Environmental Impacts

Will genetically engineered crops help or harm the environment? It depends on whom you ask.

Two of the most commonly used GE crops are corn engineered to resist pests (Bt corn) and soybeans engineered to tolerate herbicides (Roundup ReadyTM soybeans). Proponents of the crops say they allow farmers to apply significantly fewer chemicals to control for weeds and pests. Fewer chemical applications are certainly a beneficial environmental impact. More controversial are the potentially negative impacts from these crops, usually grouped into three main categories.

  1. Unintended Effects on the Food Chain.

    Monarch butterflies made big news when a study showed that consuming pollen from Bt corn killed the Monarch caterpillar (the larval stage of the butterfly). Bt corn is genetically engineered to produce a toxin that kills the European corn borer. The pollen from the Bt corn drifts onto nearby milkweed plants, a main food source for Monarch caterpillars, and may kill the caterpillers. Other beneficial insects like the green lacewing, a natural predator to the corn borer, may also be affected by the genetically engineered pollen. Bird populations might be affected by Bt too because fewer insects means less food for the birds.

  2. Genetic Drift

    Often referred to as transgenic pollution, genetic drift occurs when pollen from a genetically engineered crop blows into fields where other related crops grow. This could result in cross-pollination, which is of special concern for organic farmers whose bottom line depends on being GE free. (A GE variety of corn might cross-pollinate with a non-GE species.) Farmers using GE seed are supposed to follow regulations that include planting a buffer zone to prevent this pollen drift. But some farmers don't provide a buffer zone. And pollen can drift for miles on windy days.

  3. Resistant Insects

    Insecticide resistance is another concern with widespread use of Bt crops. Insects may eventually become resistant to Bt*, making the GE crops ineffective. And because Bt is also used by organic farmers, Bt resistant insects would certainly become a very challenging problem for the organic farmer. Farmers who use GE crops are encouraged to plant 20% of their crop as non-Bt corn, in order to prevent or slow the development of resistant insects.

*Bt can be applied directly to a field -- it does not have to be geneticaly engineered into a plant to be effective.

Explore More: Genetic Engineering
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