Study shows how GM crops can have diminishing success fighting off insects

A new study from North Carolina State University and Clemson University finds the toxin in a widely used genetically modified (GM) crop is having little impact on the crop pest corn earworm (Helicoverpa zea) – which is consistent with predictions made almost 20 years ago that were largely ignored. The study may be a signal to pay closer attention to warning signs about the development of resistance in agricultural pests to GM crops.

At issue is genetically engineered corn that produces a Bacillus thuringiensis (Bt) protein which, in turn produces a toxin called Cry1Ab. This GM corn was originally designed to address a pest called the European corn borer (Ostrinia nubilalis) and went on the market in 1996.

In the late 1990s, scientists found that Cry1Ab was also fairly affective against H. zea. But the scientists also predicted that enough H. zea were surviving to lead to the species developing resistance to Cry1Ab. That work was done, in part, by Fred Gould, an entomology researcher at NC State.

More than 15 years later, another NC State researcher wanted to see if Gould’s predictions held up.

“We wanted to do an observational study in the field to see how, if at all, things have changed since the work done in the ’90s – was there any indication that zea was becoming resistant,” says Dominic Reisig, an associate professor of entomology at NC State and lead author of a paper describing the new study.

Reisig and his collaborator, Francis Reay-Jones of Clemson, evaluated corn crop sites in both North Carolina and South Carolina over two years – and the results were fairly stark.

In the late 1990s, Cry1Ab reduced both the number of H. zea larvae and the size of the larvae, compared to non-Bt corn. But Reisig and Reay-Jones found that Cry1Ab now has little or no effect on number or size of H. zea larvae compared to non-Bt corn.

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