Evolution in action: insects have developed resistance to toxins secreted from genetically engineered cotton

This is the first documented case of resistance developing under field conditions against a crop containing Bt, say the University of Arizona researchers

The insects fight back against the genetic engineering of crops. The larvae of a harmful insect called Helicvara zea have for the first time succeeded in developing resistance in field conditions against plants engineered to produce an insecticide called Bt. Populations of the larvae immune to the poison have been found in more than a dozen fields in the United States.

"We're seeing evolution in action here," says Bruce Tabashnik, lead researcher on the current study and professor and head of the department of entomology (insect science) at the University of Arizona. "This is the first documented case in which resistance has developed under field conditions against a crop containing Bt."

Bt crops got their name because they were genetically engineered to produce Bt toxins, which kill certain insects. The toxins are usually produced in nature by the common bacterium Bacillus thuringiensis, hence the origin of the acronym Bt.

When you use an insecticide to control a pest population, some populations will eventually develop immunity.” says Tabashnik. According to him, Bt cotton and Bt wheat have been grown on almost one hundred million dunams around the world since 1996, "thus resulting in a very strong selection on the resistance of insects to toxins."

In order to delay the transmission of resistance from generation to generation, non-Bt producing crops are planted next to Bt crops. These crops provide a safe place where the various insects can grow, including those that are not resistant to Bt. Since the mutation that results in resistance to the poison is rare, the resistant insects are also rare. When they are looking for a mate, the chances are that the mate they will find will be an insect that is not resistant to the poison and lives among the crops that do not contain Bt. The product of mating between two such insects - one of which is resistant to the poison and the other vulnerable to it - will be an insect that is not resistant. In most insects, the offspring will be resistant to the Bt toxin only if both parents are resistant. It turns out, however, that the rules are different in the case of the same helicopter. The offspring of this insect will be resistant to the poison even if one of their parents was vulnerable. It is enough for one of the parents to be resistant to the toxin to produce offspring that are also resistant. As a result, the insect can evolve against the toxin more easily than other insects.

Is it time to stop genetically engineering plants so that they produce toxins?

The answer, unequivocally, is no. Despite the strong selection, the researchers found that most of the caterpillars that damage cotton and wheat remained vulnerable to Bt crops. "Resistance has developed in one particular pest, in one part of the United States," says Tabashnik. "The remaining common pests that attack Bt crops have not developed resistance."

In addition, the researchers emphasize that Bt cotton reduces the extensive use of traditional insecticides (which also kill the beneficial insects in the field) and increases crop yield.

Sources

For information on the University of Arizona website

A film describing the discovery

The Liquorpa is the same on Wikipedia

Previous news on the subject on the science website

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