Fangneng Huang, an LSU AgCenter entomologist, has spent years documenting the resistance of the corn earworm and fall armyworm to Bt corn and cotton, crops that have been developed to protect against certain insect pests.

Bt crops have been enhanced through biotechnological methods to include protection from a naturally occurring microorganism, Bacillus thuringiensis, that targets caterpillars in the order of Lepidoptera, according to the U.S. Department of Agriculture Agricultural Research Service.

However, in recent years the fall armyworm and corn earworm have developed resistance to Cry proteins vital to this protection. These include Cry1A, Cry2A and Cry1F. Because of the resistance, Huang is searching for other means to control these Bt-resistant pest populations.

“Those two insects have developed resistance to Bt corn and Bt cotton, particularly for some of the Cry genes — especially for the corn earworm populations in Louisiana and other southern states in the United States,” Huang said. “The corn earworm has developed a high level of resistance to Cry Bt cotton. This is very much a problem. We want good insecticides for application to control the Cry-resistant pest populations.”

Huang’s research supported by the Louisiana Soybean and Grain Research and Promotion Board focuses on how susceptible or resistant the corn earworm and fall armyworm are to common insecticides. The studies focus on corn and grain sorghum.

“We do not have other technology available at this point,” he said. “That is why we are working on the chemical insecticides.”

Research on insecticide susceptibility for these pests in Louisiana is more than 15 years old, Huang said, and some new insecticides have become available since the last studies in Louisiana.

“So far, our results have shown that resistance of the armyworm in our state and in neighboring states is very common to some of the insecticides we have evaluated, and also there are some good insecticides that are effective,” he said. “On the other hand, most insecticides we have tested are very effective against the corn earworm populations in this state.”

There is a wide variety of susceptibility and resistance depending on local populations of the insects, Huang said. Huang is studying the resistance to insecticides in Louisiana and in neighboring states.

“There are a few populations that really show a relatively high level of resistance to some of the chemicals, particularly for the fall armyworm,” he said. “For the corn earworm, basically, the insecticides are pretty good.”

Huang expects to have results available in the next year.

Huang continues to study insects’ resistance to the common Bt toxins, the Cry proteins. He is completing research on an exciting development now. A decade ago, his lab found that fall armyworm populations from Florida were highly resistant to Cry1F corn, a common Bt corn trait expressing the Cry1F protein, but the lab’s current tests show that the populations from the same locations are now susceptible to the common Bt proteins expressed in corn and cotton that target caterpillars, including the fall armyworm.

“The reversed Cry1F susceptibility in the fall armyworm identified in this study represents the first case of documented resistance reverting to susceptible status in Bt crop-insect systems, and thus has important implications for Bt crop resistance management.” Huang said.

“That is very good news,” he added. “The resistance is just cured. We are working on the manuscript now, and it is going to be published soon.”