Abstract: Phenolic acids are the important secondary metabolites associated with induced plant responses. Taking the Larix gmelinii seedlings with their needles on 4 selected branches being partially cut off or fed by Dendrolimus superans (Lepidoptera: Lasiocampidae) larvae as test objects, this paper quantitatively determined the phenolic acid concentrations in the undamaged needles by using HPLC. One day after 50% of the needles on the branches were cut off or fed by D. superans larvae, the concentrations of benzoic acid, caffeic acid, gallic acid, phenylaetic acid, cinnamic acid, vanillic acid, syringic acid, sylicylic acid, and chlorogenic acid in undamaged needles had significant difference with the control; and one day after 75% of the needles were cut off or fed by D. superans larvae, the concentrations of the 9 phenolic acids and ferulic acid changed significantly. These results implied that cutting off or feeding with 50% or 75% of the needles could cause the concentrations of phenolic acids in needles reach the damage thresholds to induce chemical defense of larch seedlings. On the first day after treatment, the concentrations of caffeic acid, phenylaetic acid, cinnamic acid, vanillic acid, and gallic acid in needles induced by 50% and 75% of cutting were all significantly higher than those induced by larvae feeding; on the 5th day after treatment, the concentrations of these 5 phenolic acids induced by 50% and 75% of cutting were significantly lower than those induced by feeding; while on the 10th day after treatment, the concentrations of the 5 phenolic acids had no significant difference between cutting and feeding. It suggested that the quantitative changes of phenolic acids in larch needles induced by cutting were more rapidly than those induced by feeding, and the induced defense response intensity of phenolic acids was correlative with cutting degree. All of the results showed that it was possible to control the pest damage of L. gmelinii by using appropriate methods to induce the quantitative change of phenolic acids in needles.

Key words: Larix gmelinii, Dendrolimus superans, phenolic acid, damage from cutting needles, insect feeding, soil, glomalin, arbuscular mycorrhizal fungi, environmental function