Understanding the impact of management strategies and relevant spatial scales on western corn rootworm resistance to Cry3Bb1

Abstract

<p>Transgenic Bt corn that produces insecticidal Cry toxins, such as Cry3Bb1, has</p> <p>revolutionized management of western corn rootworm, Diabrotica virgifera</p> <p>virgifera LeConte. However, insect resistance threatens Bt technology. This research</p> <p>investigated the relationship of western corn rootworm to landscape-level factors by</p> <p>examining local and regional spatial scales. Rootworm abundance, injury to corn,</p> <p>resistance to Cry3Bb1, and field management strategies were examined in local</p> <p>landscapes of previous problem fields (<2.2 km) and in counties where previous problem</p> <p>fields had been observed compared to counties where no problem fields had been</p> <p>detected. Also, geospatial tools were used to quantify continuous corn growth in areas</p> <p>surrounding previous problem fields. Rootworm abundance and root injury were similar</p> <p>in problem fields compared to the surrounding landscape, and resistance to Cry3Bb1 was</p> <p>uniform with slight variation in the magnitude of resistance. Previous problem fields had</p> <p>grown more Cry3 corn in the past six years than fields in the surrounding landscape.</p> <p>Additionally, abundance and injury did not differ between problem and non-problem</p> <p>counties, and resistance to Cry3Bb1 was similar between county types. Management</p> <p>strategies favored increased corn growth, soil insecticide use, and use of Cry34/35Ab1 in</p> <p>problem counties. Geospatial analyses showed that areas surrounding previous problem</p> <p>fields had grown more continuous corn compared to randomly selected point in the</p> <p>landscape, and this effect was most pronounced within 1.6km of the field centroid. These</p> <p>data present useful information for understanding relevant spatial scales of western corn</p> <p>rootworm management in Iowa, and will inform future strategies for extending the</p> <p>efficacy of transgenic technologies.</p>