Taxonomic revision of the robber-fly genus Acronyches (Diptera: Asilidae)

The Asilidae genus Acronyches Williston, 1908 is reviewed. Acronyches is distinguished from other Leptogastrinae by the face being wide ventrally and narrow dorsally, the long antennal postpedicel, the absence of setae on the metathoracic femur, the short and wide abdominal segments 1-3, and a closed wing cell cup. Acronyches is known from 10 species that occur from northern Mexico to southern Paraguay. The last review of these large robber flies was published in 1971. Since then new material has accumulated in many natural history collections extending the known range of several species and also including a potentially new species from Brazil. This revision is based on external morphological characters of the adult flies and includes studies of the male and female terminalia. A new synonym for Acronyches fenestratulus (Hermann, 1921), which is senior to Acronyches giganteus (Hull, 1962), has been discovered. All 10 currently recognized species and potentially new species are re-described, a dichotomous key for their identification will be developed, and illustrations and photographs are provided to support the descriptions and facilitate future identification.  In addition, the biogeography of Acronyches will be discussed.