1. The distribution of numbers of injured ears per plant caused by feeding of rice stem maggot were in good agreement with the theoretical values of Poisson distribution.
2. The numbers of injured ears per plant were positively correlated with the numbers of total ears per plant and so the percentage of injured ears were generally constant in spite of the difference of total ears within variety.
3. There was pretty negative correlation between the percentage of injured ears and the heading period of rice varieties. Rice varieties could be divided in three groups, i.e., extremely resistive, resistive, susceptive.
4. The CV of percentage of injured ears per plant among individuals of one variety varried logarithmicly accompanied with the increase of maen of them. (Fig. 4; L_1, L_2)
5. Then, the populations having large CV showed genetically to be unpure lines. Thus, F_2 populations and F_3 lines seemed to be segregated in 1 : 2 : 1 ratio concerning with resistance as the results of these CV analysis.