Abstract: 【Aim】 In order to study how  Breynia vitis-idaea controls the population of  Epicephala vitisidaea.【Methods】 The phenology of B. vitis-idaea  and the biology of E. vitisidaea  were recorded.The flower-visiting Epicephala  moth species were identified by dissecting their genitalia. For calculating larval survivorship, the number of larvae inside the fruit, the number of exit holes and oviposition scars on the fruit were counted by dissecting the stalked and non-stalked fruits in summer and late autumn. Finally, the proportion of stalked and non-stalked fruits in summer and late autumn was calculated. 【Results】 In Xiamen, Fujian Province, B. vitis-idaea plants have five peak fruiting stages annually and the flower-visiting Epicephala moths have five generations each year. The species of moth was identified as E. vitisidaea by contrasting its genitalia. E.vitisidaea  larvae need to consume 2-4 seeds to develop into mature larvae. B.vitis-idaea could produce two types of fruits, stalked and non-stalked. The larval survivorship of E.vitisidaea was obviously higher in non-stalked fruits than in stalked fruits as well as in late autumn than in summer. Meanwhile, the proportion of non-stalked fruits of B.vitis-idaea was obviously higher in late autumn (82.04%) than in summer (31.53%). 【Conclusion】 This study revealed the mechanism by which mutualistic interactions are more stable. B. vitis-idaea can control the larval survivorship of E. vitisidaea by producing the stalk in base of fruits. By seasonally regulating the ratio of stalked and nonstalked fruits, Breynia plants prevent seed overconsumption in summer and ensure Epicephala survival through the winter. The auto-regulating mechanism of B. vitis-idaea plays an important role in keeping stability of mutualistic system between B. vitis-idaea and E. vitisidaea.

Key words: Breynia vitis-idaea, Epicephala vitisidaea, fruit stalk, larval survivorship, obligate pollination mutualism, regulation mechanism