The effect of different adult sex-ratios on fecundity in Spodoptera litura was investigated using a Latin square design divided into 9 divisions. The total number of eggs deposited in a division tended to decrease with the lowering of the male ratio, although the results of an analysis-of-variance test proved insignificant. Hatchability, however, was not affected by the sex-ratios. In consequence of the above experiment, the 9 divisions were divided into 2 groups of high and low larval densities. One day after hatching, a drastic decrease in larval number was observed in both of the 2 groups. No fundamental difference in the trend of survivorship curves existed between the groups. Thus, the decline in fecundity due to the lowered male ratio brought about a maintenance of a relatively low level population density during the larval stage. Additionally, the relationships of mean crowding to mean density were also examined with regard to the larvae on the respective plants in a division.