Discovery of the gall midge Schizomyia castanopsisae (Diptera: Cecidomyiidae) inducing inflorescence galls on Castanopsis sieboldii (Fagaceae) from Honshu, Japan and the possibility of its recent range expansion

Outbreaks of herbivorous insects result in serious damage to forest trees. The gall midge Schizomyia castanopsisae (Diptera: Cecidomyiidae) induces inflorescence galls and causes severe loss of acorn production for Castanopsis sieboldii (Fagaceae). The outbreaks of gall midge have been occurring in these decades in the southern parts of the Izu Islands, Tokyo, Japan. In this study, we first found S. castanopsisae on Toshima Island, the Izu Islands, and in Izu Peninsula, Honshu. A genetic analysis showed that the genotype of the gall midge collected from the Izu Peninsula was identical to that from the Izu Islands, and only the haplotype was distributed in these areas. In contrast, the analysis of S. castanopsisae populations on the Nansei Islands of Japan found five haplotypes, including the one common to the Izu Peninsula and the Izu Islands. These results support the hypothesis that the gall midge populations occurring on the Izu Islands originate from the Nansei Islands, and the invaded populations have been expanding their range to the northern areas there. To monitor the distribution range and abundance of S. castanopsisae and its influences on the acorn production of C. sieboldii in Honshu are of urgent necessity.