Abstract: Cephalcia infumata Zhang & Wei, sp. nov., a new species of Pamphiliidae (Hymenoptera) defoliating Picea crassifolia Kom.was collected from Helanshan Mountains, Inner Mongolia, China. The new species is similar to Cephalcia alashanica and C. masuttii. The larvae of the three species make conspicuous nests with silk and dung on the twigs. The new species differs from Cephalcia alashanica by the characters as follows:1) wings in both sexes deeply infuscate; each femur largely black on ventral side and largely pale brown on dorsal side; 2) the middle and lower parts of hind orbit without occipital carina; 3) the antennomere 3 clearly longer than the sum of antennomeres 4 and 5 together, and longer than the longest axis of eye as well; 4) the inner apical corner of valviceps aubquadrate. The new species differs from Cephalcia masuttii as follows:1) wings in both sexes deeply infuscate; 2) the mesoscutal lateral lobes and metascutellum in both sexes, male mesoscutellum, the ventral side of each femur and the abdominal tergites 1-6 in both sexes largely black; 3) the ventral 2/5 of paraantennal area naked and smooth; 4) antenna with about 26 antennomeres; 5) the valviceps without distinct anal corner. The K2P distance between the COⅠ of Cephalcia infumata and C. alashanica is 5.2%.

Key words: Hymenoptera, Pamphiliidae, Cephalcia, new species, China, Picea crassifolia