Corn Earworm
Egg - The dome-shaped egg, about 0.5 mm in diameter, is pale white when first laid and develops a reddish-brown band before hatching.
Larva - The five to six larval instars vary greatly in color. Newly hatched larvae are about 1.5 mm long and yellowish-white with dark head capsules. Second instars are yellowish-green and frequently have orange and brown longitudinal stripes; their head capsules are reddish-brown or brown. Up to 44 mm long, later instars are greenish-yellow, reddish or brown with pale, longitudinal stripes, raised black spots (chalazae), and brown to orange heads. All instars have five pairs of fleshy prolegs. Color plate.
Pupa - About 31.4 mm long and 6 mm wide, the pupa is reddish-brown to dark brown.
Host Plants - During late summer, soybeans become one of the corn earworm's primary host crops. In North Carolina, late planted soybeans of maturity group VI and beans of groups VII or VIII are most likely to be moderately or severely damaged by corn earworms. Early maturing beans and beans with closed canopies usually have fewer larvae per unit area. See the corn earworm note (CORN/SORGHUM section) for more details concerning hosts.
Damage - Young larvae feed on flowers and tender foliage. Soybean defoliation by corn earworms is a problem typically confined to some areas of the South, and occasionally, the East Coast. This injury normally occurs on late-maturing varieties prior to seed enlargement.
Later in the season, corn earworms prefer to feed on soybean pods, often causing a serious yield loss. During heavy infestations (20 or more large worms per meter of row, or six or more per foot of row), most pods may be destroyed, forcing the larvae to become foliage feeders. Entire 8-hectare fields (roughly 20 acres) have been stripped of pods and foliage during such heavy infestations.
Life History - Overwintering and spring development is the same as in the other crops which serve as hosts for this insect (see CORN/SORGHUM section). However, after most corn ears begin to dry (late July), the female earworm moths deposit their eggs on other crops. Soybean, sorghum, peanut and cotton are preferred host crops at this time of year. In soybean fields, earworm eggs are laid largely on tender terminal foliage and near the blooms. Young larvae feed on the developing leaves, flowers, and pods. As the larvae develop, they feed more heavily on the pods. During heavy infestations all pods may be removed, forcing the larvae to complete development on the leaves. Soybean fields which are blooming and have an open foliage canopy during years with heavy moth flights are most likely to have damaging infestations. Apparently, this situation occurs because both egg-laying and larval development are increased under these conditions.
