Bt corn is a novel solution for insect control
Syngenta Bt corn has been enhanced through biotechnology to enable it to protect itself against the corn borer, which is one of the most destructive insects to damage or reduce corn production and one of the most economically significant crop pests in the world.
For 8,000 years, corn has been a staple in the diet of livestock and humans alike. It is a versatile crop with many important uses.
The mechanism that Bt corn uses is based on a naturally occurring bacterium
Bacillus thuringiensis, also known as Bt, is a naturally occurring soil bacterium. Bt bacteria produce proteins that stop specific target insects in their tracks while being safe for non target animals. One of these proteins, produced from the gene Cry1Ab, targets corn borers. The tools of biotechnology were used to insert the Cry1Ab gene into Bt corn, providing a novel solution for protection of corn from corn borer attack.
Once corn borers enter the corn stalk to attack the plant from the inside, conventional treatments are not always effective, or even possible. Since conventional pest sprays cannot reach the attacking corn borers, they continue to eat away at the inside of the corn stalk. Eventually, enough damage is done that the corn plant can be easily blown over by wind or even knocked down by rainfall, preventing the corn from maturing and making harvesting difficult.
As with any other genetically modified crop, the safety of Bt corn has been thoroughly assessed, both during development, and on an ongoing basis in the areas in which it is grown. The process of developing and marketing a genetically enhanced crop is carefully regulated and Syngenta, academic researchers and national regulatory bodies have concluded that Bt corn is safe for food, feed and for the environment.
In fact, experience has shown significant benefits of growing Bt corn. Bt corn can make the farmer's life easier, allows more targeted use of pesticides, and can improve the quality and quantity of the harvest.
Why does corn need protection from corn borers?
It is estimated that, each year, 40 million tons of corn never reach the market because of damage by the corn borer - equivalent to the entire production of Brazil. amage and control costs in North America alone are thought to exceed US$1 billion per annum.
Chemical insecticides and biological control methods are available to control outbreaks of corn borer, but the nature of the infestation makes it difficult and expensive to control. The adult corn borer, a moth, lays its eggs on the corn plant and then the young larvae tunnel into the corn plant, eating it as they go. Eventually, the larvae eat so much of the inside of the corn plant that the plant can fall over or stop growing. If corn borers are not controlled, the larvae will eventually turn into moths and the cycle continues. To be effective, pesticides must be applied when the larvae are exposed on the surface of the plant. Once they start burrowing into the plant, conventional control methods are often ineffective.
Bt corn produces a protein that gives Bt corn built-in resistance to the corn borer - offering protection throughout the plant where the insect attacks.
How does Bt corn work?
Bt maize has built-in protection against corn borers, achieved through modern biotechnology, where the Cry1Ab gene has been added. The Cry1Ab gene produces a Bt protein (Cry1Ab) which protects the plant from insect damage. This gene was derived from the common soil bacterium Bacillus thuringiensis, widely used as a biological control agent against various insect pests.
Additionally, a marker gene (pat), has been added which gives the plant a tolerance to phosphinothricine, the active ingredient of glufosinate ammonium herbicides. This gene is derived from the soil bacterium Streptomyces viridochromogenes. The herbicide tolerance gene allowed selection of transformed plants in the development stage.
Bt-11 insect-protected maize produces the Bt protein in its leaves, silks, stalks and ears throughout its life, enabling it to provide season-long protection against these devastating insect pests.
What are the benefits of Bt corn?
Bt corn offers many benefits. It represents an environmentally sustainable way to control devastating insect pests and, therefore, to ensure yield. Also, grain from Bt corn is often of better quality than grain from conventional corn hybrids, since insect damage reduces grain quality.
Studies show that there is a significant economic return from growing Bt corn, with yields protected in years when there is a heavy outbreak of corn borer. There is also evidence that Bt corn provides a form of protection to non-Bt corn by reducing the overall population of corn borers. In some areas, the moth can go through three generations in one summer, and controlling the first generation larvae in Bt corn means fewer moths emerging to start the second and third generations.
The benefits of reducing the corn borer population are not limited to decreasing the direct damage caused by the larvae. The tunnels that the larvae bore in the ears also provide an entry point for other pathogens, particularly fungi. These fungal infections affect the quality of the grain and reduce yields. One in particular, Fusarium, or "ear rot", produces molds that are unhealthy for animals eating the infested grain - meaning that Bt corn is also in a position to make an important contribution to grain quality and safety.
How do you know Bt corn is safe?
Countries across the world have worked together to develop very strict food safety assessment procedures. These require a thorough analysis of scientific data by independent government experts prior to approval. The extensive information required in order to address the food safety assessments covers many areas.
The plant biology of Bt corn and its characteristics have been determined to be comparable, or substantially equivalent, to non-Bt corn. These tests assess the composition, nutrition, and general wholesomeness of Bt corn compared to non-Bt corn. Before Bt corn was approved for sale, it had to be demonstrated that any minor differences that were observed in scientific testing were within the range of normal variations in corn.
The safety of Bt corn for human and animal health has also been thoroughly addressed. These assessments considered and tested the possibility of allergic reactions. The assessments also evaluated the possibility that earlier techniques, which were used to select transformed plants, could be linked to antibiotic resistance. This extensive research led to the conclusion that Bt corn is as safe as non-Bt corn for human and animal health. Bt corn has a long history of safe use in many countries. Since Bt corn was first planted commercially in the United States in 1996, acreage has grown to about 12.3 million hectares (approximately 30 million acres).
What about the possibility of allergic reactions?
Bt corn has a long history of safe use and consumption.
Included in the regulatory process is an assessment of potential allergenicity that carefully examines all introduced proteins to evaluate their potential to cause allergies. The question of whether Bt corn could cause a food allergy centers on the fact that Bt protein is not normally found in corn.
Proteins that cause allergies have a very specific and well-characterized structure that "locks" onto the body's immune system, prompting the allergic reaction. If an introduced protein shows a similar structure to a known allergen, then a series of further tests is required to provide more information on the protein's potential to actually cause an allergy. This makes it possible to assess the likelihood of a new protein causing an allergy by comparing it with known allergens. Such evaluation is a requirement for the registration of genetically enhanced plants. The analysis conducted on the Bt protein in Syngenta Bt corn did not demonstrate any allergenic potential.
Does growing Bt corn have any adverse effects on the environment?
Before Bt corn could be approved, regulatory authorities thoroughly considered a wide range of research examining the possible impacts of Bt corn on non-target organisms including bees, ladybirds, butterflies, beetles, birds and small mammals.
The mechanism whereby Bt protein controls the corn borer is highly specific, and most non-target organisms in the field are not affected by it. Rather, these animals digest the protein along with all the others in their diet.
What about the Monarch butterfly?
In 1999, scientists at Cornell University reported that eating Bt pollen could harm a cherished and popular symbol of American wildlife, the Monarch butterfly. The finding was based on a laboratory study in which Monarch caterpillars were fed leaves of milkweed - the plant that forms their exclusive diet - coated with Bt pollen.
This prompted the US Environmental Protection Agency (EPA) to call for more data to see if there was a threat to the Monarch in the wild. Several field studies, in corn growing areas across North America, demonstrated that field conditions were quite different from those in the laboratory. For instance, the levels of Bt pollen on milkweed growing on the edge of cornfields were far lower than in the laboratory study.
The research also showed that handling the plant material in the laboratory study released far more of the Bt protein than is the case if caterpillars ingest it in the wild.
In October 2001, the EPA announced the results of a two-year scientific review of Bt corn that found it "poses no risks to human health or to the environment". The scientific evidence shows that the risk to the monarch butterfly by Bt corn pollen in the field is negligible.
How exactly does Bt corn protect itself from the corn borer?
The source of Bt corn's resistance to the corn borer is Bacillus thuringiensis (Bt), a naturally occurring bacterium found in soils around the world.
Specific strains of Bacillus thuringiensis produce a protein, often called "Bt protein". When eaten by a corn borer, Bt protein is broken down by digestive enzymes in the larva's alkaline (basic pH) intestine, generating a shorter protein that binds to specific receptor proteins in the wall of the intestine of the target insect pest. This damages the cell membrane, making it leaky, and stopping the larva in its tracks.
Bt is the active ingredient in sprays that have been used by farmers and gardeners for over 40 years. The mode of action is so specific that, while these sprays are very effective against the corn borer, in general they have no effect on non-target insects and are safe for humans and animals. Bt breaks down rapidly in the environment and, as it is naturally occurring, the sprays are accepted for use in organic farming systems.
However, the spray has one main limitation. The corn borer moth lays its eggs on the outside of the plant but, once they hatch, the larvae eat into the plant, destroying it as they go. Once inside the plant, the larvae cannot be touched by insecticide sprays or other control methods. Therefore, farmers have to carefully monitor their crops and hope the weather won't prevent spraying during the short time period that the larvae are outside the plant.
Won't the corn borer develop resistance to the built-in pesticide of Bt corn in the same way as some pests have become resistant to chemical pesticides?
The Bt protein that protects the plant against the corn borer is the active ingredient of a number of pesticide sprays employed to protect conventional and organic corn. In the decades they have been in use, there has been no evidence of the corn borer becoming resistant to Bt sprays in the field.
However, pests do find ways around plant control mechanisms. This is a well-known natural phenomenon, and can occur regardless of whether the protection is chemical or biological.
In order to prevent corn borers developing immunity to Bt protein, planting systems have been introduced in which Bt corn is grown surrounded by refuges, or blocks of non-Bt corn. These recommendations were developed based on the results of independent scientific recommendation. Even if any corn borers on the Bt corn are resistant to the Bt protein, they are likely to mate with non-resistant moths from the conventional corn, and the resistance will not be passed on to future generations.
In addition, in areas where Bt corn is grown commercially, insect populations are monitored to watch for resistance. In the many years since Bt corn was first planted, there have been no signs of resistance developing in target insects due to the use of Bt corn in the field.
What about the regulation of Bt corn and other genetically enhanced crops?
Genetically enhanced plants represent a class of crop that is subject to careful scrutiny and assessment before being approved for planting and consumption.
The process of developing a GM plant is carefully regulated in order to ensure it is carried out in a safe and responsible manner. During development, plants must be assessed first in the laboratory, then in the greenhouse, and finally in the field. There are also intensive studies of possible environmental impacts of the plant, and of the safety of the food and feedstuffs derived from them.
This research follows safety requirements and guidelines laid down by each country, and involves collaborating closely with regulators to address any questions they raise. Products such as Bt corn are assessed to ensure they have no toxic properties, that they do not cause food allergies, and that the modification process has not unintentionally altered the nutritional value. In addition, possible environmental effects of the genetically enhanced plant are considered.
Overall, genetically enhanced plants and their produce are subject to far more rigorous regulatory regimes than conventional crops. Governments around the world, from the US, Canada, Argentina, Japan, South Africa, Uruguay, and the European Union, which have approved the commercial planting of Bt corn, to Switzerland, the Philippines, Taiwan, China, Korea, Russia, Australia and New Zealand, which have approved the food use of Bt corn, have all put in place strict and thorough regulations.
For example, in the case of Bt corn, the US Environmental Protection Agency (EPA) considered many years of human, animal and environmental safety data before allowing it to be registered. Approval by the EPA, in August 1995, was granted on condition that a program is put in place to monitor for the possible development of Bt resistant populations of corn borers. Elsewhere too, implementing a resistance management plan has been a requirement to obtain registration. The US regulatory checks did not stop at approval by the EPA. Bt corn also had to satisfy the requirements of the US Food and Drug Administration (FDA), acknowledged as one of the most stringent regulatory bodies in the world, and the US Department of Agriculture (USDA).
In Europe, genetically enhanced plants have been subject to intense scrutiny by the European Union. As well as in-depth safety assessments leading up to registration, European legislation dictates that genetically enhanced plants and food produced from them should be labeled as such. Approval for the first Bt corn product in the EU was granted in 1997.
In total, Bt corn has been assessed and endorsed by more than 30 scientific committees and authorities. In all countries where Bt corn is approved for planting and/or for consumption, the regulatory authorities have concluded that it is as safe as conventional varieties of corn.
What future improvements to corn and other plants are planned?
As the example of Bt corn demonstrates, genetically enhanced crops can offer significant benefits. It is an illustration of how a single modification - enabling Bt corn to protect itself against the corn borer - can make a tremendous difference. But developments to date have only offered a glimpse of the contribution that genetically enhanced crops will make to world food production and human health in the future.
At Syngenta, we are working on further improvements in corn and other crops. This includes a type of corn that will protect itself against other significant pests, such as corn rootworm. Another type of corn in development will produce its own amylase, an enzyme for converting starch to sugar. This can reduce the costs involved in processing corn during the early stages of producing ethanol, a renewable fuel source for cars.
At the same time, we are refining and enhancing the techniques used in plant biotechnology. One example is Positech®, a method of selecting plants. This provides a novel alternative to antibiotic and herbicide resistance markers. Another future development may be directing how introduced genes are activated so that the protein for which they code is only produced where it is required - in the roots to combat a pest that attacks from the soil, or in the stem and leaves for airborne and crawling pests.
Where can I learn more about.