Michael Fields Agricultural Institute logo
At the intersection of food, soil, climate, farming and water.

Bacillus Thuringiensis, Bugs, and Humans

Insects are building resistance to genetically-modified crops, and bio-pesticides are found in the human bloodstream.

Bacillus thuringiensis (Bt) is a bacterium that lives in soil and is deadly to insects.  When ingested, Bt produces a crystalline protein that kills cells and dissolves holes in an insect’s gut.  It has been used as a pesticide for decades and is approved for organic production, due to the fact that it occurs naturally in the soil and doesn’t persist in the environment long after spraying.

Field corn, cotton, potatoes, and sweet corn are now genetically-modified with Bt genes.  When a plant produces the Bt toxin, it’s referred to as a plant-incorporated protectant or a bio-pesticide.  During its growth period, the entire plant – leaves, stems, roots, seeds, etc. – manufactures the Bt toxin.     So when certain insects eat any part of the plant they consume the Bt toxin and die.   Compared to a spray application of Bacillus thuringiensis, a genetically- modified crop produces Bt at concentrations thousands of times higher.  After Bt is sprayed, it breaks down fairly soon.  With a genetically-modified crop, the Bt survives in the plant tissue long after harvest and winds up in the soil and waterways.  Nobody knows the effects of inundating ecosystems with massive quantities of the bacterium.

Selection pressure increases when insects are bombarded with pesticides or bio-pesticides, and insects evolve to resist the pesticide more quickly than they otherwise would (if they would at all).  So an invaluable pest management tool can be rendered useless if the target pest population is over-exposed to it.  Bt corn was released in 1996 and pests are already becoming resistant to it.  Since 2009, farmers in Iowa growing genetically-modified crops have found Bt-resistant corn rootworms.  Bt-resistant fall armyworm populations have shown up in Florida and Puerto Rico.  Mississippi and Arkansas now have a Bt cotton-resistant bollworm.  These resistant populations will undoubtedly spread to other parts of the country.  Farmers are having the same problem with weed management.  There are now 21 weed species resistant to Monsanto’s herbicide Roundup.  Genetically-modified Roundup-Ready (or glyphosate-tolerant) crops are engineered to be utilized with herbicide.  Over eleven million acres of farmland are infested with these “super- weeds”.

Since the release of Bt crops, farmers have been required to plant refuge zones.  If a farmer is planting Bt corn, anywhere from 5 – 20% of the crop planted cannot be genetically-modified.  This strategy was put in place to “forestall” insect resistance to Bt.  Ignoring the evolutionary capabilities of insects, seed companies blame farmers for non-compliance with refuge zone requirements.

In the past, Bt corn had one gene inserted into its DNA to target a specific pest (e.g. European corn borers or corn rootworms).  Now the makers of this seed are stacking up to six different genes – Bt genes and glyphosate-tolerant genes – into one corn plant.  This seed comes with a requisite 5% refuge.  Rather than forestalling insect resistance, this approach will probably accelerate it.  The EPA recently granted approval for Syngenta’s Agrisure 3122, corn seed stacked with multiple genetically-modified traits.  According to the USDA, seed corn prices rose 146% from 1999-2011.

In the U.S., genetically-modified corn accounts for about 86% of the nation’s crop.  The Center for Food Safety estimates that 70% of processed foods contain genetically-modified organisms.  The public knows very little about the health effects of eating food with Bt genes.  Short term studies have shown signs of toxicity with kidney and liver damage in mammals.  A 2009 study in the International Journal of Biological Sciences found a “clear negative impact on the function of these organs in rats consuming GM maize varieties for just ninety days”.  What happens when humans and livestock eat food with Bt for fifteen years?

When it was released, regulators claimed that Bt corn was safe because the Bt was degraded in the intestinal tract.  Now the Bt toxin is showing up in the bloodstream of humans.  Researchers in Canada looked for signs of the bio-pesticide in the blood of pregnant and non-pregnant women.  A study published in Reproductive Toxicology in February 2011 found the Bt toxin in 93% of maternal blood samples, 80% of fetal blood samples, and 69% of non-pregnant women blood samples. 

With their diminishing effectiveness and new health concerns, it’s time to re-examine whether planting genetically-modified crops is a good idea.  Farmers should be encouraged to adopt more sustainable practices for long-term productivity and food safety.