RESUMO
The species richness of black flies in the Simulium (Trichodagmia) orbitale (Diptera: Simuliidae) species group is greatest in southern Brazil, where 9 of 19 species are found. A new species in the S. orbitale group was collected during a survey of black flies in Minas Gerais state, Brazil, in the Espinhaço Mountains, an area rich in endemic taxa. The new species is morphologically similar to Simulium guianense Wise (Diptera: Simuliidae), the main vector of the causal agent of onchocerciasis in Brazil and Venezuela. It can be identified in the male by the unpatterned scutum and slightly concave ventral plate with a prominent median projection, in the female by the bilobate anal lobe, in the pupa by the 12 slender gill filaments with nonsclerotized apices, branching in a rake-like pattern, and in the larva by the elongated abdominal segments V-VIII and ventrolaterally lobulate segment IX. The polytene chromosomes have one unique fixed inversion in the IS arm, relative to all other Brazilian members of the group, confirming the morphological evidence of a distinct species.