The Belgian company
Plant Genetic Systems (now part of
Bayer CropScience) was the first company (in 1985) to develop
genetically modified crops (
tobacco) with insect tolerance by expressing
cry genes from
B. thuringiensis; the resulting crops contain
delta endotoxin. The Bt tobacco was never commercialized; tobacco plants are used to test genetic modifications since they are easy to manipulate genetically and are not part of the food supply. leaves (bottom dish) protect it from extensive damage caused to unprotected peanut leaves by
lesser cornstalk borer larvae (top dish).
Usage In 1995, were approved safe by the
Environmental Protection Agency, making it the first human-modified pesticide-producing crop to be approved in the US, though many plants produce pesticides naturally, including tobacco,
coffee plants,
cocoa,
cotton and
black walnut. This was the 'New Leaf' potato, and it was removed from the market in 2001 due to lack of interest. In 1996, was approved, which killed the
European corn borer and related species; subsequent Bt genes were introduced that killed corn rootworm larvae. The Bt genes engineered into crops and approved for release include, singly and stacked: Cry1A.105, CryIAb, CryIF, Cry2Ab,
Cry3Bb1, Cry34Ab1, Cry35Ab1, mCry3A, and VIP, and the engineered crops include corn and cotton. Corn genetically modified to produce VIP was first approved in the US in 2010. In India, by 2014, more than seven million cotton farmers, occupying twenty-six million acres, had adopted .
Monsanto developed a and the
glyphosate-resistance gene for the Brazilian market, which completed the Brazilian regulatory process in 2010. - specifically
Populus hybrids - have been developed. They do suffer lesser leaf damage from insect
herbivory. The results have not been entirely positive however: The intended result - better
timber yield - was not achieved, with no growth advantage despite that reduction in herbivore damage; one of their major pests still preys upon the transgenic trees; and besides that, their
leaf litter decomposes differently due to the transgenic toxins, resulting in alterations to the
aquatic insect populations nearby. Bt corn
Safety studies The use of Bt
toxins as
plant-incorporated protectants prompted the need for extensive evaluation of their safety for use in foods and potential unintended impacts on the environment.
Dietary risk assessment Concerns over the safety of consumption of
genetically modified plant materials that contain
Cry proteins have been addressed in extensive dietary risk assessment studies. As a toxic mechanism,
cry proteins bind to specific receptors on the membranes of mid-gut (
epithelial) cells of the targeted pests, resulting in their rupture. While the target pests are exposed to the toxins primarily through leaf and stalk material, Cry proteins are also expressed in other parts of the plant, including trace amounts in maize kernels which are ultimately consumed by both humans and animals. However, other organisms (including humans, other animals and non-targeted insects) that lack the appropriate receptors in their gut cannot be affected by the
cry protein, and therefore are not affected by Bt. Research on other known toxic proteins suggests that , further suggesting that Bt toxins are not toxic to mammals. The results of toxicology studies are further strengthened by the lack of observed toxicity from decades of use of
B. thuringiensis and its crystalline proteins as an insecticidal spray.
Allergenicity studies Introduction of a new protein raised concerns regarding the potential for allergic responses in sensitive individuals.
Bioinformatic analysis of known
allergens has indicated there is no concern of
allergic reactions as a result of consumption of Bt toxins. Additionally,
skin prick testing using purified Bt protein resulted in no detectable production of toxin-specific
IgE antibodies, even in
atopic patients.
Digestibility studies Studies have been conducted to evaluate the fate of Bt toxins that are ingested in foods. Bt toxin proteins have been shown to digest within minutes of exposure to simulated
gastric fluids. The instability of the proteins in digestive fluids is an additional indication that Cry proteins are unlikely to be allergenic, since most known food allergens resist degradation and are ultimately
absorbed in the small intestine.
Persistence in environment Concerns over possible environmental impact from accumulation of Bt toxins from plant tissues, pollen dispersal, and direct secretion from roots have been investigated. Bt toxins may persist in soil for over 200 days, with
half-lives between 1.6 and 22 days. Much of the toxin is initially degraded rapidly by microorganisms in the environment, while some is
adsorbed by organic matter and persists longer. Some studies, in contrast, claim that the toxins do not persist in the soil. Bt toxins are less likely to accumulate in bodies of water, but pollen shed or
soil runoff may deposit them in an aquatic ecosystem. Fish species are not susceptible to Bt toxins if exposed.
Impact on non-target organisms The toxic nature of Bt proteins has an adverse impact on many major crop pests, but some ecological risk assessments has been conducted to ensure safety of beneficial non-target organisms that may come into contact with the toxins. Toxicity for the monarch butterfly, has been shown to not reach dangerous levels. Most soil-dwelling organisms, potentially exposed to Bt toxins through root exudates, are probably not impacted by the growth of Bt crops.
Insect resistance Multiple insects have developed a resistance to
B. thuringiensis. In November 2009,
Monsanto scientists found the
pink bollworm had become
resistant to the first-generation
Bt cotton in parts of
Gujarat, India - that generation expresses one Bt gene,
Cry1Ac. This was the first instance of Bt resistance confirmed by Monsanto anywhere in the world. Monsanto responded by introducing a second-generation cotton with multiple Bt proteins, which was rapidly adopted. Additionally, resistance to Bt was documented in field population of
diamondback moth in Hawaii, the continental US, and Asia. Studies in the
cabbage looper have suggested that a mutation in the membrane transporter ABCC2 can confer resistance to Bt
Cry1Ac.
Secondary pests Several studies have documented surges in "sucking pests" (which are not affected by Bt toxins) within a few years of adoption of Bt cotton. In China, the main problem has been with
mirids, which have in some cases "completely eroded all benefits from Bt cotton cultivation". The increase in sucking pests depended on local temperature and rainfall conditions and increased in half the villages studied. The increase in insecticide use for the control of these secondary insects was far smaller than the reduction in total insecticide use due to Bt cotton adoption. Another study in five provinces in China found the reduction in pesticide use in Bt cotton cultivars is significantly lower than that reported in research elsewhere, consistent with the hypothesis suggested by recent studies that more pesticide sprayings are needed over time to control emerging secondary pests, such as aphids, spider mites, and lygus bugs. Similar problems have been reported in India, with both
mealy bugs and aphids although a survey of small Indian farms between 2002 and 2008 concluded Bt cotton adoption has led to higher yields and lower pesticide use, decreasing over time.
Controversies The controversies surrounding Bt use are among the many
genetically modified food controversies more widely.
Lepidopteran toxicity The most publicised problem associated with Bt crops is the claim that pollen from Bt maize could kill the
monarch butterfly. The paper produced a public uproar and demonstrations against Bt maize; however by 2001 several follow-up studies coordinated by the USDA had asserted that "the most common types of Bt maize pollen are not toxic to monarch larvae in concentrations the insects would encounter in the fields." Similarly,
B. thuringiensis has been widely used for controlling
Spodoptera littoralis larvae growth due to their detrimental pest activities in Africa and Southern Europe. However,
S. littoralis showed resistance to many strains of
B. thuriginesis and were only effectively controlled by a few strains.
Wild maize genetic mixing A study published in
Nature in 2001 reported Bt-containing maize genes were found in maize in its center of origin,
Oaxaca, Mexico. Another
Nature paper published in 2002 claimed that the previous paper's conclusion was the result of an
artifact caused by an
inverse polymerase chain reaction and that "the evidence available is not sufficient to justify the publication of the original paper." A significant controversy happened over the paper and
Natures unprecedented notice. A subsequent large-scale study in 2005 failed to find any evidence of genetic mixing in Oaxaca. A 2007 study found the "transgenic proteins expressed in maize were found in two (0.96%) of 208 samples from farmers' fields, located in two (8%) of 25 sampled communities." Mexico imports a substantial amount of maize from the U.S., and due to formal and informal seed networks among rural farmers, many potential routes are available for transgenic maize to enter into food and feed webs. One study found small-scale (about 1%) introduction of transgenic sequences in sampled fields in Mexico; it did not find evidence for or against this introduced genetic material being inherited by the next generation of plants. That study was immediately criticized, with the reviewer writing, "Genetically, any given plant should be either non-transgenic or transgenic, therefore for leaf tissue of a single transgenic plant, a GMO level close to 100% is expected. In their study, the authors chose to classify leaf samples as transgenic despite GMO levels of about 0.1%. We contend that results such as these are incorrectly interpreted as positive and are more likely to be indicative of contamination in the laboratory."
Colony collapse disorder As of 2007, a new phenomenon called
colony collapse disorder (CCD) began affecting
bee hives all over North America. Initial speculation on possible causes included new parasites, pesticide use, and the use of Bt transgenic crops. The
Mid-Atlantic Apiculture Research and Extension Consortium found no evidence that pollen from Bt crops is adversely affecting bees. According to the USDA, "Genetically modified (GM) crops, most commonly Bt corn, have been offered up as the cause of CCD. But there is no correlation between where GM crops are planted and the pattern of CCD incidents. Also, GM crops have been widely planted since the late 1990s, but CCD did not appear until 2006. In addition, CCD has been reported in countries that do not allow GM crops to be planted, such as Switzerland. German researchers have noted in one study a possible correlation between exposure to Bt pollen and compromised immunity to
Nosema." The actual cause of CCD was unknown in 2007, and scientists believe it may have multiple exacerbating causes. ==Beta-exotoxins==