Positive and negative externatilities of Bt corn

Evolution of resistance to Bt pesticides is a negative externality of Bt crops, but a recent paper in Science (DOI: 10.1126/science.1190242) has found that immediate pest control on non-Bt crops is a large positive externality.  The Bt corn growers also benefit from having non-Bt corn around to slow the evolution of resistance.

The New York Times reports Modified Corn Benefits Nearby Farmers, and Vice Versa:

A long-term study of corn production in the Midwest has found that the widespread use of varieties engineered with a bacterial gene that kills insect pests has had big benefits in adjacent fields of conventional corn — cutting infestations there and boosting farmers’ income by billions of dollars. The paper, “Areawide Suppression of European Corn Borer with Bt Maize Reaps Savings to Non-Bt Maize Growers,” is being published in the Oct. 8 edition of the journal Science.

According to the paper, maintaining “refuges” of conventional corn varieties helps prevent the corn borer from developing resistance to the engineered variety, and the yields in such areas — because of a combination of reduced insect damage and lower costs of the non-engineered seed — ensure that such plantings are profitable.

Last year, Andrew Pollack reported in The Times that a growing number of corn farmers were violating federal requirements to maintain 20 percent of fields in conventional corn varieties. The new study says that any shift to wall-to-wall Bt corn is bound to backfire and makes little economic sense, Hutchison said.

A separate analysis of the new research in Science, written by Bruce E. Tabashnik, an entomologist at the University of Arizona, describes another approach to fighting insect resistance, in which farmers — instead of setting aside certain areas as refuges — buy a seed mix blending both engineered and conventional corn varieties. He said this could be the ideal way to maximize corn production in developing countries where small farm plots still predominate.

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