The surprising finding is good news for the environment. Arizona farmers who plant the biotech cotton known as Bt cotton use substantially less chemical insecticides than in the past.
Insect pests sometimes evolve resistance to such chemicals in just a few years, a fate that was predicted for biotech crops genetically altered to produce Bt toxin, a naturally occurring insecticide.
"This is the most complete study to date for monitoring resistance to Bt crops," said team leader Bruce E. Tabashnik, the head of UA's department of entomology, a member of UA's BIO5 Institute and an expert in insect resistance to insecticides.
"We found no net increase in insect resistance to Bt. If anything, resistance decreased. This is the opposite of what experts predicted when these crops were first commercialized." He added, "I'm definitely surprised."
Tabashnik, Timothy J. Dennehy, a UA Distinguished University Outreach Professor of Entomology and extension specialist and a member of BIO5, and Yves Carriere, UA associate professor of entomology, will publish their research in an upcoming issue of the Proceedings of the National Academy of Sciences.
Bt cotton has been planted in Arizona since 1996. Now more than half of the state's 256,000 acres of cotton fields are planted with the biotech plants. Without the protection provided by Bt cotton, some fields can have 100 percent of plants infested with pink bollworm caterpillars, which live inside the cotton boll, destroying the crop.
Dennehy said, "In an extreme infestation, you can have every single boll in the field infected." The caterpillars eat the seeds and damage the developing cotton fibers.
In contrast, when the caterpillars eat Bt cotton, they die.
Before the use of Bt cotton became widespread, pink bollworm was one of t
Source:University of Arizona