Southern Armyworm
Spodoptera eridania (Cramer), Noctuidae, LEPIDOPTERA


DESCRIPTION

Adult - The southern armyworm moth has a wingspan of 30 to 36 mm. The forewings may vary in color from pale yellowish to dark brown. A darker streak extends from the center of each forewing almost out to the wing tip. The hind wings are white with brown veins and margins.

Egg - The circular greenish egg is about 0.5 mm wide and 0.4 mm high. Viewed under magnification, the egg can be seen to have a ridged surface.

Larva - The fully grown caterpillar is gray or nearly black with whitish stripes tinged orange or pink and is about 36 mm long. The background body color sometimes has a green or pink tint. Viewed from above, the larva has a pair of black triangular spots on each body segment, except the segment near the head bearing the first pair of legs. The larva has 3 pairs of true legs and 5 pairs of prolegs. The head capsule is pale yellow with bright reddish-brown markings. The southern armyworm does not have a white inverted "V" on its head capsule.

Pupa - The darkly colored pupa is about 18 mm long and 5 mm wide.


BIOLOGY

Distribution - Florida, California, New Mexico, and central South America are year-round homes for the southern armyworm. Each year moths migrate northward as far as Tennessee and Virginia. In North Carolina, this armyworm is only an occasional problem.

Host Plants - This armyworm is a general feeder with a wide host range. Weeds like spiny amaranth and pokeweed are preferred food plants. Some vegetable crop hosts include beet, cabbage, carrot, celery, collards, corn, cowpea, eggplant, okra, pepper, potato, rhubarb, sweet potato, and tomato.

Damage - Though southern armyworms feed primarily on leaves, they have been known to consume tender stems and tips of branches. These caterpillars feed freely during the daytime but often are not observed because they tend to congregate around the bases of plants. Here they gnaw on stems or feed on potato tubers or sweet potatoes near the soil surface. During the morning and evening, or on cloudy days, southern armyworms are likely to be found on foliage.

Life History - Southern armyworms overwinter either as larvae or pupae in Florida. Egg-laying moths probably arrive in North Carolina in July. Each female deposits hundreds of eggs in masses on foliage. These masses are fuzzy in appearance since they are covered with scales from the bodies of moths. Eggs hatch in 4 to 6 days. For approximately 17 days, larvae feed and develop through 6 instars. At the end of this time, larvae drop by means of silken threads to the soil surface, enter the soil, and pupate. Nine to 13 days later a new generation of moths emerge. About 5 weeks elapse from egg stage to adult emergence during the summer. As many as 5 generations occur each year in Florida, but only 2 or 3 are likely to be completed in North Carolina.


CONTROL

The variety NC Porto Rico 198 has been found to have some resistance to the southern armyworm. Populations of this armyworm species rarely reach high enough numbers to warrant chemical control in North Carolina.

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