Seasonal variation of the ovaria n activity of Unaspis yanonensis Kuwana, an important pest of Citrus in Japan, was investigated. The ovary of Unaspis yanonensis belongs to the acrotrophic-type, and a highly positive correlation exists between the ovarian development and oviposition especially in the first generation. Forecasting of the occurrence of this species may be made by examining the degree of egg development in the ovary, because the adult female does not begin oviposition until the body cavity is filled with full of mature eggs. Just before oviposition about 170 to 200 mature eggs are found in the body cavity.