Behavioral, Movement and Egg-Laying Pattern Changes in the Western Corn Rootworm, Diabrotica virgifera virgifera, in Southwest Michigan and Mid-Michigan Corn and Soybean Fields
Western corn rootworm (WCR), Diabrotica virgifera virgifera, an important corn pest in the Midwest, has recently exhibited a behavioral change by laying eggs in soybean fields rather than corn. This activity disrupts crop rotation as a meaningful control of western corn rootworm larvae. This phenomenon, first reported in eastern Illinois in 1986, has rapidly spread throughout Illinois and Indiana. A field study was conducted during 1997 to determine if WCR beetles were active in Michigan soybean fields. Fields were monitored by sweepnet sampling at three locations in Michigan (1-15 km, 40-50 km, 120-125 km north of the Indiana border), where the phenomenon was reported in 1996. Sticky traps were also placed in two soybean fields in southwest Michigan to determine if rootworm activity was confined to the portion of the field adjacent to corn. Western corn rootworm beetle activity was confirmed in soybean fields in southwest Michigan. Significantly higher beetle activity was found in southwest Michigan sites as compared to the intermediate and control (northernmost) sites on July 29th and August 13th. WCR activity in treatments adjacent to corn was not significantly different from beetle activity in the center of the soybean field. Sticky trap and sweepnet sampling methods yielded many more female than . male beetles in soybeans, indicating that WCR may be in soybeans to lay eggs.
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