GMO Cotton Loses Its Natural Defenses As A Result Of Less Competition With Their Primary Natural Pests

New research from the Swiss National Science Foundation (SNSF) has found that genetically modified Bt cotton crops, which contain the Bt toxin poisonous to the primary enemies of cotton, have considerably weaker defenses against their secondary enemies, such as aphids, as a result.


Many plant species when attacked by insects release poisons that protects them from their most significant enemies. But because of the genetically modified resistance to their primary pests, these GMO Bt cotton plants end up relying far less on their own defenses, making them more susceptible to the secondary enemies that they were previously protected against.

This reality matches up very well with one of the most common and most convincing arguments against GMOs; the myriad qualities, traits, and systems of organisms have developed to a point of relative equilibrium with their environment over, generally, very long periods of time, arbitrarily changing the traits of an organism is inevitably going to have unforeseeable results and ripple effects.

In a recent press release, the Swiss National Science Foundation reported that: “Just ten years ago, genetically modified cotton grew on 12% of all fields — today it is cultivated on over 80% of all cotton fields around the world. Bt cotton contains a gene of Bacillus thuringiensis, a species of soil bacteria. The plant uses it to produce a poison whose effects are fatal to the principal cotton pests — voracious caterpillars. However, certain types of bugs and other pests begin to spread across cotton fields instead, as is the case in China. The decline in the use of chemical pesticides may be partly responsible for this development, but it is probably not the only factor.”

“A team of researchers led by Jörg Romeis from the Agroscope Reckenholz-Tänikon Research Station has now identified a biological mechanism that offers an additional explanation for the increase in new pests in Bt cotton fields. Cotton plants have a sophisticated defense system. When caterpillars begin to nibble on them, they form defensive substances, so-called terpenoids. This spoils the appetite of not only the caterpillars, but of many other nibblers as well.”

“Cotton aphids generally do not cause severe agricultural damage because they succumb to their natural enemies out in the open. His results are therefore not relevant to farming, says Romeis. However, he has for the first time revealed an indirect effect of Bt cotton: the killing of the caterpillars also affects other plant-eating insects because the plants’ defence system remains inactive. Romeis now wants to investigate whether this effect is relevant to aphids only or also to the bugs that are creating problems for cotton farmers in China and in other cotton-growing regions of the world.”

Image Credits: © Lawo Nora, Agroscope ART

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