Bt Crops

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Bt Crops are named for Bacillus thuringiensis (Bt), a bacteria that naturally produces a crystal protein that is toxic to many pest insects.[1] Bt crops are crops that are genetically engineered to produce the same toxin as Bt in every cell of the plant, with the goal of protecting the crop from pests. Due to widespread use of Bt crops, Bt resistance has now been observed in some pests. This is a major threat to organic agriculture, as it would render one of organic agriculture's most powerful pest control tools useless if Bt-resistance to pests evolved on a large scale.

Bt Crops are often touted as safe because Bt is a common, organic form of insecticide. However, when applied by farmers, Bt degrades within one week, and sometimes after just 24 hours.[1] Conversely, the toxic crystal proteins from Bt that are produced by Bt crops are constantly present in the environment, as they are continually produced by each cell of the plant.

Crops Genetically Engineered to Produce Bt Proteins

In March 1995, the first Bt crop deregulated in the U.S. were seven lines of Colorado Potato Beetle Resistant Bt Potato by Monsanto. Since then, many more Bt crops have been deregulated, engineered to produce a variety of different Bt proteins from various subspecies of Bt. Bt crops include:




  • Bt Eggplant (not yet deregulated or commercialized anywhere in the world)



  • Bt Soybean (first deregulated in the U.S. in October 2011, not yet sold commercially)



Insect Resistance

Prior to the use of Bt in GMOs, issues with Bt resistance evolving in pests were unlikely due to the brief and infrequent exposures to Bt pests experienced. Following an application of Bt, the majority of pests would die, and then the Bt would degrade within a week. A farmer might apply Bt one more time, to kill any insects that hatched after the first application of Bt. Still, insects were not exposed to Bt for a very long period of time, giving them little opportunity to evolve resistance.

However, with the advent and widespread use of Bt toxin by GMOs, pests have more opportunities to evolve resistance to Bt. Bt resistance in corn pests was first observed in 2011. For more information, see the article on Bt-Resistant Insects.

Safety of Bt Crops

A 2010 study published in the journal Reproductive Toxicology found that "3-MPPA and Cry1Ab toxin are clearly detectable and appear to cross the placenta to the fetus."[2] 3-MPPA, or 3-methylphosphinicopropionic acid, is a metabolite of the pesticide gluphosinate ammonium, which is used in some genetically engineered crops. The Cry1Ab is the insecticidal protein produced by Bt crops. The study found that the "Cry1Ab toxin was detected in 93% and 80% of maternal and fetal blood samples, respectively and in 69% of tested blood samples from nonpregnant women." The study authors speculated this was due to consumption of contaminated meat, i.e meat from animals fed Bt corn that had retained the Cry1Ab protein in their flesh.

Articles and resources

Related SourceWatch articles


  1. 1.0 1.1 W.S. Cranshaw, "Bacillus thuringiensis," Colorado State University Extension, December 2008, Accessed September 8, 2011.
  2. Aziz Aris and Samuel Leblanc, "Maternal and fetal exposure to pesticides associated to genetically modified foods in Eastern Townships of Quebec, Canada," Reproductive Toxicology, February 13, 2011.

External resources

External articles