Abstract: Results of the field observations in Yangzhou showed that S. yamato could complete 11-12 generations in a year. Adult overwintered in ground crevices and leaf litter until the following April. Aphids, mainly Rhopalosiphum nymphacae, on aquatic plants were the, preferred prey by the predator. tfJBachadult cold prey on a maximum of 66 aphids per day. The correlation between the functional response of the predator and the prey density was found to be Holling Ⅱ.type. The average adult daily feeding and prey density were fitted with BeddihgtonModel.