integrated pest management

Corn Flea Beetle
Chaetocnema pulicaria

The adult is a very small, smooth, shiny, roundish, black beetle. The hind legs are distinctly enlarged and thickened, and the beetles jump readily when approached. The larvae are small, white, and not very active. Full-grown larvae are 1/6 in. long and most body segments are nonpigmented. Only the prothorax and the last abdominal segment are slightly darkened.

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Corn Flea Beetle Adult and Damage to Leaf
Figure 1. Corn Flea Beetle Adult and Damage to Leaf

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Adult Corn Flea Beetle
Figure 2. Adult Corn Flea Beetle

Life Cycle
The corn flea beetle passes the winter as an adult, hibernating in debris and other suitable cover in fencerows, roadsides, or the edges of woodlands. It becomes active early in the spring and even feeds on grasses on warm days during the winter. After mating, the females lay their eggs on plant leaves or in the ground, on or near underground stems and roots. Not much is known about the larvae, but they probably feed on the roots of grass plants. In Illinois, the larvae complete growth, pupate, and emerge as adults during June. They lay eggs for another generation; the second-generation adults appear in early August and feed until late in the fall before entering winter quarters.
Little is known about damage caused by the larvae, but damage by the adults is very evident. They feed on both the upper and the lower epidermis of corn leaves, but they do not chew completely through the leaves. When adults are abundant early in the spring, they will feed heavily on the primary leaves and first three or four true leaves, often causing the seedling to appear whitish or silvery and sometimes killing the plant. Luring 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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Corn Flea Beetle Damage
Figure 3. Corn Flea Beetle Damage

During the feeding process, the adults disseminate a bacterial wilt of corn called Stewart's disease. This disease infests the water-conducting tissues of the plant. 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 or accentuate 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. A large percentage of sweet corn plants infested in the seedling stage will die or dwarf and produce no harvestable ears. Plants not showing these drastic effects may produce normal ears if they get plenty of water.

The bacteria that cause Stewart's disease, or bacterial wilt of corn, overwinter in the body of the adult corn-flea beetle. Because the corn-flea beetle is verv sensitive to temperatures, a criterion to predict the extent of overwintering heetles has been developed called the Winter Temperature Index. This index is based on the suin of the average monthly temperatures for December, January, and February. A sum of 100 and above for the three months indicates that the wilt phase of Stewart's disease will probably be severe; a sum of 90-100 indicates a moderate wilt infection, ranging from light to severe, depending on the area. Slight infection may occur when the sum totals 85-90, and no infection will occur below 85.

Scouting Procedures
Examine newly emerged corn for the presence of the beetles and count the approximate number per plant. They will first appear around field edges as they move from grassy areas and other overwintering sites.

Threshold Guide
Control may be justified when there is an average of 5 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 of the leaves are whitish, it may be profitable to treat.

Although feeding damage is seldom economic, the beetles can transmit Stewart’s disease to susceptible varieties of corn. Most varieties of commercial field corn are resistant to this diseases. In a situation where the corn variety is susceptible to Stewart’s disease, control should be applied as soon as flea beetles have been detected, even in low numbers.

The Winter Temperature Index is useful in indicating the probability of wilt infection for the coming season. When the index suggests successful overwintering of beetles, damage can be reduced by avoiding early planting and by planting resistant varieties of field or sweet corn.

Susan T. Ratcliffe (
Michael E. Gray (
Kevin L. Steffey (