Technical Abstract: Rootworm Resistant Varieties. Here we report the results of a two-year ongoing research project assessing the resistance and tolerance of 14 maize genotypes to western corn rootworm larvae, Diabrotica virgifera virgifera LeConte (Coleoptera: Chrysomelidae). Corn lines were planted in field plots using a randomized complete block design with 10 hand-planted seeds of each corn line per plot, replicated four times. Plots were mechanically infested with 1,000 D. virgifera eggs per 30 cm using Sutter and Branson’s technique (1980). Rootworm eggs were suspended in an agar solution and were obtained from colonies maintained at the North Central Agricultural Research Laboratory in Brookings, SD. Resistance and tolerance to rootworms was evaluated using previously established methods, including: the Iowa 1-6 root damage rating scale, percent of plant lodging, adult rootworm emergence, and compensatory root growth ratings. In 2005, the genotype with the least damage had an average root damage rating of 2.10, while the genotype with the most damage had an average root damage rating of 3.95. We will also present data from 2006. Many historical evaluations of corn germplasm have focused solely on resistance to western corn rootworms, even though different rootworm species frequently co-exist. Therefore, maize genotypes also will be tested for resistance and tolerance to northern corn rootworm larvae, Diabrotica barberi Smith & Lawrence. Improved Rootworm Egg Infestation Methods. We will also discuss modifications to Sutter and Branson’s mechanical rootworm egg infester. The new apparatus is capable of delivering variable egg rates of multiple rootworm species. This will allow us to conduct more realistic experiments examining the susceptibility of corn lines to several rootworm species simultaneously, and to determine whether specific genotypes exhibit resistance and/or tolerance solely to D. virgifera, D. barberi, or to both.