Abstract: Ontsira palliatus, an exopprasitoid of Semanocus sinoauster, was propagated and used to control the pine sawyer, Monochamus altercatus, a primary vector of the nematode, Bursaphelenchus lignicolus. Laboratory observations indicated that adult wasps had a strong ability to locate their hosts underneath the bark. In laboratory propagations of the parasitoid, larvae of M. alternatus were placed in a wood slot covered with a wood slice which had many fine holes for the ease of oviposition by the vasps. The thickness of the cover slice should not exceed 3mm. The parasitization of M. alternatus by the parasitoid was 94.1% in the laboratory and about 24% in the forest.