LSU AgCenter entomologist Fangneng Huang has spent the last few years trying to get to the bottom of what is causing Cry1A and Cry2A toxin resistance in the fall armyworm and corn earworm. Progress is being made, but there is still a way to go.
“The fall armyworm and the corn earworm are the two most damaging pests being studied, but they’re not as dangerous to corn as they are to other crops,” Huang said. “Both can damage many different crops in Louisiana and other southern states.”
Huang says that this is becoming a bigger problem now than it was five years ago due to the resistance to the Cry proteins, which have been used for pest control for more than two decades in some cases.
Vip3A, an insecticidal protein produced during the vegetive stages of Bacillus thuringiensis, or Bt, has shown promise as the only fully active toxin expressed in transgenic crops to control the corn earworm in the United States.
Huang says multiple field trials in three years demonstrated that natural corn earworm populations in Louisiana were highly resistant to maize expressing Cry toxins only, but susceptible to all tested hybrids containing Cry and Vip3A genes combined.
Like the corn earworm, the fall armyworm, Spodoptera frugiperda, is a polyphagous pest, meaning it feeds on a variety of plants. In the Americas it is targeted by transgenic corn and cotton expressing Bt proteins. In 2021, the species, which typically shows up in the fall, arrived in Louisiana earlier than expected and has been a problem ever since for rice, soybean and sugarcane farmers.
During 2021 and 2022, a total of 23 fall armyworm populations were collected from seven U.S. southern states, including nine populations from the southeastern coastal region.
A previous study during the 2011-2013 period demonstrated practical fall armyworm resistance that caused field control problems of corn producing the Cry1F Bt protein in the southeastern seaboard of the U.S. The main objective of this study was to investigate the current susceptibility status to four Bt proteins commonly expressed in Bt corn plants, including Cry1F, Cry1A.105, Cry2Ab2 and Vip3A, in fall armyworm populations from the U.S. southern region.
Overall, the current study does not provide evidence of practical resistance in the fall armyworm to any of the four tested Bt proteins. The detected Cry1F susceptibility in the fall armyworm represents the first case of documented practical resistance to a Bt crop and has important implications for insect resistance management.
“We are collaborating with industry and other universities, so we will keep an eye out and monitor progress year by year,” Huang said.
Vip3A has shown promise as the only fully active toxin expressed in transgenic crops to control the corn earworm (seen here) in the United States. Photo by Fangneng Huang
The detected Cry1F susceptibility in the fall armyworm (seen here) represents the first case of documented practical resistance to a Bt crop. Photo by Blake Wilson
The LSU AgCenter and the LSU College of Agriculture