(Beyond Pesticides, February 16, 2012) Newly released data indicates that more than 40% of American farmers who planted certain varieties of genetically engineered (GE) corn in 2011 failed inspections to verify compliance with mandatory management practices to prevent insect resistance. The farmers involved planted corn varieties that are genetically engineered to express toxins that kill western rootworm. The toxins are derived from Bacillus thuringiensis (Bt), a naturally occurring soil bacterium that when used in non-genetically engineered forms is an important pesticide for organic and sustainable farmers. The non-compliant farmers were specifically cited for failure to establish adequate refuges of non-Bt corn on their farms that the U.S. Environmental Protection Agency (EPA) has determined are necessary to prevent the western rootworm from developing resistance to all forms of Bt.
Originally reported on February 9, the results are derived from GE Bt seed suppliers who are required to report refuge data to EPA. As a condition of registering Bt seed varieties as pesticides, EPA requires that farmers using them also plant an appropriately-sized refuge of non-Bt varieties adjacent to the genetically engineered crop. In theory, western rootworms that develop resistance to Bt through constant exposure to the toxins in the genetically engineered varieties will mate with non-resistant rootworms that are harbored in the refuge. This crossbreeding is intended to reduce the likelihood that the genes that impart resistance will be successfully transferred to the succeeding generations of the pest.
Organic and sustainable agriculture researchers and advocates have long warned that the EPA’s refuge requirements and other preventive measures are inadequate to prevent resistance from rapidly emerging once Bt corn became planted widely. Alternating between Bt and non-Bt varieties and planting varieties that express different Bt toxins are the other primary management tools for delaying the onset of resistance. While slightly more than one million acres of Bt corn were planted in 1996, that number rose to nearly 50 million acres in 2008. Cumulatively, more than 280 million acres of Bt corn and 75 million acres of Bt cotton were planted in the United States between 1996 and 2008.
In 2011, entomologists at Iowa State University published a study verifying the first field-evolved resistance of corn rootworm to a Bt toxin. The researchers documented resistance to the Bt toxin Cry3Bb1, which has been inserted into nearly one third of the corn planted in the United States.
The study found the western rootworm’s ability to adapt was strongest in fields where Bt corn was planted for three consecutive years and suggested that insufficient planting of refuges may have contributed to the resistance. The study concluded that, “Even with resistance management plans in place, sole reliance on Bt crops for management of agriculture pests will likely hasten the evolution of resistance in some cases, thereby diminishing the benefits that these crops provide.”
The data documenting the widespread failure of farmers to plant refuges as required was compiled by the Agricultural Biotechnology Stewardship Technical Committee (ABSTC), which represents Bt seed suppliers including Monsanto, Syngenta AG, Dow Chemical and DuPont. The 41% non-compliance rate was based upon 3,053 farm inspections and represented a nearly threefold increase from the 15% rate which ABSTC reported in 2010. The American Corn Growers Association attributes the higher incidence of non-compliance to increased monitoring of sales records that identified farmers who did not appear to purchase the quantities of non-Bt varieties to plant suitable refuges. The EPA mandated that seed suppliers enhance their refuge enforcement activities as a condition of re-registering Bt corn varieties. Farmers who were found to be deficient with their mandatory resistance management practices will be visited at least twice over the next five years by their seed supplier and may lose access to Bt varieties should they fail a follow-up inspection.
The higher rates of non-compliance with refuge responsibilities now being reported by ABSTC are more consistent with previous findings of the Center for Science in the Public Interest. Using EPA data obtained through the Freedom of Information Act, the Center determined that American farmers maintain refuge compliances rates in excess of 90% between 2003 and 2005. However, the Center determined that non-compliance spiked to 25% in 2008 and affected more than 13 million acres altogether. The Center also notes that as Bt corn varieties take over a greater share of the market (reaching 57% in 2008), the likelihood that coincidental non-Bt refuges on neighboring farms could help delay resistance grows less and less probable.
The Western corn rootworm is a potentially devastating pest that does its greatest damage during its larval stage by feeding upon the plant’s roots. Severe feeding inhibits the plant’s ability to absorb moisture and nutrients and opens a pathway for attack from soil-borne pathogens. Before monoculture production became standard practice for many farms, the western rootworm could be effectively managed by crop rotations, including pasture, hay and legume crop components because the insect starves in fields not planted in corn.
For more on genetically engineered agriculture, read Beyond Pesticides’ article “Ready or Not, Genetically Engineered Crops Explode on Market.”
Source: Bloomberg Business Week
All unattributed positions and opinions in this piece are those of Beyond Pesticides.