Science in Society Archive

Bt Crops Failures & Hazards

The claim that genetically modified organisms are the most promising way of increasing crop yields is falsified by many independent scientific studies, as well as direct experience with GM crops in India, China, Argentina and the United States. Dr. Eva Sirinathsinghji reviews evidence on Bt crops

This report has been submitted to the EPA on behalf of the Institute of Science in Society. Please circulate widely and forward to your policy-makers

Rising insect resistance to genetically modified (GM) crops including Monsanto’s biggest selling crop, Bt corn, is threatening their utility and profitability. Insect resistance has prompted a new investigation by the Environmental Protection Agency (EPA). According to documents in the newly opened docket (Docket No: EPA-HQ-OPP-2011-0922) [1], “severe” damage to corn by rootworm has occurred in four states in the US. Further, the EPA describe Monsanto’s insect resistance monitoring program as “inadequate”. The EPA will collect public information to tackle the damage that could cause serious crop and economic damage. Amidst this investigation, Monsanto are seeing significant falls in their share prices [2]. Comments and information regarding insect resistance can be submitted to the EPA on their website [1].

In 2010, GM crops engineered to produce insecticidal toxins from the Bacillus thuringiensis (Bt) bacterium, were grown on more than 58 million hectares of land globally [3]. First commercialised in the US in 1996, it is also the only commercialised GM crop grown in the EU, with Spain being the largest producer. Despite their widespread commercialisation, the evidence for their functionality is still elusive, while evidence of their harm to the environment, people’s health, economic security and self-determination is continually mounting.

GM proponents have repeatedly claimed that Bt crops can help combat world hunger by increasing crop yields while reducing pesticide use, thereby providing a more productive and environmentally safe option over traditional varieties. However, as highlighted by a recent report conducted by 20 Indian, Southeast Asian, African and Latin American food and conservation groups representing millions of people, these claims are false. Pesticide use has increased, while GM crop yields are lower than conventional varieties (see [4] Transgenic Cotton Offers No Advantage, SiS 38) and world hunger is at epic proportions [5].

Risk assessments of Bt toxins to date have been inadequate, not least due to inexplicable lack of reliable data on the concentrations of Bt toxin produced in plants, including the roots and pollen. The purported efficacy and safety of these products cannot be established when exposure levels have not be reliably determined. A new study reported a standardised method to test Bt toxin levels and still found significant variation in results, highlighting the variability in previous studies [6]. In particular, reports of declining concentrations in the food chain and soils are unreliable and need to be re-evaluated and repeated. Despite these inadequacies in risk assessments so far, evidence of the Bt toxicity to environment and health is steadily accumulating.

The present review summarises all the evidence surrounding the efficacy and safety of Bt crops with regards to pest control, human health and environmental impact.

Breakdown of pest control

The hypothesis that Bt crops can boost yields by reducing pest numbers can be questioned on three levels. First, the expression of the toxin is not reliably sufficient to kill all target pests. Second, secondary pests that are not susceptible to the Bt toxins can emerge as a result of reduced pesticide use, bad agricultural practices e.g. monoculture farming, and the reduction of food or niche competitors (target pests). Third, pests can develop resistance to Bt toxins, rendering them completely ineffective.

Bt toxin levels are not sufficient to kill pests

Genetic modification of plants is unpredictable by nature. Bt toxins were inserted in plants so that they can be expressed consistently, across the whole plant. However, studies have found that expression of the Bt toxin is not even across the whole plant or its life-span, resulting in parts of the plant not containing enough toxin to kill pests [7,8]. Low levels of toxin can also exacerbate pesticide resistance. Indeed, farmers have reported crop failures as a result of target pests. In the US, 25 farmers filed a law suit against Monsanto for the failure of their Bt cotton to protect from bollworm infestation [5]. A 2005 survey of over 100 Indian farmers in Andhra Pradesh found that 32.5 percent of farms had infestations of American bollworm (see [9] Organic Cotton Beats Bt Cotton in India, SiS 27). Interestingly, organic farmers reported a 4.1 percent incidence of infestation, suggesting that the Bt cotton approach may not be the best for pest control, at least in this region.

Secondary pest and disease infestations

The rationale that Bt crops reduces pesticide use is also challenged by the emergence of secondary pests. A study published in Science last year found that over a period of 10 years, the mirid bug, previously considered an occasional or minor pest, acquired pest status, with increasing population sizes that corresponded with decreased pesticide use on Bt cotton fields in Northern China. Not only is this a problem for Bt crops, but many others as well. The emergence of secondary pests that are not susceptible to Bt toxin now means that alternative pesticides are necessary [10] (see [11] GM-spin Meltdown in China, SiS 47). With expensive GM seeds and additional pesticide costs, farmers are left worse off than before. Bt cotton fields in India are also showing infestations of new pests such as the mealy bug, gall midges, mosquitos and safflower caterpillars that were not previously a problem (see [12] Mealy Bug Plagues Bt Cotton in India and Pakistan, SiS 45). Although initially, Bt cotton had partial success in reducing bollworm infestations, cotton can be targeted by 165 different species of pests that are not all susceptible to the Bt toxin, and secondary pest infestations as well as new illnesses such as leaf ‘streak’ virus and lalya are on the rise (see [13] Farmer Suicides and Bt Cotton Nightmare Unfolding in India, SiS 45). The new mealy bug infestations seen across India and Pakistan are causing considerable reductions in crops yields (45-50 percent in 2007-2008); the two predominant species originate from the U.S and have arrived since the introduction of Bt cotton. They have also now been found on other crops including brinjal, okra, tomato, chilli, potato, cluster bean, green gram, papaya and sunflower [14]. Independent studies in India show significant reductions in crop yields that correlate with reduced profits as well as devastating numbers of farmer suicides due to indebtedness from expensive Bt seed varieties, combined with the low yielding crops [13]. A study comparing organically grown cotton and Bt cotton on over 200 farms in Andhra Pradesh in India have highlighted the propensity of Bt cotton to accumulate diseases and pests, along with reduced yields [9].

Bt resistance in target pests

As predicted by many scientists as the cultivation of Bt crops expanded, Bt resistance has now emerged and is spreading. So far, 8 populations of Bt resistant pests have been documented, 2 of those resistant to Bt sprays, with the rest resistant to Bt crops (see [15] Bt Resistant Rootworm Spreads, SiS 52). This is not a surprising consequence of Bt crop cultivation, and even Monsanto admit it to be a natural and expected biological process. It now appears that the resistance, at least in the Western rootworm in Iowa fields, is not a recessive trait, meaning that only one copy of a resistant gene is necessary to survive, as opposed to two copies. This has major consequences for the speed at which resistance can spread through pest populations.

As a consequence of Bt resistant pests, Agrotech businesses are busy making next generation crops that carry more and more Bt toxins. For example, the original Bolgard Cotton contained one Bt toxin Cry1Ac, Bollgard II cotton contains 2 toxins, while Bollgard III contains 3 toxins. The latest Smartstax has 8 genes, 6 for insecticide resistance and two for herbicide resistance.

Although on the surface it may appear that failures of GM crops may prove bad business for agrotech companies, the failure of first generation transgenic crops can actually prove profitable business for Industry. Farmers become locked into a cycle of dependency, having to return to buy stronger or more expensive products. The business term to describe the design for a limited useful life-span of a product is ‘planned obsolescence’ [16].

With regards to human health

The Bt toxin has been shown to cause damage to multiple organs including the heart, kidney and liver in lab animals [17]. Furthermore, adverse immune responses have been observed in lab animals as well as humans. One study has found immune responses from the Bt toxin to be similar to that seen with the Cholera toxin [16]. Allergenicity has also been observed in farmers and factory workers handling Bt crops, with effects in eyes, skin and the respiratory tract (see [19] (More illnesses linked to Bt crops, SiS 30). Contrary to industry’s claims, the Bt gene as well as the toxin, remain in the body; it is not degraded in the gut as has been claimed. A recent study in Canada found that over 90 percent of women and their unborn babies had the toxin in their blood streams, just from eating a typical Canadian diet [20]. Crossing the placental barrier is of obvious concern. Reduced fertility in mice fed Bt maize has been documented in a lab study (see [21] GM Maize Reduces Fertility & Deregulates Genes in Mice, SiS 41).

Additional concerns of environmental and ecological damage

In addition to human health, the Bt toxin has consequences on the planets ecosystems, spreading to aquatic and soil organisms. A common model organism of ecotoxicological studies is the water flea Daphnia magna. One study has shown that when fed a diet of 100 percent Bt maize, these organisms showed increased mortality, reduced numbers of females reaching sexual maturity, and overall egg production was reduced [22]. Overall mortality was also higher. The authors concluded that the effects caused by Bt maize were a result of toxic effects and not decreased nutritional content of thee Bt maize. Pollen from Bt maize has also been shown to increase mortality of monarch butterfly larvae. This along with glyphosate destruction of their habitats, may be at least partially responsible for declines in Monarch butterfly numbers migrating from the US to Mexico for winters [23,24] (see [25] Glyphosate and Monarch Butterfly Decline, SiS 52).

Because the toxin is also expressed in the roots of the plants, it also seeps into the soil where it has shown to persist for 180 days. This affects the soil fertility by harming soil organisms, thereby depleting the land and reducing crop yields. A study conducted in India found that soil bacteria in Bt cotton fields were reduced by 14 percent, while total microbial biomass was reduced by 8.9 percent (see [26] Monsanto's Bt Cotton Kills the Soil as Well as Farmers, I-SIS Report 23/02/09). This has implications for yields of crops as well as illnesses, with a new disease termed lalya emerging as a result of nutrient deficiencies in the soil. This causes the plants to redden and wilt. Cross contamination of GM varieties with non-GM varieties also poses big risks for biodiversity, as has been documented with GM corn in Mexico [27].

By-products of Bt crops have been shown in field studies to reduce the growth rate of aquatic insects (caddisflies) by 50 percent and increase mortality rates [28] (see [29] Bt Crops Threaten Aquatic Ecosystems, SiS 36). Half the caddisflies living near Bt maize fields were shown to have Bt maize pollen in their guts. Potential off-target effects are possible in soil as well as streams and rivers.

To conclude

Bt crops are at best useless in pest control, and at worst, an exacerbating factor for pest infestation and reducing crop yields. They are also proving hazardous to non-target species in the ecosystem and to human health. All the evidence favours non-GM integrated pest control as a far superior strategy.

Article first published 14/12/11


  1. EPA ‘Memorandum to Open Docket Plant-Incorporated Protectant Insect Resistance Management (IRM)’. Briefing 30th November 2011. (Docket No: EPA-HQ-OPP-2011-0922)!searchResults;rpp=10;po=0;s=EPA-HQ-OPP-2011-0922
  2. “Monsanto Corn May Be Failing to Kill Bugs, EPA Says”, Bloomberg, December 3rd 2011,
  3. James C. Global Status of Commercialized Biotech/GM Crops: 2010. ISAAA Brief No. 42. 2010, Ithaca, New York: ISAAA
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  5. “The GMO Emperor has no Clothes” Navdanya International report, 2011
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There are 6 comments on this article so far. Add your comment above.

Prof Amyan Macfadyen Comment left 15th December 2011 03:03:28
this really ought to put the final nail in the coffin of Bt but of course it won't. What is to be done to bring to heal both Monsanto and its friends and also the Canadian and U.S. government agencies which are in hock to the cemical maunfacturers?

James Cooley Comment left 15th December 2011 07:07:43
One promising strategy to eliminate GM crops is the California citizens initiative to require labeling of all GM foods. If this initiative passes, food manufacturers will either have to label their foods or(more likely)abandon GM ingredients. Congress seems willing to eat any GM crap Monsanto puts before it, but consumers don't have the same economic incentives.

ajhelms Comment left 16th March 2012 17:05:57
this looks like the end of mansanto corp watch the ceo dump there stock and run, the world is fixing to sue the hell out of mansanto for shipping bad seed filled with insect eggs they have infected the world with insect that never should have left the usa by seed sack,stock dump I not buyin any not after reading this sue happy farmer statement.

aj Comment left 16th March 2012 17:05:42
I am not going to buy any stock not with all this sue happy farmer world wide, and the thought of mansanto distribution of insects world wide with the seed in sack program is not going to go over good either might as well flush mansanto stock down the toilet for what it worth it all ready sliding down and the ceo with start to dump next the law suet will mount up in the 100's billions before it over and if the us farmer grap a wind of this it over no body will buy corn chips any more, what a dummer deal for me, first bernake rapes us of our money now this crap! way to go mansanto you lyin piece of crap company!I like to kick them scientist ass.

Eva Sirinathsinghji Comment left 21st March 2012 02:02:51
Hi Eric, from what I can gather Bt toxins, whether natural or expressed in GM crops, are toxic to many insects, so inevitably will have effects on off-target insects. However, the natural sprays allow topical application whenever necessary, and in addition, it can be washed off. Bt toxins in GM crops on the other hand, are expressed throughout the life-time of the plant and in all the cells including roots, therefore giving more potential to damage biodiversity. I would expect that minimal applications of pesticides only when strictly necessary would be best.Bt toxins are potential allergens so this is something else to consider.

eric Comment left 21st March 2012 02:02:37
so, im confused if the same harm can be caused by spraying bt on crops, or is the harm coming from the genetic modification of the plant? i am a small scale organic farmer who debated using bt for quite a while because of the harm to benficial insects. I finally broke down this winter and sprayed my brassicas. any thoughts?