Pacific Northwest Moths

Identification

Adults

Agrotis ipsilon is our largest Agrotis species (FW length 18 - 24 mm). The forewing is dull black-brown with darker costa and lighter brown at the forewing base and lateral to the postmedial line. The antemedial and postmedial lines are black and double, but less prominent than the irregular postmedial line. The postmedial line is scalloped and nearly straight across the forewing. The postmedial line is preceded by a series of lines and two black wedges opposite the reniform spot. The claviform, orbicular and reniform spots are black. The reniform spot is fairly large and has a thick black wedge-shaped mark extending laterally from the outer indentation to cross the postmedial line. The terminal area is marked with dark gray, widest opposite the cell. The hindwing is pearly light gray with darker gray margin and veins; its discal spot is barely evident. The head is brown. The thorax is dark gray-brown with a double black collar. The abdomen is gray. The base of the male antenna is bipectinate, tapering to filiform post its midpoint.

This species can be identified by the long wing that is blackish brown medial to the postmedial line and paler brown distally with three black wedge-shaped marks on the distal to the reniform spot. No other species in our area has this combination of features.

Larvae

Larva is smooth, gray to black without markings.

Habitat

This species is migratory and distributed throughout most of the world.  In North America, it over-winters in Mexico and the southern United States, migrating northward in the spring.  Thus, this species is not a permanent year-round resident in the Pacific Northwest.  It may become common in mountain meadows at higher elevations in late summer, particularly during warm, dry years.  However, the primary habitat is disturbed agricultural and urban areas at low elevations both west and east of the Cascades, and it may attain epidemic outbreaks in these habitats.

Distribution

Pacific Northwest

Agrotis ipsilon is found throughout our region as far north as southern British Columbia.

Global

This species is found throughout most of the world except in the arctic and subarctic zones of the Northern Hemisphere and Antarctica.

Life History

Larvae

This species is a soil-burrowing cutworm that feeds on general herbaceous vegetation in such families as Fabaceae, Asteraceae, Brassicaceae, Rosaceae, Solanaceae, Malvaceae, Chenopodiaceae, Apiaceae, and Poaceae, and is often a major pest in various agricultural crops.  The larva is one of the few Lepidoptera that is largely immune to the pathogenic soil microbe, Bacillus thuringiensis.

Adults

Adults are migratory, and migrate northward from Mexico in the spring with a return migration in the fall.  Thus, adult moths that emerge in the Pacific Northwest in late summer are non-reproductive, and do not become reproductive until they return to agricultural lands in Mexico during the fall and winter. The moths have been collected beginning in May and June in our area, but do not become common until late July. This species flies into late fall, with records through November. They are nocturnal and come to light.

Economic Importance

This species is a major agricultural pest feeding on many herbaceous crops, particularly in eastern North America.  In the Pacific Northwest, it is usually a minor pest, except during warm, dry years when it may attain epidemic outbreaks.

Literature

BugGuide

Lafontaine (2004)

Moth Photographers Group

Powell & Opler (2009)