University of Illinois

No. 17/July 18, 1997

Grape Colaspis Adults Observed in Some Cornfields

With scouting efforts under way for corn rootworm adults and corn leaf aphids in many areas of the state, some observers have indicated the presence of very small brown beetles feeding on corn leaves. Don't be alarmed. Grape colaspis adults are common inhabitants of cornfields by the time mid-July "sends" our way high temperatures and humidities for us to enjoy. Recall that the larval stage of this insect can cause root injury in corn as well as soybeans, although corn is most often at economic risk, particularly if grown in rotation with clover. Soybeans have been affected most significantly when drought conditions persist.

Following the completion of the larval stage, adults begin to emerge during July as light brown beetles that are about 1/6 inch in length. The wing covers have several rows of evenly spaced punctures. Don't be surprised to see some very minor defoliation on corn leaves that, although noticeable, is rarely, if ever, of any economic importance.

Mike Gray, Extension Entomology, (217)333-6652