(Beyond Pesticides, November 21, 2014) Researchers of a new study published on Monday find increased resistance in the fall armyworm to Bacillus thuringiensis (Bt)-incorporated genetically engineered (GE) maize in the southeastern region of the U.S., calling this evolution of insect resistance to transgenic crops âa serious threat to the sustainability of this technology.â
The pest was found to be resistant to a toxin derived from Bacillus thuringiensis, or Bt, which is inserted into seeds. Bt is a naturally-occurring soil bacterium that, when used in non-genetically engineered forms, is an important biological pesticide for organic and sustainable farmers. This study is just one of many that show increasing insect resistance to Bt crops, which are produced by Dow and DuPont, but is the first to document field resistance related to the reduced efficacy of Bt maize in a lepidopteran pest in the mainland U.S.
The study, âCry1F Resistance in Fall Armyworm Spodoptera frugiperda: Single Gene versus Pyramided Bt Maize,â led by Fangneng Huang, Ph.D., an entomologist at Louisiana State University, finds that the fall armyworm has exhibited increased resistance to the Bt subspecies Cry1F protein. When expressed, the protein controls larvae from an order of insects known as Lepidoptera, which includes pests such as the European corn borer, southwestern corn borer, and black cutworm, as well as beneficial organisms such as butterflies and moths. Armyworms can plague farmers in many parts of the U.S., but these resistant insects have been documented only in some areas of Florida and North Carolina. The range of these resistant armyworms is unknown, researchers said.
The researchers recommended that farmers should plant more non-GMO corn as a refuge and possibly increase the use of pesticides to control the resistance.
Newer types of Bt corn with multiple modes of action are still showing effectiveness, Dr. Huang said. He added, “We don’t know how long they can last.â
Dr. Huangâs uncertainty is not only suggested by the results of his most recent study, but is also supported by a growing literature of cross-resistance in regards to other resistant insects.Â A 2013 study,Â Â âPotential shortfall of pyramided transgenic cotton for insect resistance management,â by Thierry BrĂ©vaul, Ph.D., and colleagues found that stacking severalÂ Bt-incorporated traits does not stop resistance. Researchers assumed that caterpillars resistant to the firstÂ BtÂ toxin would survive on the one-toxin plants, but die when consuming two-toxin plants because they had not yet developed resistance to the new formulation. However, caterpillars selected for resistance to one toxin survived significantly better than caterpillars from a susceptible strain.
Several additional studies have documented growing insect resistance to Bt maize. In 2011, the study âField-Evolved Resistance toÂ BtÂ Maize by Western Corn Rootworm,âÂ led by Aaron Gassmann, Ph.D., verified the first field-evolved resistance of corn rootworm, from the order Coleoptera, Â to aÂ BtÂ toxin, Cry3Bb1. The study found the western corn rootwormâs ability to adapt is strongest in fields where BtÂ corn is planted for three consecutive years and suggests that insufficient planting of refuges contributes to the problem. This study was cited by a group ofÂ 22 prominent entomologistsÂ who submittedÂ formal comments to the U.S. Environmental Protection Agency (EPA)Â on their concerns about the viability of Cry3Bb1 corn. In January 2013, EPA concluded that, âCorn rootworm may not be completely controlled by Cry3Bb1 in certain parts of the corn belt.â However, after this release, EPA did little to mitigate resistance beyond announcing that Monsanto had committed to conducting grower education programs demonstrating the value of crop rotation.
Other consequences related to growing insect resistance to GE technology include an increase in insecticide use. According to a report by theÂ Wall Street JournalÂ in 2013, insecticide sales soaredÂ in 2013 as target insects have developed resistance to genetically engineered insecticide-incorporated crops. Pesticide manufacturers American Vanguard, FMC Corp, and Syngenta have all reported higher sales in 2012 and 2013 than in previous years. Syngenta alone reported doubling sales in 2012. Similarly, American Vanguard reported soil insecticide revenues rose by 50% in 2012.
Beyond Pesticides believes that whether it is the incorporation into food crops of genes from a natural bacterium (Bt) or the development of an herbicide-tolerant crop, the GE approach to agriculture and pest management is short sighted and dangerous. There areÂ serious public healthÂ andÂ many other problemsÂ associated with GE crops. The failure of EPA to properly exercise its authority to regulate the plant-incorporated protection used in Bt corn products is unacceptable. Further delay on EPAâs part to implement refuge requirements and compliance activities that seek toÂ preserve the efficacy of Bt corn products and extend their utility in the field will result in undue adverse environmental, human health, and economic consequences, as well as undermine the use of Bt as a biological pest management tool in organic production.
For more information on the hazards associated with GE technology, visit Beyond PesticidesâÂ Genetic Engineering webpage.
All unattributed positions and opinions in this piece are those of Beyond Pesticides