Degree Type


Date of Award


Degree Name

Doctor of Philosophy





First Advisor

Aaron J. Gassmann


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 (<2.2 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.

Copyright Owner

Coy Ray St. Clair



File Format


File Size

165 pages

Included in

Entomology Commons