Plant Resistance to Insects: A Resource Available for Sustainable Agriculture

Varying levels of resistance to insects occur naturally in crop plants and closely related species. Historically, plant breeders have developed resistance to insects in situations where it was perceived to provide economic advantages over the use of insecticides in conventional agriculture: in field crops with low value per unit area and high acreage, and in staple food crops of developing countries. Under these circumstances, the use of resistant varieties is the principal method of control for many key insect pests. The process of identifying new sources of resistance and moving genes for resistance into commercial varieties through conventional breeding can be slow, often taking 12 years or longer. There is interest in more rapidly creating plant resistance to insects using genetic engineering. Technologies for gene transfer have been developed for most crop plants, but current prospects for engineering resistance to insects are limited by our lack of identified candidate genes to transfer, our elementary stage of understanding of gene regulation in plants, and uncertainty about the acceptance of engineered organisms by society. Most plants genetically engineered for resistance to insects and currently being tested in the field derive their resistance from a protein endotoxin from one of the many strains of Bacillus thuringiensis, a bacterium long used as a microbial insecticide. Insects are capable of evolving to overcome plant resistance, and several have overcome resistance in conventionally bred varieties. This needs to be considered in the development and deployment of resistant varieties. There has been, and continues to be, an enormous amount of germplasm developed by breeders for resistance to insects. This is a resource that should not be overlooked in redesigning agricultural systems to be environmentally and economically sustainable. Much more work needs to be done to integrate plant resistance to insects with other insect control methods and into sustainable agricultural systems.