Abstract.1Two closely related species ofColocasiomyia alocasiae(Okada) andC.xenalocasiae(Okada) (Diptera, Drosophilidae) breed in inflorescences ofAlocasia odoraC. Koch (Araceae), a hermaphroditic understorey clonal herb.2The two drosophilid species form a synhospitalic pair in Okinawa withalocasiaebreeding in the upper half of the inflorescence andxenalocasiaebreeding in the lower half.3C.alocasiaealso has the following combination of life history traits: small body size, many eggs, and early reproductive maturity. In contrast,xenalocasiaecan be described as having larger body size, fewer eggs, and delayed reproductive maturity.4Resource partitioning between the two species on the same host may be affected by these life history traits which are associated with their larval habitats.