Submitted to: Journal of Agricultural and Food Chemistry
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 7/1/1998
Publication Date: N/A
Interpretive Summary: Corn feeding insects cause hundreds of millions of dollars of damage each year. They are also responsible for introducing molds that make toxins harmful to people and animals. Conventional insect control is usually too costly to be effective. Producing plants with insect resistance, either through breeding or genetic engineering, is a potentially lower cost and environmentally more acceptible control strategy. A protein that occurs in the kernels of some varieties of corn was found to reduce feeding by beetle pests at naturally occurring levels. An enzyme-activated form of this protein reduced feeding by both beetles and caterpillars. Production of natural levels of this protein in corn tissues that are deficient in it, through breeding or genetic engineering, should reduce insect damage and associated toxic mold problems in an economically and environmentally acceptable manner.
Technical Abstract: The relative toxicity of proenzyme and protease-activated forms of maize seed ribosome-inactivating protein (b-32) to several insect species was determined. Only the protease-activated form had significant toxicity to any caterpillars when fed in diets at 1000 ppm. Activity ranged from 70% mortality to cabbage looper (Trichoplusia ni) to no effect to Indian meal moth (Plodia interpunctella). Neither form of the protein showed activity against larvae of the Freeman sap beetle (Carpophilus freemani). However, the proenzyme and protease-activated forms were approximately equally deterrent in choice assays to other sap beetles and maize weevils (Sitophilus zeamais), with relative feeding rates reduced by up to sixfold. Because this protein can naturally occur at the 1000 ppm range in the endosperm of Opaque 2 (normal) plants vs. two orders of magnitude lower in Opaque 2 mutants, it is likely that this RIP plays a natural defensive role against insects. However, some insects appear to have adapted to this protein.