Yellowstriped armyworm

Spodoptera ornithogalli

Distribution. The yellowstriped armyworm, Spodoptera ornithogalli (Guenée), is common in the eastern United States as far west as the Rocky Mountains, and occurs in southern Canada. However, it also is reported from southwestern states, including California. The distribution of this native insect includes Mexico, Central and South America, and many Caribbean islands. As a pest, however, its occurrence is limited principally to the southeastern states. A very similar species, western yellowstriped armyworm, Spodoptera praefica (Grote), is known only from the western states, principally California and Oregon. In California, Spodoptera praefica is much more important than Spodoptera ornithogalli.
Life Cycle and Description:
There apparently are three to four generations annually, with broods of adults present in March to May, May to June, July to August, and August to November. Some of the latter brood of yellowstriped overwinter as pupae rather than emerging as adults. Although eggs, larvae and adults of yellowstriped armyworm may be present in autumn or early winter they cannot withstand cold weather, and perish. Development time, from egg to adult, is about 40 days.
Eggs: The eggs are greenish to pinkish brown in color and bear 45 to 58 small ridges. In shape, the egg is a slightly flattened sphere, measuring 0.46 to 0.52 mm in diameter and 0.38 to 0.40 mm in height. Females typically deposit clusters of 200 to 500 eggs, usually on the underside of leaves. Total fecundity was determined to be over 3000 eggs under laboratory conditions. The eggs are covered with scales from the body of the adults. Duration of the egg stage is three to five days at warm temperatures.
Larvae: Larvae initially are gregarious in behavior, but as they mature they disperse, sometimes spinning strands of silk upon which they are blown by the wind. There usually are six instars, although seven instars have been reported. Head capsule widths are about 0.28, 0.45, 0.8-1.0, 1.4-1.6, 2.0- 2.2, and 2.8-3.0 mm, respectively, for instars one through 6. The larva grows from about 2.0 to 35 mm in length over the course of development. Coloration is variable, but mature larvae tend to bear a broad brownish band dorsally, with a faint white line at the center. More pronounced are black triangular markings along each side, with a distinct yellow or white line below. A dark line runs laterally through the area of the spiracles, and below this is a pink or orange band.
Dark subdorsal spots are found on the mesothorax of yellowstriped armyworm, and the triangular shape of these spots aids in distinguishing this insect from sweetpotato armyworm, Spodoptera dolichos, and velvet armyworm, Spodoptera latifascia, in eastern states. The head is brown but has extensive blackish markings. Duration of the larval stage is 14 to 20 days, with the first three instars requiring about two days each and the last three instars requiring about three days each.
Pupae: Larvae pupate in the soil within a cell containing a thin lining of silk. The reddish brown pupa measures about 18 mm in length. Duration of the pupal stage is nine to 22 days, normally averaging 12 to 18 days.
Adults: The moths measure 34 to 41 mm in wing span. The front wings are brownish gray with a complicated pattern of light and dark markings. Irregular whitish bands normally occur diagonally near the center of the wings, with additional white coloration distally near the margin. The hind wings are opalescent white, with a narrow brown margin. Under laboratory conditions average longevity of adults is 17 days, with most egg production completed by the tenth day.

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