Tephritidae and Lonchaeidae (Tephritoidea) are major pests of horticultural crops worldwide. Knowledge of the interactions between these flies and their host plants is needed for rational methods of population control. In the South Pantanal and adjacent areas in Brazil we sampled fruits from 92 plant species (22 orders and 36 families) in natural environments. Fifty-three species of plants were infested, and 39 not infested. Some aspects of the biology and patterns of species diversity, abundance, frequency, pupation period for males and conspecific females, and the interactions among species of frugivorous flies and their host plants were quantified. Twenty-six species of flies from 4 genera and 2 families were reared from the fruits: 17 species of Tephritidae (16 Anastrepha spp. and Ceratitis capitata), and 9 species of Lonchaeidae, comprising 8 species of Neosilba McAlpine, and 1 species of Lonchaea Fallén (Lonchaeidae). The lonchaeids infested 48 species of fruits, and the tephritids 30 species. The most polyphagous species were Neosilba zadolicha McAlpine & Steyskal (36 hosts), Neosilba pendula (Bezzi) (18 hosts), and Neosilba inesperata Strikis & Prado (14 hosts) (Lonchaeidae); and Anastrepha sororcula Zucchi (10 hosts), Ceratitis capitata (Wiedemann) (10 hosts), Anastrepha obliqua (Macquart) (7 hosts), and Anastrepha zenildae (6 hosts) (Tephritidae). All the males of Tephritidae (16 Anastrepha spp. and C. capitata) emerged before their conspecific females. Conversely, all females of the 8 species of Neosilba emerged in advance of their conspecific males.