Value of Adult Corn Rootworm (Coleoptera: Chrysomelidae) Population Estimates in Pest Management Decision Making

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Abstract
Corn root worm adult densities were monitored in 31, 43, and 44 Iowa cornfields in 1979, 1980, and 1981, respectively. The season after monitoring, plots with no soil insecticide were left in most fields. Root worm larval damage was measured in untreated areas, and yield was estimated in both treated and untreated areas of each field. Linear regressions indicated significant relationships between adult densities and larval damage and yield loss, but much of the variation in damage or yield loss was not explained by the model. Current economic thresholds did not accurately predict economic damage or appreciable yield loss >50% of the time. Addition of edaphic and agronomic variables improved the models, but 60% of the variation in yield loss was still unexplained. Value of adult sample information was determined by Bayesian analysis to be zero. A 6-fold increase in ability to predict when economic loss would not occur would be necessary for sampling to be worthwhile. The optimal strategy for managing corn root worms in Iowa in our study was not to sample for adults and always to treat corn following corn with a soil insecticide at planting time.