Rotation-Resistant Corn Rootworms 2006

Corn rootworms have been, and in many cases still can be, managed with crop rotations. However, some populations of both northern and western corn rootworms (CRWs) have adapted to the com-soybean rotation. Regular, annual rotations between corn and soybeans have selected for a variant of the northern CRW that has a two-year life cycle, referred to as extended diapause. Female northern CRWs deposit eggs in the soil within cornfields. When the field is rotated to soybean the next year, most eggs hatch and the larvae starve. However, a portion of the eggs remain dormant in the soil for a second winter and do not hatch until the following spring when corn is planted back into the field resulting in damage to the rotated corn. Extended-diapause northern CRWs originally caused severe injury to rotated corn in NW Iowa, SW Minnesota, SE South Dakota, and NE Nebraska during the late 1980s. Since then their range has expanded until it is now found throughout most of Iowa. South Dakota has estimated that nearly 50% of their northern CRWs are the extended-diapause variant