ENVIRONMENTAL BENEFITS ASSOCIATED WITH GM CROPS:

Issue: Reduced Pesticide Usage

Reduced pesticide usage is one of the benefits of genetically modified crops that are pest resistant. Currently, genetically modified pest resistant crops include Bt cotton, Bt corn, Bt sweet corn, Bt potatoes, and virus resistant squash. These crops are able to resist certain pests and need fewer pesticide sprays. In the past, pesticide usage on cotton, sweet corn and potatoes has been very high with some of these crops requiring more than a dozen insecticide sprays per season. However, Bt sweet corn needs less than 15 percent of the insecticide sprays than does traditional varieties.

But Bt crops still do need some insecticide sprays. Bt is very selective and only controls some insects, and the protection provided by the Bt only protects against some pests. So while Bt crops are protected from the primary pests, control of secondary pests may sometimes require the use of insecticide sprays.

Issue: GM Crops Compliment Biological Control

One group of non-target organisms that need to be encouraged is the natural enemies of our crop pests. Natural enemies are composed of a wide array of parasitic and predatory insects and other arthropods. Control of crop pests by natural enemies is referred to as biological control. Universities, as well as Federal and State agencies has been working for many years to increase the effectiveness and reliance on biological control. Unfortunately, biological control cannot prevent crop damage in all circumstances and farmers often need to apply pesticide sprays.

When these sprays include non-selective insecticides, the natural enemy populations are often hurt more than the pest that needed controlling. The reason is that while the pesticide may kill both the pest and its natural enemies, by killing the pest it has also eliminated the food source that the natural enemy populations will need to recover. Because of this, it often takes much longer for the natural enemy populations to recover than the pest population. In the absence of natural enemies, pest populations are able to increase much more rapidly. This can result in greater reliance on pesticide sprays after the natural enemies are eliminated.

Genetically modified crops that produce their own plant pesticides are more compatible with biological control. The plant pesticides are more selective than most insecticide sprays.
In addition, because the need fewer pesticide applications, they preserve natural enemies populations and are more compatible with biological control.

Issue: Plant Pesticides Impact less on Non-target Organisms

Genetically modified plants that produce their own plant pesticides include Bt cotton, Bt corn, Bt sweet corn, and Bt potatoes. These plant pesticides are very selective, for example, the type of Bt in Bt corn only controls the caterpillars of some moths and butterflies. The type of Bt in Bt potatoes controls Colorado potato beetles. In addition, the Bt is inside the plant, so only insects that feed on the plant or plant parts are exposed to the plant pesticide. An exception to this is with the pollen from Bt corn which is wind blown. The Bt-corn pollen also contains the Bt toxin. It has been shown in the laboratory to reduce the survival of monarch caterpillars that have been feed on milkweed plants that were dusted with this pollen.

But it is important to keep in mind that these genetically modified crops that produce their own plant pesticides require fewer pesticide sprays. Most of the commonly used insecticide used on these crops are referred to as broad spectrum insecticides. They are generally as toxic to non-target organisms as they are to the target pest. Plants that produce their own plant pesticides are more selective in terms of controlling pests without damaging non-target organisms. Their impact on non-target organisms is further reduced because they require fewer broad spectrum pesticide sprays.

Issue: Increased Yields, Reducing the Need to Expand Agricultural Acreage

While the genetically modified crops on the market today do not increase yields. For example, the GM crops that produce their own plant pesticides do not yield more than traditional varieties, they just protect the plants from yield loss. Differences in yield do not represent the ability of the plant to produce more. In fact, in the absence of pests, these hybrids should have yields equal to comparable to traditional hybrids.

However, GM crops that increase yields are under development and the future looks very promising. Unless yield increases are able to keep in pace with population growth, more land will be need to be devoted to commercial agriculture. Current tends show that the amount of prime agricultural land available is decreasing. Crop yields may need to increase by 20 to 40 percent in the next 20 years in order feed an expanding population. Biotechnology provides some of the tools needed to continue to increase the yields of the world's important staple crops.

Issue: Some GM Crops May Reduce Soil Erosion

New herbicide resistant crops may help to reduce soil erosion. We need to prevent soil erosion in order to maintain farm sustainability and to reduce pollution of streams, rivers and wetlands. These crops are tolerant of certain non-selective herbicides such a Roundup™ or Liberty™. This allows the producer greater flexibility in terms of when to control weeds. Rather than using preemergence herbicides that may need to incorporated into the soil, these are applied over the crop and the weeds as they are actively growing. GM herbicide resistant crops are compatible with and encourage no-till agriculture.

ENVIRONMENTAL ISSUES ASSOCIATED WITH GM CROPS:

Issue: Herbicide Resistant Crops Possibly Becoming Weeds in Following Years

One environmental and agronomic issue associated with transgenic crops that have been developed to be resistant to broad spectrum insecticides, is that seeds left behind after harvest may sprout and become weeds the following years. For example, if a farmer uses Roundup Ready™ corn one year then Roundup Ready™ soybeans the next year, the Roundup herbicide will not control volunteer corn that is Roundup Ready™. As more corps are developed that are resistant to the same herbicides, this will become more problematic.

While this is true that if producers rotated among crops with the same type of herbicide tolerance that the volunteers from previous crops would become weeds, relying solely on a single type of herbicide year after year generally is not a good idea. Whether or not multiple crops are tolerant of the same herbicide, relying exclusively on the same herbicide for a long period of time will select for weeds as well as volunteers that tolerate the herbicide. With the example of Roundup Ready™ corn one year then Roundup Ready™ soybeans the next year, there are many available herbicides that can control Roundup Ready™ corn in Roundup Ready™ soybeans and visa versa.

Issue: Potential Gene Escape and Development of 'Superweeds'

One fear with the development of herbicide tolerant, viral resistant or insect resistant GM plants is that they will outcross with wild relatives resulting in superweeds that are more competitive. More competitive weeds are more difficult to control and may make weed management more complicated, expensive, all chemically intensive. Weeds that have a competitive advantage will produce more seeds and be serious in following years.

The potential for outcrossing with weeds exists when crops are grown in areas with weedy relatives that inter breed. In the US for example, we do not have weeds that interbreed with corn, soybeans or potato, so genes inserted into these plants have a negligible chance of escaping into weedy relatives. However, GM squash and canola varieties can interbreed with wild relatives in the US, so the potential for outcrossing with wild relatives and the effect that it may have on weed populations needs to studied and considered prior to GM crops receiving government approval for commercial production.

Issue: Impact on non-target organisms

There has been much media attention given to the potential impact of GM crops on non target organisms. An ideal pest control tactic would be one that controls the pest, but does not harm other non-target organisms in any way. Non-target organisms include all organisms except for the pest to be controlled, this includes mammals, fish, birds, reptiles, and other insects.

Examples of non-target insects to be protected include lady beetles, lacewings, and other insect predators, honey bees and other insect pollinators, and butterflies and other aesthetically pleasing insects.


Media attention has focused on Bt-corn and the impact that it may have on monarch butterflies. At one time, some believed that Bt plants would be the idea control of some crops pests, because only the pests that fed on the plant would ingest the toxin and the toxin is only toxic to some plant feeding insects. However, some Bt-corn plants have relative high levels of the Bt protein in their pollen, and pollen released from these plants may fall on other plants and be eaten by other insects that are not pests. In the case of the monarch caterpillars, pollen from the Bt corn drifts onto milkweed plants which are common in and near corn fields. As the monarch feeds on the milkweed leaves, it ingests the Bt pollen and some caterpillars are killed.

Effects on non-target organisms is and will continue to be an important issue. New GM crops will need to be evaluated for their potential effects on non targets. However, a double standard has arisen for regulating non target effects, one for insecticides and the other for GM crops. Many of the insecticides used today are considered broad spectrum, they kill a wide range of insects including beneficials. Many are classified as Restricted Use Pesticides due to their toxicity to fish, birds, or other wildlife. Relative to most insecticides on the market, Bt-crops are more selective and potentially less damaging to non-target organisms.

Issue : Development of Pest Resistance:

Widespread and intensive use of GM crops that are resistant to pests has the potential of selecting for pests that are resistant to the GM crops. While the possibility of pest developing resistance to GM crops like Bt corn is only a theory, pests have a long history of developing resistance to any pest management tactic that is used for a long period of time over a wide area.
The examples pests being able to overcome pest management strategies are too numerous to list! Consider the western corn rootworm beetle in Illinois and Indiana. For more than 20 years it was effectively controlled through the use of a corn-soybean rotation. The eggs that were laid one summer in a corn field would hatch the following year in what has become a soybean field. This pest had been a problem only with continuous corn. But it adapted. Now a portion of the female beetles lay their eggs in soybean fields and rootworms are now a serious problem in first-year corn in this area. Don't underestimate the ability of insect pests to adapt!

To counter the ability of pests to develop resistance, farmers are required to use resistant management strategies. For example, the required resistance management plan with Bt corn is to plant some acreage with non-Bt hybrids. This is called the refuge strategy. In it, non-Bt acreage on each farm serves as a refuge, allowing some Bt-susceptible corn borers to survive. Use of resistance management strategies are required and will delay or prevent the development of pest resistance.

Issue: Antibiotic Resistance Marker Genes

One concern that has been expressed is that the use antibiotic resistance marker genes in some transgenic crops may foster the development of antibiotic resistance by harmful microbes. There is a possibility that harmful microbes may be able to capture antibiotic resistance genes either in the field from transgenic crops or their decaying crop residues or when the transgenic grains are feed to livestock or other animals. Antibiotic resistance remains a serious issue confronting clinical medicine.

However, others argue that the type of antibiotic resistance markers that are used today are common in nature. In fact, the antibiotic resistance used does not provide resistance to most of the antibiotics used in clinical medicine.

Issue: Biodiversity

Many environmentalists, including farmers themselves, are very concerned about the loss of biodiversity. Although the increased adoption of conventionally bred crops has raised similar concerns, we want to make sure that we maintain the pool of genetic diversity needed for time the future. Scientists continue to work actively to preserve plant species through the preservation of genetic material (DNA). The science of biotechnology has dramatically increased our knowledge of how genes express themselves and highlighted the importance of preserving genetic material.

Another related concern relates to the narrow range of crops that farmers currently grow. There are only about 35 crops with significant world production. For example, if all farmers grew the same variety of corn, one unstoppable corn blight could easily destroy a huge amount of our corn production. This has been a concern with conventionally-bred crop varieties as well. Biotechnology can help in two ways. Crop varieties can be developed that are "disaster-resistant" much quicker than through conventional breeding. And biotechnology has the increased capability of developing multiple sub-species of the same crop, tailored to specific agronomic conditions and consumer needs, thereby reducing the chance of an entire corn crop being wiped out.

In addition, because some biotech crops produce their own plant pesticides and reduce pesticide sprays, the potential non-target effects of these pesticides on other organisms is reduced. A concern with traditional pesticide applications has been the movement of pesticides out of the field through movement of soil and water. GM crops can lessen this concern.

Link:
http://www.ca.uky.edu/brei/Environment/environm.htm