THIRD WORLD NETWORK BIOSAFETY INFORMATION SERVICE
Dear Friends and Colleagues
Fall armyworm shows high resistance to Bt maize in the U.S.
A new study has produced “compelling evidence” of resistance of fall armyworm in some southeastern U.S. farms to maize genetically modified (GM) with Bacillus thuringiensis (Bt) genes to kill them.
The study found that field populations of the fall armyworm (Spodoptera frugiperda) exhibited a high level of resistance to Bt maize expressing the Cry1F toxin. The researchers postulate that the occurrence of Cry1F resistance in U.S. mainland populations of S. frugiperda likely represents migration of insects from Puerto Rico, which is an indication of the great challenge in achieving effective resistance management for long-distance migratory pests like the fall armyworm.
They describe the evolution of insect resistance as “a great threat” to the long-term sustainability of the GM crop technology. The three-year study was conducted by researchers from Louisiana State University, North Carolina State University, the University of Florida, the University of Minnesota, the University of Georgia and the U.S. Department of Agriculture.
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Cry1F Resistance in Fall Armyworm Spodoptera frugiperda: Single Gene Versus Pyramided Bt Maize
Huang F, Qureshi JA, Meagher RL Jr, Reisig DD, Head GP, et al. (2014) PLoS ONE 9(11): e112958. doi:10.1371/journal.pone.0112958
http://www.plosone.org/article/info%3Adoi%2F10.1371%2Fjournal.pone.0112958
Abstract
Evolution of insect resistance to transgenic crops containing Bacillus thuringiensis (Bt) genes is a serious threat to the sustainability of this technology. However, field resistance related to the reduced efficacy of Bt maize has not been documented in any lepidopteran pest in the mainland U.S. after 18 years of intensive Bt maize planting. Here we report compelling evidence of field resistance in the fall armyworm, Spodoptera frugiperda (J.E. Smith), to Cry1F maize (TC 3507) in the southeastern region of the U.S. An F2 screen showed a surprisingly high (0.293) Cry1F resistance allele frequency in a population collected in 2011 from non-Bt maize in south Florida. Field populations from non-Bt maize in 2012–2013 exhibited 18.8-fold to >85.4-fold resistance to purified Cry1F protein and those collected from unexpectedly damaged Bt maize plants at several locations in Florida and North Carolina had >85.4-fold resistance. In addition, reduced efficacy and control failure of Cry1F maize against natural populations of S. frugiperda were documented in field trials using Cry1F-based and pyramided Bt maize products in south Florida. The Cry1F-resistant S. frugiperda also showed a low level of cross-resistance to Cry1A.105 and related maize products, but not to Cry2Ab2 or Vip3A. The occurrence of Cry1F resistance in the U.S. mainland populations of S. frugiperda likely represents migration of insects from Puerto Rico, indicating the great challenges faced in achieving effective resistance management for long-distance migratory pests like S. frugiperda.
Nov 17 (Reuters) – Crop-devouring armyworms are showing increasing resistance in some U.S. farm fields to a popular type of genetically modified crop that should kill them, scientists said on Monday.
The evolution of insect resistance "is a great threat" long- term to the sustainability of the GMO crop biotechnology that has become a highly valued tool for many U.S. farmers, according to Fangneng Huang, an entomologist at Louisiana State University (LSU) and lead researcher for a three-year study.
The study was published on Monday in the PLOS One online journal (http://www.plosone.org) for peer-reviewed research, after being presented at the Entomological Society of America annual meeting in Portland, Oregon.
The research documents resistance by fall armyworms in the southeastern United States to the Cry1F protein found in many corn products developed Dow AgroSciences and DuPont to fight off the destructive pests.
It is the latest evidence in recent years showing that insects are developing resistance to crops that have been genetically modified to kill them.
Like the "super weeds" that have developed resistance to glyphosate-based herbicide and make it harder for farmers to keep fields from being overrun with weeds, the armyworms are starting to devour corn crops that should repel them, said Dominic Reisig, an entomologist at North Carolina State University.
Armyworms can be a problem for farmers in many U.S. states, but the resistant armyworms have been documented only in some areas of Florida and North Carolina. The range of these resistant armyworms is unknown, researchers said.
They said farmers should plant more non-GMO corn as a refuge and possibly increase the use of pesticides to control the resistance.
Dow and DuPont did not respond to requests for comment.
The GMO corn at issue contains Bacillus thuringiensis (Bt) genes. Bt corn, popular with farmers throughout the Americas, has been on the market roughly 18 years. Newer types of Bt corn with multiple modes of action are still showing effectiveness, Huang said.
"We don’t know how long they can last," Huang said.
Researchers have also expressed concerns about Bt resistance in western corn rootworm.
The study was conducted by researchers from LSU, North Carolina State University, the University of Florida, the U.S. Department of Agriculture, the University of Minnesota and the University of Georgia.
Financial support came in part from USDA.