The Latest News on Bt

A GMO, or genetically modified organism, is a plant, animal, microorganism or other organism whose genetic makeup has been modified in a laboratory using genetic engineering or transgenic technology. This creates unstable combinations of plant, animal, bacterial and virus genes that do not occur in nature or through traditional crossbreeding methods. Nearly all GMOs are created to tolerate an herbicide (HT), produce an insecticide (Bt), or both. Let’s take a closer look at Bt and some of the latest findings on the potential impacts of this trait in genetically engineered crops.

What is Bt?

Bacillus thuringiensis under 1000 X magnification, courtesy of Dr. Sahay

Bt crops are a type of transgenic crop that has been engineered with DNA from the naturally-occurring bacteria Bacillus thuringiensis (Bt). Some strains of Bacillus thuringiensis produce a protein that crystallizes as it accumulates. These are called Cry proteins, and specific types of them are toxic to insects that possess the corresponding receptors to activate those proteins. Naturally-produced Cry proteins are largely harmless to other organisms that do not possess these receptors.

This toxicity has made Bt a popular insecticide for several decades. It is not just used in genetic engineering, but in organic farming as well. Organic farmers make use of this naturally-occurring bacteria by putting it in a solution and spraying it on their plants as an alternative to chemical pesticides. In more recent years, crops including corn, cotton, and soybeans have been genetically modified using DNA from Bacillus thuringiensis so that they express their own Cry proteins. As these GMOs produce Bt toxins directly inside their cells, the resulting insecticide is always being produced and cannot be washed off.

The biotechnology industry maintains that the Bt genes expressed by their GMOs are identical to the Bt genes found in nature. These companies often say that transgenic Bt crops must be safe because natural Bt has a long history of safe use, but this recently-published paper in the journal Biotechnology and Genetic Engineering Reviews calls this assertion into serious question.

In this report, researchers reviewed the documents that accompanied 23 different Bt crops when those crops obtained approval for commercial production. Of the 23 specimens evaluated, not a single one was found to be identical to its naturally-occurring counterpart. According to co-author Jonathan Latham, the Bt proteins found in GMOs are more active and impact a wider range of organisms than expected.

The biotechnology industry is quick to point out that humans do not possess the receptors necessary to activate Cry proteins in the digestive system. Consuming this compound does not affect humans in the same way it does pests such as corn borers, but the full extent of Bt’s impact on human health has not been studied sufficiently.

Resistance and Ecological Complexity

There are other reasons to worry about the widespread and prolonged use of genetically modified Bt. Genetic resistance is chief among these reasons. Just as bacteria can become resistant to drugs and medications, pest populations can become resistant to Bt crops over time. These so-called “superbugs” are a function of natural selection. Pests that are not killed by consuming Bt are more likely to live long enough to reproduce and make more Bt-resistant larvae. Resistance presents a major concern because when one pesticide stops working, the typical solution is to use more pesticides. The pattern of requiring more and more pesticides to control a pest problem is called a pesticide treadmill, and it represents a significant problem in modern agriculture. We can’t outrun or outsmart evolution, but biotech companies keep trying!

A report published in September explains how researchers from the University of Arizona analyzed global data on Bt crop use to learn more about Bt resistance and the conditions that make it occur. They looked at 36 different cases with data on 15 pest species across 10 countries.

Their findings suggest that Bt resistance is speeding up over time. Between 1996, when GMOs were introduced, and 2005, researchers found three cases of Bt resistance developing. By 2016, researchers had identified a total of 16 of such cases, and three more in which early warnings of resistance were observed. In many cases, pest populations developed resistance in as little as five years.

Another recently-published report by Thomas Bøhn and Gabor L. Lövei (read the full paper hereit’s fascinating) takes an in-depth look at pest control using transgenic plants. It also provides case studies to illustrate how GMOs and other modern approaches to pest management can lead to unanticipated externalities. A butterfly effect, if you will.

Case study: Bt cotton in China

Chinese cotton farmers turned to Bt crops to fight off the pesky cotton bollworm. At first, the new GMO caused a significant decline in cotton bollworm attacks at a regional level. This created an opening for another type of pest: mirid bugs. These cotton-eating bugs flocked to Bt cotton in droves once the bollworms were gone and created a brand new pest problem. This underscores the importance of taking ecological complexity into account and the potential consequences of failing to do so.

B. fusica

B. fusca, courtesy of Paul-andre Calatayud

Case study: Bt corn in South Africa

Another case study from Bøhn and Lövei’s paper involves the Busseola fusca, or the maize stalk borer in South Africa. Corn was genetically engineered with the Cry1AB toxin to fight off these pests, which worked for about six years. Once the Busseola fusca became resistant to Cry1AB, the single-toxin corn was replaced with a new GMO that expresses two Cry proteins instead of one.

The practice of adding more and more Bt genes to a GMO crop is called stacking, and it represents a growing problem in the world of agriculture. Back in 1996 when Bt crops were first introduced, it was normal for them to express only one transgene. One crop, one Bt gene, one type of toxic Cry protein. Today, a typical Bt crop may express six different Bt proteins, and in the next few years we can expect to see up to 14 transgenes stacked. These transgenes don’t just interact with each other, but also with the many dynamic parts of the organism and ecosystem they are a part of.

All of the recent reports on Bt reflect the fact that like all GMOs, these crops are experimental and we are still learning about their impacts. This is one of the many reasons the Non-GMO Project exists. We believe that all shoppers deserve to know what is in their food so that they can make informed purchasing decisions. When you purchase Non-GMO Project Verified products, you are telling the retailers and brands you support that GMO transparency is important to you. The Non-GMO Project butterfly also tells you that the product you are purchasing has met North America’s most rigorous standard for GMO avoidance. Remember to Look for the Butterfly when you shop!!

Here are the full details of the reports mentioned in this blog:

Jonathan R. Latham, Madeleine Love & Angelika Hilbeck (2017) The distinct properties of natural and GM cry insecticidal proteins, Biotechnology and Genetic Engineering Reviews, 33:1, 62-96, DOI: 10.1080/02648725.2017.1357295

Bruce Tabashnik and Yves Carrière (2017) Insect Resistance to Transgenic Crops: Second Decade Surge and Future Prospects. Nature Biotechnology. DOI: 10.1038/nbt.3974

Bøhn T and Lövei GL (2017) Complex Outcomes from Insect and Weed Control with Transgenic Plants: Ecological Surprises? Front. Environ. Sci. 5:60. doi: 10.3389/fenvs.2017.00060




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