Spodoptera exempta (Walker)

Scientific name: Spodoptera exempta (Walker)
Common name: African Armyworm
Synonyms: Laphygma exempta (Wlk.)
Ethiopian name: Temch

Order: Lepidoptera
Family: Noctuidae

HOSTS:
Main hosts: Grasses, Maize, Sorghum, Tef, Rice
Alternative hosts: Many species of cereals and wild grasses

IMPORTANCE IN ETHIOPIA:
During outbreaks a major pest of: Barley, Maize, Sorghum, Tef, Wheat

DISTRIBUTION IN ETHIOPIA:
Outbreaks usually start during May in the southern provinces. During the main growing season they move northwards.

DAMAGE:
The caterpillars feed on the leaves eating them down to the midrib.

INSECT BIOLOGY & RECOGNITION:
Egg: The eggs are laid in groups of 100-400. A female lays several egg masses until a total of up to 1000 eggs. The eggs are laid in single or multi layers on the leaves. They are covered with black hair scales. When they are laid, the colour of the eggs is yellowish. Just before hatching they turn black. The diameter of the eggs is about 0.5 mm. Hatching takes place after 2-4 days.

Larva: There are six larval instars. On hatching the larvae are colourless or whitish. They have black heads. As they feed the colour becomes green. During the first three instars the caterpillars remain green. After this they turn black when there are many caterpillars together (gregarious form) or they will remain in various shades of green or brown when there are only few caterpillars together (solitary form). In a typical armyworm outbreak the caterpillars are velvety black on top with pale lines on each side. The underside is greenish yellow. There is a pale stripe along the top of the body. The caterpillars do not have obvious hairs. The head is shiny black and shows a V shaped white mark. The upper side of the first segment behind the head is black and has three narrow white stripes. A full grown caterpillar is 25 35 mm long. The larval stage takes 14 21 days. (see Figure 29 and 30) The solitary form is a sluggish caterpillar which usually feeds at the bases of plants. Usually they have a pale head.

Pupa: The mature caterpillars burrow into the soil. They pupate in chambers 2 3 cm below the surface. The pupa is brown or black in colour. It is about 17 mm long. The pupal period takes 7 12 days.

Adult: The adult is a grey brown night flying moth. The wingspan is 20 35 mm for males and 22 37 mm for females. The hind wings are pale white with dark veins. The forewings are dull grey brown. They have two spots. The inner (orbicular) spot is elongate and pale. The outer (reniform) spot is kidney shaped and more clearly visible in males than in females. The moths are attracted by lights at night.

REMARK:
A related species, Spodoptera exigua (Lesser Armyworm) feeds not only on Gramineae but also on many other crops, including cotton, tobacco, tomato, groundnut and beans. Unlike S. exempta, this species does not migrate over long distances, but the caterpillars are gregarious and move in swarms. The grey brown adult moth is 12 15 mm long and has a wingspan of about 25 mm. The hind wings are white with grey brown margins.