Pacific Northwest Moths

Identification

Adults

Euxoa nevada is a fall-flying, small to medium-sized Euxoa (FW length 12–16 mm) with streaky gray and olive-tan forewings, elongate fused orbicular and reniform spots, and hindwings that are pure white with dark terminal line in males and gray with dark veins and white fringe in females. Females are variable in size, but are often smaller than the males. The forewing has a relatively sharply pointed apex for the genus, with a slight angle of the outer margin on vein CuA1. Its color is olive-tan and gray, lightest in the distal subterminal area and at the apex and slightly darker gray between the veins. The veins near the costa the cubital vein, and 1A+2A are powdery light gray, while the other veins are dark. The terminal area is dark gray, and the cell is often dark brown-gray. A black basal dash is present. The basal and antemedial lines are evident on the costa in some specimens but are absent otherwise. The postmedial line is only visible as spots on the costa and an angled lightly scalloped gray line below the reniform spot. The subterminal line is evident as the uneven transition between the light subterminal area and gray terminal area, approaching the outer margin near the apex and as a "W" mark on the mid-forewing. The forewing spots are outlined in gray or black, lined by gray, and filled centrally with the ground color. The orbicular spot is very long, usually fused to the C-shaped reniform spot. The claviform is absent or relatively weak, small or moderate-sized when present. The male hindwing and fringe are white, with darker gray veins near the outer margin and a dark terminal line; that of the female is light brown-gray with gray marginal suffusion, darker veins and terminal line, and a white fringe with a patchy gray base. The head and thorax are powdery olive gray with a black line across the mid-collar. A frontal tubercle is present. The male antenna is weakly bipectinate. Euxoa nevada is a member of the large subgenus Euxoa.

This species can be identified by its fall flight period, streaky gray and olive-tan forewing, and fused orbicular and reniform spots. Other species with similar fused spots are brown (Euxoa atristrigata) or smaller with light costal margins (Euxoa hollemani and Euxoa subandera).

Euxoa is a very large genus with many similar species, many of which are also quite variable. The genus is defined by a saccular extension of the valves in males and sclerotized plates on the dorsal and ventral ductus bursae in females. The genus was revised by Lafontaine (1987) in the Moths of North America series and is divided into eight subgenera based on structural characters. These moths are amongst the most difficult to identify. Even though the forewing color and strength of various markings can vary significantly in some of the species, the shape of the lines and spots and the color of the hindwings (often different in the sexes) are more constant. The habitat and flight period are also important in helping to narrow the possibilities.

Habitat

This species is widely distributed on arid rangelands throughout much of western North America, including dry short-grass prairie on the Great Plains and dry sagebrush steppe west of the Rocky Mountains.  In the Pacific Northwest, it flies in juniper woodlands and sagebrush steppe at low to middle elevations.  It is particularly common on rangelands that have been disturbed by over-grazing, especially during drought years.  In a study in central Oregon, E. nevada was almost completely eliminated from sagebrush steppe that had been burned over by a wildfire two years earlier, while it remained common in adjacent unburned habitat.  Thus, this species appears to be particularly intolerant of fire.

Distribution

Pacific Northwest

Euxoa nevada is widely distributed in the dry interior steppe regions of the Pacific Northwest as far north as southern British Columbia. Its range is more extensive in eastern Oregon than in Washington where it is mostly restricted to the driest part of the Columbia Basin near the Columbia River. Euxoa nevada also occurs in southern Idaho and western Montana.

Global

Euxoa nevada has a similar distribution in western North America to many other Euxoa species. It extends east across southern Canada to Saskatchewan and the western Dakotas, and south through the western Great Plains as far east as northeastern Colorado. The southern limits are northern New Mexico, northern Arizona, and southern California.

Life History

Larvae

No information is presently available regarding larval foodplants of this species, but it is probably a soil-surface feeding cutworm that feeds on herbaceous vegetation based on related species.  The sensitivity to wildfires suggests that it may be a foodplant specialist feeding on semi-woody plants such as buckwheats (Eriogonum spp.) in the Polygonaceae.

Adults

Adults of E. nevada are on the wing during the fall. It has been collected from late August to early October in the Pacific Northwest. It is nocturnal and comes to lights. Males are fairly common at most sites where it occurs but females are collected infrequently at lights.

Economic Importance

None.

Literature

Lafontaine (1987)

Moth Photographers Group