There’s a new paper in this week’s issue of Science that suggests that growing a landscape mixed with genetically modified (GM) Bt corn and non-GM hybrid varieties of corn can be mutually beneficial to all corn farmers.
Why? They argue that the populations of GM corn knock down the populations of insect herbivores enough that, on a landscape scale, this effect spills over to nearby farmers growing non-GM corn, which raises yields and profits:
[W]e estimate that cumulative benefits for both Bt and non-Bt maize growers during the past 14 years were almost $6.9 billion in the five-state region (18.7 million ha in
2009)—more than $3.2 billion in Illinois, Minnesota, and Wisconsin, and $3.6 billion in Iowa and Nebraska. Of this $6.9 billion total, cumulative suppression benefits to non-Bt maize growers resulting from O. nubilalis [European corn borer] population suppression in non-Bt maize exceeded $4.3 billion—more than $2.4 billion in Illinois, Minnesota, and Wisconsin, and $1.9 billion in Iowa and Nebraska—or about 63% of the total benefits.
They suggest that the populations of non-GM corn also benefit the Bt corn farmers because the non-GM corn maintains a genetically diverse population of insects, helping prevent the evolution of herbivores resistant to Bt corn.
These results are interesting and —if they hold—could be an example of how GM crops bring environmental and social benefits. A good outcome for all.
However, there are a couple of important things to consider:
(1) The notion of mixing crop types to minimize herbivory is the one of the fundamental tenets of traditional agroecology and organic agriculture, but instead of relying on GM crops, it could be done with a mix of hybrid crop varieties that doesn’t risk the potential environmental side effects of Bt corn or other unexpected outcomes of GM crops. This is a major value judgment. Does having one GM crop and a few dominant corn varieties count as diversity when the Midwest becomes a giant sea of maize? As I explain in #2 below, probably not. Could we achieve the same kind of insect pest management using a diversity of non-GM crops? Yes—it happens all the time in midwestern organic farms. Multi-crop organic farming is often more labor intensive than industrial agriculture, making the food produced more expensive. But do we only care about cheap food?
(2) I’ve lived in southern Minnesota, where it’s a giant rotating monoculture of corn and soybeans. If you look at Figure 1 in this paper, you will see that 50-75% (or more) of the corn grown in many regions of states like Iowa, Nebraska, and Minnesota is Bt corn. When so much of your landscape is Bt corn, the evolution of resistance to Bt is most likely inevitable, as we saw in a previous post with the use of Roundup-ready crops like soybeans, which are often grown in rotation with Bt corn in these regions. Acknowledging this fact of life, EPA recommends mixing GM and non-GM corn in an effort to delay the evolution of resistance, not prevent it:
To delay evolution of resistance, the U.S. Environmental Protection Agency (EPA) mandated that a minimum 20 to 50% of total onfarm maize be planted as non-Bt maize within 0.8 km of Bt fields as a structured refuge for susceptible O. nubilalis. Use of non-Bt maize refugia is an important element of long-term insect resistance management.
…Sustained economic and environmental benefits of this technology, however, will depend on continued stewardship by producers to maintain non-Bt maize refugia to minimize the risk of evolution of Bt resistance in crop pest species, and also on the dynamics of Bt resistance evolution at low pest densities and for variable pest phenotypes.
Hutchison, W., Burkness, E., Mitchell, P., Moon, R., Leslie, T., Fleischer, S., Abrahamson, M., Hamilton, K., Steffey, K., Gray, M., Hellmich, R., Kaster, L., Hunt, T., Wright, R., Pecinovsky, K., Rabaey, T., Flood, B., & Raun, E. (2010). Areawide Suppression of European Corn Borer with Bt Maize Reaps Savings to Non-Bt Maize Growers Science, 330 (6001), 222-225 DOI: 10.1126/science.1190242
Photo credit: Ian Hayhurst
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