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A Case of Mistaken Caterpillar Identity

Tweets about European corn borer (Ostrinia nubilalis) caterpillars in the stems of conventional corn and feeding in the whorls of corn are crossing my Twitter feed. Unfortunately, there is a problem with some of these tweets. Not all of the caterpillars that are being identified as European corn borer caterpillars are actually European corn borer caterpillars!

The tweets about caterpillars present in the stalk of the corn and identifying them as the European corn borer are correct. As the number of conventional acres planted in South Dakota increases, we will more than likely continue to see an increase in European corn borer reports. However, the other Tweets about caterpillars feeding on the whorl are actually of the corn earworm caterpillar, Helicoverpa zea.

European Corn Borer

Straight line of small holes in the corn leaf.
Figure 1. Shot hole injury on a corn leaf after European corn borer caterpillar feeding. Courtesy: Frank Peairs, Colorado State University, Bugwood.org

During their lifecycle, European corn borer moths lay their eggs on the underside of corn leaves. When the caterpillars hatch, they initially feed on the leaf and then journey into the whorl. Initial feeding will often appear as if the epidermis of the leaf has been stripped away. As they mature and feed in the whorl, the caterpillars leave behind the characteristic shot-hole feeding injury (Figure 1). However, these caterpillars don’t stop in the whorl, but will continue down the whorl and bore into the stalk itself (Figure 2).

Small white caterpillar with dark head capsule feeding within a corn stalk.
Figure 2. European corn borer caterpillar feeding within a corn stalk. Courtesy: John C. French Sr., Retired, Universities: Auburn, GA, Clemson and U of MO, Bugwood.org

In addition, European corn borer caterpillars have a dark brown head capsule with a light brown or tan body (Figure 3). Small brown circle markings can often be observed on each segment of their body. These caterpillars can be observed on the leaves when they are recently hatched and occasionally in the whorl. However, they are almost always found within the corn stalk where they feed and reduce stalk integrity. The feeding often results in lodging and weakened shanks (i.e., when ears are present during feeding).

Tan caterpillar with dark brown head on corn stalk.
Figure 3. European corn borer caterpillar. Note the dark brown head capsule. Courtesy: Frank Peairs, Colorado State University, Bugwood.org

Corn Earworm

Black caterpillar with light stripes and yellow-brown head capsule. Caterpillar also has small spines on body segments.
Figure 4. Corn earworm caterpillar. Courtesy: Clemson University-USDA Cooperative Extension Slide Series, Bugwood.org

The corn earworm caterpillars are highly variable in color, and can range from yellow, green, pink, or black. They will almost always have alternating light and dark stripes on their body and small spines (sometimes they look like little hairs) across the surface of their bodies. With the exception of newly hatched corn earworm caterpillars, they will always have a yellow to brown head capsule (Figure 4).

: Green corn plant with ragged defoliation holes in leaves.
Figure 5. Corn earworm caterpillar defoliation. Courtesy: Clemson University-USDA Cooperative Extension Slide Series, Bugwood.org

During the first generation, corn earworm caterpillars feed in the corn whorls or on nearby leaves. This feeding often results in somewhat irregular shaped holes with jagged lines (Figure 5).

Second generation caterpillars feed on corn silks, and eventually bore into the ear through the silk channel to the ear tip where they feed on developing kernels (Figure 6).

Green caterpillar with yellow head feeding on yellow corn kernels.
Figure 6. Corn earworm caterpillar feeding on developing kernels. Courtesy: R. L. Croissant, Bugwood.org

What Are the Differences Between These Species?

Table 1 compares the key identifying characteristics between these two species.

Table 1. Characteristics of European corn borer and corn earworm caterpillars.
  European Corn Borer Corn Earworm
Head Capsule Dark brown Tan, yellow
Body Color Tan, relatively smooth Wide range, but with stripes and spines
Primary Feeding Location Inside stalk

1st Generation: Whorl

2nd Generation: Developing ears

Related Terms

Corn, Crop Management