A blast search using SPODOBASE gave 10 chymotrypsin (CHY) candidate genes with complete open reading frames (ORFs) of Spodoptera exigua. Among these candidates, Se-CHY2 was chosen and further analyzed in expression and RNAi. Se-CHY2 was expressed only in larval stage and especially in midgut. Its RNAi was successfully performed by double injection of specific double-stranded RNA (301 bp). qPCR showed a decrease of Se-CHY2 expression level by ~50% at 48 h and ~83% at 72 h. RNAi resulted in significant larval mortality. All treated larvae died at 96 h after dsRNA injection. In contrast, control dsRNA treatment did not give any mortality. Enzyme activity of gut juice was measured with N-succinyl-alanine-alanine-prolin-phenylalanine-p-nitroanilide substrate and significantly decreased in larvae treated with dsRNA. These results indicate that Se-CHY2 is a chymotrypsin that is secreted into midgut lumen and plays a role in nutrient digestion.

• Mohammad Vatanparast(Department of Plant Protection, Bu-Ali Sina University, Hamedan, Iran)
• Yonggyun Kim(Department of Bioresource Sciences, Andong National University, Andong 36729, Korea)