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Host plant selection by insects has evolved through various interactions with their environments. In phytophagous insects, the chemistry and ecology of plants are important factors governing host selection. Plants have unique chemicals, some of which, such as toxicants, have evolved as defense mechanisms against insect attacks, and plants also show species specific distribution and phenology. Insects, then, have evolved metabolic systems to utilize such chemicals or to detoxify, and also bionomic strategies to adapt to the plant phenology. Specialization of phytophagous Lepidoptera is governed by interactions with host-plant chemistry, but also with host abundance and predictability (cf. Gilbert, 1979). In addition to plant chemistry and ecology, the existence of species having similar nutritional requirements influences their selection of hosts through interspecific competition. The validity of these conceptions needs to be examined in various phytophagous insects and also in insects feeding on materials other than plants. This paper deals with food preferences and nutritional requirements of the fungus-feeding Drosophila with reference to factors governing their selection of hosts. The original feeding habit of the family Drosophilidae was saprophagous: fermenting or decayed plant parts such as fruits, tree sap, leaves, stems, flowers, or mushrooms. Today many species belonging to various taxonomic units continue with this original feeding habit (Carson, 1971; Kimura et al., 1977). However, several species have come to feed and breed on living or fresh plant parts, e.g., the leaf miners of Scaptomyza (Frost, 1924) and the flower feeders of Drosophila (Brncic, 1966; Pipkin et al., 1966). Kimura (1976) observed that adults of some species of Hirtodrosophila were attracted to fresh mushrooms. In this study, the food preferences of these fungus feeders were examined in laboratory tests and field observations in relation to the phenology and abundance of mushrooms. The species studied included three members of the Hirtodrosophila radiation, D. trivittata Strobl, D. sexvittata Okada, and D. alboralis Momma and Takada, and five species of the immigrans radiation, D. immigrans Sturtevant, D. nigromaculata Kikkawa and Peng, D. brachynephros Okada, D. testacea van Roser, and D. confusa Staeger. All species except D. immigrans and D. nigromaculata depend on mushrooms. Drosophila immigrans feeds on fruit and D. nigromaculata feeds on leaves (Kimura et al., 1977).