Cereal Leaf Beetle
Oulema melanopus (Linnaeus), Chrysomelidae, COLEOPTERA

DESCRIPTION

Adult-The head and wing covers of the cereal leaf beetle are a metallic blue-black, the legs brownish yellow, and the area behind the head reddish brown. Length varies from 5 to 6 mm, the female being slightly larger than the male. Color plate.

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.


BIOLOGY

Distribution-Recently introduced into the Americas, cereal leaf beetles are common throughout Europe, the British Isles, North Africa, the Middle East, and parts of Siberia. In the United States, they have been found from eastern Wisconsin, Iowa, and Missouri eastward into New Hampshire, Massachusetts, Connecticut, and New Jersey and southward into Tennessee and North Carolina. Detection in North Carolina was made in 1977 and, at this writing, infestations were restricted to the tier of counties along the Virginia line.

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.


CONTROL

Cereal leaf beetles are controlled by the use of favorable planting dates and release of parasitoids. Fall wheat should be planted immediately after the Hessian fly-free date for each county. Crops planted this early will be more advanced in growth the next spring than late-planted small grains. Therefore, they will be less attractive and, at the same time, more tolerant to the beetles. Cereal leaf beetle infestations on spring-planted wheat cannot be avoided by means of planting date.

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.