Genetically modified crops that produce insect-killing proteins from the bacterium Bacillus thuringiensis (Bt) have reduced reliance on insecticide sprays since 1996. These proteins are lethal to some devastating crop pests, but do not harm most other creatures including humans.
Yet, just as insects become resistant to conventional insecticides, they also can evolve resistance to the Bt proteins in transgenic crops.
To delay pest resistance to Bt proteins, the U.S. Environmental Protection Agency, or EPA, has required farmers to plant "refuges" of crops that do not produce Bt proteins near Bt crops. Refuges are planted with standard, non-Bt crops that pests can eat without ingesting Bt toxins.
Planting refuges promotes survival of susceptible pests. If susceptible pests greatly outnumber resistant pests, resistant individuals are unlikely to mate with each other and produce resistant offspring.
But how much refuge acreage is enough?
In an article appearing in the June 2012 issue of the Journal of Economic Entomology, authors Bruce Tabashnik from the University of Arizona and Fred Gould from North Carolina State University conclude the EPA should more than double the percentage of corn acres planted to mandated refuges to delay insect resistance, encourage integrated pest management, or IPM, and promote more sustainable crop protection.
To slow resistance in the western corn rootworm (Diabrotica virgifera virgifera), a beetle that is one of the most economically important crop pests in the U.S., the EPA currently requires 20 percent of the total acreage being set aside as refuges for corn producing one Bt protein (Cry3Bb1), and a 5 percent refuge portion for corn that simultaneously produces two different Bt proteins.
However, the authors note that this adaptable pest has rapidly evolved resistance to Cry3Bb1 in some areas of the U.S. Corn Belt. For Bt corn to remain effective aga
|Contact: Daniel Stolte|
University of Arizona