Descriptions of two new Celticecis species (Diptera: Cecidomyiidae) that induce leaf galls on Celtis boninensis (Cannabaceae) in Japan.

Two new species Celticecis insulicola Sato and Yukawa and Celticecis gracilicornis Sato and Yukawa (Diptera: Cecidomyiidae) are described from Japan based on morphological comparison with other congeners in the world. The definition of the genus Celticecis is broadened to include the two new species. Molecular phylogenetic analysis supported the results of identification. C. insulicola induces bullet-shaped galls, and C. gracilicornis induces slender conical galls on the leaves of Celtis boninensis Koidzumi (Cannabaceae), a plant of the southern part of Japan, mainly on the Nansei Islands in Kagoshima and Okinawa Prefectures. Both species are univoltine, mature larvae overwintering in the galls on the ground and adults emerging in early spring. C. insulicola was found on Amami, Uke and Okinoerabu Islands, Kagoshima Prefecture, and Okinawa Island, Okinawa Prefecture. C. gracilicornis was found on Amami and Okinawa Islands.