부산대학교 도서관

Insecticidal substances produced in transgenic crops for insect resistance can generally be divided into 4 groups, δ-endotoxin of Bacillus thuringiensis (Bt), lectins, enzyme inhibitors and enzymes. The δ-endotoxin major toxic substance of Bt. The gene for the endotoxin from Bt is inserted into plants to produce insect-resistant crops. The most common modifications of crops are to insert the cry1 gene for the control of lepidopterans and to insert the cry3 gene for coleopterans. Since 1995, the main lectin studied has been the snowdrop lectin (Galanthus nivalis agglutinin, GNA). The gene is inserted to produce proteins in tobacco, potato, rice, and wheat which inhibit the growth of insect pests such as moths, aphids, and hoppers. Enzyme inhibitors include protease inhibitors and α-amylase inhibitors. Genetically modified rice, wheat, tobacco, and potatoes with protease inhibitors show various degrees of resistance to leaf hoppers and lepidopteran larvae. Research has mainly been conductedα-Amylase inhibitors on beans for resistance to bean weevils. Enzymes include chitinase and cholesterol oxidase. Transgenic crops with a chitinase-producing gene which is found in microorganisms to insects show resistance to their pest insects. Such food injures the peritropic membrane of the midgut of the target insect and hence normal food consumption and nutrition absorption are disturbed. Cholesterol oxidase isolated from bacteria reduces the growth rates of insects by destroying cell membranes in the digestive tract. Among the transgenic crops with the above insecticidal substances, Bt crops such as Bt cotton, Bt corn, and Bt potatoes have been commercially cultivated in large areas. Insect-resistant transgenic crops are considered to benefit the insects of environment by allowing the reduction or elimination of the use of broad-spectrum and highly toxic synthesized insecticides during cultivation. To assess the environmental risks, the following factors need to be considered and analyzed. I. Insect resistance. Transgenic crops which contain the Bt gene constantly expose insects to this toxin. This creates strong selection pressures and increases the risk of development of resistance in insects. Various resistance management strategies for transgenic crops have been evaluated and suggested. II. Impacts on non-target insects, such as natural enemies, minor insect pests, soil insects, insects of conservation concern, and pollinators. III. Impact on biodiversity. The rich and diverse insect fauna here in Taiwan is one of our precious natural resources. Along with the development of transgenic crops, efforts should also be devoted to the research and conservation of biodiversity to avoid any negative impacts.