Macronoctua onusta

Easily identified by large size combined with dark gray anterior and lateral wing margins. Diagnostic features include: reniform spot with dark posterior outline forming straight black line below cubital vein, plus spike-like process extending toward base from posteromedial end; postmedial line with serrate anterior portion and straight posterior segment. Similar dark brown moths lack these specific reniform spot and postmedial line characteristics.

Large moth with forewing length 18–21 mm. Forewing broad with scalloped outer margin, dull brown base color with broad smoky dark gray suffusion on costa, in cell, terminal area, and fringe. Antemedial and postmedial lines thin, dark gray; antemedial line drawn far lateral above posterior margin. Median line dark brown, strongly arched across median area below cell. Postmedial line jaggedly zigzagged anteriorly, straight from anterior cubitus vein to posterior margin. Subterminal line evident only as transition from brown subterminal area to black terminal area. Terminal area a black line. Three spots outlined in thin black: orbicular spot small oval; reniform spot large, asymmetrically kidney-shaped with lower end curved toward outer margin touching postmedial line, darker posterior outline forming straight black line below cubital vein, with spike-like process extending toward base from posteromedial end; claviform spot small elongate with rounded end. Hindwing dirty brown-gray with slightly darker discal spot and veins, scalloped terminal line, light gray fringe with brown base. Head and thorax even smoky dark gray. Male antenna broad and bead-like.

North America; recorded from Vermont and presumably widespread across range

Adults active in fall, primarily September and October

Larval stage feeds exclusively on rhizomes of Iris species (Iridaceae); adult diet not described

• Iris - larval foodplantlarvae bore into rhizomes

Eggs laid in fall; single female produces 150–200 eggs over several days. Larvae develop as borers in iris rhizomes. Adults emerge in autumn.

Adults attracted to lights, though not strongly. Best obtained by rearing from larvae rather than collecting at lights.

Pest of cultivated irises; larvae damage rhizomes through boring activity, potentially affecting plant health and ornamental value

• Similar dark brown NoctuidaeLack the diagnostic dark posterior outline and spike from medial reniform spot, and the distinctive postmedial line with serrate anterior and straight posterior segments

• pest
• specialist
• borer
• Noctuidae
• Lepidoptera
• North America
• autumn
• Iris

• BugGuide
• Wikipedia
• GBIF taxonomy match
• iNaturalist taxon
• NCBI Taxonomy
• Catalogue of Life