Taxonomic revision of the Tetraneura akinire species group (Insecta, Aphididae, Eriosomatinae), with description of a new species and a correction of a nomenclatural confusion

Gall-forming aphid species Tetraneura nigriabdominalis and T. fusiformis and its closely related species are taxonomically revised. By referring to the original descriptions, the name T. nigriabdominalis (Sasaki, 1899) is discarded as an erroneous combination, and T. akinire Sasaki, 1904 is adopted as a valid name. The T. akinire species group is defined as having long claws in the first instar nymphs of the root generation. Of the T. akinire species group distributed in Korea and Japan, T. ovaliformis sp. nov., which induces globular galls on the leaves of Ulmus davidiana var. japonica, is described, and T. akinire and T. sorini Hille Ris Lambers, 1970 are redescribed. A molecular phylogeny based on partial sequences of mitochondrial cytochrome c oxidase subunit I (COI) indicates that T. akinire is composed of two clusters, one (type A) which is distributed widely from Europe to East Asia on Ulmus spp., and the other (type B) which is found in Hokkaido, northern Japan on U. davidiana var. japonica and in tropical regions as anholocyclic lineages. Tetraneura fusiformis Matsumura, 1917, which has often been treated as a junior synonym of T. nigriabdominalis, likely corresponds to type B. The taxonomic status of T. fusiformis is discussed and this species is tentatively considered as a junior synonym of T. akinire sensu novo.