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Planet Earth

Genetically Modified Cotton Brings Back Nature's Pest Control: Predators

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AltLadybugAphid_300.jpg

A pest-eating ladybug attacks an aphid.

As angry debates

 about genetic modification continue, GM crops are quietly going about their business---and producing some positive side effects. In China, with Bt cotton reducing the need for insecticides, pest-eating bugs have rebounded and brought natural pest control with them. China’s genetically modified cotton is not new. Farmers used to spray their cotton with a protein, naturally produced by the Bacillus thuringiensis (Bt) bacteria, which is toxic to certain insects. As research into genetically modified crops advanced, scientists implanted the cotton itself with the Bt genes that code for production of the insect toxin, creating so-called “Bt cotton” and alleviating the need for the sprayed insecticide. Since China approved its use in 1997, Bt cotton has proved itself particularly effective against the cotton bollworm moth

, reducing the costs and side effects of spraying pesticides, but it has had may also decrease the number of non-pest insects compared with organic fields

. With the advent of Bt cotton, pesticide use became specialized, only affecting insects that both were vulnerable to Bt’s toxin and that fed on cotton, which allowed the populations of other insect species to rebound. Some of the now-thriving species, like mirids

, are pests, but others eat pests, and their recovery is making natural bug control possible. To see the overall effect, Chinese and French scientists crunched 20 years worth of information on insects at 36 crop-growing sites in northern China. Their data spans a period beginning in 1990, years before the first Bt cottonseeds hit the soil, and lasts until 2010, after the ecosystem had a chance to adjust to the modified cotton’s introduction. In a paper in the journal Nature

, the researchers describe how the resurgence of insect predators like ladybugs, lacewings, and spiders has reduced the population of aphids (a common cotton pest) in the Bt cotton plots. And even more impressive, the number of natural pest enemies in neighboring crops, consisting of non-transgenic corn plants, soybeans, and peanuts, has also gone up and driven the number of aphids down. Although this result is beneficial, it was not intended. The chain of influence---Bt cotton affected pesticide use, which affects predatory bugs, which affect pests---serves as a reminder that even small changes to an ecosystem can have far-ranging, unexpected consequences. [via The Scientist

] Image courtesy of Guoyue Yu / Nature

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