In Japan, the soy bean pod borer, Grapholitha glycinivorella MATSUMURA, is widely distributed and seriously infests the soy bean pod. However, this insect pest has been little known in the southern half of the country so far. This paper gives an account of both laboratory and field observations on the seasonal occurrence of the borer and the damage caused by it. The observations were conducted at Kanto-Tosan National Agricultural Experiment Station, from 1955 to 1959 inclusive.<br>The first brood moths commenced the emergence in the middle of July and showed the peak emergence at the beginning or in the middle of August. The second brood moths emerged from the middle of September to early October, although less in number than the first.<br>The seasonal fluctuation of the number of eggs investigated in the field at about five day interval, almost coincided with the fluctuation of moth population. Two peaks, one in the middle of August and the other at the end of September or at the beginning of October, were observed. The first brood larvae were found from late July or from early August, and their number increased rapidly, reaching the peak at the end of July. Then the population of the first brood inclined. The second brood larvae were observed from October to November, but in small number. This minority of the second brood seems to be attributable to the greater environmental resistance caused by the low temperature in autumn, or the poor ripening of late varieties of soy bean which serve as the host plant of the second brood larvae.<br>To study the hibernating ratio of the first brood larvae, matured larvae were collected periodically in the field. The hibernating larvae were found from the batches collected at the beginning or in the middle of August. All the larvae collected in the middle of September hibernated. Thus the existence of the partial second brood is evident in this district.<br>The existence of just one brood of this pod borer is known in the area north of Tohoku. district, but the partial second brood seems to exist in the area south of Kanto district. The second brood seems to be more dominant in the warmer region.<br>The damage caused by this pod borer differs considerably by the soy bean varieties. The earliest varieties escape from the attack by the first brood larvae, while the early and middle varieties are damaged to a greater extent by the attack of the first brood larvae. The late varieties are less damaged by the larvae of the second brood.