Reading Practice 3

[1] Ranging from viruses to humans, genes from virtually all kinds of organisms can now be inserted into plants, creating what are known as transgenic plants. Now used in agriculture, there are approximately 109 million acres of transgenic crops grown worldwide, 68 percent of which are in the United States. The most common transgenic crops are soybeans, corn, cotton, and canola. More often than not, these plants will contain a gene that either makes them resistant to the herbicide glyphosate or produces an insect-resistant protein called Bt toxin.

 

[2] Advocates of transgenic crops argue that the benefit of these crops is that they’re environmentally friendly, allowing farmers to use smaller amounts of less noxious chemicals for crop production. For example, there has been a 21 percent reduction in the use of insecticide reported on Bt cotton (transgenic cotton that produces Bt toxin). In addition, when glyphosate is used to control weeds, other more persistent herbicides do not need to be applied.

 

[3] However, adversaries of transgenic crops suggest that there are still many unanswered questions that must be addressed before transgenic crops will be safe to grow on a larger scale. Some questions concern the effects that Bt plants have on non-target organisms, such as beneficial insects, worms, and birds that consume the genetically engineered crop. For example, monarch caterpillars feeding on milkweed plants near Bt cornfields feed on corn pollen that has fallen on the milkweed leaves. Laboratory studies indicate that caterpillars can die from eating Bt pollen. However, field tests indicate that Bt corn is not likely to harm monarchs. Furthermore, the application of pesticides (the alternative to growing Bt plants) has been demonstrated to cause widespread harm to non-target insects.

 

[4] Another question that remains unanswered is whether herbicide-resistant genes will move into the various populations of weeds. Crop plants are sometimes grown in areas where weedy relatives also live. If the crop plants crossbreed and reproduce with weedy relatives, then this herbicide-resistant gene will be perpetuated in the offspring. In this way, the resistant gene can make its way into the weed population. If this happens, a farmer can no longer use glyphosate, for example, to kill those weeds. This scenario is not likely to occur in many instances when there are no weedy relatives growing near the crop plant. However, in some cases, it may become a serious problem. For example, canola readily hybridizes with mustard weed species and could transfer its herbicide-resistant genes to those weeds. We know that evolution will occur when transgenic plants are grown on a large scale over a period of time. The development of insect populations resistant to the Bt toxin is of particular concern. This pesticide has already been applied to plants for decades without the development of insect-resistant populations. However, transgenic Bt plants express the toxin in all tissues throughout the growing season. Therefore, all insects carrying genes that make them susceptible to the toxin will die. Such an event would leave only the genetically resistant insects alive to perpetuate the population. When these resistant insects mate, they will produce a high proportion of offspring capable of surviving in the presence of the Bt toxin. Farmers are using different methods in an attempt to slow the development of insect resistance in Bt crops. For example, some farmers are planting nontransgenic border rows to provide refuge for susceptible insects. These insects may allow Bt susceptibility to remain in the population.

 

[5] Perhaps the most serious concern about the transgenic crop plants currently in use is that they encourage farmers to move farther away from sustainable agricultural farming practices, meaning ones that allow natural resources to continually regenerate over the long run. Transgenic plants, at least superficially, simplify farming by reducing the choices made by the manager. Planting a glyphosate-resistant crop commits a farmer to use that herbicide for the season, probably to the exclusion of all other herbicides and other weed-control practices. Farmers who use Bt transgenic may not feel that they need to follow through with integrated pest-management practices that use beneficial insects and timely applications of pesticides to control insect pests. A more sustainable approach would be to plant non-transgenic corn, monitor the fields throughout the growing season, and then apply a pesticide only if and when needed.