alfalfa webworm moth

not listed

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SNR - Unranked

not listed

Alfalfa webworm moth is a common, small to medium sized, roughly triangular (deltoid) moth. It occurs throughout the contiguous United States, but it is absent from the Great Basin, and it is mostly absent from the southeast. It also occurs across southern Canada and in Mexico.

The larvae feed on the leaves of a wide variety of plants, including alfalfa, sugar beet, vegetables, and other agricultural crops. They prefer broadleaved species to grains and other grasses. When they occur in large numbers, they can destroy an entire crop. They sometimes migrate in masses, like armyworms, from decimated fields. Adults are found from May to September in prairies, meadows, weedy fields, gardens, and agricultural crops.

Adults are ⅜″ to ½″ (10 to 13 mm) in length and have a 13⁄16″ to 1⅜″ (30 to 34 mm) wingspan. Moth sizes are sometimes given in terms of forewing length, which for this moth is ½″ to ⅝″ (13 to 16 mm). The body is slender.

The sensory mouthparts (labial palps) are moderately long and are projected forward. The compound eyes are large. The simple eyes (ocelli) are small but well developed.

The forewing is broadly triangular and pale gray, grayish brown, or brown, with dark brown to black lines and streaks, and tan shading. In the basal area there is a long, longitudinal, black dash at the middle and a pale patch at the wing base on the inner margin. The middle part of the postmedial (PM) line is expanded on the veins into small, black, narrow, forward-pointing wedges. At the leading edge (costal margin), the PM line is expanded into a broad, black or dark brown patch. There is a pale patch between the round spot in the upper median area (orbicular spot) and the kidney-shaped spot (reniform spot) in the lower median area, and there is sometimes a black dash connecting the spots. The subterminal (ST) band is sharply defined and yellowish or tan. It is evenly tapered at both the inner and costal margins. The terminal line is relatively broad and is shadowed on the inside by a similar but more diffuse line.

The hindwing is gray or brownish gray with a variable amount of dark shading along the veins and near the outer margin.

On the middle legs, the fourth segment (tibia) is thickened.

Total length: ⅜″ to ½″ (10 to 13 mm)

Wingspan: 13⁄16″ to 1⅜″ (30 to 34 mm)

Prairies, meadows, weedy fields, gardens, and agricultural crops

Two or more generations per year in most areas: May to September

First and second stage (instar) larvae skeletonize leaves, eating the tissue and leaving the major veins. Later instars feed communally in webs and consume entire leaves. They often make a silk tube leading from their feeding site to the ground or other protected site.

Adults are active at night and are attracted to light.

The eggs are flat and are laid end to end in a few overlapping rows.

A wide variety of mostly broadleaved plants

Sources

4, 21, 29, 30, 71, 75, 82, 83.

Common and widespread

Loxostege cereralis alfalfa webworm moth

Loxostege cereralis, alfalfa webworm moth, Barnes Prairie Remnant, Racine Co., WI August 31, 2021.

Location: Barnes Prairie, Racine Co., WI

Loxostege cereralis, alfalfa webworm moth, Barnes Prairie Remnant, Racine Co., WI August 31, 2021.