A new species of Closterocerus (Hymenoptera: Eulophidae: Entedoninae) is described from South Korea. The species is reported for the first time as an egg parasitoid of Pachynematus itoi Okutani (Hymenoptera: Tenthredinidae), of which recent sudden outbreak caused severe damage in larch forests. In total 61 species in Chalcidoidea are recorded as primary parasitoids of various tenthredinid sawflies in the Palaearctic area. However, no chalcidoid parasitoids have previously been recorded from P. itoi. The genus Closterocerus is cosmopolitan in distribution, and with an extremely wide host range from Symphyta, leaf-mining and gall-inducing insects to scale insects and plant lice. In Korea, one species of Closterocerus, three Chrysonotomyia, two Desmatocharis, one Neochrysocharis and one Teleopterus were known; most of them, except Chrysonotomyia sudoensis Paik, now are placed under Closterocerus. The new species is compared with 13 other species of Closterocerus that are known from the Far East.

Platygaster robiniae Buhl and Duso (Hymenoptera: Platygastridae) is a gregarious koinobiont endoparasitoid of Obolodiplosis robiniae (Haldeman) (Diptera: Cecidomyiidae). The life cycle and development of the parasite is described. P. robiniae proves to be an egg-larval parasitoid, parasitizing eggs of O. robiniae and emerging from host larvae, and eggs of the wasp develop monembryonically. Its egg and embryonic stages are prolonged to some extent. The parasitoid undergoes only one larval instar, and total development time from egg to adult takes about 28 days to complete. The life cycle of a parasitoid generation is perfectly synchronized with that of the host: the waps emerges near the emergence time of the host, so that they can parasitize host eggs.