Cereal leaf beetle adults are about 3⁄16 inch long and 1⁄16 inch wide. The adults have dark, metallic blue wing covers, orange legs, and an orange collar. The head and the rest of the body are black.
Eggs are cylindrical with rounded edge. They are light orange when laid and darken gradually over time to almost black. Eggs are deposited singly or in rows of two to four on the topside of the leaves.
Each female lays from 12 to 50 eggs.
Cereal leaf beetle larvae are pale yellow with a brown head and legs. In the field, they look mostly black because they smear excrement over their bodies. People walking through a field infested with cereal leaf beetle larvae may emerge with black stained pants legs because this black coating easily rubs off the larvae. The larvae are about 1⁄16 inch long just after hatching and 1⁄4 inch long when fully grown.
Cereal leaf beetle larvae feed on the leaves. Feeding activity results in long, window like slits in the leaf blade. When feeding is severe, the entire leaf becomes brown and ragged. Cereal leaf beetle larvae are especially damaging when they feed on the flag leaf and when large numbers of larvae are found before head emergence.
The cereal leaf beetle has one generation per year. Adult beetles spend the winter in the woods and field borders. During the first warm days of spring, the beetles disperse into small grain fields, mate, and begin to lay eggs. Eggs hatch in about 7 days, and larvae (immatures) begin to feed on the cereal leaves. Larvae are usually first found after flag leaf emergence but before the heads have emerged. The larvae feed for about 3 to 4 weeks, then leave the plant, and move down into the soil.
Check fields weekly for about a month. Check the middle of the field as well as the edges. One way to check fields is to walk back and forth in the field in a zigzag pattern. Look for feeding damage, adult beetles, eggs, and larvae. Stop in five to ten areas in each field, and count eggs and larvae on the top two leaves of five stems. If cereal leaf beetle larvae have begun to hatch and there is more than one cereal leaf beetle egg or larva per two stems, treat with one of the suggested insecticides. All suggested insecticides provide good control of cereal leaf beetle larvae. Because dying larvae are hard to distinguish from living ones, wait 2 to 3 days after treatment before checking to make sure the treatment was successful.
Other Management Strategies
Beetles prefer thin stands so follow good agronomic practices that promote full stands and high-yielding wheat. Also avoid late planting because adult beetles typically prefer less mature plants to more mature plants. Heavy rains can kill immature cereal leaf beetles. If heavy rains occur between the time a field is checked and insecticides are to be applied, wait for the foliage to dry and check the fields again. Cereal leaf beetles are controlled by natural enemies. Eventually, this and other natural enemies will help keep cereal leaf beetle populations below economically damaging levels. Ladybird beetles are also important predators and can destroy many eggs and larvae.