Tarache abdominalis Grote
Tarache abdominalis Grote, 1877, Canad. Ent, 9:157.
Diagnosis: The male forewing may be nearly completely white from its base to the postmedial line and with only a triangular streak from the costa just basad of the orbicular. Alternatively the costal streak may be larger reaching nearly an inward pointing projection of the postmedial line. In this second alternative the basal area of the wing is usually heavily suffused with gray. In both of these forms the inner margin of the forewing near the base has an elongate, ovate, gray circle. The orbicular is a small, black dot. A reniform is present, but usually obscured by the dark brown postmedial band. The costa near the apex has a small, rectangular spot and the lower half of the subterminal line is marked with dull white. The hindwing is mostly suffused with dull brown, although the base is usually lighter than the outer half of the wing. The underside of the hindwing is mostly dull white with black streaks on the veins , a linear discal dot, and a dark brown streak from the inner third of the costa. Forewing expanse from base to apex 11 mm.
Females are more heavily marked than males. In particular there is a slanting dark brown band from the costa inward and joining with the postmedial line. The basal area of the wing always has distinct gray streaks and blotches. The hindwing is completely dark brown without a lighter basal region.
Distribution: (USNM collection only) Tarache abdominalis is a species of the southern and central Great Plains of the United States. The species is found from central Texas northward through the Great Plains to Nebraska.
There is a single male species of abdominalis in the USNM marked “White Mountains, Ariz.” This specimen has the male genitalia of abdominalis, but the superficial appearance of knowltoni. This locality is far outside the prairie range of abdominalis. This situation needs to be resolved.
In Texas specimens fly in April, September, and October. Further north adults are mostly found in June.
Identification Quality: Good
Distribution map based on specimens in the USNM
Tarache abdominalis is most likely to be confused with knowltoni. The males of knowltoni have the basal area of the forewing completely suffused with gray-brown. The white streak near the apex of the costa is almost always smaller and narrower than in abdominalis. The basal area of the hindwing in knowltoni is either distinctively white contrasting with the dark outer third of the hindwing, or completely suffused with dark brown. In contrast the male hindwing of abdominalis has a lighter brown inner portion. The vesica of the male genitalia of abdominalis has 4 major spines. The vesica has 5 to 6 major spines in knowltoni. The clasper of the male valve is larger and longer in abdominalis than it is in knowltoni. Females of abdominalis and knowltoni are similar in appearance. However the female forewing of abdominalis has a distinctive diagonal band from the costa joining the postmedial line. In contrast this diagonal band is absent in knowltoni and replaced by a consistently dark, triangular basal region.