Abstract: Twelve species of the genus Cecidomyia have been reported from north America and Eurasia, They are known 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 Jiang-Bian Forestry Bureau, Mi-Le County in 1973. The larvae feed on the resin of new twigs retarding the tree growth. The infestation has now extended to approximately 60 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 insect is described. The bionomics of this resin midge is closely studied to provide a reference for suggesting the management measures of the pest.