[Objectives]  To identify the preference of Pseudotorymus jaapiellae for different volatiles emitted from galls induced by Gephyraulus lycantha, and clarify the effect of semiochemicals on host selection by this parasitoid. [Methods]  The preference of pregnant female P. jaapiellae for specific volatiles emitted from young and mature galls induced by G. lycantha was measured in a Y-tube olfactometer under laboratory conditions. Headspace solid phase microextraction and gas chromatography-mass spectrometry were used to analyze the compositional difference in volatiles emitted from galls at different stages of development. [Results]  Pregnant female P. jaapiellae preferred galls induced by G. lycantha to healthy flower buds of L. barbarum. Young galls were particularly attractive (P<0.01), with 95% of females choosing these compared to only 5% choosing healthy flower buds. There were significant differences in the volatiles emitted from healthy flower buds and from galls at different developmental stages. More volatile compounds were emitted from young galls (61 compounds) than from healthy flower buds (54 compounds) or mature galls (52 compounds). Ketones and terpenoids were emitted from damaged L. barbarum flower buds, but only terpenoids were emitted from young galls; the ketone content of gall volatiles increased gradually as galls matured. [Conclusion]  P. jaapiellae can identify and locate galls induced by G. lycantha and distinguish between the volatiles emitted by galls of different developmental stages, thereby both locating suitable galls and regulating G. lycantha populations.