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Resistance management of Western corn rootworm, Diabrotica virgifera virgifera LeConte, to corn traits in Nebraska
The Western corn rootworm, Diabrotica virgifera virgifera LeConte, is the most economically important pest of field corn in the U.S. Larvae feed on corn roots causing root injury and reduced yield. Corn hybrids expressing rootworm-active Bt proteins have been widely adopted as control tactics in continuous corn. In Nebraska, reduced control (problem fields) was observed from 2010-2014 in some fields planted to Cry3Bb1 corn for 3 or more consecutive years. Studies were conducted to investigate possible cause(s) of greater than expected injury to Cry3Bb1 in various areas of Nebraska from both insect and plant perspectives. A single-plant larval bioassay technique was used to characterize susceptibility and fitness (survival, development, weight) of populations from Cry3Bb1 problem fields, supplemental non-problem fields, and laboratory control colonies. Bioassays conducted during 2012-2015 confirmed field-evolved resistance to Cry3Bb1 and cross-resistance to mCry3A in some populations collected in Northeastern, Central, and Southwestern Nebraska. No resistance to Cry34/35Ab1 or cross resistance of Cry34/35Ab1 with Cry3Bb1 or mCry3A was detected. Range of larval survival in Cry3Bb1 bioassays among populations indicates a geographic mosaic in susceptibility occurs across Nebraska. Populations from problem fields exhibited both complete and incomplete resistance. In problem field populations, there was a significant positive correlation between mean proportional survival and both mean proportion of survivors in third instar and larval weight; indicating mean development time decreases as frequency of Cry3Bb1 resistance increases. In populations exhibiting complete resistance, larval progeny from adults that emerged early or later in emergence curve from Cry3Bb1 plants did not exhibit a significant difference in susceptibility to Cry3Bb1. ELISA was used to measure Cry3Bb1 expression in roots to determine if high pH calcareous soils and associated poor corn growth in some Southwestern Nebraska fields negatively impact expression and efficacy. Results indicate calcareous soil did not compromise Cry3Bb1 expression and efficacy. Overall, field-evolved resistance to Cry3Bb1 is a key contributor to greater than expected injury. This study increases our understanding of the distribution of Cry3Bb1 resistance in Nebraska and fitness attributes of populations that exhibit complete and incomplete resistance. Also, results contribute to development of appropriate resistance mitigation and sustainable rootworm management strategies.
Wangila, David Sindani, "Resistance management of Western corn rootworm, Diabrotica virgifera virgifera LeConte, to corn traits in Nebraska" (2016). ETD collection for University of Nebraska - Lincoln. AAI10100904.