Corn earworm, Helicoverpa zea (Boddie) (Lepidoptera: Noctuidae), in sweet corn.
Photo by G. McIlveen, Jr.
Common Name: Corn earworm
Scientific Name: Helicoverpa zea (Boddie)
Order: Lepidoptera
Description: Caterpillars can grow up to about 1 5/8 inches in length and vary in body color from yellowish, greenish, reddish or brownish with more or less prominently colored longitudinal lines. The body is covered by regularly occurring body-colored to black bumps sporting stiff black hairs or setae. The head capsules are tan to dark brown. Adult moths are brown with darker brown patterned wings.
There are a large number of species with in the noctuid family. In agriculture, however, the tobacco budworm (Heliothis virescens (Fabricius)), is similar to the corn earworm and presents control problems because of insecticide resistance. Tobacco budworm caterpillars can be separated from the corn earworms by the shape of the mandible (basal molar or mandibular retinaculum is absent on corn earworm) and by the presence of microspines on the bumps (spinules on the chalazae of setae D1 of abdominal segments 1, 2, and 8 on late instar larvae are absent on corn earworm) along the body sporting black hairs. Caterpillars of the fall armyworm, Spodoptera frugiperda (J. E. Smith) and, in the northwestern corner of the Texas panhandle, the European corn borer, Ostrinia nubilalis (Hübner) and the western bean cutworm, Loxagrotis albicosta (Smith) also enter the ears of corn and feed on kernels. Full grown western bean cutworm caterpillars are light brown to pale gray with light brown heads, behind which is a wide, dark brown collar (prothoracic shield) marked with three narrow, pale stripes.
Another “headworm” affecting sorghum production is the sorghum webworm, Nola sorghiella Riley (Lepidoptera: Noctuidae). Adult moths have a 5/8 inch wingspan, with whitish, poorly-patterned forewings. Females lay eggs on sorghum heads. Caterpillars grow to about ½ inch long and have bodies that are covered with spines or hairs, green to tan in color, and marked with four reddish-brown lengthwise stripes. Caterpillars feed on ripening grain, consuming the contents and leaving the hull intact. They develop through five stages (instars) over about 13 days before pupating. Development from egg to adult can be completed in 24 days. Sorghum grains with compact heads suffer more damage, and alternate hosts include Sudangrass, Johnsongrass, corn, rye, and timothy.
Life Cycle: Corn earworm eggs are pin-head sized and has characteristic ridges. They are laid singly by female moths and turn from white to dark brown before hatching in 3 to 10 days. Larvae pass through six instars with the first being about 1/16 inches long. Larval development takes about 18 days before they pupate in the soil and remain for about 8-14 days. Development from egg to adult takes 3 to 4 weeks during the summer. There are several generations per year.
Habitat and Food Source(s): Caterpillars have chewing mouthparts. Adults have siphoning mouths. The newly hatched caterpillar will eat its egg shell and then feed on tender leaves. Older caterpillars feed on older leaves and tunnel into fruit. A wide variety of wild plants and crops including beans, corn, cotton, peanuts, sorghum, tomato, and ornamental (bedding and flowering) plants are suitable hosts. Caterpillars have silk glands and produce silk threads around feeding sites. They also leave excrement in and underneath feeding sites. Caterpillars can be picked from plants or collected using a sweep net or drop cloth. Adults are attracted to pheromone traps or black light traps.
Pest Status: Caterpillar stages are pests of many agricultural crops; medically harmless.
For additional information, contact your local Texas A&M AgriLife Extension Service agent or search for other state Extension offices.
Literature: Mock et al.1981; Neunzig 1964. Stinner et al. 1980.