Field-Evolved Resistance to Transgenic Crops

A report in the Information Systems for Biotechnology on the evolution of insect resistance to transgenic Bt crops was released by Bruce E. Tabashnik and colleagues from the University of Arizona and Iowa State University. The report answers the questions on how quickly insects evolve resistance to Bt crops and the effectiveness of planting refuges in delaying resistance. The authors reported that most insect pests targeted by Bt crops in Australia, China, Spain and the U.S. did not evolve resistance during the first decade the crops were grown, except for Helicoverpa zea.

Focusing on the resistance of H. zea against the Bt toxin Cry1Ac in cotton, the report explained that the resistance occurs in conventionally-sprayed crops as well as in the transgenic crops because the resistance is governed by a dominant gene. The evolution of resistance also depends on the size of the refugia - faster in states with lower refuge percentages. It is noteworthy that the negative effects of resistance will decline further as the acreage of cotton producing this Bt toxin decreases. In addition, the second generation of crops genetically-engineered for protection against insects offers greater diversity of toxins and more stable control.

For details, read the full report at: http://www.isb.vt.edu/news/2008/aug08.pdf