Farmers can plant Bt corn to get protection from an important pest of corn, the fall armyworm. But LSU AgCenter entomologist Fangneng Huang said populations of the pest in some areas have developed resistance to one type of Bt corn.

Bt corn, a transgenic crop, gets its name because it contains genes from a bacterium, Bacillus thuringiensis, which is a naturally occurring insecticide. This trait helps farmers control pests including the fall armyworm.

“The fall armyworm is the first corn pest to develop resistance to Bt corn,” Huang said.

Resistance to one commonly used, first-generation Bt corn product, which contains the Cry1F protein, was first documented in Puerto Rico, where seed corn is planted.

“We plant seed corn in Puerto Rico because it can grow year-round, but that means the insect can develop year-round,” Huang said. “It developed resistance in just three years after commercially planting Bt corn in Puerto Rico.”

The fall armyworm feeds on the vegetation and immature grains of corn. Huang is involved in a long-term study to evaluate the susceptibility of the fall armyworm to the second-generation Bt corn.

Second-generation Bt corn contains multiple Bt genes and offers better protection from fall armyworms.

He has collected armyworms from two sites in Louisiana, one in southern Florida and another in southern Texas.

“We suspect because the fall armyworm migrates, it moved from Puerto Rico to the eastern United States, and we could see some resistance in U.S. populations, especially in southern Florida,” Huang said.

The entomologist is looking at the frequency of Bt resistance in fall armyworms from each area. He said he is seeing a much higher frequency of resistance in the Florida population than in those from Louisiana and Texas.

He is using the resistant armyworms to evaluate new varieties of Bt corn to identify products that can overcome the resistance.

“We evaluate the resistant population against our new Bt corn,” Huang said. “The resistant population cannot survive on some of the new-generation Bt corn products.