Abstract: Plant proteinase inhibitors (PPIs) are important defensive substances. In order to understand the effects of damage degrees on the activities of PPIs, the activities of trypsin inhibitors (TI) and chymotrypsin inhibitors (CI) in Larix gmelinii seedling needles after being cut with scissors or fed by the larvae of Dendrolimus superans at three various degrees, respectively, were assayed with UV-spectrometry. The results showed that both TI and CI activities in the seedling needles increased significantly after the two treatments from 1 to 20 days, compared with the control. However, there was no significant relationship between PI activities and the damage degrees. TI activities induced by insect feeding were higher than those by needle cutting under the same injured degree whereas the differences were not significant. CI activities induced by larva feeding were all higher than those by needle cutting only on the 5th day no matter what damage degrees. Our research clearly demonstrated that making appropriate injury intentionally to mimic well the effects of herbivory feeding could in crease larch defence, which can be used as a new method to control the larch pests.

Key words: Larix gmelinii, Dendrolimus superans, trypsin inhibitors, chymotrypsin inhibitors, needle cutting, herbivore feeding