Date: 3/30/99

Time: 4:05

Type: Symposium

Number: 157

Monitoring western corn rootworm susceptibility to carbaryl in areawide management programs

*M.E. Scharf, L.J. Meinke, B.D. Siegfried, Department of Entomology, University of Nebraska, Lincoln, NE 68583-0816; R.J. Wright, , South Central Research and Extension Center, University of Nebraska, Clay Center, NE 68933 and L.D. Chandler, USDA-ARS NGIRL, Brookings, SD 57006
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The development of insecticide resistance in populations of insects targeted by areawide management is a concern because of the relatively severe selective pressures that may be exerted by these programs. Our role in the present rootworm areawide management program is to assess carbaryl susceptibility in associated populations using insecticide bioassays, and to develop resistance monitoring techniques that use resistance-associated biochemical markers to further evaluate populations. Insecticide bioassays are used in both concentration range and diagnostic concentration formats. Concentration range bioassays allow for the calculation of LC50, LC90 and slope estimates for populations, while diagnostic concentrations identify the proportion of populations that exceed the LC99 for a standard susceptible population. Concurrent use of both of these bioassay formats ensures thorough population assessment, and will therefore appropriately identify evolving resistance. Using these two bioassay approaches, changes in carbaryl susceptibility were noted in areawide rootworm populations between the 1997 and 1998 growing seasons. Using carbaryl-resistant rootworm populations from Nebraska, we have also determined that oxidative and hydrolytic enzymes are each involved in carbaryl resistance. Of these two enzymes, hydrolases (i.e., non-specific esterases) are particularly amenable to study and show a great deal of promise as resistance-associated biochemical markers for resistance monitoring. In 1998 areawide rootworm populations, electrophoretic esterase patterns appear to correspond with elevated tolerance in some treated populations. Although trends for resistance development have been identified in some populations, it will be essential to monitor these populations over the course of the entire pilot program to realistically document impacts on resistance development posed by rootworm areawide management.

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