The population peak usually occurs soon after tassel formation. About this time, their natural enemies become established and the aphid population rapidly falls off. Some varieties of corn are more susceptible than others to leaf aphids. They overwinter in litter and trash around fields. In early spring, beetles are active on weeds and then move to corn seedlings during May through June.
Infestations are more severe when a cold spring follows a mild winter.
Adult beetles leave numerous, small, circular feeding holes and bleached out spots or stripes on the corn leaves. Such direct feeding is insignificant unless large numbers of beetles attack slow-growing corn, especially during a cold spring. Infestations are generally uniform throughout the state. In untreated plots, up to 90 percent of the ears can be expected to show feeding signs. Eggs are laid on the leaves when the plants are small.