Is the Diversity of Trypsins in the Insect Midgut a Determinative Factor in Host Plant Selection?

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Lay Abstract 9507361 As one defense against herbivory, many plants produce proteinase inhibitors that interact with digestive enzymes produced by insect herbivores. The inhibitors reduce the insect's ability to digest plant tissue. Some insects, however, respond to proteinase inhibitors by producing forms of the digestive enzymes that are not susceptible to the inhibitor. This ability may permit some insects to feed successfully and grow rapidly on a wide range of plants, using a different suite of digestive enzymes for each. This research will test that hypothesis by comparing two insects, a dietary specialist (the black cutworm) and a dietary generalist (the corn earworm). The genes that code for the digestive enzymes called trypsins will be isolated and characterized in each species, and the susceptibility of each form of trypsin to inhibitors will be determined. The results should yield insight into the diversity and regulation of digestive enzymes in plant-eating insects, the importance of plant proteinase inhibitors as defenses against insect attack, and the importance of digestive physiology in controlling the range of plants on which a particular insect can feed. Ultimately, the research may lead to development of effective strategies for controlling herbivorous insects by manipulating the level and diversity of proteinase inhibitors in agricultural and horticultural plants, and/or disrupting the mechanisms that insects use to regulate digestive enzyme production and secretion.