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Maize Billbug

Sphenophorus maidis Chittenden

Appearance and Life History

Maize billbugs are found throughout the cultivated and grassland regions of the United States and Canada. Although other billbug species also inhabit these regions, the maize billbug is the species of greatest importance to corn producers.

The maize billbug is a reddish-brown to black snout beetle. The adult billbug ranges from 3/8" - 1/2" inch (10 to 15 mm) long. It is rarely seen, but when found and disturbed it becomes motionless. This beetle hides in the soil during the day and is active only at night.

The maize billbug overwinters as an adult in soil, coarse grass, or plant litter, becoming active when corn begins to emerge. Although winged, this insect seldom flies and crawls over the ground in search of food. It can migrate 1/4 mile (0.4 km) or more. In addition to corn, this billbug will attack other grass species and sedges. Damage in corn has often been associated with the presence of yellow nutsedge.

Adults feed at the base of corn stalks, often below ground level. They move from plant to plant at night. Egg laying starts about 10 days after the adults first feed. Females lay white to gray kidney-shaped eggs in a hole they gouge in the plant stem with their mouthparts. These gouges later appear as a transverse row of punctures in the expanded leaves. It is not uncommon for a single female to deposit 200 eggs or more over a two-month period. Eggs hatch in 4 to 15 days depending on temperature. The small, legless, off- white, humpbacked grubs feed and develop for several weeks in the center of stalks, either below or just above the ground. Later they move to the soil and feed in or around the roots. Pupation occurs in the stems, roots, or soil. Adults, which transform into this stage in the fall, may remain in the pupal case or move out and feed before entering hibernation. The life cycle requires several months for completion. There is one generation each year.

Damage

Adults gouge small holes in the stem to feed on the tender inner plant tissue. Small plants may be killed if beetles feed on the growing point, while larger plants may continue to grow normally. On larger plants, one visible sign of billbug activity may be the transverse row of holes across the leaves. Also, suckering (tillering) and distorted growth are other symptoms that may be observed.

The grubs can cause serious injury to stems and roots of corn. Severe feeding can result in plant lodging. If several larvae feed within a stalk of corn, it is unlikely that an ear will be produced. Billbug damaged plants are usually stunted.

Sampling Method

If one finds high numbers of billbugs during regular early season field surveys or the damage symptoms are characteristic of this beetle's feeding, 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 feeding damage. Examine the soil near freshly damaged plants for billbug adults. Billbugs look very similar to clods and when disturbed they play "possum," so thoroughly examine the soil.

Record the number of plants within each sample set that is damaged by billbugs. Sum the number for each set and determine the percentage of billbug damaged plants in the field.

Management Guidelines

Corn Insect Control Recommendations: E-series 219-W (PDF)

Control of billbugs is warranted only when the feeding damage of the adults is killing plants and reducing stands to critical levels. Plants with leaf feeding damage usually recover. There is no rescue treatment for larvae feeding inside corn stalks.

Maize billbug is attracted to yellow nutsedge for feeding and egg laying. Control of this weed before planting should reduce billbug establishment and damage.

If control is necessary, contact your state Cooperative Extension Service or click here for control materials and rates.