Cereal Leaf Beetle
Oulema melanopus Linnaeus
Appearance and Life History
Cereal leaf beetle has been in the United States since about 1962. It spread rapidly throughout the Great Lakes area in the 1960's. Although not the pest it once was, cereal leaf beetle can still damage corn.
Adult cereal leaf beetle is very distinctive. It is about 3/16 inch (4.7 mm) long, with a metallic bluish-black head and wing covers. Its legs and thorax, area just behind the head, are reddish-orange.
Cereal leaf beetle overwinters as an adult in clusters wherever it can find shelter; under crop debris, in fence post cracks, behind the loose bark of trees, etc. Once springtime temperatures exceed 60°F (16°C), the beetle emerges from its hibernation site to feed, usually attacking wild grasses, such as quack grass and orchard grass. It then flies to corn fields.
While feeding in the corn during the early spring, the female beetle lays tiny (smaller than a pinhead), elliptical yellow eggs usually next to the mid-rib. On the upper surface of the leaves the eggs are deposited singularly or in rows of up to three or four, but never in clusters.
The larva of the cereal leaf beetle is slightly longer than the adult and is slug-like. Actually, the larva is yellow to yellowish-brown in color, but it is almost always covered with its own fecal material. This fecal material is deposited on its back for protection against predators.
The larva pupates in the soil of small grain fields. The adult emerges by mid-June. The young beetle typically migrates to corn fields where the plants are young and succulent. The beetle feeds on corn leaves for several weeks. The plants usually outgrow the damage before aestivating, a state of inactivity, for the remainder of the summer.
Adult cereal leaf beetle damage appears as longitudinal slits eaten out from between the leaf veins. High populations on small grain seedlings may kill plants. It is the larva that causes the most injury to corn. It eats the outer surface of leaves, giving the plants a silver cast. A badly infested field will look frost damaged.
To check for cereal leaf beetle, carefully examine 20 stems in each of 5 areas of the field. Record the number of eggs, larvae, and/or adults found on each stem and also determine the percentage of leaf area damaged. Also, note the stage of development of the plants.
Corn Insect Control Recommendations: E-series 219-W (PDF)
Control may be advisable if more than 1 larva or adult per stem can be found.
If control is necessary, contact your state Cooperative Extension Service or click here for control materials and rates.