Abstract: Based on the in vitro effect on protease activity of larval midgut,soybean trypsin inhibitor (STI) was suggested as the potential resistant agent to cotton bollworm, Helicoverpa armigera. It was incorporated in the larval artificialdiet at 0.84-4.2% (dry weight) to determine its acute and chronic effects on the growth and in vivo midgut protease activity of cotton bollworm. Ingestion of 4.2% STI in short term resulted in reduced larval growth rate, increased low alkaline trypsin-like enzyme activity, decreased high alkaline trypsin-like enzyme activity,decreased chymotrypsin-like enzyme activity, and decreased total proteolysis. When the larvae chronically ingested 0.84% STI, low alkaline trypsin-like and chymotrypsin-like enzyme activities were significantly elevated, high alkaline trypsin-like enzyme activity was markedly declined, and total proteolysis had no significant change. When the larvae chronically ingested 4.2% STI, high alkaline trypsin like enzyme activity and total proteolysis were significantly decreased, but there was nosignificant elevation of low alkaline trypsin like and chymotrypsin-like enzyme activities. Retarding effect of STI on growth of the larvae was significant but not proportional to the dosage of STI. Thus, the mechanism of anti-nutritional action of proteinase inhibitor seems to be complicated, and pernicious hyperproduction ofsome protease may be only one aspect of the action. Influence of cooperative prote ases activity may still be the basis in mode of action.

Key words: Soybean trypsin inhibitor, Helicoverpa armigera, protease