Cabbage Integrated Pest Management : An Ecological Guide.

Major Cabbage Insect PestsDescription and life cycleAdults of armyworms are gray to gray-brown in appearance, with a wingspan of about 25 mm. Theforewings are yellow-brown with white and black patterns. The hindwings are whitish. They do not usuallyfly far and lay their eggs close to the place of emergence. Eggs are laid in large masses on the undersidesof host plant leaves. Each egg mass has a fuzzy appearance because it is covered in fine hairs andscales from the body of the female. About 500 - 2000 eggs per female are deposited in batches of 50 -200 over a few days period. The eggs are ribbed, and range in color from green-gray when freshly laid,becoming very dark in color just before hatching.Egg hatch occurs 2 - 6 days after laying. Caterpillars of armyworms feed in groups together for a whilebut spread out when they become older. They usually feed at night.Newly hatched caterpillars are light green in color and about 1 mm in length with relatively large heads.They undergo five or six moults and reach a length of 35 - 50 mm before burrowing into the soil forpupation. When fully grown, caterpillars vary in color from light tan or green to almost black. Larvae of S.exigua are often green in color with a white line along the side; S. littoralis are often brown to black andcan have more black spots/stripes on the body. They are also usually a bit larger than S. exigua. Larvaeof S. litura and S. littoralis have a distinct black band on the first abdominal segment. The head is black.They feed together in groups. The pupa is dark red in color, 15 - 20 mm long. The pupal stage takes about12 days.Plant damageArmyworms skeletonize host plant leaves. Egg batches are laid closetogether and in a severe year clusters of many caterpillars may rapidlydefoliate of cabbage plants. This is usually a problem from seedlinguntil cupping stage. When the cabbage head is formed, usually notmuch damage is done.Natural enemiesGood results have been achieved with the use of nuclear polyhedrosis viruses (NPV) for the control ofarmyworms. These NPVs have become an important biocontrol agent in IPM systems. There are differentstrains of the NPV:SlNPV for control of Spodoptera lituraSeNPV for control of Spodoptera exiguaNPV is being tested at various locations in Asia, e.g. Vietnam, Philippines and Indonesia. Some countriesare already using it on large scale.Cabbage Ecological Guide - 200092