Abstract: The effect of tea plants Camellia sinensis induced by exogenous methyl jasmonate (MJA) on lipoxygenase (LOX), polyphenol oxidase (PPO) and proteinase inhibitor (PI) activity in the leaves of tea plants, as well as the growth and midgut proteinase activity of geometrid Ectropis obliqua larvae were studied. MJA significantly induced LOX, PPO and PI activity in tea leaves of tea plants. When geometrid larvae have fed on leaves of tea plants treated with MJA, the activities of the high alkaline trypsin-like enzyme and chymotrypsin-like enzyme in their midgut were significantly inhibited, but the activities of the low alkaline trypsin-like enzyme in their midgut were unaffected, leading to imbalance between different types of proteinase activity in the midgut of the larvae and in turn, the growth were inhibited. This chain of responses may be an important mechanism of the direct resistance induced by MJA-treatment of tea plant on geometrid larvae.

Key words: Methyl jasmonate, Proteinase inhibitors, Midgut proteinase, Ectropis obliqua, Camellia sinensis