Debunking Denialism

Fighting pseudoscience and quackery with reason and evidence.

GMOs and the Monarch Butterfly Issue

The vast majority of the opposition against genetically modified foods and biotechnology in general is rife with scientific inaccuracies, fear mongering and outright falsehoods, as Chassy and Tribe so amply demonstrates in their criticisms of many of the standard anti-GMO claims and canards. The main problems is that the anti-GMO denialists makes claims that either contradicts research published in serious scientific journals, is based on journals no serious scientist would even wipe the dirt of their shoes with, based on elementary misunderstandings of the science or just plain made up.

To be sure, there are real issues concerning food safety that needs to be addressed, such as the enormous amount of chemical pesticides being sprayed around the world that is harmful to both humans and the environment, shortage of vitamins and minerals (as well as calories), drought and pathogenic organisms like viruses or fungi. Genetically modified foods must be a partial solution to these issues in the future as we will need to grow more food on less arable land. Sadly, few opponents of genetically modified foods seem to care about it.

While it is true that genetically modified products should be examined on a case-by-case basis, most anti-GMO groups reject all not only genetically modified products, but the technology itself, out of hand. There is, however, one interesting exception to the analysis of anti-GMO arguments outlined above. One of them are actually based on a research article published in one of the most renowned peer-reviewed scientific journals in existence.

The article is called Transgenic pollen harms monarch larvae written by John E. Losey, Linda S. Rayor & Maureen E. Carter (henceforth Losey et. al.) working out of Cornell University and publish in the prestigious science journal Nature. Their basic claim was that a certain form of transgenic pollen is dispersed over a large area by the wind and that these pollen, after they landed on other neighboring plants, can be ingested by other organisms. They claimed to have showed that larvae of the monarch butterfly that ate milkweed leaves with these particular types of transgenic pollen where harmed by it compared with the controll. Here is the entire abstract:

Although plants transformed with genetic material from the bacterium Bacillus thuringiensis (Bt) are generally thought to have negligible impact on non-target organisms1, Bt corn plants might represent a risk because most hybrids express the Bt toxin in pollen2, and corn pollen is dispersed over at least 60 metres by wind3. Corn pollen is deposited on other plants near corn fields and can be ingested by the non-target organisms that consume these plants. In a laboratory assay we found that larvae of the monarch butterfly, Danaus plexippus, reared on milkweed leaves dusted with pollen from Bt corn, ate less, grew more slowly and suffered higher mortality than larvae reared on leaves dusted with untransformed corn pollen or on leaves without pollen.

The Bt toxin is a toxin produced by a specific bacteria called Bacillus thuringiensis. This has been used in traditional farming for many decades. Farmers go out and spray a mixture of these bacteria on the plans and the toxin produced kills certain parasites. What is different with the genetically modified situation is that the plants themselves have been equipped with a gene isolated from the bacteria that makes the plants themselves produce this toxin.

The toxin is very specific so it does not harm organisms that do not fulfill the criteria. To be lethal, the toxin requires an alkaline stomach environment (humans have acidic). This dissolves the aggregate of the inactive protein precursor. A specific protease enzyme that humans do not have is required to turn the inactive protein precursor into the active form of the toxin. An finally, a specific receptor on the mucous membrane of the stomach is needed for the toxin to have a harmful effect. Humans, and most other organisms, do not have this receptor. So the product is highly specific and kills basically only the pest, and leaves other organisms unharmed.

The reason that this paper sparked controversy was that the monarch butterfly has such as strong cultural status as it is recognized by many people and because of its colorful wings. Opponents of genetically modified foods use this paper to attempt to demonstrate the significant environmental harm it would cause. However the methodology of the paper was flawed and the results were merely preliminary.

To investigate this issue in more depth, scientists from the United States and Canada investigated the toxicity of Bt pollen and the effects it has on the larvae of the monarch butterfly. The study made by Sears et. al. was published in another prestigious journal called Proceedings of the National Academy of Sciences during 2001 with the title Impact of Bt corn pollen on monarch butterfly populations: A risk assessment.

Sears et. al. (2001) drew the following conclusions from their data:

  • The levels of Bt toxin differs among variants.
  • The levels are low and no acute toxin effects at any pollen density that reasonably could be encountered in the field by the monarch butterfly.
  • The overlap between the time when the pollen are shed and when larvae are active is minor and differs.
  • Only a minor portion of monarch larvae feeds on milkweed stands in close proximity to cornfields.
  • The specific version used in the original study, Bt176 is no longer available in American maize.

Because of this, they concluded that their study, which was more extensive than the original Losey et. al. study, showed that “the impact of Bt corn pollen from current commercial hybrids on monarch butterfly populations is negligible”. This issue highlights the need to separate the technology form specific products and that genetically modified products need to be investigated on a case-by-case basis.

References and Further Reading:

Losey, J. E., Rayor, L. S., & Carter, M. E. (1999). Transgenic pollen harms monarch larvae. Nature, 399(6733), 214-214.

Sears, M. K., Hellmich, R. L., Stanley-Horn, D. E., Oberhauser, K. S., Pleasants, J. M., Mattila, H. R., . . . Dively, G. P. (2001). Impact of Bt corn pollen on monarch butterfly populations: A risk assessment. Proceedings of the National Academy of Sciences, 98(21), 11937-11942.

Slater, A., Scott, N. W., Fowler, M. R. (2008). Plant Biotechnology: The Genetic Manipulation of Plants (2nd Edition). New York: Oxford University Press. (particularly pp. 145-146).

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