Resurrection of Rabdophaga salicivora Shinji (Diptera: Cecidomyiidae), a Japanese gall midge formerly misidentified as a North American species, Rabdophaga rigidae (Osten Sacken), with observations on the phylogenetic relationships of its populations in Japan and the Russian Far East

Intercontinental biotic connections between Eurasia and North America are common in many gall midge genera (Diptera: Cecidomyiidae), but only a few species have been recorded from both continents. In Japan, four gall midge species had been previously considered to be identical to North American species, but three of these cases have already been disproved. We examined the remaining species, Rabdophaga rigidae , which had been originally described from Japan as Rabdophaga salicivora in 1938, later recorded from the Russian Far East in 1967, and synonymized with a North American species, R. rigidae , in 1982. Morphological features and partial sequence data of the mtDNA cytochrome oxidase subunit I (COI) region suggested that the Japanese species is a distinct species and is identical to the species recorded from the Russian Far East. We therefore apply the original name, R. salicivora , to the Japanese and the Russian species. In addition, on the basis of a molecular phylogenetic analysis, we conclude that R. salicivora possibly came to the Japanese Archipelago through the Korean Peninsula and established itself first in the southern parts of Japan. Then, it expanded its distribution range to northern parts of Honshu, but could not reach Hokkaido, probably because of the Tsugaru Strait between Honshu and Hokkaido.