Abstract
Seasonal fluctuations, namely, seasonal changes of the rise and fall, of the instar composition, and of the distribution pattern of both species were examined during the rice crop season in a paddy field in Sakai in 1970. Their seasonal changes showed patterns which have only one peak during the rice crop season. The maximum number of O. insecticeps was shown on the last day of September when 425 individuals were counted on 25 stubbles. The maximum number of E. japonica was shown early in October with the density of 294 individuals per 25 stubbles. It seems that the rate of predation of O. insecticeps increases in early and mid August and again from late September to the harvest time, and that of E. japonica increases from late July to early August and again in late October. It is concluded that both species have a specific pattern of distribution respectively which varies according to the stage of their development.
