where Bt crops are grown. The insects are genetically programmed to die before adulthood and are supposed to reduce the population by mating with wild insects.

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