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According to a US study, the insecticide produced by genetically modified corn Bt, widely used in the United States, would also act on the insects of rivers, including via pollen.

In the saga of GMOs , here is a new episode where scientists bring evidence. A group of researchers led by Indiana University’s Todd V. Royer investigated the effects of Bt corn on aquatic ecosystems . Genetically modified, this cereal has a gene from the bacterium  Bacillus thuringiensis, which causes the production by corn of a substance that is toxic to insects , to reduce the amount of insecticides spread in the fields.

Between 2005 and 2006, the team combed through twelve rivers in the state of Indiana to understand what became of the inputs of plant products emitted by cornfields: pollen but also leaf debris and debris. ears. Their results are published this week in the Proceedings of the National Academy of Sciences ,  Proceedings of the National Academy of Sciences.

An effective insectide

The first observation is that these products reach well in the rivers bordering the cornfields. The second is that insects living in these waters, trichoptera, ingest these plant debris, found in their digestive system. The third is more disturbing. In the laboratory, caddisflies fed on plant material derived from Bt corn showed a growth rate that was half that of animals fed only with normal maize. As long as the proportions of Bt maize are two to three times higher than those found in the streams studied by the team, mortality of caddisflies increases considerably. Researchers indicate that, from one river to another, the quantities of Bt maize vary enormously. But in other states, like Iowa and

Why have these consequences not already been observed? Before the marketing of Bt maize in 1996, the researchers explain, tests were carried out to estimate the effect on aquatic fauna but they were conducted on daphnia. These animals are crustaceans , and therefore quite far from insects. It is not surprising that Bt toxin has more effect on trichoptera. The impact of the vast areas of crops of this insecticide-producing corn could therefore be larger than expected on aquatic ecosystems.

Dr. Kanika Singla

Ph.D., IARI Postdoctoral Scholar, UC Berkeley

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