抗蟲基因轉殖植之類別與其對環境中昆蟲之影響

Insect-resistant transgenic plants and the environmental impact assessment -- special concern for insects

"在抗蟲基因轉殖植物的研究上，利用於抗蟲的物質主要有蘇力菌內毒素、凝集素、酵素抑制物與酵素等四類。蘇力菌內毒素（毒蛋白）（δ-endotoxin of Bacillus thuringiensis）為蘇力菌殺蟲之主要成分，基因轉殖作物以殖入抗鱗翅目的cry1與抗鞘翅目的cry3最普遍。凝集素（Lectins）以雪花蓮凝集素（Snowdrop lectin, Galanthus nivalis agglutinin, GNA）為主，轉殖入煙草、馬鈴薯、稻米、小麥等作物，對於某些鱗翅目害蟲如蛾類與同翅目害蟲如蚜蟲、飛蝨類有抑制作用。酵素抑制物中常被利用的有豆類所含之蛋白酶抑制物（Protease inhibitor）與澱粉酶抑制物（α-amylase inhibitor）。蛋白酶抑制物轉殖於水稻、小麥、菸草、馬鈴薯等，可防治飛蝨、蛾類等幼蟲，具不同程度之殺蟲效果；澱粉酶抑制物主要研究於豆象類的防治。酵素類研究較多的是幾丁質分解酶（Chitinase）與膽固醇氧化酶（Cholesterol oxidase），幾丁質分解酶為昆蟲或菌類產生的幾丁酶，可破壞昆蟲中腸壁之圍食膜，擾亂取食與營養的吸收；膽固醇氧化酶分離自細菌，可破壞昆蟲消化道之細胞膜，抑制昆蟲的消化作用。實際栽種推廣之抗蟲基因轉殖作物，均利用轉殖蘇力菌內毒素基因，如Bt棉花、Bt玉米、Bt馬鈴薯等，涉及其餘之抗蟲物質則多數仍在研發階段。抗蟲基因轉殖作物因於栽種期間，可減少廣效性與劇毒性殺蟲藥劑的使用，故對於生態環境的維護具有正面之意義；然而評估其對生態環境中昆蟲類是否有不利影響時，尚需考慮以下諸因子。害蟲產生抗性：栽種基因轉殖之抗蟲作物，即等於使害蟲長期暴露於該抗蟲物質的毒性下，提高害蟲產生抗性的機率，可能導致作物再度蒙受蟲害損失，使蟲害管理更加困難，因此針對Bt作物，亦衍生有關抗性管理之配套措施。非目標昆蟲之衝擊：例如對天敵昆蟲、次要害蟲、土壤昆蟲、保育類昆蟲、授粉昆蟲等之影響。昆蟲多樣性之影響：台灣為居處深具昆蟲多樣性的地域，在研究基因轉殖作物的同時，需投注人力與物力研究並維護昆蟲及其生物多樣性，避免基因轉殖作物對環境產生負面影響。"

"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."