Maize Billbug
Sphenophorus maidis (Chittenden), Curculionidae, COLEOPTERA


DESCRIPTION

Adult - The robust adult is a shiny black weevil when clean; in the field, however, it is often so covered with dirt that it resembles a small clod. It ranges from 10 to 14 mm long and is often found attached upside down to seedling cornstalks near the ground line.

Egg - The cream colored, kidney-shaped egg is about 3 mm long and 1 mm in diameter.

Larva - The larva is cream colored and legless, with a distinct reddish-brown head capsule. It varies from 5 to 15 mm in length.

Pupa - The pupa is cream colored to reddish-black, depending upon its age, and ranges in length from 15 to 20 mm. Some adult features - legs, antennae, and beak - are apparent.


BIOLOGY

Distribution - The maize billbug first attracted attention during the late 1800's in the corn fields of Alabama, South Carolina, and Kansas. Although this species has been found as far north as Michigan, it is a more serious pest in the southern states. In North Carolina, this billbug occurs over the entire Coastal Plain. Close field observations and a recent survey indicate that the heaviest infestations occur in the western Coastal Plain counties bounded on the north by Wilson, Johnston and Wake counties. Surveys for billbug detection should be directed toward border rows and volunteer clumps.

Host Plant - Corn is the preferred host of maize billbugs. However, these insects have been collected from sorghum, cattails, and many species of wild grasses, reeds, rushes, and sedges.

Damage - The maize billbug is one of two billbug species which annually damage corn in the Coastal Plain of North Carolina. Although it causes similar damage, the other species, S. callosus, is apparently more abundant and difficult to control in both North and South Carolina. The adult billbug pierces corn seedling stalks with its beak, damaging the tender inner tissue. This injury often causes stunting or death of seedlings. Stunted plants usually produce excessive suckering and become deformed and nonproductive. Plants which survive attack are marked by rows of holes across the blades. In addition to adult attack, maturing larvae tunnel in the basal area of the stalk. Extensive damage is generally restricted to non-rotated corn fields or areas adjacent to the previous year's corn.

Life History - During April and May, the overwintering adults, which rarely fly, emerge from litter in the field, ditches or hedgerows. After feeding and mating, females lay about 200 eggs. Eggs are deposited in holes chewed out by females in the basal area of host plants. The tiny, legless larvae hatch from the eggs in 4 to 15 days and feed for several weeks in and around the taproot. Although several larvae have been observed in the taproot area of a single corn plant, there is usually only one larva per infested stalk. Larval development is complete in 40 to 50 days, and pupation occurs in cells in or near the excavated taproot. After a 2-week pupal stage in August or September, the adults emerge from pupal skins and either remain within pupal cells or exit and feed before entering hibernation. Only one complete generation occurs each year.


CONTROL

Rotation is the cheapest and most effective method of control. After overwintering, the adults crawl to the corn; therefore, rotating the corn approximately 0.4 kilometer (1/4 mile) from its previous location will provide effective control. A 5 percent loss of an optimum stand is recognized as an economic threshold in North Carolina. For additional control information, consult the current North Carolina Agricultural Chemicals Manual.