What is BT Corn?

Mary McMahon
Mary McMahon

Bt corn is a genetically modified organism (GMO) that has been bioengineered to resist the European corn borer, a crop pest that can cause significant damage to crops. Many nations plant this type of corn, and it is in use in a variety of industries. Studies conducted on this GMO seem to suggest that it has no adverse human health effects, leading many government agencies to certify it as safe for use.

The European corn borer will suffer ruptured intestines and eventual death if it ingests the Bt toxin found in the bioengineered corn.
The European corn borer will suffer ruptured intestines and eventual death if it ingests the Bt toxin found in the bioengineered corn.

This corn takes advantage of a toxin produced by the Bacillus thuringiensis bacterium. The toxin, known as Bt, ruptures the intestines of the corn borer and related organisms when it is ingested. The pests typically die within two to three days of ingesting the toxin. As early as the 1930s, farmers were cultivating the bacterium as a method of pest control, and spraying the toxin on their crops to prevent infestation by the pest.

The butterfly population is at risk because butterfly larvae are negatively affected by Bt corn pollen.
The butterfly population is at risk because butterfly larvae are negatively affected by Bt corn pollen.

Topical application of this natural pesticide had some flaws, including uneven coverage and its eventual washing away. As a result, researchers started to explore the idea of inserting the genes that code for the toxin directly into the genetic code of the corn, along with a section of code known as a promoter, which would encourage the corn to produce the toxin, and a marker that could be used to track and identify modified corn.

After some trial and error, several companies had developed Bt corn, and the plant underwent inspection by government agencies to determine whether or not it was safe. Once approved, it could be planted by farmers, along with so-called “refuge” crops of non-Bt corn. The refuge crops are used to discourage Bt resistance by providing fodder for the European corn bearer that is safe to eat. The idea is that if a few insects develop resistance, they may mate with insects who ate from the refuge crop, diluting or eliminating the resistance. By contrast, a field covered in only Bt corn would promote resistance by killing off all of the insects which were vulnerable to Bt, and promoting the survival of resistant insects.

While this corn clearly has some advantages, it has not been without controversy. Some researchers have raised concerns that the corn or its pollen could impact butterfly populations, as butterfly larvae are vulnerable to the toxin. Studies have also shown that it has interbred with regular corn, creating weak amounts of the toxin in strains of corn that should not have any Bt present. Some opponents of GMOs have also argued that not enough is known about their potential impacts on human health, making them safety risks.

BT corn is a genetically-modified food.
BT corn is a genetically-modified food.
Mary McMahon
Mary McMahon

Ever since she began contributing to the site several years ago, Mary has embraced the exciting challenge of being a wiseGEEK researcher and writer. Mary has a liberal arts degree from Goddard College and spends her free time reading, cooking, and exploring the great outdoors.

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Discussion Comments


@StreamFinder: The study that said Bt maize pollen was toxic to Monarch larvae (Losey et al 1999) was a laboratory study in which Bt pollen was applied to the Monarch larvae food plant, Milkweed. They did indeed observe a decrease in the feeding and growth rates, as well as increased mortality of the larvae.

However, a more recent study by Gathmann et al (2006) did a field study into the effects of Bt maize pollen on Lepidopteran (butterly and moth) larvae and found that the pollen had no effect on their growth or mortality. Also, they observed that it was very uncommon that the flowering of Bt maize even overlapped with the development of Lepidopteran larvae.

It should be noted, furthermore, that laboratory studies cannot effectively predict the effects of a given substance in the field (e.g., GM pollen) where many more factors come into play. In this case, one of those factors was the overlap between flowering time and larval development.

So, before you try to demonize GM Bt maize on the grounds of evidence from a study that you have not read and that has since been discredited, I suggest you check for yourself.


The cells of cancer patients with impaired immune systems have had problems battling toxins, so it's safer to wash off pesticides rather than eat them.


@gregg1956: You ask if I would rather eat BT corn or corn coated in pesticides? BT is a natural biotoxin. Every cell in the plant is emitting the stuff even after it is pulled from the stalk of the plant. Pesticides only cover the surface of the plant. Genetic modification alters every cell. So, I would much rather eat pesticide coated corn. I can at least wash it off.

Of course, there are the issues of pesticide runoff and whether or not we really need pesticides or just more crop diversity.

Instead of planting one type of crop in one location, plant a variety of crops that support each other and protect each other.


gregg1956, There is no way to know if genetically modified corn is healthy or even can be healthy. There are no long term studies done that verifies Bt corn is safe for human consumption. Therefore I am against GMO food of any kind.


Although I can understand the BT corn controversy (as well as that surrounding any genetically altered good, like BT cotton), I think that people can sometimes lose perspective when discussing it.

Although I personally don't really care too much either way on the BT corn debate, I think it's important to look at the benefits that BT corn can bring us.

For instance, think about the farmers that lose their crops to pests, and end up with nothing at the end of the growing season.

Likewise, think about the amount of pesticides sprayed on regular corn to keep that very situation from happening.

I guess all I'm saying is consider -- would you rather be eating healthy, genetically modified corn, or regular corn coated in pesticides? Although there are alternatives in organic corn, the majority of the population is still eating either BT corn or corn raised with pesticides, so the choice remains largely the same.

Where do you stand on it?


When you're buying sweet corn seed, say for a home garden, how do you know whether you're getting BT Corn or a GMO?

I'd love to start a garden in my backyard, but I love my local butterfly population, and after reading about BT corn on a wiki, I'm really worried that I may accidentally plant some and harm my local ecosystem.

Is there a way to know if you're buying BT corn or not?


I'm really glad you mentioned the connection between BT corn and monarch butterflies. For instance, I find that so many people are unaware of the fact that BT corn pollen can kill monarchs!

Though I'm certainly not against agricultural biotechnology per se, I really think that we should be a little more responsible with what we put out there in nature.

The little things make more of a difference than we could ever think of -- for instance, look at how the introduction of kudzu to the US has turned into a nightmare. What started as a harmless decorative plant is not overrunning buildings on the side of the highway.

Just some (non-bt) food for thought.

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