Beet Armyworm, Spodoptera exigua (Hbn.)

Description and Life Cycle: Seasonal activity varies considerably according to climate. In warm locations such as Florida, all stages can be found throughout the year, although development rate and overall abundance are reduced during the winter months. The life cycle can be completed in as few as 24 days, and six generations have been reared during five months of summer weather in Florida.

Egg: Eggs are laid in clusters of 50 to 150 eggs per mass. Normal egg production is about 300 to 600 per female. Eggs are usually deposited on the lower surface of the leaf, and often near blossoms and the tip of the branch. The individual eggs are circular when viewed from above, but when examined from the side the egg is slightly peaked, tapering to a point. The eggs are greenish to white in color, and covered with a layer of whitish scales that gives the egg mass a fuzzy or cottony appearance. Eggs hatch in two to three days during warm weather.

Larva: There normally are five instars, although additional instars are sometimes reported. The larvae are pale green or yellow in color during the first and second instars, but acquire pale stripes during the third instar. During the fourth instar, larvae are darker dorsally, and possess a dark lateral stripe. Larvae during the fifth instar are quite variable in appearance, tending to be green dorsally with pink or yellow color ventrally and a white stripe laterally. A series of dark spots or dashes is often present dorsally and dorsolaterally. Sometimes larvae are very dark in color. The spiracles are white with a narrow black border. The body is practically devoid of hairs and spines. In the southern states, the larva of beet armyworm is easily confused with southern armyworm, Spodoptera eridania (Cramer), but southern armyworm can be distinguished by the presence of a large dark spot laterally on the first abdominal segment that disrupts the lateral stripe. Beet armyworm occasionally bears a spot laterally, but if present it occurs on the mesothorax, not on the first abdominal segment.

Pupa: Pupation occurs in the soil. The chamber is constructed from sand and soil particles held together with an oral secretion that hardens when it dries. The pupa is light brown in color and measures about 15 to 20 mm in length. Duration of the pupal stage is six to seven days during warm weather.

Adult: The moths are moderately sized, the wing span measuring 25 to 30 mm. The forewings are mottled gray and brown, and normally with an irregular banding pattern and a light colored bean-shaped spot. The hind wings are a more uniform gray or white color, and trimmed with a dark line at the margin. Mating occurs soon after emergence of the moths, and oviposition begins within two to three days. Oviposition extends over a three to seven day period, and the moths usually perish within nine to 10 days of emergence.

Damage: Larvae feed on both foliage and fruit. It is regarded as a serious defoliator of flower crops and cotton, though much of the injury is induced by insecticide use that interferes with natural enemy activity. Young larvae feed gregariously and skeletonize foliage. As they mature, larvae become solitary and eat large irregular holes in foliage. They also burrow into the crown or center of the head on lettuce, or on the buds of cole crops.