Fall armyworms and corn borers have long been a concern for Louisiana corn growers. While farmers in the U.S. have planted transgenic Bt corn varieties since the 1990s to biologically control pests, staying ahead of their ability to develop resistance is a constant battle.
SU AgCenter entomologist Fangneng Huang is studying how insects become resistant to Bt corn, which refers to corn that is genetically modified to contain Bacillus thuringiensis proteins. These proteins are toxic to caterpillar pests such as corn borers and armyworms, enabling plants to kill the pests directly without the use of chemicals.
Bt corn is usually excellent against its target pests, Huang said.
"Those pests had been a problem in Louisiana, and now they are under control," he said. "The corn borer population has been low for a few years."
Maintaining that low population is a challenge, however. Like any other pest-control methods, Bt corn kills most pests but leaves behind a few that are resistant to the Bt proteins. As those remaining insects reproduce, they can develop a resistant population that is not susceptible to the Bt proteins.
Huang is working to identify effective ways that can delay resistance development. He hopes to determine exactly when populations become resistant and how to slow down resistance development.
Knowing this will help detect the possibility of resistance development in the field, Huang said, giving farmers time to take action. For example, they can spray pesticides or use other Bt corn products to control the Bt-resistant pests.
Meanwhile, scientists are constantly updating Bt corn varieties, Huang said. His efforts to understand how pests develop resistance is helpful in that Bt corn breeders will know which resistance genes last the longest and are most effective. They can also identify ideal gene pyramids, or multiple resistance genes, that are harder to overcome.
Resistance of fall armyworms to Bt corn is already an issue in Florida and North Carolina. The insect is a migratory pest that can move from the Caribbean islands into the U.S. mainland, Huang said. It is therefore important to study conditions in the Caribbean and around the U.S. to understand other factors that else may be influencing the worms' resistance.
Huang said about 76 percent of the corn grown in the U.S. in 2013 contains Bt proteins. Most of that corn is for feed grains and not human consumption.
Insect resistance management is critical for Bt corn to remain an effective pest control tool.
"Bt corn has been very effective in Louisiana so far,” Huang said. “Our goal is to have safeguards to ensure the long-term success of Bt corn products.”