A new species of cynipid gall wasps, Periclistus orientalis Pang, Liu & Zhu, sp. nov., is herein described from Hunan, China in the tribe Diastrophini (Hymenoptera: Cynipoidea: Cynipidae). The phylogenetic relationship between Periclistus and all the other Diastrophini genera, except the recently described XestophanopsisPujade-Villar et al., 2019, was analyzed using a fragment of the mitochondrial COI gene and a fragment of the nuclear 28S gene. A taxonomic key to the known genera of Diastrophini and an updated taxonomic key to the known Eastern Palearctic species of Periclistus were provided. In addition, an updated checklist of the known species of the genus from the world is given.

In the present paper, a new species of cynipid gall wasp, Andricus elodeoides Liu & Pang, is described from several provinces in southern China. The new species is closely related to the recently redescribed A. mairei (Kieffer, 1906). In addition to differences in adult and gall morphology, the new species is also readily separated by COI sequences, with a 6.2–8.9% genetic distance between populations of the new species and those of A. mairei. A contrasting difference in sex ratios was also observed between the two species, with A. elodeoides extremely female-biased (95.5–97.8% female) while A. mairei male-biased to more balanced (5.4–43.5% female). PCR screening for Wolbachia infection further revealed contrasting infection rates between populations of A. elodeoides and A. mairei: the Wolbachia infection rate was 0% in A. elodeoides and 100% in A. mairei. Cytoplasmic incompatibility induced by Wolbachia is proposed as a potential mechanism of speciation of the sympatric A. elodeoides and A. mairei.