Bollworm

The bollworm is the larva of Helicoverpa zea, a noctuid moth also widely known as the corn earworm or tomato fruitworm depending on the crop it is found feeding on. Despite the different common names, all refer to the same highly adaptable species, one of the most widespread crop-feeding caterpillars in the Americas.

The caterpillar is notable for its extremely variable coloration, ranging from green to brown, pink, or nearly black, often with pale longitudinal stripes, making color alone an unreliable way to identify it. It is instead recognized by its habit of boring directly into fruiting structures such as cotton bolls, corn ears, and tomato fruit.

Because a single species causes damage across such a wide range of crops, from cotton to corn to tomatoes to beans, it is one of the most closely monitored agricultural caterpillars in North America, with long-term research focused on its population cycles and movements.

• Body color is highly variable, ranging from green to brown, pink, or dark, often with faint pale stripes running the length of the body
• Reaches about 4 cm (1.6 in) in length at maturity
• Body surface is covered in short, coarse microspines giving it a slightly rough texture compared to smooth-skinned caterpillars
• Most reliably identified by its behavior: boring directly into the tip of a corn ear, a cotton boll, or a tomato fruit
• Head is pale yellow-brown and unmarked

Found across most of North and Central America wherever host crops are grown, including cotton, corn, tomato, and a range of other row crops and garden vegetables. It is present from spring through fall in temperate regions and can persist year-round in warmer climates.

Larvae feed on a very broad range of host plants, but are best known for tunneling directly into fruiting structures, where they are partially sheltered from predators and weather while consuming developing seeds, kernels, or fruit tissue. Individual larvae are often cannibalistic when they encounter one another within a single boll or ear, which tends to limit the number of larvae that mature within a single fruiting structure. The species also serves as a host for a range of parasitic wasps and flies, which play a role in naturally regulating its populations.

Adult moths lay single eggs on host plant silks, leaves, or developing fruit. Larvae hatch and quickly move to feeding sites such as corn silks or developing bolls, passing through six instars over about two to four weeks depending on temperature. Mature larvae drop to the soil to pupate a few centimeters below the surface. Multiple generations occur per year across most of the range, with the species overwintering as a pupa in the soil in temperate regions, while it can breed continuously in frost-free areas.