Abstract: Thirteen species of the genus Cecidomyia have been reported from North America and Eurasia.They are know n as pine resin midges infesting mainly the pines and also spruce and fir. The species studied was first discovered in a Pinus yunnanensis plantation of Jiangbian Forestry Bureau, Mile County of Yunnan Province in 1973.The larvae feed on the resin of new twigs retarding the tree grow th.The infestation has now extended to approximately 6000 hectares reaching an injury rate up to as high as 79.6%~100% including killed trees in some seriously infested stands. The morphological characteristics of the pest are discribed.The biology and of this resin midge are closely studied to provide a reference for suggesting the management measures of the pest.The key factor analysis based on its 5-generation life-table data has been made to help formulate population trend prediction.