Lance J. Meinke
Date of this Version
Reinders, J. D. 2017. Spatial variation in western corn rootworm (Coleoptera: Chrysomelidae) susceptibility to Bacillus thuringiensis corn events in Nebraska. Thesis. University of Nebraska-Lincoln. 1-111.
The western corn rootworm (WCR), Diabrotica virgifera virgifera LeConte, is an economically important pest species of field corn (Zea mays L.) in the U.S. Corn Belt. Yield losses and control costs exceed greater than $1 billion annually. Over the past 10+ years, growers have adopted transgenic corn hybrids expressing rootworm-active Bacillus thuringiensis (Bt) proteins as a primary WCR management tactic. Field-evolved resistance to Cry3Bb1 and mCry3A proteins expressed in single-trait Bt hybrids has been confirmed in some areas of Nebraska. Growers have used different tactics as needed to prevent or mitigate resistance, resulting in a mosaic of selection pressure placed on local populations. Currently, research is needed to characterize WCR susceptibility to these Bt toxins on a local spatial scale.
Therefore, this study was conducted to characterize spatial variation in WCR susceptibility to Bt corn events in two corn-intensive production areas of Nebraska. Single-plant larval bioassays were conducted in 2016 and 2017 to characterize the susceptibility of populations from pre-established grids in Keith and Buffalo counties to single-trait Cry3Bb1 and mCry3A proteins. Bioassay results confirmed a mosaic of susceptibility to Cry3Bb1 and mCry3A existed within the two landscapes. Patterns at several spatial scales were observed and some gene flow of resistant alleles was indirectly documented in the landscape.
A field history index, comprised of additive and weighted WCR management tactics and agronomic practices was developed in an attempt to explain variation in WCR susceptibility. Regression analyses indicated a strong relationship between past management practices and WCR survival on Cry3Bb1, indicating that localized selection pressure is a major contributing factor in determining current susceptibility. These two study areas can be viewed as model systems to draw potential inferences about the relationship of susceptibility to past Bt management histories. These retrospective case histories will inform use of current rootworm-Bt technologies and contribute to the future development of sustainable rootworm management strategies conducted within an IPM framework.
Advisor: Lance J. Meinke