Abstract: The scale Eulecanium gigantea Shinji.injures mainly on Robinia pseudoacacia L.and Sophora japonica L.in Lanzhou.It has one generation a year and serious damages may be occurred during April-May of the year.The 2nd instar nymphs overwinter mainly on the 1 or 2-year branches.The development time for adult females,males,eggs,nymphs and pupae usually takes 27.2,2.7,25.1,321.8,and 14.5 days respestively on average. Parthenogenesis is not occurred in this species.A female scale lays 2888 eggs on average.The fluctuations of daily temperature and relative humidity have profound effect on this insect. A species of encyrtids and a parasitic moth seem to play an important role in the natural control of this insect. For chemical control 90% fluoroacetamide (1:1500—1000),50% fenitrothion emulsion (1:500—350) and 50% carbophenothion emulsion (1:1500—1000) applied at early nymphal stage gave good control and resulted in 94.3—99.7% mortality.