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Controlling the Negative Effects of Bt Plants

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Environmental Reclamation

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Although the negative aspects of Bt plants are difficult environmental problems, there are procedures in place to limit the effects these negative aspects have. For example, Bt plants are tested on non-target insects before they are introduced into the wild (DeMaagd, R. A., and et al., 1999). Currently, there are several measures thought to remedy the negative effects of Bt plants. The most popular are refuges, crop rotation, and varied expression patterns of Bt toxins in plants.

permission pending from Bacillus thuringiensis

Refuges are one general precaution taken with Bt plants. Refuges are sections of non-transgenic plants planted around or among Bt plants. Refuges are required in any field containing Bt plants. There are various patterns that refuges occur in. The non-transgenic crops and Bt plants may be planted in alternating rows-known as strip refuges. Another popular pattern is to surround the Bt plants with non-transgenic crops around the outside-called the border pattern. This type of refuge provides a barrier between Bt plants and non-transgenic plants in nature. Refuges allow susceptible insects to mate with resistant insects, because they can live in close proximity of resistant insects without being killed by the Bt toxins. Also, refuges are supposed to limit dispersal of seeds and pollen into the wild (Bacillus thuringiensis).

EPA's Farmer Refuges Guidelines

At least 20% of crops have to be non-transgenic crop used for a refuge (Bacillus thuringiensis).
Refuge areas must contained in, near, or adjacent to Bt plant fields (Bacillus thuringiensis).
The refuge must be at least one half mile of the Bt field (Bacillus thuringiensis).
If refuges are in the strip pattern, there must be at least four strips of non-transgenic plants (Bacillus thuringiensis).

Crop rotation is another method used to thwart insecticide resistance (Bacillus thuringiensis). Crop rotation occurs two different ways. One type of crop rotation changes the Bt toxin expressed in the plant, without changing the actual plant grown. Rotating the toxins gives the insects less time to develop resistance and reduces selection pressure for resistant insects (Bacillus thuringiensis). The other method of rotation is to plant Bt plants one season and non-transgenic plants the next season (Wu, K., and Guo, Y., 2003). The rotation of transgenic plants with non-transgenic plants keeps resistance genes from becoming stable in the insect population (DeMaagd, R. A., 1999). If non-trangsenic plants are grown one season it gives the susceptible insects a chance to mate and out-compete the resistant strains (Wu, K., and Guo, Y., 2003).

The different gene expression techniques are overexpression of one Bt toxin, expression of multiple Bt toxins in one plant, and tissue–specific expression of a Bt toxin (DeMaagd, R. A., 1999; Wu, K., and Guo, Y., 2003; Zwahlen, C., and et al., 2000). See Insecticide Resistance for more information on each of these techniques.

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Kevin Saunders, Helen Nguyen, and Chris Wrobleski
as part of an undergraduate assignment at Davidson College.

Send questions or comments to chwrobleski@davidson.edu.