Issue No. 21, Article 10/August 15, 2008
Caterpillars in Corn Ears
I recently received a specimen of yet another caterpillar that we can add to our list of corn ear-attacking caterpillars--the yellowstriped armyworm, Spodoptera ornithogalli. During teleconferences on August 4 and 11, other extension entomologists in the north-central states also reported that they had observed yellowstriped armyworms in corn this year.
Although yellowstriped armyworms are not known to be numerous enough to cause economic damage to corn ears very often, their presence may create some confusion regarding identification. Some specimens appear velvety black with a bright yellow stripe on each side of the body, and those are relatively easy to identify. However, the less strikingly colored specimens may be brown or gray, with light-colored stripes on each side of the body, and these can be confused with other caterpillars that feed in corn ears--corn earworm, fall armyworm, and western bean cutworm. Regardless of color, however, the most characteristic markings on yellowstriped armyworms are the dark, triangular spots along the midline of the back, adjacent to the lighter colored stripes on the sides of the body. The head of a yellowstriped armyworm larva is brown, with a netlike pattern. I tried to take a close-up shot of the specimen I received, but my limited photography skills left me unable to snap an image worth sharing. For an array of photos, you can type "yellowstriped armyworm" in a Google search field and view the resulting images on the Web.
Again, the primary significance of this insect's infesting corn ears is its potential misidentification as a more economically important insect. Don’t mistakenly identify yellowstriped armyworm as a western bean cutworm because the insect looks unfamiliar to you. Accurate identification will enable you to make informed management decisions, both this year and next.--Kevin Steffey