Abstract:Tettigoniella viridis (Lennaeus) damages trees principally by ovipositing activities.When saplings or young trees of Populys alba var. pyramidalis (Bunge) are infested,the thinner bark becomes rough,and its colour turns yellow,growth of the saplings slows down,leaves fall earlier while sprouting delays,What is more that the scars caused during oviposition on the bark multiply saplings‘water losses,greatly decrease water content of the stemsand branches,and make tops of the young trees wither easily, Number of the oviposition scars on the stems of one-year saplings of Popelys alba var.Pyramidalis (Bunge) distinctively correlates to the latio of water decrement.The regressive equation is y=8.5001+0.1809x. Its coefficient of interrelation is 0.9482,which is extremely significant.The younger saplings are,the more serious damage is.It is worked out through three years‘ experiment that ec onomic injury level(EIL) of Tettigoniella viridis(Lennaeus) to one-year poplar trees is 19.54 egg lumps/0 -50cm,to two-year trees is 24.98 egg lumps/0 -50cm. Control index of adult pests for the former is 10.7 heads per sapling, for the latter is 13.7 heads per sapling. Tettigoniella viridis(Lennaeus) is less harmful to trees older than three years since they possess more branches and their stem bark becomes lignified.