Pests Are Adapting To GM Crops In Unexpected Ways
June 21, 2012

Pests Are Adapting To GM Crops In Unexpected Ways

Brett Smith for

Modern science is no match for Mother Nature when it comes to agriculture, a new research paper has revealed.

The report, published in the Proceedings of the National Academy of Sciences by a team of scientists, showed that pests are adapting faster than expected to the genetically modified (GM) crops that have been altered to repel them.

Many GM crops were originally created to reduce the amount of pesticides used to repel the insects and larvae that feed on their naturally occurring counterparts. Scientists accomplished this in some plants by engineering them to produce toxins derived from the bacterium Bacillus thuringiensis, or Bt, which kill certain insect pests but are harmless to most other creatures including humans.

As expected, initially rare genetic mutations that conferred toxin resistance in these pests became more common. This allowed a growing number of pest populations to adapt to the GM crops.

"Scientists expected the insects to adapt, but we're just finding out now how they're becoming resistant in the field," said one of the study´s co-authors Bruce Tabashnik, head of the department of entomology at the University of Arizona.

One strategy used to combat the pest adaption mechanism was the creation of refuges. Refuges involve planting crops that do not have a Bt toxin gene. This allows for insects that are susceptible to the toxin to mate with resistant insects. The genetic dilution would then decrease the chances that any toxin-resistance would not be passed along to future populations of insects.

However, the refuge strategy turned out to be far from foolproof. The initial problem with using refuges is that, by its very nature, it eliminates the possibility of pest eradication.

The latest study reported another problem – as the research team identified two unrelated, dominant mutations in the field populations. This means that one copy of the genetic variant is enough to confer resistance to Bt toxin. This renders the refuge technique irrelevant since an insect carrying a dominant resistance gene can mate with a non-resistant insect and produce resistant offspring.

"Dominant resistance is more difficult to manage and cannot be readily slowed with refuges, which are especially useful when resistance is recessive," Tabashnik said.

The Arizona scientist praised the field work he and his colleagues did in the study and said he was optimistic that it will be used to enhance the potential of GM crops.

"We have been speculating and using indirect methods to try and predict what would happen in the field,” Tabashnik said.

“Only now that resistance is starting to pop up in many places is it possible to actually examine resistance in the field. I think the techniques from this study will be applied to many other situations around the world, and we'll begin to develop a general understanding of the genetic basis of resistance in the field."

Huge sums of money are at stake with respect to the use of GM crops, which have been around since the mid 90s. In 2011, farmers planted 160 million acres of Bt cotton and Bt corn worldwide.