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Bt Corn – What it is, and Why Should You Care About it

Most of the corn grown in the United States is Bt corn, but what is it, and why should you care? In this post, we explain the basics of Bt corn and some pros and cons.

bt corn closeup of corn kernals

What is Bt corn?

Bt corn is corn that is genetically engineered to produce insecticidal proteins from the bacterium Bacillus thuringiensis (Bt). In simple terms, scientists combine corn genes and bacteria genes to make corn that kills bugs that eat the corn.

Bacillus thuringiensis (Bt) bacteria strains occur naturally in the soil. Bt was registered for use as a pesticide with the Environmental Protection Agency (EPA) in 1961. Bt corn came on the market in 1996. There is Bt sweet corn (eaten directly by people) and Bt field corn (used in fuel, animal feed, other products and processed foods).

How does Bt corn kill insects?

Bt affects the larval (caterpillar or grub stage) of the insect. Bt toxins dissolve in the alkaline insect gut, become active, and punch holes in the gut lining. The spores spread out of the gut and germinate in the insect, killing the insect within days of ingestion. (The bug's guts explode, more or less.)

“Fun” fact – crops that combine the pesticide into the food crop are no longer regulated as food, but as a pesticide. They are regulated by the EPA. (Those tasty corn chips we all enjoy are technically pesticide chips…)

This has been used in court to force municipalities to allow growing Bt crops within their jurisdictions.  They can ban food crops, but they can't ban the use of pesticides. The EPA controls pesticide use, and the EPA says Bt crops are fine. Well, they're not food, but otherwise they're fine.

bt corn chips

What are the benefits of Bt corn?

The case for Bt corn has always been that it reduces the uses of more toxic, non-specific pesticides. The corn kills the the insects that eat it. As of 2018, about 82% of the corn produced in the United States was genetically modified to include Bt (Bt corn hybrids), according to the USDA.

So what's the problem with corn that has pesticide built in?

Nature adapts. Corn earworm, western corn rootworm and fall armyworms are developing resistance to Bt corn toxins. The chemical agriculture companies keep creating new hybrids – which work for a while.

Now we see recommendations to plant Bt corn and use insecticide sprays. This is what the corn was supposed to prevent.

From Rutger's University cooperative extension, “Corn Earworm Developing Resistance to Bt Toxins in Sweet Corn“:

Based upon Galen Dively’s twenty-one years of research comparing non-Bt sweet corn varieties with Bt varieties in plot studies, the proportion of damaged ears in Bt varieties has dramatically increased over that time.

What does this mean for our sweet corn farmers? Effective, almost 100% control of European corn borer can be achieved with any of the Bt sweet corn hybrids. Bt hybrids that express only the Cry1 Ab toxin will not control corn earworm and fall armyworm sufficiently so that silking sprays will be needed to maximize marketable yields. Those hybrids expressing Cry1 A.105 and Cry2 ab will probably require some silking sprays, as well.

Non Target Insects Can Die

Pollen from Bt corn kills monarch butterflies. Milkweed is a common weed around the edges of corn fields. Pollen drifts onto the milkweed, and the monarch caterpillars eat it and die.

I'm sure other species are affected, too, like painted ladies, who lay their eggs on thistles. That drifting pollen may also be carried back to the hive by foraging bees, and contributing to colony collapse disorder.

What about livestock?

This is harder to sort out. Adding the Bt gene for pest management isn't the only modification made to transgenic crops. Many are modified to live through weed killer applications (“RoundUp Ready”). With animals eating genetically modified organisms, impact may be from the food itself or the chemicals sprayed on the food.

A recent Australian study compared pigs fed a diet of genetically modified grains, versus pigs fed non-GMO grains (including Bt corn). The pigs eating GM grains showed much higher levels of severe stomach inflammation.

Is Bt Corn harmful to humans?

Officially, as far as the government and most corporations are concerned – nope. According to UCbiotech.og, “Is the Bt Protein Safe for Human Consumption?“:

The EPA does not require long-term studies because the protein’s instability in digestive fluids makes such studies meaningless in terms of consumer health.

Does Bt really break down in the human gut?

I have concerns about this. If Bt corn (and soy) toxins break down in the digestive system, how do they end up in human blood?

Here's an example – “Toxin from GM crops found in human blood: Study“:

Till now, scientists and multinational corporations promoting GM crops have maintained that Bt toxin poses no danger to human health as the protein breaks down in the human gut. But the presence of this toxin in human blood shows that this does not happen.

Scientists from the University of Sherbrooke, Canada, have detected the insecticidal protein, Cry1Ab, circulating in the blood of pregnant as well as non-pregnant women.

They have also detected the toxin in fetal blood, implying it could pass on to the next generation. The study covered 30 pregnant women and 39 women who had come for tubectomy at the Centre Hospitalier Universitaire de Sherbrooke (CHUS) in Quebec.

None of them had worked or lived with a spouse working in contact with pesticides.

They were all consuming typical Canadian diet that included GM foods such as soybeans, corn and potatoes. Blood samples were taken before delivery for pregnant women and at tubal ligation for non-pregnant women. Umbilical cord blood sampling was done after birth.

Cry1Ab toxin was detected in 93 per cent and 80 per cent of maternal and fetal blood samples, respectively and in 69 per cent of tested blood samples from non-pregnant women. Earlier studies had found trace amounts of the Cry1Ab toxin in gastrointestinal contents of livestock fed on GM corn. This gave rise to fears that the toxins may not be effectively eliminated in humans and there may be a high risk of exposure through consumption of contaminated meat.

How Much Bt Corn are We Eating?

According to the Corn Refiners Association, nearly 4,000 food items in a typical grocery store contain corn ingredients. And that number doesn’t include all the products—milk, eggs, meat, poultry—that come from corn-fed animals. Or the sweet, whole-kernel corn that comes in cans and freezer bags, and on the cob.

Corn sugar, corn syrup, high fructose corn syrup, corn starch, and thousands of other products  – corn is king in the modern grocery store. This link gives a LONG list of potential corn allergens.

This is why we buy organic corn products, as well as organic versions of the other high risks crops (when we buy them at all). It seems like everyone I know is dealing with some sort of inflammation. Maybe this is a piece of the puzzle?

Commonly genetically modified crops include:

  • alfalfa
  • canola
  • corn
  • cotton
  • papaya
  • soy
  • sugar beets
  • zucchini and yellow summer squash

Does genetic modification concern you or influence your shopping choices, or are you comfortable that GMOs are safe?

bt corn close up of corn kernals

You may also find interesting, “Is commercial bread making you sick?

Originally published in 2011, last updated in 2019.

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