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The western corn rootworm, Diabrotica virgifera virgifera LeConte, is one of the most economically important insect pests threatening the production of corn, Zea mays (L.), in the United States. Throughout its history, this insect has displayed considerable adaptability by overcoming a variety of pest management tactics, including the cultural practice of annual crop rotation. Since first reported in Illinois in the late 1980s, populations of the rotation-resistant western corn rootworm have spread over a wide area of the eastern Corn Belt. Currently, little information is available concerning the interaction of rotation resistance with the use of genetically modified corn expressing insecticidal toxins from Bacillus thuringiensis Berliner (Bt), a popular tactic for preventing larval injury and its associated yield loss. The goal of this greenhouse experiment was to determine whether rotation-resistant and rotation-susceptible western corn rootworm larvae differ with respect to survival or development when exposed to single- or dual-toxin (pyramided) Bt corn. Individual corn plants were infested with 225 near-hatch eggs at the V5 (five leaf collar) growth stage. Larvae developed undisturbed on the root systems for 17 days, after which they were recovered using Berlese–Tullgren funnels. Surviving larvae were counted to estimate mortality, and head capsule widths were measured to assess development. Rotation-resistant and rotationsusceptible larvae had statistically similar mean levels of mortality and head capsule widths when exposed to both single-toxin (Cry3Bb1 or Cry34/35Ab1) and pyramided (Cry3Bb1+ Cry34/35Ab1) Bt corn, suggesting that these two populations do not differ with respect to survival or development when exposed to Bt corn. Additionally, the statistically similar mean levels of mortality for larvae exposed to single-toxin and pyramided Bt corn suggest that pyramided Bt hybrids containing the Cry3Bb1 and Cry34/35Ab1 toxins do not result in additive mort

Since the discovery of the pest in 1992, western corn rootworm (Diabrotica virgifera virgifera LeConte (WCR)) populations in Serbia have successfully been kept low with crop rotation. This has reduced the efficiency of screening maize for WCR resistance. A cooperative project between Iowa State University and the Maize Research Institute, Zemun Polje evaluated 13 Serbian commercial maize varieties in Ames, Iowa over a two-year period using the difference approach. Maize hybrids were planted on trap crops where high WCR populations were assumed. Hybrids were evaluated for WCR resistance using a randomized complete block design with four replications. Treatments were paired-rows arranged in split plots with one row in each pair treated with insecticide and the other row left untreated. WCR injury was evaluated using a rating of root size and root re-growth (1-6 scale), root injury (0-3 Node-Injury Scale), root mass, lodging, and yield. The results indicated significant differences among the Serbian hybrids in the presence of moderate-to-high levels of western corn rootworms. The relative benefit of insecticide treatments for maize hybrids was a useful tool in evaluating resistant germplasm. However, conducting analyses on relative differences between insecticide treated and untreated plots was not as effective at detecting differences as comparing the plots independently.