Coy St Clair, Iowa State University, Department of Entomology
Ph.D. defense seminar.
Abstract. Prior to Bacillus thuringiensis (Bt) technology, U.S. corn farmers lost one billion dollars annually to western corn rootworm (WCR), Diabrotica virgifera virgifera LeConte, due to yield loss and chemical costs. Transgenic Bt corn that produces insecticidal Cry toxins, such as Cry3Bb1, has revolutionized management of this pest, but insect resistance threatens Bt technology. This study investigated the relationship of WCR to landscape-level factors by examining local and regional spatial scales. WCR abundance, injury to corn, resistance to Cry3Bb1, and field management strategies were examined in (1) local landscapes of previous problem fields and (2) in counties where previous problem fields had been observed compared to counties where no problem fields had been detected. WCR abundance and root injury were similar in problem fields compared to the surrounding landscape, and resistance to Cry3Bb1 was uniform with slight variation in the magnitude of resistance. Management strategies were not different, with the exception that previous problem fields had grown more Cry3 corn in the past six years. Additionally, abundance and injury did not differ between problem and non-problem counties, and resistance to Cry3Bb1 was similar between county types. Management strategies favored increased corn growth and use of Cry34/35Ab1 in problem counties. These data present useful information for understanding relevant spatial scales of WCR management in Iowa, and will inform future strategies for extending the efficacy of transgenic technologies.