Detail of head, antennae. Syrphidae of Oklahoma says, about genus Helophilus:
antennae short, third segment approximately orbicular; arista basal, bare

Note also the statements about the two species (apparently) found in the East ("front" corrected to "frons"):
-Frons of male much wider than width of antennal process; female with yellow pile on lower portion of frons -- >
latifrons
-Frons of male as narrow or narrower than width of antennal process; frons of female entirely black pilose -- > fasciatus