Hiding in Plain Sight: An Abundant and Widespread North American Horse Fly (Diptera: Tabanidae) in the Tabanus sulcifronsGroup, Tabanus variegatusFabricius, Redescribed

Tabanus variegatusF. 1805 has been called by the name Tabanus sulcifronsMacquart 1855for over 80 yr; T. variegatusis one of the most common large horse flies attacking livestock in much of the southeastern U.S. Morphological, ecological, and molecular evidence indicates that T. variegatusis a distinct species, and we redescribe the female and describe the male. The Fabricius holotype, heavily damaged after over nearly 220 yr, is nevertheless taxonomically sound. Morphology (size, color, palp shape, and r5wing cell shape) can usually distinguish T. variegatusfrom T. sulcifrons, but some specimens remain difficult to separate, especially in and west of the Mississippi River Valley. Using geometric morphometric analyses of the wing vein arrangement and palp shape the two species are significantly different. The wings of T. variegatusfemales also have more microsetae and sometimes a “frosty” appearance. Where they are common and sympatric, as in eastern Tennessee, they are temporally separated such that T. variegatusflies later (August-October) than T. sulcifrons(June-August), minimizing opportunity for gene flow. Museum specimens allow the approximate range of T. variegatusto be compared with that of T. sulcifronss.l.; T. variegatusis particularly abundant from the coast of the Carolinas and Georgia east to central Tennessee and south to about central Alabama. DNA evidence (COI gene) recovers T. variegatusand T. sulcifronss.s. in separate clades. Further studies on the T. sulcifronscomplex are needed to fully resolve the range of both species, assess the degree of genetic substructuring, and examine relationships with other members of the T. sulcifronscomplex.