Plant Host Specificity Among Flower-Feeding Neotropical Drosophila (Diptera: Drosophilidae)

A study has been made of plant host specificity of flower-feeding Drosophila collected in western, central, and eastern Panama, the west coast of Colombia, Trinidad, W. I., and Leticia, Colombia, on the headwaters of the Amazon River. Three and four species of single host flower-feeding Drosophila species were found in each of two collecting areas, respectively, in central Panama. These flies were bred only from flowers of their special hosts and never from other plants in the vicinity. A fluctuation of population numbers of the drosophilid is correlated with the period of blossoming of the plant species. Monophagous flower-feeding Drosophila occupy plants with long blossoming periods of four to nine months. Other adaptations of monophagous drosophilids to the host plant concern body color and structural details of the ovipositor and egg filaments. About 5% of flies bred from flowers of plants serving monophagous Drosophila are polyphagous drosophilids; i.e., flower-feeders, ground-feeders, or fungus feeders, No evidence was found of larval competition between a monophagous Drosophila species and a polyphagous drosophilid sharing the same plant. Polyphagous flower-feeding drosophilids use a variety of host plants which generally have a short blossoming period of one to three months. These more versatile species have a wide range of distribution and include the cosmopolitan Drosophila busckii. Preferences for one plant host but tolerance for another have been found in the case of two sibling species of Drosophila using, respectively, two different members of the genus Calathea as primary hosts and each having as secondary host the primary host of its sibling Drosophila species. In addition, two monophagous flower-feeders belonging to the same species group use two different Heliconia species in the same area. In different geographical areas, a monophagous Drosophila species depends either on the same plant host or on plant species very closely related within the genus. An association of the same two distantly related host specific drosophilids in different geographical areas is presumed to have been established in the Pliocene at least, antedating the differentiation of the ancestral Heliconia into five closely related plant species. A number of polyphagous flower-feeding Drosophila species can be cultured on laboratory medium. With one exception monophagous flower-feeders on this medium either (1) refuse to oviposit, or (2) undergo a prolonged larval and pupal state and fail to eclose. It has been possible to adapt one host specific Drosophila species to laboratory culture medium.