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Small farms in developing countries that embrace genetically modified (GM) maize could benefit from planting a mixture of GM and non-GM maize seeds, according to a leading GM crop scientist.

Such plantations would reduce losses to pests, through the GM maize, and slow down the development of pest resistance to GM maize through the 'refuges' where ordinary maize is planted, Bruce Tabashnik, an entomologist from the University of Michigan, United States, wrote in Science last week (8 October).

He was commenting on findings, published in the same issue of Science, that planting GM maize alongside non-GM crops can significantly decrease pest damage in both crops.

The transgenic maize has been engineered to express a toxin from the bacterium Bacillus thuringiensis (Bt) to fend off the European corn borer moth (Ostrinia nubilalis). Female moths cannot distinguish between the two types of maize and so lay eggs on both. But caterpillars that hatch on GM crops die, reducing the overall population of the pests in the area.

Although this has been reported before, this is the first study to show that it can have substantial economic benefits to non-GM farmers, based on long-term and large-scale data. Since GM maize was introduced in the United States in 1996 it has saved money for both GM farmers and non-GM growers, saving US$4.3 billion for the latter across five US states investigated.

"Before Bt introduction there were 59 moth larvae per 100 plants in Minnesota. However, when Bt corn levels reached 40 per cent [of maize planted in an area], it dropped to just 16 per 100," lead author William Hutchison, head of the department of entomology at the University of Minnesota, United States, told SciDev.Net.

He added that the same technique could be beneficial to developing countries. This could have the effect of "doubling or tripling the yields of small farmers [within 5–6 years]," he said.

Jörg Romeis, senior scientist at Agroscope, an agricultural research institute in Switzerland, called the finding a "very positive, valuable result" but warned that it has to be carefully managed, citing difficulties with Bt cotton in China. "The major pest was controlled and so the farmers stopped spraying insecticides," he told SciDev.Net. "New plant bugs then filled the niche left behind."

But, if done right, "the positive effects seen in the United States and China with Bt might also work in places like Burkina Faso where adoption is quite high now", Romeis added.

However, Hossein Azadi, a food security and land use expert at the University of Ghent, in Belgium, told SciDev.Net that the benefits of introducing GM crops should be assessed on a "case by case, country by country" basis.

Link to full study in Science [722kB]

Link to full perspective article in Science 286kB]


Science 330, 222 (2010)

Science 330, 189 (2010)