A new species, Sclerodermus alternatusi Yang, sp. nov. (Hymenoptera: Bethylidae), is described and illustrated. Its cerambycid host, Monochamus alternatus Hope, a severe wood borer attacking many pine trees (Pinus spp.), is also a vector of pine wood nematode, Bursaphelencus xylophilus, which cause severe damages to pine forests in China. The new species is a gregarious ectoparasitoid of junior larva of M. alternatus. The number of adult wasps reared from a single host larva ranges from 6 to 45. The ratio of female to male is 20 : 1. The new parasitoid species has a high potential in using as a biocontrol agent for the wood borer. Diagnosis of the new species with comparisons to its related species, S. pupariae Yang & Yao and a key to known species of Sclerodermus from China is provided.

A new species, Sclerodermus alternatusi Yang, sp. nov. (Hymenoptera: Bethylidae), is described and illustrated. Its cerambycid host, Monochamus alternatus Hope, a severe wood borer attacking many pine trees (Pinus spp.), is also a vector of pine wood nematode, Bursaphelencus xylophilus, which cause severe damages to pine forests in China. The new species is a gregarious ectoparasitoid of junior larva of M. alternatus. The number of adult wasps reared from a single host larva ranges from 6 to 45. The ratio of female to male is 20 : 1. The new parasitoid species has a high potential in using as a biocontrol agent for the wood borer. Diagnosis of the new species with comparisons to its related species, S. pupariae Yang & Yao and a key to known species of Sclerodermus from China is provided.