Moths of North Carolina
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Eucosma Members:
1 NC Records

Eucosma formosana (Clemens, 1860) - Beautiful Eucosma Moth

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Taxonomy
Superfamily: Tortricoidea Family: TortricidaeSubfamily: OlethreutinaeTribe: EucosminiP3 Number: 51a0763 MONA Number: 2916.00
Comments: Eucosma formosana is a member of the radiatana species group of Wright and Gilligan (2015). This group includes a complex of 9-13 species that have been difficult to resolve due to their overall external appearances, suspected sexual dimorphism in forewing coloration and patterning in some species, and a scarcity of well-defined diagnostic features in the genitalia. Wright and Gilligan (2015) recognized only nine species in North America and relegated four previously recognized species to synonymy.
Identification
Field Guide Descriptions: Online Resources: MPG, BugGuide, iNaturalist, Google, BAMONA, GBIF, BOLDTechnical Description, Adults: Wright and Gilligan (2015)                                                                                 
Adult Markings: The head, palps, and antennae vary from reddish brown to grayish brown. The thorax varies from warm brown to cream-colored and has a thin central dark line and a broader dark lateral line along each side. The forewing has a pale ground color that varies form tan to light grayish brown and is overlain with dark brown to rusty brown shading and horizontal streaking that may cover much of the wing. The apical third of the costa has a series of irregular dull silvery to tan streaks that tend to anastomose and fill much of the area between the costa and the ocellus. The ocellus is well-defined and is pale in the middle with two horizontal black streaks. The proximal and distal margins have dull silvery to tan lines that often connect with the irregular lines of similar color that extend from the costa. The light ground color in some areas of the range tends to be well developed below the dorsal margin near the middle of the wing. The fringe is reddish-brown to grayish-brown, and the hindwing varies from brown to blackish with a paler fringe. Females tend to have darker markings and dark brown to black hindwings, but otherwise resemble the males in size and forewing pattern (Wright and Gilligan, 2015).
Wingspan: 18-20 mm (Heinrich, 1923)
Forewing Length: 8.0 to 9.5 mm (Miller, 1987); 8.3-10.0 mm; mean = 9.1 mm (Wright and Gilligan, 2015)
Adult Structural Features: Wright and Gilligan (2015) provide illustrations of the male and female genitalia, along with a general description of the genitalia that applies to all members of the radiatana species group. The general description for members of this group follows. In males the uncus is weakly developed and sometimes reduced to a slight bulge. The valva is variably arched laterally, with costal margin weakly concave and the ventral emargination moderate. The neck is somewhat elongate and nearly uniform in width, and the saccular corner is usually angulate. The cucullus has the dorsal and ventral lobes moderately developed. The distal margin varies from convex to nearly straight, and the basoventral margin projects in a ridgelike manner onto the medial surface of the neck. Wright and Gilligan (2015) noted that the male valva of E. formosana is long-necked (length about 1.75 times the width) and strongly arched laterally, much like that of E. radiatana and E. umbrastriana.

In females the papillae anales are moderately setose and microtrichiate. The lamella postvaginalis is rectangular and microtrichiate with the central trough slightly depressed. Sternum 7 has the posterior lobes moderately to broadly rounded and joined to the lateral margins of the lamella postvaginalis by moderately broad bands of sclerotized membrane. The posterolateral margins are straight to weakly concave, while the lateral extremities are triangular and well developed. Scaling of sternum 7 is dense on the posterior lobes and lateral extremities, and moderate elsewhere. The ductus bursae is encircled and somewhat contorted by a broad sclerotized band at the juncture with the ductus seminalis.
Adult ID Requirements: Identifiable from good quality photos of unworn specimens.
Immatures and Development: Cappuccino (2000) reported that the females lay eggs singly and that the larvae bore in the stems of goldenrods.
Distribution in North Carolina
Distribution: The range extends across much of southern Canada from British Columbia to Prince Edward Island. In the US specimens have been observed from the New England states westward to Minnesota, and southward to West Virginia, Ohio, and Illinois. Scatter records also occur in Virginia, North Carolina and Tennessee. As of 2022, our one record is from a mountain bog in Ashe County.
County Map: Clicking on a county returns the records for the species in that county.
Flight Dates:
 High Mountains (HM) ≥ 4,000 ft.
 Low Mountains (LM) < 4,000 ft.
 Piedmont (Pd)
 Coastal Plain (CP)

Click on graph to enlarge
Flight Comments: The adults have been observed from April through August, with a strong seasonal peak typically in May and June. As of 2022, our one record is from early June.
Habitats and Life History
Habitats: This species is commonly found in open habitats such as old fields, roadways, prairies, and open woodlands.
Larval Host Plants: Eucosma formosana is known to feed on goldenrods (Heinrich, 1923; Cappuccino, 2000), particularly Tall Goldenrod (Solidago altissima). - View
Observation Methods: The adults are attracted to lights.
Wikipedia
Status in North Carolina
Natural Heritage Program Status:
Natural Heritage Program Ranks: GNR [S1-S2]
State Protection:
Comments: This species is at the southern limit of its range in western North Carolina and is seemingly rare within the state.