M.M. ELLSBURY
USDA-ARS, Northern Grain Insects Research Laboratory, 29 23 Medary Avenue; Brookings, SD, USA, 57006; E-mail: mellsbur@ngirl.ars.usda.gov
D.D. MALO, S.A. CLAY, D.E. CLAY, C.G. CARLSON
Plant Science Department; South Dakota State University; Brookings, SD, USA, 57007

Survival and development of the soil-dwelling immature stages of northern corn rootworms are influenced by soil-mediated processes that produce spatial variability in larval injury to corn roots and in patterns of adult rootworm emergence from the soil. The influence of the soil environment on survival of corn rootworm immature stages begins at the time eggs are laid in the soil and continues through one or two overwintering seasons and into the pupal stage.  The existence of spatial variability in corn rootworm distributions suggests that site-specific management of these insects may be possible.  However, the high cost of grid sampling prevents use of this approach for determining spatial distributions of rootworms or identifying management zones for application of site-specific control measures.  Soil properties such as soil moisture, pH, and clay content are known to affect rootworm survival.  We hypothesize that measurable soil parameters, particularly soil electrical conductivity, may be useful as ancillary variables to predict corn rootworm spatial distribution because, like the immature stages of rootworms, these soil properties also are influenced by soil moisture, pH, and clay content.  Grid-sampled data for distribution of rootworm eggs in the soil, larval injury to corn roots, emergence patterns of adult corn rootworms, and soil electrical conductivity in relation to landscape position are discussed comparatively with reference to prospects for the site-specific management of corn rootworms in two corn fields with distinctly different topography and soil types.  These results suggest that the complexity and field-to-field variability of insect pest/soil interactions is such that a multivariate approach rather than use of a single predictor such as soil electrical conductivity may be necessary for site-specific management of insect pests in the soil environment.