3.3—Bt crops are less likely to cause allergies or illness

Bt crops don’t create allergies or illness

See Genetic Roulette’s False Claims at Bottom of Page

Analysis of Peer-Reviewed Research:

The more than 50 years of large-scale use of Bt preparations in agriculture and forestry have been accompanied by an enviable record of safety. It is remarkable that despite concentrated spraying on large areas of crops and forests in intimate contact with people, very few adverse reactions have been recorded.  Organic farmers have come to depend on these safe biopesticides.  Bt preparations have proven to be specific and non-toxic.  There are few topics in scientific literature that are as well established as the biological selectiveness of each kind of Bt protein for a few closely related insects.  The studies cited by Genetic Roulette make weak claims of non-specific binding of Bt proteins to various types of cells but do not show that Bt is toxic to those cells.  What Jeffrey Smith has shown is that when whole bacteria are sprayed by workers onto crops a few unfortunate workers will experience ill effects—none of them due to the Bt protein itself.  The effects have been attributed to exposure of workers to billions of live bacteria.  GM crops protected by Bt have none of the bacteria. Moreover, no allergy to the Bt protein itself has ever been observed.

1. Bt sprays have been used for over 50 years and have a good record of safety. The US EPA regulates Bt as a biopesticide.  Bt sprays have been used in very large quantities in many areas and around many people in agriculture and forestry (Siegel 2001). They are favored because they are non-toxic to most living things since they are highly selective for one type of insect or a closely related family of insects.  There are many scientific publications that examine the safety of Bt proteins and which have explored the very specific mechanisms by which they kill insects.  Reported adverse reactions are rare (Siegel 2001).

2. Bt sprays contain billions and billions of whole live bacteria that could occasionally cause adverse effects.  Bt pesticides are actually preparations containing the cells of the bacteria that produce the Bt protein.  These bacteria are generally safe and non-pathogenic to humans, but occasionally somebody working with very concentrated bacterial preparations becomes infected—this happens more easily in people whose immune systems are compromised in some way (age, sickness, HIV).  Many other bacteria that are considered non-pathogenic occasionally cause infections when we are exposed to large numbers of bacteria and they gain entry into our bodies.  These are called “opportunistic infections.”  These occasional events among millions of safe uses do not mean that Bt sprays are unsafe. Quite the contrary, they prove that Bt is safe (Siegel 2001). Genetic engineering of crops to produce the Bt protein does not introduce any of these bacteria into food.

3.  Bt sprays can occasionally cause allergic reactions but the allergies aren’t to the Bt, they are to other proteins in the bacteria. Recall that Bt sprays contain billions of whole bacteria cells.  Each of these cells may contain 2000 or more novel proteins.  Any of these proteins could produce an allergic response in a person if they were repeatedly exposed to high doses of Bt.  That’s why farm workers very infrequently do develop sensitivities.

4.  Allergies to the Bt protein have never been observed. Smith cites papers that show that various types of antibodies can be formed against Bt.  He does not bother to tell the reader that when almost any protein is injected under our skin or in our veins, our immune system will develop antibodies to it.  This is a normal process. We also have antibodies to many different environmental and food proteins circulating in our bloodstreams where they do absolutely no harm.  The antibodies associated with allergy are called IgE antibodies.  IgE antibodies to Bt have never been reported.  There are scientific articles showing this that Smith fails to cite (Siegel 2001; Betz and others 2000).

5. Bt protein binding sites are not present on mammalian cells. Bt proteins are known to act by binding to specific sites on insect gut cells—these sites are called binding sites.  For Bt to kill an insect it must be activated by partial digestion, it must then attach to the binding site, and the protein must be inserted into the insect  cell membrane where it forms a pore or hole in the cell membrane that eventually kills the insect (Whalon and Wingerd 2003).  Mammalian cells lack these specific binding sites needed for Bt attachment.  Proteins like Bt can sometimes stick to cells or other proteins in a non-specific or random way and it is not surprising that various investigators have found Bt binding to other kinds of cells, although high quality studies not mentioned by Smith that found no Bt binding to mammalian cells have been published (Betz and others 2003).  Often this binding is weak and is easily reversed.  These studies have never shown that mammalian cells binding Bt under these conditions are killed the way cell lining insect guts are killed by the toxin.  To date all these studies have been categorized as “gratuitous binding” unrelated to the mode of action of Bt.  Smith admits the results he cites are “ambiguous.”

6.  Thousands of organic farmers depend on Bt as their most effective pesticide.  The most common pesticides used by organic farmers contain Bt preparations.  Organic farmers find them effective and innocuous (Zehnder and others 2007).  Genetic Roulette seems to be casting doubt on their safety and is indirectly criticizing the regulation of biopesticides by the EPA.  We find it hard to imagine organic agriculture without Bt products.  We have to wonder if Smith is also opposed to organic agriculture.


Siegel JP (2001). The mammalian safety of Bacillus thuringiensis- based insecticides. J. Invert. Pathol. 77:13-21

Betz FS, Hammond BG, and Fuchs, RL. (2000). Safety and advantages of Bacillus thuringiensis-protected plants to control insect pests. Regulatory Toxicology and Pharmacology 32:156-177. A key review which summarises the uses of Bt proteins to control insect pests in agriculture. Importantly provides key data substantiating the ~million-fold safety margins for Bt proteins

Whalon ME and Wingerd BA (2003). Bt: Mode of action and use Archives of Insect Biochemistry and Physiology, 54: 200-211

Zehnder, G-F , Gurr GM, Kuehne S, Wade MR, Wratten SD and Wyss E  (2007). Arthropod pest management in organic crops. Annu Rev Entomol. 52: 57-80

Genetic Roulette Falsely Claims:
Bt crops may create allergies and illness
  1. Soil bacteria (Bt) create a natural pesticide that has been used in spray form for years
  2. Genes from the bacteria are inserted into crop DNA, so the plant produces Bt-toxin.
  3. Approvals of Bt crops are based on the claim that the spray is harmless and Bt-toxin does not react with mammals.
  4. In reality, Bt spray is linked to allergies and illness in humans and mammals
  5. Bt-toxins also elicit immune responses in mice.
  6. Smith claims that Bt proteins are toxic to mammals and that they cause allergies.

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