Lesser Armyworm

Pests of Field Crops in Southern Africa

LESSER ARMYWORM

(Lepidoptera: Noctuidae)

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Text Box: This pest, Spodoptera exigua, is a close relative of the probably better known armyworm, which attacks graminaceous crops. The moth has pale grey forewings with brown markings and whitish hindwings with dark veins and fringe at outer edge. The caterpillars reach about 40 mm in length, and are pale to dark green, with a conspicuous line running along each side of the body. They are sometimes found in dense populations, but tend to be more individual in their feeding habits than armyworm, and their green coloration gives them some camouflage. TOP

Text Box: Lesser armyworm has been recorded feeding on a variety of host plants, amongst which are peas, beans, groundnuts, lucerne, tobacco, tomato, cotton, potato, very occasionally maize and various weeds. It is a widely distributed species, and an important pest of beet and rice in other countries. TOP

Text Box: Lesser armyworm is essentially a leaf feeder. When small, the caterpillars feed on the leaflets at the growing points, spinning fine webbing and tying them together. Larger caterpillars tend to be found on older leaves, and feeding tends to take place at night. Sometimes heavy infestations in warmer growing areas can be responsible for considerable foliar damage. TOP

Text Box: Female moths are capable of laying several hundred eggs in clusters of up to 100 on the lower surface of the leaf. They hatch in 2-4 days, and the larvae pass through six instars in just under two weeks in the warmer months. Pupation takes place in the soil, and adults emerge a week or two later. Development continues, although much more slowly, throughout the winter months, with no diapause. TOP

Text Box: When control is considered necessary, the normal contact sprays, such as carbaryl and malathion, can be applied to the foliage, taking care to observe harvest intervals in bearing crops. In general, however, low populations do not require control and are probably reasonably controlled by a number of parasitoids. Clean cultivation and ploughing between crops will destroy many of the subterranean pupae. TOP

Lesser armyworm. (Photo: A N Sparks Jnr. Univ. Georgia. Bugwood .org