Evolution thumbs its nose at genetically modified Bt corn.

In the proverbial case of an evolutionary na na na na an insect has evolved to thrive on the very genetically modified corn that was designed to eradicate it. A devastating pest, the Western Corn Rootworm, has evolved resistance to Monsanto’s Bt resistant corn. The corn, launched in 2003 and grown on some 37 million acres in 2011, is engineered to produce the fatal protein derived from a bacterium, bacillus thurigiensis, or Bt.

In a case where nature proves beyond a reasonable doubt that it will evolve to survive any attempts to eradicate pests the rootworm has become even more of a problem than it was previously. Scientists have predicted for years that the worm will develop resistance and become even more ferocious and provided recommendations for farmers when planting BT-corn. Farmers overwhelmingly failed to follow these recommendations.

A new research study published by Aaron Grassman, an Iowa State University entomologist who has followed the rootworm evolution, points to the serious nature of the resistance and that rootworms were also resistant to a second variety of Bt corn. Evolving resistance to one variety heightened the chances of resistance to another Bt corn variant. That means corn engineered to produce multiple Bt toxins, (stacked varieties), won’t do much to slow the evolution of rootworm resistance, as was originally hoped.

“Unless management practices change, it’s only going to get worse,” said Aaron Gassmann, co-author of a March 17 Proceedings of the National Academy of Sciences study describing rootworm resistance. “There needs to be a fundamental change in how the technology is used.”

There has been considerable concern over the safety of Bt corn based on a number of studies that have documented serious side effects. Monsanto has used the gene from Bacillus thuringiensis (Bt) to genetically modify certain crops to be Bt resistant. Bacillus thuringiensis produces BT-toxin. It’s a pesticide; and it breaks open the stomach of certain insects and kills them.

The new study reveals that the Bt toxins Cry1Aa, Cry1Ab, Cry1Ac or Cry2A have toxic effects in the blood of mice and that the claims by policy regulators of the presumed nontoxicity of Bt toxin to mammals, on which all regulatory approvals of Bt crops are based, is false.

The mechanism of operation of BT toxin on insects (the target population for the pesticide) is to break holes in the gut and rupture cells. In mice in this experiment Bt toxins, caused red blood cells to rupture and is highly disconcerting as BT toxin has crossed the placenta and was found in the umbilical cord in over eighty percent of mothers tested suggesting that it crosses into the blood stream of babies.

The study authors stated: “It has been reported that Cry toxins exert their toxicity when activated at alkaline pH of the digestive tract of susceptible larvae, and, because the physiology of the mammalian digestive system does not allow their activation, and no known specific receptors in mammalian intestinal cells have been reported, the toxicity [of] these MCAs [microbial control agents] to mammals would negligible. However, our study demonstrated that Bt spore-crystals genetically modified to express individually Cry1Aa, Cry1Ab, Cry1Ac or Cry2A induced hematotoxicity, particularly to the erythroid lineage. This finding corroborates literature that demonstrated that alkali-solubilized Bt spore-crystals caused in vitro hemolysis in cell lines of rat, mouse, sheep, horse, and human erythrocytes and suggested that the plasma membrane of susceptible cells (erythrocytes, in this case) may be the primary target for these toxins”.

” In conclusion, results showed that the Bt spore-crystals genetically modified to express individually Cry1Aa, Cry1Ab, Cry1Ac or Cry2A can cause some hematological risks to vertebrates, increasing their toxic effects with long-term exposure. Taking into account the increased risk of human and animal exposures to significant levels of these toxins, especially through diet, our results suggest that further studies are required to clarify the mechanism involved in the hematotoxicity found in mice, and to establish the toxicological risks to non-target organisms, especially mammals, before concluding that these microbiological control agents are safe for mammals.”

The toxicity of Bt proteins in mammalian cells was also the subject of an in vitro (test-tube) study (Mesnage et al., 2012; http://onlinelibrary.wiley.com/doi/10.1002/jat.2712/abstract). In this study, Bt toxin Cry1Ac was found to be substantially toxic to human cells, raising substantial concerns in the human population.


Mezzomo, B. P., et al. (2013). Hematotoxicity of Bacillus thuringiensis as spore-crystal strains Cry1Aa, Cry1Ab, Cry1Ac or Cry2Aa in Swiss albino mice. J Hematol Thromb Dis 1(1). http://dx.doi.org/10.4172/jhtd.1000104

Aaron J. Gassmann, Jennifer L. Petzold-Maxwell, Eric H. Clifton, Mike W. Dunbar, Amanda M. Hoffmann, David A. Ingber, and Ryan S. Keweshan. Field-evolved resistance by western corn rootworm to multiple Bacillus thuringiensis toxins in transgenic maize. PNAS. Early Edition Aaron J. Gassmann, doi: 10.1073/pnas.1317179111

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