Five of 13 major crop pests studied have shown resistance to genetically engineered corn and cotton crops, according to a research review from the University of Arizona.

Researchers are looking to put additional insight on genetically modified technologies. The researchers reviewed data from 77 studies on 13 pest species on five continents.

They evaluated field monitoring data for resistance to crops engineered to produce insecticidal proteins derived from Bacillus thuringiensis. The Bt protein can be engineered into crops, but also is a component of spray solutions used by organic farmers to kill pests.

The researchers found evidence of resistance to the Bt in five pests, and three of the five were in the United States. Most recently, rootworms showed resistance to Monsanto's rootworm-control corn in at least two states, according to the Environmental Protection Agency. At the same time, armyworms in Puerto Rico and maize-stem borers in South Africa also developed a resistance to the Bt corn, researchers said.

Pink bollworms in India and bollworms in the United States have in some instances developed a resistance to Bt cotton, they said.

"When risk is indicated, either take more stringent measures to delay resistance, such as requiring larger refuges, or this pest will probably evolve resistance quickly to this Bt crop," Bruce Tabashnik, a University of Arizona entomologist and the paper's lead author, said in a statement accompanying the study.

A lengthy description of the research can be read here and a link to read the abstract and possibly buy a copy of the study is here.