Life Cycle of Corn Earworms

Egg

• The female corn earworm moth usually lays her eggs on the silk of corn ears, although she may lay them anywhere on the plants. She lays one egg, or sometimes more, on each ear. Corn earworm eggs are very tiny, about 0.5 to 0.6 mm in diameter, and start off as a pale yellow or green color. They darken over the next few days, turning brown or gray and developing a distinct darker band. The eggs hatch in two to 10 days, sooner in warm climates and later in cool areas. At this stage, the Trichogramma can destroy the eggs. This egg parasite wasp lays its own eggs inside the corn earworm's eggs, preventing the eggs from hatching.

Larva

• Pale yellow larvae hatch from the eggs and live for about three to four weeks. This is the destructive stage of corn earworms. They eat all parts of the corn, from the silk to the kernels. At this point in their life cycle, the corn earworms resemble striped caterpillars. Spotted lady beetles and green lacewings will eat larval corn earworms. The larvae go through several growth stages, called instars, before they enter the next stage. When they grow to about 1 1/2 inches long, the larvae crawl down the corn plant or drop to the ground to begin their pupa stage.

Pupa

• Once on the ground, the larvae dig into the soil and bury themselves about 6 inches deep. Their outer shell darkens and hardens into a pupal chamber. They remain underground for 10 to 25 days, eventually emerging as an adult corn earworm moth. Insecticides and other biological methods have little effect on the buried pupae. Plowing the soil exposes the pupae to the sun and weather, killing them before they can become moths. Turning the soil also collapses the tunnels any remaining moths would need to reach the surface.

Adult

• The adult corn earworm moth leaves the pupa and makes its way above ground. They appear anytime from April to August, depending on the area temperatures. The moths are shades of brown and have a 1 1/2-inch wingspan. The females can begin laying eggs only three days after emerging, and they can continue to lay eggs for their entire lifespan of five to 15 days. During this time, one female corn earworm moth can lay between 500 and 3,000 eggs. Insecticides, although not very effective on the other stages, can help limit the corn earworm population by killing the moths before they lay eggs.