Abstract:The web-spinning sawfly Cephalica danbaica Xiao is an important insectpest of Picea crassifolia Kom,and causes severe infestation in the eastern part of Qinghai Province. It was obsevered that the sawfly took 2 years tocomplete its life cycle which may extend to the third year after infestation. Dueto the succession only with a single year-group, it rests in the soil duringthe year of even number and infests on the trees during the year of oddnumber. The adults and eggs presented in mid June to early July. The firstinstar larvae occurred in July. The mature larvae leave away from the treesin early August to mid September, and dig into the soil where it remainsinactive about 21 months within the earthen cell. The larval stage consistsof 6 instars. In the forest which is infested seriously,the use of insecticidalsmokes to kill the pest on the trees is effective. To the trees of sporadicinfested with the larvae cutting away the larval rests is also effective.