The southern corn billbug (Sphenophorus callosus), a weevil that damages corn crops in North Carolina, has the potential to become a damaging pest over a larger geographic range. A new article in the Journal of Integrated Pest Management outlines current knowledge about the southern corn billbug and suggests further research to keep the species in check. (Photo by Anyi Mazo-Vargas, University of Puerto Rico, Bugwood.org)

By John P. Roche, Ph.D.

The southern corn billbug (Sphenophorus callosus) is a weevil that damages corn crops in the U.S. Its range extends from New York to Florida on the east coast and west to Kansas to Nebraska in the Midwest. Currently, it is only a serious problem in eastern North Carolina, where it can destroy entire fields of corn if they are not protected with insecticidal seed treatments. But, before the advent of insecticidal seed treatments in the mid-1990’s, the species had a wider range of impact, and it has the potential to become a damaging problem over a larger geographic range again. Thus, gathering information on the species is crucial. In an article published in January in the Journal of Integrated Pest Management, Dominic Reisig, Ph.D., of North Carolina State University provides a summary of what is known about the southern corn billbug and what research is needed to survey and control the species.

The southern corn billbug (Sphenophorus callosus), a weevil that damages corn crops in North Carolina, has the potential to become a damaging pest over a larger geographic range. A new article in the Journal of Integrated Pest Management outlines current knowledge about the southern corn billbug and suggests further research to keep the species in check. Shown here is a southern corn billbug larva in the crown of a corn plant. (Image originally published in Reisig 2025, Journal of Integrated Pest Management)

The life history of southern corn billbugs begins when adults lay eggs into seedling stalks of corn or other hosts. The larva feed and develop inside of the stalks, inside the roots, or in the soil. After several larval stages, southern corn billbugs go through a pupal stage and then emerge as adults. Billbugs overwinter in the adult stage and become active, feed, and mate the following spring.

Adult billbugs feed on the leaves of corn plants, and they are the stage that are observed to do the most damage to corn. But larvae feed on corn, too, and larval feeding can cause significant damage to corn crops. Billbugs feeding on young seedlings can kill the plants. Feeding on slightly larger plants stunts the plants but doesn’t kill them. Once corn plants are even larger—to the six- or eight-leaf stage—they are much less susceptible to damage from billbugs.

When feeding, Sphenophorus callosus prefers corn, rice, and several sedge species in the genus Cyperus, including yellow nutsedge (Cyperus esculentus). It also feeds on sorghum. For depositing eggs, the southern corn billbug prefers field corn and yellow nutsedge.

This species has a lot of historical significance for eastern North Carolina. “It’s not often that an insect can limit whether or not growers choose to plant a crop,” Reisig says. “This insect is one of the few that has had a regular destructive potential.”

The most effective methods of control are cultural control tactics, such as rotation of corn fields, providing good drainage, and eliminating weeds. Rotating a field from corn to a crop that the billbugs do not eat decreases the numbers of the pest in a given field, and adequate drainage and control of weeds boosts the vigor of the corn plants, helping them resist attack. These cultural control practices have been successful in reducing the abundance and impact of the southern corn billbug. “They were once so numerous that local fishermen would pull them up in their nets,” Reisig says. But numbers of the pest are much more manageable now.

The southern corn billbug (Sphenophorus callosus), a weevil that damages corn crops in North Carolina, has the potential to become a damaging pest over a larger geographic range. A new article in the Journal of Integrated Pest Management outlines current knowledge about the southern corn billbug and suggests further research to keep the species in check. Shown here is a corn field destroyed by southern corn billbugs; most of the plants visible are grassy weeds, with a few stunted corns seedlings mixed in. (Image originally published in Reisig 2025, Journal of Integrated Pest Management)

Another popular control tactic is the use of neonicotinoid insecticides. “Where it occurs, growers are still heavily reliant on a single management tactic—insecticidal seed treatments,” Reisig says. But the effectiveness of neonicotinoid seed treatments has decreased over time, and without adequate management it is possible that the pest will spread to become a problem again over a wider geographic region.

Little research has been done on this species since the 1980s. Agricultural practices have changed a lot since then, so new data on the species is essential. One type of information that is valuable is surveys of the abundance and distribution of billbugs. Currently, the distribution of damage from the southern corn billbug is believed to be very limited. But the species is widely distributed, and it may be causing damage to corn crops that is not being reported. And the southern corn billbug is extremely similar in morphology to other species in the genus Sphenophorus, further complicating surveys. “A survey of corn across the United States, paired with modern taxonomic support could clarify if species distribution has shifted,” Resieg writes.

John P. Roche, Ph.D., is an author, biologist, and science writer with a Ph.D. and postdoctoral fellowship in the biological sciences and a dedication to making rigorous science clear and accessible. He authors books and articles, and writes for universities, scientific societies, and publishers. Professional experience includes serving as a scientist and scientific writer at Indiana University, Boston College, and the UMass Chan Medical School; and as editor of science periodicals at Indiana University and Boston College.