Abstract: Rhus gall aphids include six genera and 12 species, and are mainly distributed in East-Asia with only one species Melaphis rhois in North America. Based on morphological characteristics and molecular data, we studied the taxonomic status of the North America species M. rhois. The numerical taxonomy on eight species from six genera of Rhus gall aphids was studied using hierarchical clustering analysis. A total of 108 morphological characters from 179 individuals of the alate adults were evaluated from all parts of aphid body, among which 48 characters from head, thorax and abdomen were directly measured, 31 characters were the ratio from two measured characters, and the rest were numerical values converted from morphological characters. The cladistic analysis based on the Euclidean distance showed that the eight Rhus gall aphid species are clustered into three clades, among which the North America species M. rhois is closely clustered with the two species from the genus Schlechtendalia; the two species from Nurudea and Floraphis meitanensis, Meitanaphis elongallis and two subspecies from the genus Kaburagia are clustered as a group, respectively. In addition, the 1.2 kb DNA sequences of mtDNA COI gene from 16 individuals of eight Rhus gall aphid species were obtained. Both of the MP and ML phylogenetic trees showed that the eight Rhus gall aphid species are clustered into three clades, and the North America species M. rhois clustered closely with the genus Schlechtendalia, which are consistent with the results of the morphological analysis. However, the relationship between the three clusters are inconsistent with that based on the morphological data. In molecular trees, North America species M. rhois and two species from the genus Schlechtendalia, F. meitanensis and M. elongallis, and two species from Nurudea and two subspecies from the genus Kaburagia are clustered as three groups I, II and III, respectively. The group I and II have relatively close relationship, but with very low bootstrap value (<50%). It is necessary to collect more species and use more molecular data to resolve the phylogeny of Rhus gall aphids.

Key words: Rhus gall aphids, Melaphis rhois, numerical taxonomy, COI gene sequence, phylogeny