Egg-Wben first deposited, the cylindrical egg, 1 to 2 mm in length, is yellow and covered with a shiny, sticky film. It turns black just before hatching.
Larva-The yellow larva is usually covered with a brown or black coating of fecal material. It reaches a maximum length of 6 mm. Color plate.
Pupa-Approximately the size of the adult beetle, the yellow pupa gradually becomes blue-black.
Host Plants-Cereal leaf beetles are not known to feed or breed on broadleaved plants. They often infest late-planted winter grains, but are most damaging to spring-planted oats. The beetles also feed on many wild and cultivated grasses including corn, sorghum, timothy, orchard grass, ryegrass, reed canarygrass, quackgrass, bluegrass, fescue, millet, rice, brome, wild oats, mouse barley, and foxtail grass.
Damage-Larvae and adults both are voracious feeders. They prefer seedling plants or new growth on older plants. The larvae consume one to ten times their weight each day. Since larvae eat so much and rarely move from plant to plant, their damage is more noticeable than that of adults. Seedlings in the one-leaf stage are often killed by a single larva per plant. Both larvae and adults feed between the leaf veins. Adults, however, chew completely through the leaf while larvae feed superficially. The tips of damaged leaves turn white, giving infested fields an overall whitish appearance.
Life History-Adult cereal leaf beetles overwinter in field debris, soil and bark crevices, crowns of grasses, and similar sheltered places. From early March in North Carolina to early April in Michigan. the first beetles emerge and mate. For the next 6 weeks, the beetles, which are strong fliers, will be active on sunny days. Shortly after mating, each female begins to lay 150 to 400 eggs on the upper leaf surfaces of host grasses, especially oats, wheat and barley. The eggs, which are usually deposited singly near the midvein, hatch 4 to 23 days later. The warmer the temperature, the sooner the eggs hatch. Newly emerged larvae feed voraciously on the host plant for 11/2 to 3 weeks. As they feed they develop through four larval instars. Mature fourth instar larvae pupate in earthen cells 3 to 4 cm deep in the soil. Pupation lasts 12 to 25 days.
Throughout June, summer adults emerge, fly and feed, but do not mate. In July, they become less active and hide most of the day, often in corn sheaths. As summer progresses, adults leave corn for more sheltered wooded areas or field margins and remain inactive through December. Adults become active for brief periods if temperatures reach 10 degrees C (50 degrees F) or higher. Extreme temperatures and natural enemies may reduce overwintering beetle populations 40 to 70 percent. Only one generation occurs each year.
The USDA Animal and Plant Health Inspection Service (APHIS) is currently sponsoring parasitoid release programs in many states in which the cereal leaf beetle has been found. As a result, four of five parasitoid species which help control this pest in Europe have become established in this country. These tiny wasps, released at carefully selected sites each year, have been instrumental in keeping cereal leaf beetle populations below economic damage levels. Cereal leaf beetles are chemically controlled only in scattered areas where the parasitoids fail to keep them below damaging levels. For more specific control information, consult North Carolina State Agricultural Extension Service recommendations.