Many people throughout central Illinois will remember 2000 as yet another year when grape colaspis larvae caused economic damage to corn. For some growers, 2000 is the third year in a row during which these pests have caused significant problems, and frustrations are apparent. We still know very little about the biology and behavior of these insects, and management options are few and far between. Predicting their occurrence in cornfields and knowing when the adults move into soybeans to lay eggs are crucial for the development of management strategies, yet these determinations remain unknown. It is clear that some research efforts are necessary if we expect to be able to manage this pest with any success in the future. |
Some grape colaspis larvae still can be found in a few fields, but most people primarily are finding pupae and adults. Adults have begun emerging throughout central Illinois and can be found feeding on corn leaves in the same fields in which the larvae injured the roots. At some point within the next few weeks, the adults will move into other crop fields, including alfalfa and soybeans, where they will continue to feed and lay eggs.
Pinned grape colaspis adults.
The tan grape colaspis adult is oval and about 1/6 inch long with rows of tiny punctures on its wing covers, making them appear ridged (Figure 1). They may resemble newly emerged northern corn rootworm adults; however, northern corn rootworm adults have smooth wing covers that eventually turn green. Feeding by grape colaspis adults on corn leaves and silks and on leaves of alfalfa, clover, grape, soybeans, and strawberries causes no economic damage. They also feed on bull nettle and smartweed, and possibly other species of weeds.
We would like to keep track of when grape colaspis adults move into soybeans. Many of you will be scouting soybean fields for western corn rootworm adults, so consider watching for grape colaspis adults, too. If you find grape colaspis adults on yellow sticky traps, in sweep nets, or simply by observation, please let us know. Recording their numbers over time would be especially helpful. Any information we gather this year could help a little if we have to deal with this pest again next year.--Kevin Steffey