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The Drosophilidae Family of flies is cosmopolitan and is distributed in many types of ecosystems. The knowledge about the distribution of these species in Brazil has grown since the 1940s. However, the large extension of the Brazilian territory and the complexity of its ecosystems accounts for the fact of that this research field is still underexploited. The present study brings together survey data from 12 collection sites in Santa Catarina State, southern Brazil. The flies were collected over fermented banana baits, or over their natural trophic resources. This study expands the knowledge of the geographical distribution of Drosophila ananassae Doleschall, D. aff. elliptica, D. neosaltans Pavan & Magalh es, D. pulchella Sturtevant, D. bocainensis Pavan & Cunha and D. bocainoides Carson, all from the subgenus Sophophora.

The six sibling species of Drosophila willistoni group are among the most favorable, and at the same time challenging materials for studies on the genetics of speciation processes. The species are D. willistoni Sturtevant, D. paulistorum Dobzhansky & Pavan, D. pavlovskiana Kastritsis & Dobzhansky, D. equinoxialis Dobzhansky, D. tropicalis Burla & da Cunha, and D. insularis Dobzhansky. Burla et al. (1949) found slight morphological differences that were insufficient for identification of single individuals, but Spassky (1957) noted differences in the male genitalia which do permit such identification. Unambiguous discrimination is also possible through examination of the gene arrangements in the chromosomes of larval salivary glands (Burla et al., 1949; Dobzhansky et al., 1950), and of the variant enzymes detected by electrophoresis (Ayala et al., 1970). Owing to ethological isolation, crossmating of the species occurs rarely, although under laboratory conditions some cross-inseminations can be obtained (Burla et al., 1949). Intercrosses of D. insularis females with D. tropicalis and D. willistoni males, and occasionally with D. paulistorum

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).

Sibling species are species morphologically so similar as to be practically indistinguishable from each other by inspection of their structural features. The Drosophila willistoni group consists of at least twelve species, six of which are siblings. Two of the sibling species, D. pavlovskiana Dobzhansky and Kastritis, and D. insularis Dobzhansky, are narrow endemics; the former in Guyana and the latter on some islands of the Lesser Antilles. The other four species, D. willistoni Sturtevant, D. equinoxialis Dobzhansky, D. paulistorum Dobzhansky and Pavan, and D. tropicalis Burla and de Canba, have wide and largely overlapping geographic distributions. The four species are sympatric through Central America and the northern half of continental South America; two or three of them are sympatric in the southern half of Mexico, the larger Caribbean islands, Peru, Bolivia, and the southern half of Brazil (Spassky et al., 1971). We have studied for several years genetic variation in the sibling species of the D. willistoni group, using techniques of gel electrophoresis and enzyme assay. D. equinoxialis consists of two subspecies, D. e. equinoxialis and D. e. caribbensis (Ayala, 1973). In this paper we report results of the study of reproductive isolation between these two subspecies, and we compare genetic variation within and between the subspecies. Ayala and Powell (1972) have