Two new species of gall midges (Diptera: Cecidomyiidae: Cecidomyiinae) associated with male flower buds of Phyllanthus flexuosus (Phyllanthaceae) are described and illustrated. Clinodiplosis gagnei Elsayed, new species, induces male flower bud galls, whereas Macrolabis katoi Elsayed, new species, is an inquiline. Females of both species visit the host plant at flowering in search of suitable oviposition sites and, in doing so, become dusted with pollen of the opened male flowers and come in contact with the stigmas of female flowers. Larvae of both gall midge species overwinter in the ground, and each has only one generation per year. This is the first report of the genus Macrolabis in Japan.