Corn Flea Beetle
(Chaetocnema pulicaria Melsheimer)

There are several species of flea beetles that may be found in cornfields. This species is most often the one encountered. Corn flea beetles remove leaf tissue of corn as they feed and leave long scratch marks on the leaves. More importantly, corn flea beetles are the primary vector of Stewart?s wilt bacterial disease. Stewart?s wilt is an economically important disease of sweet corn hybrids and seed corn inbreds that are not resistant to it.

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Corn Flea Beetle Adult

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Image courtesy of North Carolina State University

Description

Corn flea beetles are small, shiny, black beetles, approximately 1/16-inch long, with enlarged hind legs. Adults are easily disturbed and are known for their ability to jump long distances. The larvae are small, white, and not very active. Full-grown larvae are 1/6-inch long and most body segments are non- pigmented. Only the prothorax and the last abdominal segment are slightly darkened.

Life Cycle

The corn flea beetle passes the winter as an adult, in the soil and debris in fencerows, roadsides, or the edges of woodlands. It becomes active early in the spring when temperatures warm to 65-70°F, although they may be seenfeeding on grasses on warm days during the winter. Corn is the primary host of the corn flea beetle, but adults and larvae also feed on a number of secondary hosts such asorchard grass, Kentucky bluegrass, yellow foxtail, giant foxtail, fall panicum, and several other grasses. Wheat, barley, oats, and Timothy have also been identified as food plants for the flea beetle. In the spring, adults feed on corn and other hosts, mate and lay eggs on plant leaves, in the ground, or at the base of plants near underground stems and roots. Not much is known about the larvae, but they feed on the roots of grass plants for about two weeks before pupating. The generation time of the corn flea beetle is approximately one month. However, higher temperatures result in faster development rates. Larvae complete their development, pupate, and adults emerge in June. The adults continue to feed on available host plants and lay eggs for another generation. Second-generation adults appear in early August and feed until late in the fall before overwintering. Summer generations of thecorn flea beetle may overlap and in some circumstances, the very southern portions of Illinois may experience a third generation.

Injury

Little is known about damage caused by the larvae, but damage bythe adults is very evident. The adult corn flea beetle injures corn plants by removing leaf tissue and by transmitting pathogenic bacteria.Injury by the adults appears as scratches in the upper and lower surfaces of the leaf, usually parallel tothe veins. They feed on both the upper and the lower epidermis of corn leaves, but they do not chew completely through the leaves. The scratches, or windowpane effect, rarely result in economic injury. High densities and heavy feeding can result in the skeletonization of leaves and death of seedling. The leaves of severely injured plants appear whitish or silvery. During June and August, when the newly emerged adults appear, the leaves of corn may be partly covered with their feeding scars.

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Flea beetle injury -- "windowpane effect"

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Severe Flea Beetle Feeding

Generally, field corn infested with Stewart's disease will show little sign of disease until late in the summer when numerous leaf lesions will appear on the leaves. However, in years when flea beetles are abundant and the disease is widely disseminated, some varieties of corn will wilt and the plants may die before tasseling. Drought can aggravate oraccentuate the diseased condition of a plant. The result is often small ears or no ears at all. When conditions are favorable for both the beetles and the wilt, nearly 100 percent of the susceptible varieties of field corn will show symptoms of Stewart's disease by late fall.

Evidence of Stewart's disease is more common and the results more drastic in sweet corn than in field corn. Sweet corn plants infected at an early stage are usually most severely affected. Infected young plants usually wilt, become stunted, and exhibit water-soaked lesions with wavy margins. The late infection phase or ?leaf blight phase? of Stewart?s wilt occurs after tasseling and is generally not a concern in sweet corn because ears are harvested before damage occurs.

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Stewart's Wilt in Sweet Corn

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Corn Flea Beetles on Seedling Corn Plant

Field Corn. Control may be justified in commercial corn when there is an average of five or more beetles per plant prior to the 4-leaf stage. If the infestation is so severe that some plants are being killed, or if more than half the leaves are whitish, it may be profitable to treat.

Seed Corn. Prior to the 5-leaf stage, susceptible seedcorn inbreds may require an insecticidal treatment when 2 to 3 beetles per plant are present and 10% of the plants are silver or whitish due to severe foliar feeding.

Sweet Corn. In susceptible sweet corn hybrids, some recommendations suggestrescue treatments when the threshold of 6 beetles per 100 plants is reached.