DESCRIPTION Adult- Adult corn earworm moths vary in color and markings, but the forewings are usually light yellow or yellowish brown, with dark irregular lines and a dark area near the tip. The hind wings, usually partially covered by the forewings, are white with irregular dark markings near the border. Wingspan is about 40 mm. The eyes of the moths are green. Egg- When first laid, the hemispherical and ridged eggs are pale white. A pale reddish band develops around the egg, and then it darkens prior to hatching. Larva- Larvae vary from pale green to dark brown, with alternating light and dark longitudinal stripes, generally brown or orange, running the length of the body. The head is dark yellow or reddish orange. Newly hatched larvae are about 1.6 mm long and yellowish white with dark head capsules. Full-grown larvae are about 43 mm long. Pupa- Pupae are glossy brown and taper at one end. The pupa is about 32 mm long and 6 mm wide.
Fig. 79: Corn Earworm Helicoverpa
(=Heliothis) zea (Boddie), Noctuidae,
LEPIDOPTERA BIOLOGY Distribution- The corn earworm feeds on many plants throughout the world. In the United States, the corn earworm is a destructive pest of corn, cotton, and tomato, especially in the South. The corn earworm also is referred to as the cotton bollworm or the tomato fruitworm. Two similar and related species, the tobacco budworm, Heliothis virescens (F.), and Heliothis phloxiphaga Grt. & Rob., may be confused with the corn earworm. Damage to the plant by each species is similar. Host Plants- The corn earworm feeds on a wide variety of plant species. Ageratum, carnations, chrysanthemums, and roses are severely injured by the corn earworm in unscreened greenhouses. Additional hosts include amaranth, canna, cleome, dahlia, geranium, gladiolus, hibiscus, lathyrus, lupine, mint, morning glory, nasturtium, phlox, poppy, and sunflower. The tobacco budworm and H. phloxiphaga also feed on aster, columbine, delphinium, and snapdragon. Damage- Corn earworm larvae feed on all exposed plant parts, particularly the buds and flowers, and may defoliate the plant. Infestations on flowering plants are more likely in the fall after many of the field crops and weeds are unattractive, unsuitable, or unavailable for moths. Moths, attracted to these flowering hosts, may feed on nectar and oviposit on the plant. Moths do not damage the plant. Life History- Adult moths begin to emerge from overwintering sites in early May and are most active at night. Male and female corn earworms live about 10 to 14 days. During that period, each corn earworm female may lay 450 to 2,000 eggs singly on host plants. Eggs are laid on open foliage, but are usually densest on younger leaves. Eggs hatch in 2 to 5 days. The larval stage lasts about 2 to 3 weeks and has five or six instars. Smaller larvae tend to occur in new, still-rolled foliage, whereas larger larvae tend to feed on open leaves. All stages tend to feed on flowers, tender new leaves and fruit. Late-stage larvae tunnel 5 to 15 cm into the soil and pupate. The pupal stage lasts about 2 to 3 weeks. Adults then emerge from the soil. Duration from egg to adult emergence is 6 to 8 weeks under field conditions. Corn earworm overwinters as a diapausing pupa in the soil and undergoes several generations each year. In the North, the pupa can survive only during mild winters. Adults are strong fliers and, in the spring, are spread northward from warmer overwintering areas. Infestations in greenhouses occur when the corn earworm moths fly through open doors, windows, and vents and then deposit eggs on the plants. Corn earworm larvae are cannibalistic. CONTROL Damage by corn earworms in a greenhouse can be reduced by adequate screening of window and open areas, as well as proper sealing of door edges. Use of natural enemies (e.g., Trichogramma wasps and predatory insects) may help to reduce infestation by corn earworm. Chemical insecticides provide adequate control of corn earworm. For chemical control recommendations, consult the current Cooperative Extension Service publications on ornamental plant pest management. |
