Grape Colaspis Adults Feeding in Corn and Soybean Fields

July 2, 1999
Some pests just don't know when to give up. Grape colaspis larvae were involved in numerous reports of reasonably severe injury to root systems two to three weeks ago. In some instances, the effect on potential yield has been significant, especially in some seed cornfields. Seed corn has notoriously weak roots, and the plants were not able to "grow out" of the injury like commercial field corn did. And now the adults are causing some headaches in several areas of the state. Grape colaspis adults can be observed in both corn and soybean fields right now. Although you might be able to find them with ease, don't overreact. I suspect that their feeding will not result in economic damage in most fields.

Grape colaspis adults.

The adult grape colaspis is tan, oval, and about 1/6 inch long with rows of tiny punctures on its wing covers, making them appear ridged (Figure 2). Colaspis adults sometimes are confused with newly emerged northern corn rootworm adults, which have smooth wing covers. Grape colaspis adults will feed on corn leaves and on silks, when they are available, but there have never been any reports that this injury is economic. I have heard at least one rumor that some cornfields have been sprayed for control of this insect. I am fairly certain that the sprays were not necessary. Even though we don't see this pest frequently, let's not overreact just because we are finding them in larger-than-ordinary numbers.

You also will find grape colaspis adults in soybean fields. After all, some of the females obviously laid eggs in soybeans in 1998, resulting in injury to corn in 1999. Colaspis adults are defoliators of soybeans, but they seldom, if ever, cause economic damage.

After a couple of years of noticeable injury caused by the larvae, some people are scratching their heads and wondering what to expect from the grape colaspis next year. The simple truth is that this insect has not been studied for decades. Although we have stated repeatedly that corn planted after red clover can be threatened by grape colaspis, how much red clover is available in Illinois? This species now is laying eggs in soybeans, and the surviving larvae are causing injury to corn planted after soybeans. We need a lot more information before we can develop reliable management strategies for this infrequent but occasionally injurious pest.--Kevin Steffey

Author: Kevin Steffey