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Science: Planting Both GM and Unmodified Crops Pays Off
Fourth- and fifth-stage European corn borer larvae commonly tunnel into corn stalks. The tunneling can disrupt the flow of water and nutrients between the roots and the growing parts of the plant.
[Image © Science/AAAS]
Genetically modified (GM) corn plants can reduce damage to other neighboring, unmodified crops too—and farmers who plant both types of crops are experiencing the economic benefits, researchers say this week in Science. This finding comes after William Hutchison from the University of Minnesota, along with colleagues from across the United States, studied the effects that genetically engineered corn has had on European corn borer moths in the United States over the years.
The corn borer moths are devastating pests that were accidentally introduced to the Midwestern United States in 1917. Each year, the insects are estimated to cause approximately $1 billion dollars in crop losses in that region. The modified corn under scrutiny in the study was engineered to express insecticidal proteins from the bacterium Bacillus thuringiensis (Bt), which are known to kill a variety of insect pests.
Hutchison and his team of researchers found that this Bt-expressing corn, which has become widely adopted in U.S. agriculture over the past decade, generally reduces populations of the corn borer moths so that both Bt-expressing corn and non-Bt corn both benefit from fewer insect pests. In this way, the researchers suggest that non-Bt corn pays off because farmers are spared the increased price of Bt seed, even though they still receive some pest control from the neighboring Bt corn.
Their report is published in the 8 October issue of the journal Science.
“About five or six years ago, there was a lot of anecdotal or local on-farm observations indicating that European corn borer suppression was occurring, and the natural hypothesis was that it could be due to the increased use of Bt corn,” Hutchison said. “Fortunately, via the work of many university and Department of Agriculture colleagues over the past 50 years, we had huge data sets to evaluate with a ‘before and after’ retrospective analysis. Using some standard population growth rate analyses, we were able to tease out the Bt corn effect from other sources of natural mortality, such as weather, predators, pathogens, and other natural enemies affecting European corn borer moths.”
Hutchison and his colleagues, however, warn that too many Bt crops in one area could promote strong resistance among the moths to the insecticidal proteins. They highlight the need for “refuges” of unmodified crops in order to temper such resistance in the pests—a strategy that the U.S. government already requires of farmers.
The researchers say that the economic benefits of these refuges can equal or exceed the benefits of Bt corn, and that the best strategy for the long term seems to be growing both types of corn at the same time. They suggest that, over the past 14 years, the states of Illinois, Minnesota, and Wisconsin have saved approximately $3.2 billion by growing both types of corn simultaneously, and that Iowa and Nebraska have saved an approximate total of $3.6 billion doing the same thing.
“When female European corn borer moths seek corn to lay their eggs, they cannot distinguish between the Bt and non-Bt plants. If 80% of a farm is [planted with] Bt corn—with more-or-less random dispersal of the moths—then roughly 80% of the eggs will be laid in the Bt field and 20% will be laid in the non-Bt field,” said Hutchison. “Virtually all of the larvae hatching on the Bt plants will die, leaving only moths in the non-Bt field to emerge and contribute [their genes] to the next generation of moths, which in turn will lose another 80% of their progeny. So, with two generations of corn borer moths per year in most states and the continued high efficacy of Bt corn, it is easy to conceptualize a continued population decline over time... ”
7 October 2010