Corn Flea Beetles
Chaetocnema pulicaria Melsheimer
Appearance and Life History
The corn flea beetle, though minute, can cause considerable damage to corn. Damage is most likely to occur when corn plants are growing slowly due to poor growing conditions, and flea beetle populations are high because of a mild winter.
The corn flea beetle is a tiny pinhead-sized [1/16 inch (1.6 mm) in length] black insect with thickened hind legs that enable it to leap considerable distances when disturbed.
Flea beetle eggs are deposited on weeds, corn, other cultivated crops, or in the soil near the host plant. Larvae hatch, feed on the roots of plants, pupate in the soil and emerge as adults in late July. The corn flea beetle overwinters in the adult stage.
The corn flea beetle feeds on corn leaves by stripping away the top layer of plant tissue. This feeding leaves gray to brown lines or "tracks" etched on the leaf surface. Heavily infested plants may appear gray as their leaves shrivel and die.
Although flea beetle feeding damage can appear to be quite serious, economic injury is generally sustained only by seedlings less than 6 inches (15 cm) in height that have high numbers of beetles, or on those plants suffering from environmental stress. The most serious problem caused by the corn flea beetle is through its possible transmission of the bacterium Erwinia stewartii, the resulting plant damage is referred to as Stewart's bacterial wilt. This disease can severely reduce yields, especially in sweet corn and seed corn inbreds.
If one finds high numbers of corn flea beetle or the leaf damage symptoms characteristic of beetle feeding, during early season field surveys, immediately sample the field to ascertain the extent of the infestation and damage. In each of 5 areas of the field, begin sampling with a randomly selected plant and carefully check 20 consecutive plants for corn flea beetle and feeding damage. Examine the upper portion of the corn leaves as well as the undersides of the lower two leaves since this is where beetles may be found during the day.
Record the number of plants within each sample set that are damaged. From these numbers determine the percentage of damaged plants in the field. Also note the severity of the damage (percent of leaf area damaged, leaves shriveled, plants killed, etc.) in the field, as well as average number of beetles/plant.
Normally, once a corn plant reaches the growth stage V5, it is no longer susceptible to significant corn flea beetle damage. Therefore, sampling for corn flea beetle typically will not be necessary once the plants reach V5 stage.
Corn Insect Control Recommendations: E-series 219-W (PDF)
Prior to Corn Growth Stage V4 on dent corn, control may be necessary if 50% of the plants inspected show severe corn flea beetle feeding damage (plants begin to look silvery or whitish, or leaves begin to die), approximately 5 or more corn flea beetle per plant are found, and poor growing conditions are causing slow corn growth.
Corn flea beetle may also transmit the bacterium that causes Stewart's wilt as it feeds. In sweet corn the disease may result in ears that are smaller than normal, or some infected plants may die. In seed production fields, severe leaf blight may cause lightweight, chaffy ears and increase the likelihood of stalk rots. Mild winters favor the survival of this insect and thus may increase the chance of this disease being transmitted to corn plants. If the sum of the mean daily temperatures for the months of December, January, and February total above 90, flea beetle survival will be moderate to high thus increasing the chance of disease problems. The beetles alone are seldom severe enough to kill plants. They may kill plants if there is a combination with the disease. In seed production fields where highly susceptible inbreds are utilized, treatment is probably justified if corn flea beetles are numerous.
If control is necessary, contact your state Cooperative Extension Service or click here for control materials and rates.