• Invasiveness—genetic modifications, through traditional breeding or by genetic engineering, can potentially change the organism to become invasive. Few introduced organisms become invasive, although it is a concern for the users.
• Resistance to Bt—the biggest potential risk to using Bt crops is resistance.
• Cross-contamination of genes—although unproven, genes from genetically modified crops can potentially introduce the new genes to native species.
• For these reasons there are numerous societal concerns about the use of genetically engineered plants, including those with Bt insertions.
Adapted from "History of Bt," Dr. Raffi V. Aroian, University of California at San Diego, La Jolla, CA, USA: http://www.bt.ucsd.edu/ bt_history.html.
The gene coding for this protein has been cloned from various B. thuringiensis strains and has been incorporated into the genome of a number of plants (corn, cotton, potato). The insect against which the toxin is active dies soon after feeding on the transformed plant. A drawback to this approach is that resistance of the insect to the toxin may develop. The major advantage of the Bt toxin is that it is harmful to only a few species of insects, while it is harmless to other animals and humans. These biological pesticides also degrade rapidly in the environment. Thus, the use of such biological pesticides appears to be an environmentally safe alternative to pest control than the use of synthetic chemical pesticides.
Other examples of biocontrol agents of insects include the fungus Metarrhizium anisopliae, used to control larvae of grass grubs (Costelytra) in pastures, as well as several genera of nematode-trapping or nematophagous fungi (Arthrobotrys, Dactylella, Verticillium). Entomopathogenic nematodes of the Delanus, Neoaple-cantana, Tetradonema, and Heterorhabditis have been found to control a wide range of insect pests. The success of these nematodes lies in the fact that most plant insect pests spend a part of their life cycle in soil.
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