GM Corn Showing Diminishing Impact On Controlling Insect Pest

shutterstock_187491845One of the main objectives of cultivating GM crops is better pest control. The crops are genetically modified in order to create toxins that can guard them against insect pests. Others are genetically modified to withstand the effects of being bombarded by powerful herbicides. In both cases, GM crops stand to be better than traditional crops in the most ideal of situations. But certain studies have shown that GM crops are not actually that invincible as its makers say them to be. One example involves a study that suggests GM crops may not be able to maintain its impact on controlling pests over a certain period of time.

Researchers from the North Carolina State University and Clemson University have discovered that a type of toxin widely used in GM crops is having a diminishing impact on the crop pest corn earworm (Helicoverpa zea). It mirrored the warnings scientists made 20 years ago which went largely ignored. The study may send warning signals for biotech companies to pay closer attention to the warning signs in the development of the growing resistance by pests to GM crops.

GM corn is genetically engineered to create a Bacillus thuringiensis (Bt) protein that, in turn produces a toxin called Cry1Ab. This toxin was used to initially protect corn against the European corn borer (Ostrinia nubilalis). It was introduced in the market in 1996. By the late 1990’s, scientists discovered that the toxin is having little impact on H. zea. The scientists predicted that there were enough H.zea surviving the toxin that the species will eventually develop a resistance to Cry1Ab. The work was done in part by Fred Gould, an entomology professor at NC State University.

After 15 years later, another scientist from the same university wanted to find out if Gould’s predictions were becoming true. According to Dominic Reisig, an entomology professor at NC State and lead author of the said study, “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,”

Along with study collaborator Francis Reay-Jones of Clemson University, Reisig evaluated corn crop fields in both North and South Carolina for a period of two years and determine whether the effects of the Cry1Ab toxin is still effective against corn pests.

In the 1990’s, the Cry1Ab in Bt corn effectively reduced the number and size of the H.zea larvae better compared to non-Bt corn. But with current studies, the scientists found out that the said toxin has little or no effect on the number or size of H. zea larvae when compared to non-Bt corn.

Reisig notes, “There was a warning that zea could develop a resistance to this toxin. But no changes were made in how to manage Cry1Ab, and now it appears that zea has developed resistance.” However, Reizig also says that they cannot definitively say that H. zea has developed resistance to the said toxin since it was a field study and not an experiment in a laboratory setting that made use of pure Cry1Ab for testing.

Reisig explains, “Our focus was on determining if there were real-world effects, and there were. This may also explain why zea – a significant cotton pest – is becoming less responsive to a related toxin used in GM cotton called Cry1Ac.”

Reisig further states, “These findings are a reminder that we need to pay attention to potential clues about developing resistance. We can’t expect there to always be a new GM toxin available to replace the old one.”

Source: GM Watch

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