Evidence of evolving carbaryl resistance in western corn rootworm (Coleoptera : Chrysomelidae) in areawide-managed cornfields in north central Kansas

Susceptibility of adult populations of the western corn rootworm,Diabrotica virgifera LeConte, to carbaryl was determined by a survey in 1996 before t he implementation of an areawide, management program near Scandia in north central Kansas. Subsequently, the susceptibility of western corn rootworm a dults to carbaryl has been monitored throughout the program from 1997 to 20 00 in both control and managed areas. In 1996, adults were highly susceptib le to carbaryl with a mean LC50 value of 0.64 mug/vial. This value was comp arable to those for adults collected from other regions within Kansas. Howe ver, adult susceptibility to carbaryl decreased rapidly within the managed area, where the cucurbitacin carbaryl-based bait SLAM has been used as the primary tool to control adults in this project since 1997. In 1999, adults collected from the managed area were 9- and 20-fold less susceptible to car baryl at the LC50 and LC95 levels, respectively, than those evaluated in 19 96. In contrast, adults collected from the control area were only 2- and 3- fold less susceptible to carbaryl at the LC95 and LC90 levels, respectively , than adults evaluated in 1996. Although field adult populations of wester n corn rootworm were relatively low in 2000, evaluations showed trends simi lar to those in 1999 regarding their carbaryl susceptibility in the managed and control areas. These results provide evidence that western corn rootwo rm has been evolving carbaryl resistance rapidly in response to the use of SLAM in areawide-man aged cornfields near Scandia.