Abstract: The gall midge Obolodiplosis robiniae (Haldeman) (Diptera: Cecidomyiidae) was just recently found in China, it caused severe damage to black locust, Robinia pseudoacacia L. The pest is native to North America. Because the pest threats the health of R. pseudoacacia, it has been listed in the quarantine list in China now. For biocontrol purpose we investigated its insect natural enemy. In Qinghuangdao city of Hebei province, O. robiniae populations are affected by a parasitoid, Platygaster robiniae Buhl and Duso in the family Platygastridae, which is a new record in China. Primary field investigation indicated that the highest parasitism rate of P. robiniae could reach 84.8%, and this wasp has high application value for biocontrol. The external morphology observed with scanning electron microscopy (SEM) and the tentatively observed biology of P. robiniae are described in the present paper

Key words: Obolodiplosis robiniae, Platygaster robiniae, natural enemy, morphology, biology