Indiana: IPM Responding to Changes in Pest Dynamics: Western Corn Rootworm in First-Year Corn Following Soybean

For years, Indiana's Western Corn Rootworm (WCR) was only a pest of continuous corn. Recently, first-year corn rotated with soybean has suffered economic levels of WCR larval feeding. This injury indicates that WCR eggs are being laid in soybean fields.

In 1996, Purdue IPM specialists expanded several studies initiated in 1995 to determine the reason(s) for WCR's increased attraction to soybean.

Laboratory studies were conducted to determine if Indiana WCR's prefer certain volatile host environment components. Data were compared with results from Iowa and Nebraska WCR populations, where WCR has only plagued continuous corn.

The tests, conducted with an olfactometer, were constructed so as to allow the beetles from the three states a choice of six treatments. These treatments were water alone and in various arrangements of soil, corn residue, corn plant material, and soybean plant material.

The data show that Indiana WCR responded differently than populations from Iowa and Nebraska. For the Indiana population, significantly more beetles were found in soybean without corn residue treament while no statistical differences existed between Iowa and Nebraska populations.

This strengthens the hypothesis that a portion of Indiana's beetle population has adapted to the corn/soybean rotational system and prefers soybean to corn.

Results of this experiment have not been fully tested, but data and on-going field observations suggest WCR populations differ in attraction to soybean. Indiana producers must consider alternatives to crop rotation for preventing economic losses and Purdue's IPM program is developing management strategies to help growers meet this new challenge.