RESISTANCE OF PLANTS TO HERBIVOROUS INSECTS - CAN THIS RESISTANCE FAIL

Serine proteinase inhibitors (PIs) are common natural products in plan ts that have been extensively studied as phytochemical resistance fact ors against herbivorous insects. Recently we discovered that herbivoro us insects can overcome the activity of these inhibitors by secreting ''inhibitor-resistant'' enzymes. The insect's midgut contains a number of different proteins with trypsin-like activity. Some of these tryps in(s) are susceptible to inhibition by the PI, while other trypsin(s) are not susceptible to inhibition. When ''inhibitor-resistant'' insect s ingest PI, the level of activity of ''inhibitor-resistant'' trypsin( s) is enhanced in the midgut, thus allowing the insect to digest dieta ry protein in the presence of PI. This information suggests that a sui te of PIs may be required to inhibit the majority of proteolytic activ ity in the midgut of the target organism, and thus reduce insect growt h and/or development. Once these PIs have been identified, their genes can be transgenically inserted into plants to enhance phytochemical r esistance against herbivorous insects.