KNOXVILLE, Tenn. — Producers know actual field conditions are the final test for the claims of any crop protection product or technique. A University of Tennessee entomologist is studying Bt-resistant fall armyworms from the fields of Puerto Rico to identify how the insects develop Bt resistance.

“For years, researchers have used insects selected in the laboratory for Bt resistance,” said Juan Luis Jurat-Fuentes, associate professor of entomology and plant pathology. “Our research is different because we’re using insects that developed resistance to transgenic Bt corn in the field.”

His most recent research identifies how the armyworms actually resist Bt. “We think we have identified the insect’s mechanism of resistance to the Bt toxin,” said Jurat-Fuentes, whose lab includes Ph.D. students Siva Jakka and Liang Gong.

The mechanism they identified involves how the Bt toxin interacts with midgut cells in the resistant armyworms. “We believe that this is one of the first times that we have a gene that seems to be relevant to field resistance,” Jurat-Fuentes explained. The next step, he said, is to identify the specific gene altered in the resistant insects.

Resistance to Bt crops has emerged in India, China and Puerto Rico. Although cold temperatures prevent their northward movement, Bt-resistant fall armyworms from Puerto Rico are believed to migrate into Florida. This represents a risk to Southern growers.

“We know that resistant insects have changed their midgut proteins,” said Jurat-Fuentes. “If we can identify which genes are involved in these changes and their role in the intoxication process, then we can develop a specific method to detect these alterations so we can detect resistance in a field population.”

Once the gene linked to Bt-resistance is identified, a DNA assay could be developed. Such an assay could determine whether resistant insects are present in a field within a day or two. This would be a great improvement over current techniques to determine the presence of resistant insects.

Current techniques can take up to two months, as moths must be captured in the field with the subsequent caterpillar generations analyzed in a lab, Jurat-Fuentes said. A DNA assay will be much simpler and involve much less expense.

Producers adopting Bt crops have been mandated to plant non-Bt refuges to bolster populations of susceptible insects in their fields.

Susceptible insects emerging from these refuges mate with and dilute any resistant populations.

“Mathematical models and estimates support that the use of non-Bt refuges would render Bt crops effective for more than 20 years,” said Jurat-Fuentes. “However, we’re starting to see the first cases of field-evolved resistance, suggesting that some of the high-dose and refuge requirements have not been fulfilled.

“Companies are now developing new Bt crops containing different combinations of Bt toxins to reduce dependency on refuges and further delay resistance, while providing better control of the insects.”

Pinpointing the exact mechanism for resistance to Bt corn, he said, involves his lab’s two-pronged approach to research: “Ours is an effort, on the one hand, to try to understand how the Bt toxins work to make them more effective, and on the other hand, understand how insects change to become resistant so we can develop strategies to prevent or delay resistance from evolving.”

The forthcoming research traces back about four years, when Jurat-Fuentes obtained Bt-resistant fall armyworm caterpillars from Puerto Rico through USDA collaborators. His lab has since maintained at least 300 resistant armyworms directly descended from the first field-tested resistant caterpillars.

The research is part of a grant from the USDA National Institute of Food and Agriculture. A native of Spain who received his Ph.D. in Entomology from the University of Georgia, Jurat-Fuentes was also one of 18 researchers worldwide last year honored as a DuPont Young Professor, an honor awarding additional grant funds for researchers whose work shows promise. He joined the UT faculty in 2006.