It seems that a common genetically modified crop is beginning to develop new insect enemies. This time, the insects have developed some form of evolutionary resistance to the weapon that such GM plants use for protection. Such is the case that scientists recently have seen from Bt cotton, a genetically modified crop altered to produce Bacillus thuringiensis or Bt toxins, which can kill some insects.
According to the ScienceDaily website, a new research report have documented the first known case of pest developing resistance towards Bt cotton. The pest that have evolved resistance to the insecticide produced by Bt cotton is the bollworm Helicoverpa zea with Bt resistant populations found in more than a dozen cotton crop fields in Arkansas and Mississippi sometime between 2003 and 2006.
The resistance to the toxins produced by Bt cotton was discovered when a team of entomologists from the University of Arizona analyzed the data taken from monitoring studies done on six major caterpillar pests of Bt crops in countries such as Australia, China, Spain and the US. The data that documented the bollworm developing resistance were initially collected seven years after the said GM crop was introduced in 1996.
According to Bruce Tabashnik, lead researcher and head of University of Arizona’s entomology department, "Resistance is a decrease in pest susceptibility that can be measured over human experience. "When you use an insecticide to control a pest, some populations eventually evolves resistance".
According to the team’s report, Bt cotton as well as Bt corn have been planted in over 162 million hectares or 400 million acres of land around the world since the Bt crops were introduced in 1996. The resistant bollworm is the first documented case of a pest developing field-evolved resistance to a Bt crop.
But the researchers also added that they have found most other caterpillar pests of cotton and corn still remain susceptible to the toxins produced by Bt crops. The only other case of pest involving field-evolved resistance was due to the use of Bt sprays which has been used for decades but now represent a small proportion of this type of insecticide used to control crop pests.
Despite the report showing a certain pest evolving resistance to Bt crops, the outcome of the data collected also refuted the claims of some experts that predicted of pests becoming more resistant to Bt crops in as few as three years. The Bt crop may still provide some advantages in that they help reduce the use of broad spectrum insecticides