Common names: Cotton bollworm
Scientific names: Helicoverpa/Heliotis zea, H. armigera
Synonyms: American bollworm, Tomato fruitworm, Sorghum headworm, Corn earworm
Cotton, corn, sorghum, soybean, peanut, tobacco, cowpea, tomato, okra, pechay, radish, lettuce, beans.
Helicoverpa/Heliotis zea is found in Canada, South America, and the USA while H. armigera is found in Asia.
Cotton bollworm bore holes on the flowers and pods causing these to defoliate. The young larva feeds on tender leaves, buds, flowers, and later bore into the bolls. While feeding, its head and part of the body is inside while the other half is found outside the boll. This feeding habit distinguishes Heliotis from other bollworm species.
Eggs are pinhead-size and yellowish-green in color. They are found singly laid on the surface of the leaves. Hatching occurs within about 2-5 days.
Larvae vary in color from bright green, pink, brown, to black, with lighter undersides. Alternating light and dark bands run lengthwise along their bodies, the heads are yellow and the legs are almost black. Mature larvae vary in length from 3-5cm. They drop to the ground to burrow into the soil to pupate. The larval stage lasts from 12-24 days.
Pupae are yellowish-green and turn brown as they mature. Pupation takes place under the soil. Pupal period is 12-24 days.
Adult moths are gray to brown in color and have dark spots on the front wings. Each has a wingspread size of about 3.8 cm. A female may deposit 200-2,000 eggs in her entire lifetime. The total development period from egg to adult is 34-45 days.
Other important Bollworm species
Pink bollworm (Pectinophora gossypiela)
Pink bollworm larvae damage squares and bolls. Larvae burrow into bolls through the lint to feed on seeds. As the larva burrows into the boll, the lint is cut and stained resulting in yield and quality losses. Yield and quality losses are directly related to the percentage of bolls infested and the numbers of larvae per boll. During high humidity, 1-2 larvae can destroy an entire boll since damaged bolls are vulnerable to boll rot fungal infection.
Eggs are very small, slightly elongated, and laid under the calyx of green bolls. Young larvae are tiny, white caterpillars with dark brown heads. When mature, they are about 12 mm long and have wide transverse pink bands on the back. Pink bollworm adults are small, grayish-brown moths. They have an elongated slender appearance when their wings are folded. The wing tips are conspicuously fringed.
Spotted bollworm (Earias insulana, E. vittella)
Spotted bollworm larvae bore into the shoot of the cotton plant, this causes shoot to wilt and buds to shed. When attacking bolls, they bore holes into the bolls which do not open well. Young bolls have small holes with excreta inside.
Eggs are small slightly under 0.5 mm in diameter, roughly spherical, and light blue-green in color. A full-grown larva is 13-18 mm long and 2.5-3 mm wide. It is stout and spindle shaped, tapering after the fifth abdominal segment. The body color ranges from grayish-brown, through gray to green, with a distinctly paler or white median line. The pupa is about 13 mm long, yellow to chocolate-brown or purplish-brown in color. It is enclosed in a cocoon shaped like an inverted boat, and spun from a dirty white or pale brown, tough, felt-like silk. Cocoons may be attached to the plant, to plant debris on the ground, or to crevices up to 30 cm deep in the soil. The adult is about 12 mm long, with a wingspan of 20-22 mm. It is covered with a soft, fairly dense coating of scales. The abdomen and hind wings are plain silvery or creamy white in color. The pattern on the forewing is the most important diagnostic character, though it is very variable. The ground color varies from silvery-green to straw yellow with three transverse lines of a darker shade (CABI, 2000).