Bertha armyworm

Mamestra configurata

Identification. The adult moth is a greenish-gray or gray moth with two spots on the forewings, a small round spot with a large kidney-shaped white or gray spot on the middle of the wing, and a whitish band near the fringe of the wing. Larvae are about 40 mm long when mature. The head is pale brown with or without dark arcs and reticulations, and with an inverted white "Y". The color of the larvae varies from green to gray, brown, or black. The mid-dorsal and top-lateral lines are white, broken and inconspicuous. The inverted white “Y” does not become very noticeable until the larvae are mature, in the fifth and sixth instar.
Life Cycle. Bertha armyworm overwinters as a pupa in the soil. Adults emerge in mid-Spring, and the females lay eggs in masses on the underside of leaves of crop plants and weeds (particularly lambsquarters). Eggs hatch in 4 to 8 days. Larvae dangle from the plant by threads of silk until they reach other leaves or are blown by the wind to other plants, where they begin feeding. Thus infestations of bertha armyworm tend to occur in patches fairly close to where the eggs were deposited. Sometimes the larvae will remain on a single plant where they were laid. Larvae feed for 5 to 6 weeks in June and July. In their late stages (fifth and sixth instar) the larvae disperse. This is why they call them “armyworms”. Bertha armyworm pupate in the soil. In the Willamette Valley, some of the adults emerge from the soil during mid- to late July and begin a second generation in August. Damage caused by these larvae is noticeable in mid-August and September. There are two overlapping generations each year.

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