Do GMO Bt (insect-resistant) crops pose a threat to human health or the environment?

Pesticide products containing microbial Bt have been used in organic agriculture for many years. Bt crops have provided substantial human health, environmental and economic benefits. Growers may realize increased crop yields through better pest control and lower overall input costs. ... Bt is well known as a low risk pesticide with little or no toxicity to mammals or non-target organisms.

Reduced insecticide use has been touted as one of the significant benefits of GM crops like Bt corn, but insecticide use is now increasing as farmers attempt to save their failing Bt crops from pests. Not only is Bt corn producing resistant "super-pests," researchers have also found that the Bt toxin can be transfered [sic] to humans and may wreak havoc on your health.

At a Glance

Since 1920 in France and 1958 in the United States, farmers have used a natural insecticide, the microbial pest control Bacilllus thuringiensis, known as Bt. It is non-toxic to beneficial insects and has no impact on higher animals, including humans.

In the 1960s, environmentalists led by Rachel Carson began raising concerns that insects were developing resistance to synthetic pesticides, which spurred research into Bt pest control products by the US government and industry. Researchers engineered a way to insert Bt genes into a variety of crops, including corn, cotton and eggplant, so that the plants organically express the natural insect repellent. This eliminated the need to spray synthetic pesticides or apply Bt mixtures topically.

There are now thousands of engineered Bt varieties. More than 80 percent of US corn and cotton farmers use Bt seeds, and they are grown widely in many other countries. The Bt trait is often ‘stacked‘ with herbicide resistant (Ht) traits, which gives the crop the ability to defeat pests and survive the application of certain weed killers. Use of synthetic pesticides has fallen in every crop in every country that has adopted Bt technology.

In the US, insecticide use has plummeted over the 23 years since GMO Bt food crops were introduced, in significant measure because of the genetically engineered seeds. It’s also led to sharp reductions in the use of pesticides sprayed on cotton in the US, Australia, China, Mexico, Argentina, South Africa, India and Burkina Faso (until it was discontinued), and on brinjal (eggplant) in Bangladesh. Even small reductions in insecticide use have led to big increases in beneficial insects, as noted in an oft-cited study from China.

Anti-GMO activists have claimed that Bt crops can result in the development of new allergens and lead to serious stomach problems, although no studies support such claims. Echoing similar advocacy groups, the Organic Consumers Association, which also rejects vaccines, has warned, “Bt crops threaten public health.” Dozens of safety reviews conducted by regulatory agencies around the world and many more independent studies have shown that Bt crops pose no environmental or health concerns and have not led to an increase in allergies.

Critics have also argued that insects can become resistant to Bt crops. That has happened in some limited cases, replicating the resistance to Bt proteins that has bedeviled organic farming since 1979.

Science and Politics

Bt is a bacterium found organically in the soil. It is extremely effective in repelling or killing target insects but is harmless to beneficial insects, reptiles, birds and mammals, including humans, which cannot digest the active Bt proteins.

Bt was first used by farmers in France in 1920 and gradually adopted by organic and some conventional growers. In the US, Bt was first used commercially in 1958; by 1961 it was registered as a pesticide by the Environmental Protection Agency (EPA). Following World War II, scientists began developing powerful synthetic pesticides that were widely used into the early 1960s. Some insects evolved resistance to these chemicals, sparking research by industry and government that led to the engineering of plants that could naturally express Bt proteins. Scientists were able to transfer the genes that encode the crystal, or Cry, proteins that are toxic to insects into the genomes of certain crops. When hungry insects try to eat the plants, the pests consume the toxin and die in a matter of days.

Bt corn was the first of these crop varieties, introduced in 1996. Scientists have since isolated thousands of Bt strains, many of them incorporated into different varieties of GMO crops, including corn, brinjal (eggplant), potato and cotton. Today, Bt varieties comprise more than 80 percent of the cotton and corn (used mostly for animal feed, although also some sweet corn) grown in the US. Bt potatoes are no longer grown due to a lack of demand from farmers. At the end of 2017, an estimated 23.3 million hectares of land were planted with crops containing Bt genes. The following table shows the countries that have commercialized Bt crops (with single and stacked genes) and their products, from 1996 to 2017.

Image credit: ISAAA GM Approval Database

Overall insecticide use in the US has plummeted since the mid-1990s, largely because of Bt commodity crops. A meta-analysis published in the journal PLoS One looked at the environmental impact of Bt cotton in the US between 1995-2015. The authors found that the insect-resistant crops cut pesticide use and crop losses associated with common pests like the bollworm, corn earworm and tobacco budworm between 47 and 81 percent, depending on which region of the country they examined.

More than 17 percent of the brinjal in Bangladesh grown since 2014 is Bt engineered to kill eggplant fruit and shoot borer (BFSB). Historically, virtually all brinjal farmers in Bangladesh relied solely on insecticide sprays to control BFSB, with farmers applying as many as 84 insecticide sprays during the growing season, now reduced to 1 or 2 applications, leading to a sharp drop in pesticide-related illnesses. A 2018 study found farmers saved 61 percent of pesticide costs compared to non-Bt brinjal farmers, experienced no losses due to insect attacks (versus non-Bt farmers who experienced 36-45 percent infestation) and earned higher net returns.

Bt cotton was commercially introduced in India in 2002 (but years earlier on the black market), and now makes up 90 percent of the market. The genetically engineered crop increased yields 30-60 percent and household income by 18 percent. The Bt boom transformed the country from a net importer of cotton to the world’s third largest exporter behind only China and the United States.

The incredibly quick adoption of Bt cotton seeds by Indian farmers accelerated a reduction in insecticide use already underway in Indian cotton fields. A study pegged the drop at an estimated 60 percent, avoiding at least 2.4 million cases of pesticide poisonings each year. As a corollary benefit, Bt seeds also reduced pesticide applications by non-Bt farmers because of the halo effect of an overall smaller pest population.

An organic industry trade group called the Organic Consumers Association argues that Bt crops are “lethal” to beneficial insects including ladybugs, butterflies and honeybees. There is no evidence to support that claim. A 2003 article authored by EPA researchers and published in Nature Biotechnology found that Bt corn, cotton and potato varieties do not pose a threat to beneficial insects, including honeybees, ladybugs and butterflies.

Related article:  Are GMO foods 'substantially equivalent' to non-GMO foods, as the FDA maintains?

A 2016 review article examined 76 studies published over the preceding 20 years that investigated the impact of Bt crops on beneficial insects, natural pest controllers, bacteria, growth-promoting microbes, pollinators, soil dwellers, aquatic and terrestrial vertebrates and mammals. The authors wrote that no “….significant harmful impact has been reported in any case study related to approved [Bt crops].”

Anti-GMO osteopath and natural products salesman Joseph Mercola has maintained that Bt crops are fueling the development of “super-pests” resistant to the toxic Cry proteins produced by the plants, which in turn is driving up insecticide use.

“It’s clear that Bt plants have led to decreases in spraying,” Marcia Ishii-Eiteman, senior scientist at the Pesticide Action Network, told Grist’s Nathanael Johnson. “But,” she added, “as was predicted 10 years ago, we are starting to see the insect resistance to Bt.

There is some truth to this claim, as both organic farmers using Bt sprays and conventional farmers using Bt seeds have experienced the evolution of some insects resistant to the natural insecticide. There has been one notable problem. In Puerto Rico insects became nearly impervious to Bt corn in just three years.

Spodoptera frugiperda gained resistance to genetically engineered corn in Puerto Rico in just three years.

However, the insect-resistant crops have been a blessing to the environment, claimed University of Arizona entomologist Bruce Tabashnik. The European corn borer remains completely susceptible to Bt, a boon for corn farmers in the US Midwest. Insecticide use has continued its sharp downward trend in the US. And the use of organophosphates (a far more toxic and hazardous class of insecticide) fell 55 percent between 1997 and 2007, in large part because of the use of insect-resistant transgenics.

Anti-GMO activists have also argued for many years that Bt crops pose a serious threat to human health. Jeffery Smith, an anti-GMO activist who heads the one-man Institute for Responsible Technology has alleged without evidence that Bt crops may cause sterility and cancer. The activist website GM Watch has argued they can potentially damage vital organs such as the liver and kidneys.

Citing a small Canadian study from 2011, Dr. Mercola said in 2013:

These shocking results also raise the frightening possibility that eating Bt corn might actually turn your intestinal flora into a sort of “living pesticide factory” essentially manufacturing Bt toxin from within your digestive system on a continuing basis through the transference of the Bt-producing gene to your gut bacteria.

Mercola said consumption of Bt crops may lead to “gastrointestinal problems autoimmune diseases [and] childhood learning disorders” and that rats fed a variety of Monsanto’s Bt corn experienced an immune response indicative of “….various disease states including cancer. There were also signs of liver and kidney toxicity.”

Many activists have argued that Bt crops can produce dangerous allergens. In 2018, GM Watch said that a “study performed in mice found that the GM Bt toxin Cry1Ac is immunogenic, allergenic, and able to induce anaphylaxis (a severe allergic response that can result in suffocation).”

Following the publication of that study, in November 2018, the European Food Safety Authority (EFSA) re-evaluated the allergenicity of the Cry1Ac protein at the request of the European Commission. The EFSA wrote that it stood by its seven previous evaluations published between 2010 and 2018, noting that “….other risk assessment bodies conclude that there are currently no indications of safety concern regarding Cry proteins in the context of the GM plants assessed.”

The US Environmental Protection Agency has addressed these health concerns numerous times, beginning in 2001 when it issued a 50-page report evaluating the potential health risks, including allergenicity, posed by four Cry proteins commonly inserted into Bt corn and potato. It concluded: “None of the products registered at this time, all of which have tolerance exemptions for food use, show any characteristics of toxins or food allergens.”

The EPA noted additionally that consumers may be exposed to Bt toxins at very low levels through processed foods and drinking water, but “….a lack of mammalian toxicity and the digestibility of the plant-incorporated protectants has been demonstrated.”

The Takeaway

Insects are a serious threat to food security. According to the US Department of Agriculture, approximately 40-50 percent of crop yields in the developing world are destroyed by pests each year. In the US, 20-25 percent of crops are lost due to pest damage. This halving of crop losses is due in part to the development of GMO crops, including Bt varieties that proved more effective at controlling insects than earlier chemical sprays alone.

A study published in the Proceedings of the National Academy of Sciences in 2018 analyzed data spanning 1976 to 2016 and concluded that widespread adoption of Bt field corn in the US was “….strongly associated with marked decreases in the number of recommended insecticidal applications, insecticides applied, and damage to vegetable crops.” Depending on the crop, the researchers found that insecticide applications dropped as much as 85 percent.

Considering their overall impact, Bt crops have been an important advance for agriculture. As Matthew Niederhuber, Graduate Research Fellow at the University of North Carolina Chapel Hill, has noted:

The engineering of Bt insecticidal traits into crops like corn, cotton, and potatoes demonstrates the potential benefits and possibilities that advances in biotechnology are now providing. Perhaps most importantly, the story of Bt spotlights the thorough regulatory oversight that the governs the development and application of these GM foods, ensuring their safety and sensible use.governs the development and application of these GM foods, ensuring their safety and sensible use.

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