Abstract: The scal-insect Quadraspidiotus gigas(Thiem et Gerneck)is one of the important pests of popular trees in China,injuring chiefly Populus berolinensis and P.simonii in such an extent that the insect often completely covered their main trunk and limbs and devastated the planted forest over considerable areas. In Wangkui county of the Heilongjing province the scale insect has one generation a year and overwinters at the 2nd instar larval stage under much thicker scale.The adults emerge in the middle of May.The female deposits under scale about 93 eggs as an average.The newly hatched larvae appear in the middle of June and become abundant during late to early July. Its important natural enemies are the predacious ladybird beetle Chiloeorus kuwanae Silvestri and a parasitic aphidcholcid Prospalella sp. Several insecticides were tested for their control in the fields.In case of newly hatched larvae effects of insecticides may be arranged in following order:Calcium polysulfide >Abielic acid>Omethoale>Fussol.From late June to early July spraying the main trunk of infested trees with 5°Be.Calcium polysulfied has been proved to be must effective in killing the newly hatched larvae.