Moths of North Carolina
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Eucosma Members:
2 NC Records

Eucosma giganteana (Riley, 1881) - Giant Eucosma Moth

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Taxonomy
Superfamily: Tortricoidea Family: TortricidaeSubfamily: OlethreutinaeTribe: EucosminiP3 Number: 620745.00 MONA Number: 3098.00
Species Status: Eucosma giganteana is one of the largest species of tortricids in North America with a forewing length up to 16.2 mm.
Identification
Field Guide Descriptions: Online Photographs: MPG, BugGuide, iNaturalist, Google, BAMONA, GBIF, BOLDTechnical Description, Adults: Riley (1881); Wright and Gilligan (2015)Technical Description, Immature Stages: Johnson et al. (2019)                                                                                 
Adult Markings: This species is easily recognized by its unique forewing color pattern. The following is based in part on the original description by Riley (1881). The head, palps and thorax are white and the antenna reddish brown. The ground of the forewing is white and is overlain with a large brown patch that cover much of the apical third of the wing except for the subcostal region. The patch enclosing the anal angle and a broad region surrounding the ocellus, which has two rows of blackish spots that are often masked by the dark ground color that is in between. The basal third of the wing has varying levels of pale fuscous to grayish mottling that is concentrated on the dorsal half, and the costal has a series of widely spaced dark spots along the entire length. The hindwing is brown with a whitish fringe, and the abdomen has alternating whitish and brown bands.
Wingspan: 34-38 mm (Riley, 1881).
Forewing Length: 8.6-19.0; mean = 12.8 mm (Wright and Gilligan, 2015).
Adult Structural Features: Wright and Gilligan (2015) has illustrations of the male and female genitalia.
Adult ID Requirements: Identifiable from good quality photos of unworn specimens.
Immatures and Development: Johnson et al. (2019) conducted a detailed life history study of this species in South Dakota where Silphium perfoliatum is the host plant. Females that first emerge in June typically lay small groups of reddish eggs on the uppermost leaves, and later in the season on floral bracts, upper internodes, petioles, and peduncles. The larvae of instars one through four commonly feed communally on floral buds, developing leaves, and meristematic tissue from early July until mid-August. Communal groups of 35-60 larvae can often be found feeding in a single floral head.

The larvae of instars three or four eventually leave the floral complex and enter the crown at the base of a shoot or the upper portion of a proaxis that subtends a shoot. From there they tunnel into the stout rhizomes and create a wide burrow. They plug the entry hole with a frass plug and enlarged the hole to serve as an exit for the adult. The larvae feed on rhizomes until winter weather arrives, then overwinter and resume feeding in the spring. Pupation occurs in an enlarged chamber near the exit hole within a tightly woven cocoon. The adults emerges from the frass plug shortly before mating begins.
Distribution in North Carolina
Distribution: Eucosma giganteana is most common in prairie habitats. The range spans an area from Minnesota and Wisconsin southwestward to Kansas, Oklahoma, southeastern Colorado, eastern New Mexico, and much of Texas. It extends eastward in the north to southern Ontario, Ohio, western Pennsylvania and Kentucky, and along the Gulf Coast states to Florida, then northward to Georgia, South Carolina, and southern North Carolina. As of 2022, our only records are historical from Tryon in 1904.
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)

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Flight Comments: The adults fly from April through September, with a seasonal peak in most areas of the range from June through August. As of 2022, our very limited records are all from August.
Habitats and Life History
Habitats:
Larval Host Plants: The larvae are specialists on Silphium species, where they feed on the rhizomes or flower heads (Johnson et al., 2019; Vilela et al., 2020). The known hosts include Rosenweed (S. integrifolium), Common Cup-plant (S. perfoliatum) , Slender Rosinweed (S. radula var. gracile), and Prairie Dock (S. terebinthinaceum). Johnson et al. (2019) noted that the larva do not bore into roots even though they have been widely reported to do so (e.g., Forbes 1923; Heinrich 1923; Gilligan et al. 2008). They are stem feeders that utilize the stout rhizomes rather than the thinner roots. - View
Observation Methods: The adults are attracted to lights and can be found on the undersides of leaves during the mating season.
Wikipedia
Status in North Carolina
Natural Heritage Program Status:
Natural Heritage Program Ranks: GNR SH
State Protection: Has no legal protection, although permits are required to collect it on state parks and other public lands.
Comments: This species was last documented in North Carolina in 1904 near Tryon.