(Beyond Pesticides, February 14, 2008) Researchers have found what they are calling the first insect resistance in the field to genetically engineered plants that are modified to produce an insecticide called Bacillus thuringiensis, or Bt. The University of Arizona (UA) researchers, who have previously received research support from Monsanto and Cotton, Inc., are supportive of bioengineered crops and dismiss the findings of resistance, given that they are only in cotton and no other crops. The report, “Insect resistance to Bt crops: evidence versus theory,” is due out in the February issue of Nature. Concern about resistance has raised fears in the organic community that Bt, derived from natural soil bacterium, would be rendered ineffective as insect resistance spreads and this natural control collapses over time.In organic systems, composted manures and cover crops replace synthetic fertilizers, innovative weeding strategies are used instead of herbicides, beneficial insects and trap crops control insect pests, and alternatives to toxic defoliants prepare plants for harvest.
Bt-resistant populations of the insect bollworm, Helicoverpa zea, were found in more than a dozen crop fields in Mississippi and Arkansas between 2003 and 2006.
The bollworm resistance to Bt cotton was discovered when a team of University of Arizona entomologists analyzed published data from monitoring studies of six major caterpillar pests of Bt crops in Australia, China, Spain and the U.S.
Because they have only found resistance in one crop over a seven year period, the researchers maintain that their data refute some experts’ worst-case scenarios that predicted pests would become resistant to Bt crops in as few as three years.
To delay resistance, non-Bt crops are planted near Bt crops to provide “refuges” for susceptible pests. The biotech industry originally resisted the requirement for refuges arguing that it was unnecessary. Because resistant insects are rare, the only mates they are likely to encounter would be susceptible insects from the refuges. The hybrid offspring of such a mating generally would be susceptible to the toxin. In most pests, offspring are resistant to Bt toxins only if both parents are resistant. In bollworm, however, hybrid offspring produced by matings between susceptible and resistant moths are resistant. Such a dominant inheritance of resistance was predicted to make resistance evolve faster. It remains to be seen whether resistance will grow over time.
The UA researchers found that bollworm resistance evolved fastest in the states with the lowest abundance of refuges.
To combat resistance, researchers are adopting the more is better approach. The first-generation biotech cotton contained only one Bt toxin called Cry1Ac; however, a new variety contains both Cry1Ac and a second Bt toxin, Cry2Ab. The theory is that the combination overcomes pests that are resistant to just one toxin.
The U.S. Department of Agriculture funded the research.
As an alternative to chemical and biotech cotton, in 1996, in an effort to develop and spread knowledge about alternatives to chemical farming systems in cotton, the California-based Sustainable Cotton Project (SCP) launched its BASIC (Biological Agriculture Systems) program. In Cotton, the BASIC program includes mentor farmer outreach, step-by-step growing assistance, organic and sustainable field research trials and systematic monitoring. See http://www.sustainablecotton.org/html/growers/growers.html.