A REVISION OF THE NEARCTIC SPECIES OF THE TACHYDROMIINE FLY GENUS STILPON LOEW (DIPTERA: EMPIDOIDEA)

This revision recognizes 13 species of Stilpon Loew in the Nearctic Region, including nine new species. A key is provided for the identification of adult specimens, all species are described, and their geographical distributions are mapped. Two informal species groups are recognized in the Nearctic Region, with the following included species: (1) S . graminum group — S . campestris Cumming sp.nov. (type-locality Assiniboia, Saskatchewan, Canada); (2) S . varipes group — S . chillcotti Cumming sp.nov. (type-locality 10 km E Evergreen, Alabama, USA), S . ctenistes Cumming sp.nov. (type-locality Salmon Creek, New York, USA), S . curvipes Melander, S . limitaris Cumming sp.nov. (type-locality Sapelo Island,Georgia,USA), S . pauciseta Melander, S . pilomus Cumming sp.nov. (type-locality Franconia, New Hampshire, USA), S . spinipes Melander, S . tribulosus Cumming sp.nov. (type-locality Gatlinburg, Tennessee, USA), S . tyconyx Cumming sp.nov. (type-locality Bedford, Massachusetts, USA), S . varipes Loew, S . vockerothi Cumming sp.nov. (type-locality Ottawa, Ontario, Canada), and S . wirthi Cumming sp.nov. (type-locality Dennisport, Massachusetts, USA). A world list of described species of Stilpon , including synonyms, is provided. Stilpon pectiniger Melander is a new junior synonym of S . varipes Loew and S . demnatensis Vaillant is indicated as a nomen nudum. Stilpon pleuriticus Melander, previously considered to belong within Stilpon , is excluded from the genus, and S . obscuripes Adams is transferred as Crossopalpus obscuripes (Adams) comb.nov. Lectotypes are designated for S . pauciseta Melander and S . pectiniger Melander. Homologies of previously confused structures of the male and female terminalia are summarized with reference to other Empidoidea. The monophyly of Stilpon is justified, including discussion of the phylogenetic relationships of the genus to the remainder of the Tachydromiinae. All described species of Stilpon , including extralimital species, are assigned to one of three proposed informal species groups ( S . divergens , S . graminum , or S . varipes group), and zoogeographic patterns are discussed.