Adult population dynamics and oviposition of northern and western corn rootworms in continuous cornfields under commercial production

Adult population dynamics and oviposition of the northern and western corn rootworm, Diabrotica barberi Smith and Lawrence and D. virgifera virgifera LeConte, respectively, were studied under field conditions in a number of Iowa cornfields. An absolute sampling technique for corn rootworm adult emergence that adjusts to fit common row spacings was designed and field tested. Trap construction, efficiency, and estimated sample sizes are presented;Sex ratio sampling and sex ratio characteristics of corn rootworm field populations were studied. Sex ratio estimates, via sticky traps, were found to be dependent upon the height of sampling for both species. The optimum height of sampling for sex ratios within a field was determined to be 0.91-1.22m. The mean height of flight was estimated, and seasonal changes in sex ratios were determined for each species;Corn rootworm adult emergence, adult populations, and oviposition were monitored throughout the season in eight fields in 1981-83. Regression equations for seasonal emergence and oviposition were developed. Oviposition was found to be nearly complete by the end of the first week of Sept. Regression equations are presented for the relationship between northern corn rootworm adult population parameters and final season egg populations. The relationship between western corn rootworm adult populations and final egg populations was significant, but it was much more variable than the northern relationship. No weather factors consistently correlated with population changes. The peak population was found to have a significant correlation with the percent population decline following the peak for both species. Regression equations describing adult survival in continuous cornfields were determined for both species;Rootworm egg sampling considerations were investigated using data collected in this study. Sampling for both species should be done to at least a depth of 20 cm utilizing sampling methods that sample the entire row width. Sample cost and size estimates are presented;A model of the biotic potential of western corn rootworm adult populations was written using previous literature. The model was used to investigate population parameters in relation to emergence and oviposition