Transgenic Bt corn that produces insecticidal Cry toxins, such as Cry3Bb1, has
revolutionized management of western corn rootworm, Diabrotica virgifera
virgifera LeConte. However, insect resistance threatens Bt technology. This research
investigated the relationship of western corn rootworm to landscape-level factors by
examining local and regional spatial scales. Rootworm abundance, injury to corn,
resistance to Cry3Bb1, and field management strategies were examined in local
landscapes of previous problem fields (\u3c2.2 km) and in counties where previous problem
fields had been observed compared to counties where no problem fields had been
detected. Also, geospatial tools were used to quantify continuous corn growth in areas
surrounding previous problem fields. Rootworm 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. Previous problem fields had
grown more Cry3 corn in the past six years than fields in the surrounding landscape.
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, soil insecticide use, and use of Cry34/35Ab1 in
problem counties. Geospatial analyses showed that areas surrounding previous problem
fields had grown more continuous corn compared to randomly selected point in the
landscape, and this effect was most pronounced within 1.6km of the field centroid. These
data present useful information for understanding relevant spatial scales of western corn
rootworm management in Iowa, and will inform future strategies for extending the
efficacy of transgenic technologies
