BILLBUGS: including MAIZE BILLBUG, Sphenophorus maidis, SOUTHERN CORN BILLBUG, S. callosus, Curculionidae

ADULT: Heads of both beetle species are prolonged in front of eyes into a long, downward curving, narrow snout. Maize billbugs are 3/8 to 9/16 in. long with base color reddish-brown to gray and longitudinal shiny black lines on pronotum and wing covers (elytra). Lines on the elytra are less linear than on abdomen. The head and legs are mostly shiny black. Maize billbugs overwinter in the base of corn stalks.

Southern corn billbugs are 3/8 in. long and brown with golden reflections. Elevated bumps on pronotum and elytra are shiny black. The elytra have prominent dents at the base and humps near the end. Southern corn billbugs overwinter in field margins. Adults need corn or yellow nutsedge to reproduce, but larvae can only complete development on corn.

EGGS: Kidney-shaped, white eggs are deposited in feeding punctures in corn stalk near plant base. Larvae emerge in 4 to 15 d.

LARVA: Legless, ivory colored, soft-bodied grubs with harder yellow or brown heads tunnel within the stalk before feeding down into the roots. Development takes several weeks.

PUPA: They pupate within the base of the plant or tap root below soil level.

GENERATION TIME: Approximately 10 wk.

DAMAGE: Most damage results from adult feeding. Corn becomes less sensitive to damage with advancing age. Several species attack corn, but the one causing most damage is the maize billbug. Adults feeding near the growing point eat holes in developing leaves resulting in rows of narrow slots in emerging leaves. They also attack seedling corn at the plant base or just below soil level. They use their long beaks to feed on the inner portion of the stalk. Damage to the base of the plants causes the plant to send out numerous suckers, which usually do not produce marketable ears. Stalk damage causes stalk breakage and reduced yield due to limitation of nutrients getting to ears. While larvae of maize and southern corn billbugs feed in corn stems, other species attack corn only as adults.

CONTROL: No till production allows the pest to build up, while cultivation, subsoiling and pesticides reduce populations. Rotation also works because adult maize billbugs walk rather than fly. Most of the pesticides labeled for billbug control are applied at planting.  A few are available for post-emergence applications. Formulations, rates, and pre-harvest intervals of insecticides for billbug control are listed below for sweet corn (Table 1) and field corn (Table 2).