Previous Awardees

Project Title  
Early versus late-emerging Bt-resistant western corn rootworms in the rotation-resistant zone: seeking an optimum management strategy.  

Primary Investigator (PI)  
Joseph L. Spencer, University of Illinois

Project Summary

Documentation of western corn rootworm (WCR) resistance to Cry3Bb1 corn in 2011 revealed a threat to the primary tool used to protect U.S. corn from its most costly pest. In August 2013, we were alerted to severe corn rootworm injury and lodging in producers’ rotated cornfields in central and northeastern Illinois. Subsequent visits to these first-year cornfields confirmed excessive WCR injury on the roots of Cry3Bb1-expressing corn hybrids leading to the testable hypothesis that some WCR populations are resistant to both crop rotation and the Cry3Bb1 protein expressed in certain Bt corn rootworm hybrids. The presence of suspected Bt resistance among rotation-resistant WCR links two very significant pest management challenges and threatens management strategies used across an important portion of the Corn Belt.

We will work directly on-farm with producers to evaluate several management approaches including early vs. late broadcast applications of insecticides to soybean fields in combination with soil insecticides and Bt rootworm hybrids in rotated corn. WCR adults will be collected from rotated corn and adjacent soybean fields and Bt resistance bioassays performed on the offspring to test our hypothesis and document possible variation in resistance among early and late-emerging WCR adults. This research will answer fundamental questions about resistance and evaluate practical management options of interest to corn growers. Testing management approaches and measuring resistance will improve understanding of CRW management tactics and support the development and deployment of more effectively-targeted management strategies.


Project Title
Characterizing Resistance Evolution to Pyrethroid Insecticides

Primary Investigator (PI)
Blair Siegfried University of Nebraska-Lincoln

Project Summary

The western corn rootworm (Diabrotica virgifera virgifera LeConte) has continuously challenged our ability to develop sustainable pest management solutions. Resistance to chemical pesticides, crop rotation, and most recently transgenic plants that express toxins derived from Bacillus thuringiensis have been well documented among rootworm populations. Resistance to Bt corn hybrids has resulted in a substantial return to the use of both soil insecticides at planting and/or foliar application of adulticides later in the growing season and have increasingly relied on pyrethroid insecticides. The use of pyrethroids for adult and larval control has become an important component of best management practices designed to protect plants from rootworm injury in areas where control failures with Bt plants have been observed. Given the rootworm’s propensity to evolve resistance, sampling and bioassays of rootworm populations from across the Corn Belt were initiated in 2013 and have shown that some populations exhibit reduced susceptibility to the pyrethroid insecticide, bifenthrin. We believe that these preliminary data are indicative of a response to selection from repeated exposure to pyrethroid insecticides and reflect a possible decline in efficacy of both adult management programs and potentially some soil insecticides. As a consequence, we are proposing a set of studies to confirm resistance and document heritability, to determine the impact of such resistance on larval susceptibility, and to identify the mechanisms of resistance and associated molecular markers that can be used to characterize allele frequencies among field populations. This information is critical to developing effective resistance management and mitigation strategies.


Project Title  
The genetics of emerging resistance to Cry3Bb1 corn

Primary Investigator (PI)  
Nicholas Miller, University of Nebraska, Lincoln

Project Summary

Our research concerns a significant threat to biotechnology-based management of corn rootworms: the emergence of western corn rootworm (WCR) populations that are resistant to Cry3Bb1-expressing corn. We will characterize the genetic basis of resistance by addressing several important, unanswered questions: 1) Is the same genetic mechanism present among populations that have evolved resistance in different locations? 2) How many genes are involved in resistance?

We will use innovative population genetic methods and QTL mapping, two distinct approaches with complementary strengths to achieve our research objectives:

  1. Identify the genes that have responded to selection by Cry3Bb1, leading to resistance in the field.
  2. Map QTL for field-evolved resistance to Cry3Bb1.
  3. Identify selection-responsive genetic markers located within QTL that could be used to survey or monitor for resistance alleles.

The results of our research will have a significant impact on the future of corn rootworm resistance management. The knowledge we generate will inform the development of more effective resistance management and mitigation strategies to preserve the efficacy of Cry3Bb1 corn. The genetic markers for resistance will provide tools to survey or monitor for resistance alleles.


Project Title  
Teaching Corn Rootworm Resistance Management Strategies Through Interactive Mobile and Web-based Educational Modules

Primary Investigator (PI)  
Douglas Golick, University of Nebraska, Lincoln

Project Summary

We seek to develop a series of mobile and web-based interactive learning experiences for producers, consultants, extension educators, and post-secondary students teaching fundamental concepts related to resistance management strategies of the corn rootworm. These modules will teach science-based concepts related to current knowledge on corn rootworm biology, behavior, IPM strategies, resistance management strategies, toxicology, and population genetics through modern mobile, Web 2.0, and adaptive learning approaches.

Project Goals

  • Create research-based educational modules teaching corn rootworm resistance management strategies for use by growers, consultants, and university students
  • Employ both modern technology-enhanced (website, Mini-Online Open Courses, mobile smartphone application) and traditional instructional techniques (quick sheets, whitepapers, seminars) to reach a wide-audience
  • Create educational tools for professionals that work with growers to aid in decision making related to corn rootworm IPM and resistance management strategies
  • Evaluate short and long-term impacts of the educational materials on growers’ farm practices
  • Behavioral outcomes for growers
  • Learn basic principles of resistance management and IPM in the corn rootworm system
  • The ability to assess corn rootworm damage to determine immediate and future farming practices
  • Application of science-based resistance management practices on their farms
  • Behavioral outcomes for consultants, extension educators, seed salespersons, and industry agronomists
  • Use project’s educational tools to educate growers on resistance management issues
  • Use educational tools in the field for making management decisions


Project Title  
Estimating Dispersal And Modeling Its Impact On Resistance Remediation In Western Corn Rootworm

Primary Investigator (PI)  
Michael A. Caprio, Mississippi State University

Project Summary

Western corn rootworm (WCR) is the most serious pest of corn throughout the Corn Belt. Multiple Bt toxins have been commercialized in corn hybrids that have been effective at managing WCR populations. Recently, there have been reports of field populations with confirmed or suspected resistance to two of those toxins (Cry3Bb1 and mCry3A). Declining efficacy among Bt corn hybrids is problematic for growers, industry, scientists and regulators. There are few modeling resources for remediation of WCR Bt-resistance and virtually no theoretical framework to guide decision-making. We have identified knowledge gaps in WCR biology, particularly related to adult dispersal, critical to providing reliable models to address resistance, remediation and the optimal use of compromised traits. We will use molecular methods, field studies and two different models to address these issues relevant to program area: Characterization of the biochemical, genetic, and molecular aspects of insect resistance. DNA markers will be used to estimate typical per-generation dispersal from the natal field in Obj. 1. We will observe and measure how patterns of adult cornfield abundance and intrafield movement translate into subsequent patterns of injury and emergence and also document patterns and measure characteristics and proportions of dispersing WCR engaged in interfield movement in Obj. 2. These Obj. 1-2 data will be synthesized under Obj. 3, culminating in the modeling completed under Obj. 3-4 that will provide science-based guidance for the mitigation of developing resistance and optimal strategic deployment of compromised traits to maximize the benefit of WCR control technology to society.

 


Project Title  
Profitability of Alternative Management Strategies for Western Corn Rootworm

Primary Investigator (PI)  
Paul Mitchell, University of Wisconsin - Madison

Project Summary

The long‐term outcome this project seeks is increased farmer adoption of economically viable rootworm management strategies, including resistance management. The project’s long‐term goal is to develop interactive map‐based apps that integrate spatial databases to estimate the field‐specific profitability of rootworm management practices to help farmers improve rootworm management. We will assemble and analyze existing rootworm data to estimate infestation intensities, efficacy of alternative control methods, and yield loss functions. Second, we will combine estimated functions with yield, price and cost information to create partial budgets of net returns for different rootworm management strategies. Third, we will conduct on‐farm research trials to gather economic data under real world conditions and to receive farmer feedback on project activities and results. Finally, we will integrate these partial budgets with large, long‐term spatial databases to create a map‐based smartphone app that reports net returns for different rootworm management practices and allows farmers to enter their own data to generate field‐specific net return estimates.


Project Title  
Rootworm Refuge Function: An Empirical Field Test

Primary Investigator (PI)  
Christian Krupke, Purdue University

Project Summary

Recent reports of high rootworm damage and emergence from Bt corn hybrids have underscored the importance of effective refuges in IRM plans. Current plans were designed to facilitate random mating between susceptible and putatively resistant individuals, but there is no empirical evidence that refuges actually succeed in accomplishing this purpose. Given the intense selection pressure imposed by Bt corn, it is reasonable to re-assess whether WCR mating patterns in the field match our initial expectations. In fact, there is a growing body of evidence that rootworm mating in Bt/refuge corn fields is not random – undermining a key assumption of the current resistance management model. The overall goal of this research is to further our understanding of WCR mating behavior in Bt/refuge environments. The objectives of this proposal are to determine the influence of larval diet (Bt vs. refuge corn) on the mate choice and mating success in adult beetles, and determine the extent to which non-random mating occurs in the field. We will also collect morphometric and weight data from beetles to determine if these factors explain some of the mating patterns observed (for example, size-based assortative mating as a mechanism). Our work will generate data that can be incorporated into existing and future models of gene flow among WCR populations to enhance durability of current refuges and those for future in-plant toxins targeting WCR.

 

Dr. Brigitte Tenhumberg, University of Nebraska, Lincoln, NE
Evaluating integrated resistance management strategies in variable environments

Only six years after the commercialization of Bt corn researchers found the first signs of resistance evolution of western corn rootworm (WCR), Diabrotica virgifera virgifera, populations against one of the available Bt toxins (Cry3Bb1). We propose to use mathematical models to evaluate a range of integrated resistance management strategies to identify those that are likely to work best in delaying the onset of resistance evolution. This evaluation will build on a WCR population dynamics model that specifically considers the effect of environmental variation and the effect of underlying genetic assumptions on model predictions and empirical data derived from bioassay of specific conventional insecticides to monitor changes in susceptibility. Past models have ignored environmental variables such as temperature and precipitation despite ample evidence that they critically influence WCR vital rates (e.g. survival, developmental time). Furthermore, all past WCR models assumed a single major gene that confers resistance, even though we know that the predicted speed of resistance evolution of models assuming major gene resistance differs dramatically from models assuming resistance is a quantitative trait. This is important because some researchers suspect that WCR resistance to Bt toxins is a quantitative trait.


Dr. Marcé Lorenzen, North Carolina State University
Development of a germline transformation system for Diabrotica virgifera virgifera

The western corn rootworm (WCR), Diabrotica virgifera virgifera, is a major pest of maize and is notorious for developing resistance to management methods due to its adaptive behavior. Researchers have been stymied in their quest to discover the genetic‐basis of WCR adaptation. However, new approaches are possible with the advent of genome sequencing and functional genomics. For example, the WCR genome has been sequenced, and RNA interference (RNAi) works exceptionally well for determining gene function in WCR. However, despite this important advancement, the problem of efficiently identifying resistance genes remains. A functional genomic tool that requires no upfront knowledge of DNA sequence would be a perfect complement to sequence‐based technologies such as RNAi. Here we propose to generate such a tool by developing a germline transformation system for this economically important pest. Specifically, we will utilize piggyBac‐ and/or Minos transposons to create transgenic WCR. Establishing transgenic technologies for this beetle is the first step towards bringing a wide‐range of transformation–based tools to bear on understanding WCR biology.


Dr. Bryony C. Bonning, Iowa State University
Corn Rootworm Viruses and RNA Interference

The goal of this project is to examine viruses of western corn rootworm (CRW), Diabrotica virgifera virgifera, to Objective 1 identify viruses of the CRW; Objective 2 assess the potential for use of viruses for CRW biological control; Objective 3 develop a vector for virus-induced gene silencing (VIGS) in CRW. A VIGS vector developed from a CRW virus will allow for (i) functional analysis of CRW genes and (ii) optimization of RNA interference-based CRW management strategies through stabilization and efficient targeting of silencing RNAs. Having found evidence for the presence of eight CRW viruses, we will identify additional viral sequences from comprehensive transcriptome, small RNA and viral genomic analyses. We will amplify and assess the pathogenicity of candidate viruses for use as biological control agents. We propose to use a CRW dicistrovirus for production of a VIGS vector by constructing and engineering an infectious clone for delivery of silencing RNAs. At the conclusion of this project we expect to have identified a virus for use in biological control of CRW and developed a VIGS vector for fundamental investigation of CRW gene function and as a means for optimized delivery of dsRNA to CRW from transgenic corn. This project is relevant to three of the CRW Knowledge Grant priority areas relating to biological control of corn rootworm, rootworm physiological studies, and transgenic approaches to rootworm control.

 

Photographs kindly provided by Marlin E. Rice (CRW larvae) and Tom Sappington (CRW adult).


Aaron Gassmann, Iowa State University
Effects of Current Agricultural Practices on Western Corn Rootworm and Optimal Strategies for Management    

I am proposing field and laboratory research aimed at understanding interactions between western corn rootworm and Bt corn, and how to best manage western corn rootworm under current production practices.  In fields with greater than expected damage to Bt corn, measurements of pest abundance will be coupled with bioassays of pest susceptibility to determine the relative importance of these factors in contributing to root injury.   Additionally, bioassays will be used to measure the extent to which reduced rootworm susceptibility to Bt corn is limited to Bt fields with greater than expected damage or is found more broadly within the landscape.  Multiple regression analysis will be applied to fields with a range of cropping histories including corn-on-corn production and crop rotation to determine how current agricultural practices affect rootworm abundance, root injury and rootworm susceptibility to Bt corn.  Economic thresholds will be calculated from on-farm research that tests how root injury and yield are affected by transgenic management techniques, non-transgenic management techniques and both approaches in combination.  


Bruce Hibbard, USDA-ARS, Columbia, MO
Optimization of plant and diet assays for short-term needs and an artificial diet for rootworm rearing

The western corn rootworm (WCR) is the most important insect pest of corn in the United States. Given a history of developing resistance, a logical concern exists that WCR will develop resistance to newer management tactics. To slow resistance development of insect pests to Bt crops, the U.S. Environmental Protection Agency (EPA) has mandated that an insect resistance management (IRM) plan must be in place prior to registration of any Bt product. One component of current IRM plans are resistance monitoring plans. The EPA is currently considering replacing diet bioassays for all WCR toxins with on-plant assays. Unfortunately, there is little scientific or economic data supporting this compared to other options. For higher dose next generation products it may be likely that diet-toxicity assays will be the most appropriate assays. Precedence seems to be an important component of EPA decisions. Good science is needed prior to full implementation of a modified monitoring program being mandated by EPA.


Dr. Kenneth Ostlie, University of Minnesota
Corn Rootworm Emergence, Scouting and Contemporary Thresholds for Field-Specific Management

The expanding geography and intensification of Bt-RW performance problems with western corn rootworm are creating management uncertainties for growers.  Even as corn rootworms figure more prominently in crop management decisions, most growers are operating blind with little field-specific information on corn rootworm populations.  In the face of this uncertainty, risk-adverse growers are opting for an insurance approach by layering multiple tactics without regard to actual field realities or their economic, rootworm management, or resistance management implications.  The objectives of this research are to re-tool scouting methods and re-calibrate action thresholds for trait and insecticide management options.  Degree-day models for corn rootworm emergence will be updated using data from on-farm Bt-RW trait x soil insecticide studies conducted in problem and non-problem fields.  The implications of Bt-trait effects on beetle emergence will be explored in lab mating studies.  Corn rootworm populations will be assessed using whole-plant counts and yellow sticky traps.  Root and yield protection will be evaluated for selected management tactics the following year.  These consequences will be related to preceding population levels to determine how this data can best be used in management decisions.  Grower / ag professional surveys and focus groups will be used to provide the managerial context, economic and logistic constraints for re-designing the decision process and calculating the applicable thresholds for management actions against corn rootworms.  Decision accuracy and value of scouting will be evaluated in the second cycle of on-farm research.