Source: UNIV OF MINNESOTA submitted to
STRATEGIES FOR MANAGING CORN INSECTS IN DYNAMIC PRODUCTION ENVIRONMENTS
Sponsoring Institution
National Institute of Food and Agriculture
Project Status
COMPLETE
Funding Source
HATCH
Reporting Frequency
Annual
Accession No.
1011434
Grant No.
(N/A)
Cumulative Award Amt.
(N/A)
Proposal No.
(N/A)
Multistate No.
(N/A)
Project Start Date
Oct 19, 2016
Project End Date
Sep 30, 2021
Grant Year
(N/A)
Program Code
[(N/A)]- (N/A)
Recipient Organization
UNIV OF MINNESOTA
(N/A)
ST PAUL,MN 55108
Performing Department
Entomology
Non Technical Summary
Corn insects and their management present dynamic challenges to farmers and their agricultural advisors. Transgenic corn has revolutionized how farmers manage corn insects, especially European corn borer (ECB) and corn rootworm (CRW). With European corn borer, this revolution has largely eliminated insecticide use through a combination of high-dose events, pyramids of multiple traits, and area-wide suppression. In contrast, the corn rootworm technology encountered snags after its initial success, Since the technology is not high-dose, resistance developed within 7 years to the primary trait and has now been documented for all traits, and cross-resistance potentially compromises performance of pyramids. With a little help from Mother Nature (widespread winter mortality), intensive deployment of pyramids, and layering soil insecticides over traits as insurance, growers have maintained corn production but this situation could deteriorate. However, growers face increasing economic challenges that are softening grower enthusiasm. What's an effective IPM strategy in the face of Bt resistance and reduced economic flexibility? Doe resurging northern corn rootworm numbers mean resistance is g with risk to both continuous and rotated corn? Does increasing European corn borer abundance mean area wide suppression is less effective? This project addresses four complementary objectives necessary to further our understanding of both northern and western CRW populations, Bt resistance and insecticide use in an era of reduced inputs.
Animal Health Component
60%
Research Effort Categories
Basic
25%
Applied
60%
Developmental
15%
Classification

Knowledge Area (KA)Subject of Investigation (SOI)Field of Science (FOS)Percent
21631101130100%
Knowledge Area
216 - Integrated Pest Management Systems;

Subject Of Investigation
3110 - Insects;

Field Of Science
1130 - Entomology and acarology;
Goals / Objectives
This project consists of four objectives: 1) Quantify the impacts of cultural practices on corn rootworms (CRW), including effects of late-season weedy pollen hosts and their implications on CRW fitness, movement and egg laying, and starter fertilizer on corn rootworm survival and injury. 2) Investigate existing and new transgenic corn traits as a management tool in the face of changing CRW resistance to Bt traits, changing species composition and changing economic situation. 3) Explore economic, population and resistance management implications of transgenic traits and their integration with insecticidal and cultural options in IPM decisions. 4) Measure efficacy of biological, synthetic and non-traditional insecticides against key and newly emerging corn insect pests. The overall objective is to generate data and decision tools that will help corn growers improve their management of corn insects, the crop and risk.
Project Methods
Objective 1). On-farm studies in corn-after-corn fields with natural NCR / WCR infestations will examine role of late-season broadleaf weeds as a pollen source. Six treatments reflecting a factorial combination of crop (corn, soybean), with weedy pollen sources (none, water hemp, volunteer corn) will be established in larger plots (18 m x 18 m). Colonization, seasonal activity, and egg laying will be monitored in the establishment year as well as root injury and beetle emergence. Live collections will examine species / sex / mating / pollen utilization composition. Treatments will be repeated the following year with data collected on corn rootworm larval and adult utilization of the plots. Analyses will focus on how the presence or absence of water hemp and volunteer corn change rootworm dynamics and injury. A lab study will examine effects of pollen / food source on beetle longevity, fecundity and egg viability. Cages with 1000 emerged western corn rootworm beetles will be fed 6 diets (corn silks and pollen, corn foliage, common lambsquarter pollen, waterhemp pollen, sunflower pollen, and a mixture of corn / waterhemp pollen). At weekly intervals, survival will be assessed along with sex composition, mating and reproductive status plus a subsample of females will measure fecundity.A split-split plot study with starter fertilizer as the main plot, 3 hybrids (no Bt-RW trait, single trait, pyramid) as a split plot and five different insecticides (none, tefluthrin 3G, tebupirimphos + cyfluthrin 4.67G, bifenthrin LFR, tefluthrin CS) as split-split plots will examine how these factors affect root system biomass, corn rootworm injury, emergence, lodging and yield.Obj. 2. Ongoing on-farm trials will be conducted across central and southern Minnesota in fields with varying histories of corn rootworm infestation. These fields will encompass a range of infestation situations including various crop rotations, species mix, and Bt resistance levels. Performance of pyramided and new traits plus single traits (for interpretive purposes) with and without an insecticide will be compared on the basis of root, lodging, and yield protection as well as efficacy in terms of beetle emergence. Sites with resurging northern corn rootworm populations will be targeted for field performance and bioassay studies to determine if increasing populations might be related to a shift in Bt tolerance. Methods will parallel those used for western corn rootworm with newly developed northern-specific procedures to enhance success.Obj. 3. This objective parallels the Obj. 2 with an emphasis on unusual Bt-performance problem fields. Both on-farm and bioassays studies will document performance issues and their relationship to the complete suite of bioassays. Analyses will focus on trait efficacy and in conjunction with previous data will be used to evaluate IPM strategies in population, resistance, and crop economic perspectives. Adults will be collected to gather eggs for resistance bioassays. If or when northern corn rootworm performance problems surface, a similar approach will be used.Obj. 4. Over the next 5 years, efficacy evaluations are expected in 4 main areas: a) performance of new transgenic corn traits against both corn rootworm species; b) performance of new insecticides or new formulations of existing insecticides against various corn insects in key situations, such as corn rootworms with varying levels of Bt resistance, re-surging European corn borer populations, c) options for neonicotinoids in situations with pollinator concerns, and d) expanding pest problems, such as Japanese beetles and other grubs.

Progress 10/19/16 to 09/30/21

Outputs
Target Audience: Nothing Reported Changes/Problems:Corn rootworm resistance to Bt-RW traits is a dynamic situation reflecting ongoing selection for resistance, changes in farmer behavior towards more aggressive management, and impacts of weather and farming practices on corn rootworm populations and trait performance. Over the 2013-2014 winter, bitterly cold winter temperatures and lack of snow cover translated into spotty but significant mortality of western corn rootworm eggs. Combined with the wettest June on record, saturated soils at hatch further reduced the survival of corn rootworm larvae. This wet spring pattern continued in 2015-2017. The result has been a general, but spotty, reduction in corn rootworm abundance and a corresponding decrease in incidence of reported Bt-RW performance problems. In addition, 2017 was a very forgiving year for corn production, except for mid-season drought in western MN. This situation may lead some growers and ag professionals to incorrectly conclude that Bt resistance issues have subsided and that further resistance management efforts are not needed. In the face of continued lower corn prices, growers are looking for opportunities to reduce input costs but may not be anticipating changing corn rootworm pressure. 2017 brought excellent conditions for egg laying and the effects of an "la Niña" winter could enhance egg survival. However, the frequency of resistance genes has not changed appreciably, and conditions favoring increasing corn rootworm populations could reveal another round of Bt resistance problems even to Bt-RW trait pyramids. Cry3Bb1 resistance, cross-resistance with mCry3A and eCry3.1Ab is firmly documented. The development of resistance to Bt-RW traits and the cross-resistance between 3 of 4 traits threatens the long-term viability of Bt-RW trait pyramids, even the newest products, e.g., SmartStax Pro, build on pyramids of these older traits. Northern corn rootworm populations have been increasing over the last two years and extended diapause issues in non-Bt-RW corn have returned to parts of Minnesota. Our research is shifting to explore the performance of these pyramids and building populations of northern corn rootworm. In particular, is this increase in northern populations related to decreasing susceptibility to Bt-RW proteins? Work on diet and whole-plant bioassays will be needed on this notoriously difficult-to-rear insect. Delayed planting with heavy spring rainfall in previous years coupled with increasing volunteer corn and herbicide-resistance weeds provide late-season pollen sources that are changing the spatial dynamics of corn rootworms. The key management challenge is anticipating Bt-trait performance problems before they occur and generating the research to enable effective management decisions that mitigate current, or avoid future, resistance problems. What opportunities for training and professional development has the project provided? Nothing Reported How have the results been disseminated to communities of interest? Nothing Reported What do you plan to do during the next reporting period to accomplish the goals? Nothing Reported

Impacts
What was accomplished under these goals? This final report is being submitted to terminate this project due to the retirement of the PI.

Publications


    Progress 10/01/19 to 09/30/20

    Outputs
    Target Audience:The target audience for this project includes farmers who grow corn, whether they use transgenic corn technology or not, plus the cadre of agricultural professionals, (extension educators, ag management instructors, agronomists, seed/ag chemical dealers, crop consultants and certified crop advisors) that advise them. In addition, the audience also includes peer research scientists and staff at seed companies, agrichemical companies, and formulators affected by the changes in insect resistance to transgenic corn. Of course, there is a compelling public interest in the technology, its appropriate use, its positive and negative effects in terms of environmental, health, and economic impacts, and the consequences of insect adaptation. Planning and in-service activities involved faculty from other U of MN departments, IPM specialists, regional extension educators, and support staff from Research and Outreach Centers. Changes/Problems:CoVid19 disrupted 2019-2020 research in 4 ways: 1. The University of Minnesota instituted a travel ban that precluded on-farm research (access to Bt-RW resistance sites and resistant WCR / NCR populations). 2. Companies reduced their research investment at least 40% and the Minnesota Corn Research & Promotion Council did not even offer an Request For Proposals. 3. Students attended class remotely so there was limited opportunity to recruit undergraduate research assistants. 4. I came down with CoVid19 and was out during the month of August, our prime time to investigate Bt-RW performance problems, line up potential research sites for 2021, and collect beetles for further documentation of resistance. Corn rootworm resistance to Bt-RW traits is a dynamic situation reflecting ongoing selection for Bt resistance, changes in corn rootworm management, economic impacts on crop budgets, and impact of weather on corn rootworm populations and associated risks to corn production. Previously the combination of winter egg mortality in western corn rootworms and impacts of excessive rainfall on larval survival dramatically reduced corn rootworm populations and inverted the relative abundance of western and northern corn rootworms. Potentially, this inversion may also reflect development of Bt-RW trait resistance in northern corn rootworm. However, lower population levels have obscured the visibility of Bt-RW resistance problems in both WCR and NCR and created the false impression that further resistance management efforts are not needed. That situation, however, is beginning to change. Survival was very good in 2019-2020 and reports of performance issues with Bt-RW pyramids, notably Qrome and SmartStax, increased in 2020. Growers continue to scrutinize their crop budgets and search for opportunities to reduce input costs, such as planting hybrids w/o Bt-RW traits, switching to soil insecticides, or using nothing to manage corn rootworms. However, the frequency of resistance genes has not changed appreciable and conditions favoring increasing corn rootworm populations could reveal another round of Bt resistance problems. Northern corn rootworm populations in ND and MN have documented resistance to Cry3Bb1 and Cry34/35Ab1. Populations in Minnesota have been increasing over the last three years and extended diapause issues within rotated and continuous non- Bt- RW corn have returned to parts of Minnesota. Our research is shifting to explore the performance of Bt-RW pyramids amid building populations of northern corn rootworm. This shift appears justified: root injury and beetle emergence at our site at Litchfield in 2018-2020 demonstrates that Bt-RW resistance has developed in northern corn rootworm and is expressed. We have collected northern corn rootworms to generate eggs for diagnostic bioassays. In northern corn rootworm populations with extended diapause, Bt-RW resistance would put nearly every corn field in MN in potential jeopardy, especially if favorable weather conditions and agronomic conditions (reduced use of Bt corn, reduced use of soil insecticides) favor buildup of rootworm populations. The key management challenge is anticipating Bt-RW trait performance problems before they occur and generating the research to enable management decisions that mitigate current, or avoid future, resistance problems. What opportunities for training and professional development has the project provided?Opportunities for training and professional development for me, my graduate students and my research staff were severely curtailed by CoVid19 restrictions on group gatherings. Academic forums, sponsored by the seed companies (e.g., Corteva, Bayer) were canceled in the Spring and shifted online in the Fall. Similarly, entomology national and regional meetings, e.g., Entomological Society of America, were either canceled or went online. Previously our lab provided extension experiences for graduate students, undergraduate research assistants, and technicians at several in-person events, such as the Ag Professional Field School where they helped organize and teach sessions on Insect identification and a refresher on corn rootworm injury in corn, plus plot tours exploring soil insecticide and Bt-RW trait performance. However, all in-person events were cancelled in 2020. To cover the basics of detecting and diagnosing corn rootworm management issues, we developed a video presentation for an on-line version of the Ag Professional Field School and an in-season joint webinar on corn rootworm management between MN Extension and Iowa State University Extension. How have the results been disseminated to communities of interest?This 2020 corn rootworm research was featured in presentations targeting both farmers and their advisory ag professionals via the Crop & Pest Management Connect (a virtual Extension Short Course), Ag Professional Updates [5 in-person locations - 327 attendees influencing decisions on 9.8 million acres of cropland], Private Pesticide Applicator Training (CRW resistance part of IPM training), extension crop management updates, and industry-sponsored farmer meetings. Virtual training occurred at the Ag Professional Field School. Information on resistance status and the management implications of this research were disseminated via MN Crop News, an on-line blog. What do you plan to do during the next reporting period to accomplish the goals?Obj. 1. Impacts of Cultural Practices. Field research is completed, except the possibility of further research on extended diapause and Bt-RW trait resistance in northern corn rootworms. Obj. 2 Transgenic Traits as a Tool to Manage Corn Rootworms. Studies exploring the comparative performance of new traits and trait pyramids, e.g., SmartStax Pro expressing the RNAi DvSnf7 (mCry3Bb1 + Cry34/35Ab1 + DvSnf7) will continue. Efforts will expand into sites dominated by northern corn rootworm, including sites with 2020 trait performance problems. Development of a web site providing information on corn rootworm scouting, access to publications, photos and "how-to" videos plus on-line entry of scouting data is underway. Techniques developed to detect field resistance with an adapted nodal injury scale (0-3 with 3" pruning criteria) and through adult emergence models will be adapted from Cry3Bb1 and the pyramid Cry3Bb1 + Cry34/35Ab1 will be applied to other Bt-RW traits. Obj. 3. Explore implications of prospective resistance on corn rootworm management. On-farm comparative performance of Bt-traits and soil insecticides will be evaluated under newly developing scenarios as they arise. Specific focus will be on northern corn rootworm and fields with multiple trait problems. We will examine how to combine survey data from ag professionals regarding scouting, user input on yellow sticky traps, and surveys of farmer perceptions regarding risk perceptions into a decision framework that will provide field-specific decisions. Technology will be developed or evaluated to improve scouting of field populations of corn rootworms for field-specific management decisions. Obj. 4, Measure efficacy of insecticides against corn rootworm. Research will continue into soil insecticide performance focusing on liquid insecticides in comparison to granular standards along with new formulations and application technologies, e.g., variable rate application.

    Impacts
    What was accomplished under these goals? Impact: Our research on corn rootworm Bt-RW resistance has: documented WCR Bt-RW resistance to all traits (incl. Cry34/35 Ab1 resistance documentation in Minnesota verified in 2015); confirmed cross-resistance among Cry 3 proteins (including the newest protein eCry3.1Ab 2016-7), revealed NCR Bt-RW resistance to multiple traits in an extended diapause population (2018-2019 near Litchfield MN), and explored the role of soil insecticides in managing corn rootworm populations or managing injury when Bt-RW traits fail. The dilemma: knowing when population pressure is severe enough to warrant crop rotation, a switch in Bt-RW traits, or an overlay of soil insecticide. For that reason, scouting is critical and a primary focus of our evolving research program. A corn rootworm monitoring program using yellow sticky traps was initiated. A revised root injury rating scale (0-3 Nodal Injury Rating using 3" pruning criteria) has shown promise in detecting field resistance. Degree-day models were developed to describe adult emergence under difference Bt-RW traits for susceptible corn rootworm populations. These models can predict scouting windows. Beetle emergence and root injury also reveal potential resistance status of field populations. Bt performance problems have been increasing with WCR in MN against Bt-RW trait pyramids, such as Qrome (mCry3A + Cry34/35Ab1) and SmartStax (Cry3Bb1 + Cry34/35Ab1), and NCR performance problems have appeared with all traits. In addition, a dynamic shift in corn rootworm populations may be underway. Relative population magnitude of western and northern corn rootworms continues to be inverted for the 6th year since Bt resistance appeared in western corn rootworm. Extended diapause issues have returned. Bt-RW resistance was also confirmed with NCR extended diapause populations. This development could be a game changer since rotational resistance and Bt resistance have the potential to place all of MN corn at risk. Obj. 1. Impacts of Cultural Practices. No field research was conducted in 2020. Obj. 2 Transgenic Traits as a Tool to Manage Corn Rootworms. Comparative performance of transgenic traits was evaluated in three trials at the Rosemount Research and Outreach Center, where susceptible corn rootworms predominate. The three studies differed in their treatments. In the first trial, hybrid entries included all available Bt-RW single traits (mCry3A, Cry 34/35 Ab1, Cry3Bb1) and trait pyramids (Cry3Bb1 + Cry34/35Ab1, mCry3A + Cry34/35Ab1, mCry3A + eCry3.1Ab) with corresponding refuge (non-Bt) hybrids plus representative non-Bt-RW and Cry3Bb1 + Cry 34/35Ab1 hybrids with and without a soil insecticide overlay of Aztec 4.67G (tebupirimphos + cyfluthrin). Slight declines in performance of mCry3A and Cry3Bb1 were noticed while Cry34/35 Ab1 and all pyramids performed quite well in the face of extremely heavy pressure, The second trial was simpler, focusing only on the Bt-RW trait pyramids (mCry3A + Cry34/35Ab1, Cry3Bb1 + Cry34/35Ab1, mCry3A + eCry3.1Ab) with and without an overlay of Aztec HC. The final trial examined root protection in the trait pyramid (Cry3Bb1 + Cry34/35Ab1) with the addition of RNAi trait expressing DvSnf7. The RNAi trait (DvSnf7) performed quite well against heavy corn rootworm pressure (ca. 99.9% efficacy) but only marginally improved the pyramid's already exceptional performance against a susceptible WCR population (95-99.9% efficacy). Obj. 3. Explore implications of prospective resistance on corn rootworm management. CoVid19-related restrictions on travel and working remotely on farms precluded all on-farm research in 2020. As a result, we were unable to follow up with on-farm studies on known NCR or WCR resistance sites or visit on-farm fields with Bt-RW performance problems appearing in 2020 to personally document the situation and collect beetles for bioassays or other greenhouse research into resistance.in Work progressed on the challenge of detecting Bt-RW resistance in field populations before catastrophic performance problems develop. Degree-day models for WCR adult emergence were developed for 3 Bt-RW situations (non-Bt-RW hybrids, Bt-RW hybrids expressing only Cry3Bb1, and Bt-RW pyramids expressing Cry3Bb1 + Cry34/35Ab1) in 24 MN fields varying in Bt-RW resistance. Against susceptible populations (n=6), the best-fit model with base temp of 11C and a maximum temp of 18C with degree days accumulating from Jan. 1 explained 71.3% of the variation in emergence. In this situation, the pyramid delayed 50% emergence 13.1 days. As resistance developed this emergence delay diminished; 6.25 days under modest resistance and 5 days under higher resistance levels as revealed by root injury. Even minor increases in resistance, as indicated by root injury, substantially shifted the emergence curve towards the non-Bt-RW curve. Another avenue of detecting field resistance is through declining root protection. Root injury using two different pruning criteria (the standard 1.5" vs. 3") were examined for 4 treatments: unprotected, a soil insecticide (tefluthrin, Force 3G), or Bt-RW traits (Cry3Bb1, Cry3Bb1 + Cry 34/35Ab1) across 31 field situations from 2010 - 2019. Both criteria predicted beetle emergence, lodging and yield loss equally well. The relationship between the two criteria in describing root injury was a tight curve (R2=0.94) with the 3" criteria exhibiting greater sensitivity at lower levels while it saturated more quickly at higher levels of root injury. For example, at the EPA reporting threshold for prospective resistance field (1.0 node of root injury for a single trait on 0-3 scale), the 3' criteria reached 17.8 roots pruned compared to 10 roots on the 1.5" criteria. This greater sensitivity at the lower end of root injury means the 3" criteria could facilitate earlier detection of resistance. When a field hits the EPA reporting threshold, its already producing over 0.55 million beetles to disperse resistance genes, 35% plants lodged, and a 10% yield loss. Quite a hit for the grower and a big head start for dissemination of resistance genes. Earlier detection of resistance would minimize spread of resistant genes while avoiding lodging and yield loss. Obj. 4, Measure efficacy of insecticides against corn rootworm. With the corn price squeeze, farmers are exploring how to reduce reliance on Bt traits. Three soil insecticide studies at Rosemount examined the performance of granular and liquid insecticides, and seed treatments. Results verify that granular formulations generally work better than liquid formulations, which work better than seed treatments. Under the warmer, slightly drier conditions in 2020, the liquid insecticides generally worked better than anticipated and, in some cases, performance approached granular formulations, while seed treatments generally failed under heavier pressure. Newer products investigated included tebupirimphos + cyfluthrin (Aztec HC), imidacloprid (Ampex SC), and chlorethozyfos + bifenthrin (Index SC).

    Publications

    • Type: Journal Articles Status: Accepted Year Published: 2021 Citation: Mishra, S., J. Dee, W. Moar, J. Beattie, J. Baum, N. Dias, A. Alvokhin, A. Buzza, S. Rondon, M. Clough, S. Menasha, R. Groves, J. Clements, K. Ostlie, G. Felton, T. Waters, W. Snyder, S. Stewart and J.L. Jurat-Fuentes. 2021. Selection for highlevels of resistance to topical dsRNA in Colorado potato beetle (Leptinotarsa decimlineata Say). Scientific Reports (accepted for publication).
    • Type: Theses/Dissertations Status: Published Year Published: 2020 Citation: Benkert III, E. 2020. Detecting corn rootworm (Diabrotica spp.) resistance to transgenic Bt-RW traits: Emergence, root injury and species interactions. Ph.D.dissertation. University of Minnesota, Minneapolis, MN. 167 pp.
    • Type: Conference Papers and Presentations Status: Published Year Published: 2019 Citation: Ostlie, K. and Benkert, E.J., III. 2019. Performance of Bayer CRW II and CRW III pyramids against Diabrotica spp. In Prospective Bt-RW Resistance Situations in Minnesota. Poster presented at Annual meeting of the Entomological Society of America, St. Louis, MO, Nov. 20.
    • Type: Conference Papers and Presentations Status: Published Year Published: 2019 Citation: Benkert III, E.J., and K.R. Ostlie. 2019. Inter-specific competition of corn rootworms (Diabrotica spp.) under field conditions. Talk presented at Annual meeting of the Entomological Society of America, St. Louis, MO. Nov. 18.
    • Type: Conference Papers and Presentations Status: Published Year Published: 2019 Citation: Ostlie, K.R. 2019. Bt resistance in corn rootworm: A status report and discussion. Talk presented at Bayer  University of Minnesota Extension Crops Roundtable, St. Paul, MN. Nov. 25.
    • Type: Conference Papers and Presentations Status: Published Year Published: 2020 Citation: Ostlie, K. 2020. An Insect, Insecticide and Trait Research Update: Managing Resistance and Budgets. Research Updates for Agricultural Professionals. Minnesota Extension  Institute for Agricultural Professionals. Rochester, Waseca, Lamberton, Willmar, Morris, and Crookston, MN. Jan. 7-9, 14-16
    • Type: Conference Papers and Presentations Status: Other Year Published: 2020 Citation: Ostlie, K.R. 2020.Threat and challenge of northern corn rootworm resistance to Bt-RW traits. Presentation scheduled for Bayer Corn Insect Academic Summit, St. Louis, MO. Mar. 11. Cancelled by CoVid19 concerns. Presentation sent to participants by conference organizers.
    • Type: Other Status: Published Year Published: 2020 Citation: Ostlie, K. 2020. Essentials of Row Crop Management: Corn Rootworm. A Socially Distant Webinar Series for the Summer of 2020. Jointly hosted by Minnesota Extension and Iowa State University Extension. St. Paul, MN and Ames, IA. July 21. https://youtu.be/zbT_my6mQgY
    • Type: Other Status: Other Year Published: 2020 Citation: Ostlie, K.R. 2020. Corn insect, insecticide, and trait research update: Managing resistance and Crop Budgets. Presented during University of Minnesota Extension Crops Team Call, St. Paul, MN. June 6.
    • Type: Other Status: Published Year Published: 2020 Citation: Ostlie, K.R. 2020. The state of corn rootworm: Population dynamics, resistance and management. Presented during Bayer  University of Minnesota Extension Crop Science Collaboration Zoom Meeting. St. Paul, MN. Nov. 23. PDF sent to participants.
    • Type: Conference Papers and Presentations Status: Published Year Published: 2020 Citation: Ostlie, K. 2020. Insecticides, Transgenic Traits and insect dynamics: An update on the corn insect situation. - Presentation at Crop Pest Management Connect  A virtual event for key crop production decision-makers. Zoom presentation. Minnesota Extension  Institute for Agricultural Professionals. St. Paul, MN. Dec. 8. https://z.umn.edu/cpmconnect


    Progress 10/01/18 to 09/30/19

    Outputs
    Target Audience:The target audience for this project included farmers who grow corn, whether they use transgenic corn technology or not, plus the cadre of agricultural professionals, (extension educators, ag management instructors, agronomists, seed/ag chemical dealers, crop consultants and certified crop advisors) that advise them. In addition, the audience also included peer research scientists and staff at seed companies, agrichemical companies, and formulators affected by the changes in insect resistance to transgenic corn. Of course, there is a compelling public interest in the technology, its appropriate use, its positive and negative effects in terms of environmental, health, and economic impacts, and the consequences of insect adaptation. Planning and in-service activities involved faculty from other U of MN departments, IPM specialists, regional extension educators, and support staff from Research and Outreach Centers. Changes/Problems:Corn rootworm resistance to Bt-RW traits is a dynamic situation reflecting ongoing selection for Bt resistance, changes in corn rootworm management, economic impacts on crop budgets, and impact of weather on corn rootworm populations and associated production risk. Over the last 3 years the combination of winter egg mortality in western corn rootworms and impacts of excessive rainfall on larval survival have dramatically reduced corn rootworm populations and inverted the relative abundance of western and northern corn rootworms. This inversion could also reflect development of Bt-RW trait resistance in northern corn rootworm. However, lower population levels have obscured the visibility of Bt-RW resistance problems and created the false impression that further resistance management efforts are not needed. In the face of continued lower crop prices, export restrictions and reduced corn rootworm populations, growers are looking for opportunities to reduce input costs. However, the frequency of resistance genes has not changed appreciable and conditions favoring increasing corn rootworm populations could reveal another round of Bt resistance problems. The current Bt-RW resistance situation has expanded to include western corn rootworm resistance to Cry34/35B1 in IA. Northern corn rootworm populations in ND have documented resistance to Cry3Bb1 and Cry34/35Ab1. Populations in Minnesota have been increasing over the last three years and extended diapause issues within rotated and continuous non-Bt­ RW corn have returned to parts of Minnesota. Our research is shifting to explore the performance of Bt-RW pyramids amid building populations of northern corn rootworm. This shift appears justified: root injury and beetle emergence at our site at Litchfield in 2018-9 suggests that Bt-RW resistance may have developed in northern corn rootworm. We have collected northern corn rootworms to generate eggs for diagnostic bioassays. In northern corn rootworm populations with extended diapause, Bt-RW resistance would put nearly every corn field in MN in potential jeopardy, especially if favorable weather conditions and agronomic conditions (reduced use of Bt corn, reduced use of soil insecticides) favor buildup of rootworm populations. The key management challenge is anticipating Bt-RW trait performance problems before they occur and generating the research to enable management decisions that mitigate current, or avoid future, resistance problems. What opportunities for training and professional development has the project provided?Opportunities for training and professional development for me, my graduate students and my research staff were provided by academic forums, sponsored by the seed companies (e.g., Corteva, Bayer) and NC246, to discuss the ongoing Bt-RW resistance situation, progress on understanding traits and resistance, and best management responses. These were complemented by attendance at entomology national and regional meetings, e.g., Entomological Society of America, Bayer Corn Insect Academic Summit. Our lab also provided extension experiences for 3 graduate students, 6 undergraduate research assistants, and 2 technicians at several events, such as the Ag Professional Field School, where they helped organize and teach sessions on Insect identification, and a refresher on corn rootworm injury in corn. Situations like these also create educational opportunities to cover the basics of resistance, resistance management, and the role of IPM as it relates to corn insects. The Ag Professional Field School sessions were specifically designed to offer hands-on experience in a corn insect management context. How have the results been disseminated to communities of interest?This corn rootworm research was featured in presentations targeting both farmers and their advisory ag professionals via the Crop Pest Management Short Course [1450 attendees], Ag Professional Updates [5 locations - 327 attendees influencing decisions on 9.8 million acres of cropland], Winter Crops Days, Private Pesticide Applicator Training (CRW resistance part of IPM training), extension crop management updates, and industry-sponsored farmer meetings. Hands-on training occurred at the Ag Professional Field School [99 attendees]. Information on resistance status and the management implications of this research continued to be featured in a variety of farm and public press venues, ranging from Corn and Soybean Digest and Successful Farming, to local farm publications (The Land, AgriNews) and various farm radio stations. What do you plan to do during the next reporting period to accomplish the goals?Obj. 1. Impacts of Cultural Practices. Field research is completed, except the possibility of further research on extended diapause and Bt-RW trait resistance in northern corn rootworms. Obj. 2 Transgenic Traits as a Tool to Manage Corn Rootworms. Studies exploring the comparative performance of new traits and trait pyramids, e.g., SmartStax Pro expressing the RNAi DvSnf7 (mCry3Bb1 + Cry34/35Ab1 + DvSnf7) will continue. Efforts will expand into sites dominated by northern corn rootworm, including the 2018-2019 Litchfield site. Development of a web site providing information on corn rootworm scouting, access to publications, photos and "how-to" videos plus on-line entry of scouting data is underway. Comparative study of scouting data (sticky traps) with root injury, lodging, and yield will emphasize sites with mixed northern and western corn rootworm populations to re-evaluate various yellow sticky traps. Follow-up research from 2019 scouting will explore the relationship of beetle captures to corn rootworm injury and Bt-RW trait I soil insecticide performance and the role of soil texture. My graduate student is exploring northern and western competitive interactions under field conditions and impacts of Bt resistance levels on root injury and survivor emergence. Obj. 3. Explore implications of prospective resistance on corn rootworm management. On-farm comparative performance of Bt-traits and soil insecticides will be evaluated under newly developing scenarios as they arise. Specific focus will be on northern corn rootworm and fields with multiple trait problems. The northern corn rootworm population at the 2019 Litchfield site will be evaluated in Bt-RW bioassays to determine its resistance profile. We will examine how to combine survey data from ag professionals regarding scouting, user input on yellow sticky traps, and surveys of farmer perceptions regarding risk perceptions into a decision framework that will provide field-specific decisions. Technology will be developed or evaluated to improve scouting of field populations of corn rootworms for field-specific management decisions. Obj. 4, Measure efficacy of insecticides against corn rootworm. Research will continue into soil insecticide performance focusing on liquid insecticides in comparison to granular standards along with new formulations and application technologies, e.g., variable rate application.

    Impacts
    What was accomplished under these goals? Impact: As a result of research characterizing Bt resistance in MN and exploring management options, farmer practices continue to shift. 2013 surveys of ag professionals previously indicated ca. 12% of continuous corn acreage had suspected corn rootworm resistance problems. Educational efforts by Minnesota Extension and advisory ag professionals since this problem "blew up" in 2012 have led to changes in grower management. In contrast, only about 1.4% of corn acreage experienced a Bt performance issue in 2018, a 82% reduction since 2013. Asked about their clients' plans for 2019, 155 ag professionals opined that their growers typically invested about $37 per acre in corn rootworm management. Since 2013, over 43% of growers changed their corn rootworm management in response to Bt resistance and reduced corn market prices, primarily through increased crop rotation, decreased Bt trait use, and reduced soil insecticide use. For example, in corn after corn, crop rotation increased from 33 to 58% (2017) before dropping to 35% (2018), use of Bt corn in rotated fields dropped from 76% to 53%, and soil insecticide use dropped from 40 to 21%. Interestingly, before the advent of Bt corn, soil insecticides were used on less than 10% of the corn acreage. Despite claims of the potential for Bt corn to reduce soil insecticide use, it's ironic that Bt resistance has actually increased soil insecticide use. In the face of uncertainty about corn rootworm populations and economic risk, over 34% were planning to scout fields for corn rootworms. Our research on corn rootworm Bt-RW resistance has documented: Bt-RW resistance to all traits (Cry34/35 Ab1 resistance documentation in Minnesota was verified in 2015); confirmed cross-resistance among Cry 3 proteins (including the newest protein eCry3.1Ab 2016-7), and explored the role of soil insecticides in managing corn rootworm populations or managing injury when Bt-RW traits fail. The dilemma: knowing when population pressure is severe enough to warrant crop rotation, a switch in Bt-RW traits, or an overlay of soil insecticide. For that reason, scouting is critical and a primary focus of our evolving research program. In addition, a dynamic shift in corn rootworm populations may be underway. Relative population magnitude of western and northern corn rootworms continues to be inverted for the 5th year since Bt resistance appeared in western corn rootworm. Extended diapause issues have returned. While Bt resistance has not been confirmed yet, Bt performance problems have appeared with all available commercial traits against one northern corn rootworm population near Litchfield MN in 2018 and this problem persisted in the extended diapause portion of this population in 2019. This development could be a game changer since rotational resistance and Bt resistance have the potential to place all of MN corn at risk. Obj. 1. Impacts of Cultural Practices. No field research was conducted in 2019 except evaluation of Bt-RW resistance in the extended diapause portion of the northern corn rootworm population near Litchfield, MN as discussed above. Obj. 2 Transgenic Traits as a Tool to Manage Corn Rootworms. Comparative performance of transgenic traits, singly and as pyramids, was evaluated at three sites: 1. Rosemount Research and Outreach Center, where susceptible corn rootworms predominate; 2. On-farm study near Lake Benton, where continuous use of Cry3Bb1 enhanced Bt-RW resistance in western corn rootworm; 3. On-farm study near Litchfield MN where long-term use of Cry3Bb1 + Cry34/35Ab1 favored apparent Bt-RW resistance in northern corn rootworm. Hybrid entries featured all available Bt-RW single traits (mCry3A, Cry 34/35 Ab1, Cry3Bb1) and trait pyramids (mCry3A + Cry34/35Ab1, Cry3Bb1 + Cry34/35Ab1, mCry3A + eCry3.1Ab) with corresponding refuge (non-Bt) hybrids plus representative non-Bt-RW and Cry3Bb1 + Cry 34/35Ab1 hybrids with and without a soil insecticide overlay of Aztec 4.67G (tebupirimphos + cyfluthrin). Extremely cold winter weather at Lake Benton seems to have reduced egg survival in western corn rootworm while excessive rainfall during hatch and larval feeding reduced both western and northern corn rootworm populations at Lake Benton, Litchfield and Rosemount. Under wet conditions at the Bt-RW resistance site (Litchfield MN), the granular insecticide provided root protection exceeding the Bt-RW traits. Follow-up 2019 research at this Bt-resistance site at Litchfield confirmed this population of extended-diapause northern corn rootworm caused unexpected root injury to Bt traits and their pyramids. Research in 2017-2019 also examined performance of RNAi technology expressing DvSnf7. The RNAi trait (DvSnf7) functioned achieving 98-99% control against both western and northern corn rootworm populations in prospective Bt-RW resistance situations. Obj. 3. Explore implications of prospective resistance on corn rootworm management. On-farm comparative performance of Bt traits was evaluated in two prospective Bt-RW resistance sites in 2019 (Litchfield, Lake Banton) plus the Bt-RW susceptible population at Rosemount. Excessive rainfall reduced corn rootworm pressure at all sites. Unlike most suspected Bt-RW resistance fields, the Litchfield site featured a long history (approx. 10 years) of Cry3Bb1 + Cry 34/35Ab1 selection (as opposed to Cry3Bb1 alone).that compromised performance of Cry34/35Ab1 alone or in pyramids. Meanwhile, cross-resistance was evident among Cry3 proteins, including mCry3A and its pyramid with eCry3.1Ab. Root injury in corn after soybeans revealed a similar root injury pattern among traits in 2019 comparable to patter observed in continuous corn in 2018. Bt-RW resistance in extended diapause populations indicate northern corn rootworm resistance could threaten nearly all corn production in Minnesota. Research is exploring the outcome of western and northern corn rootworms larval competition under field conditions and how resistance ratio (% of Bt-resistance western corn rootworms) affects root injury and beetle emergence. Preliminary data from 2017-19 studies with known mixed population of northern and western corn rootworm suggests that interspecific competition favors western corn rootworm, even in mixes with only 25% western corn rootworm. Root injury reveals that western corn rootworm root injury occurs closer to the base of the corn plant, while northern corn rootworms generally feed further out. Western corn rootworms injured roots more severely than comparable proportions of northern corn rootworms. Adult emergence data reveal increased survival of western corn rootworms at all proportions of northern corn rootworms. Root injury in Bt corn from did not increase until more than 10% of the population is resistant to the Bt-RW trait, Cry3Bb1. Obj. 4, Measure efficacy of insecticides against corn rootworm. With the corn price squeeze, farmers are exploring how to reduce reliance on Bt traits in favor of seed treatments alone or soil insecticides. Six soil insecticide studies were initiated at Rosemount and three studies on-farm at Lake Benton to examine the performance of granular and liquid insecticides, and seed treatments. Results verify that granular formulations generally work better than liquid formulations, which work better than seed treatments. Under the mild, challenging wet conditions in 2019, the liquid insecticides generally worked better than anticipated and, in some cases, approached performance of granular formulations, while seed treatments generally failed under heavier pressure.

    Publications

    • Type: Conference Papers and Presentations Status: Published Year Published: 2018 Citation: Benkert, E.J., III, and K. Ostlie. 2018. Corn rootworm (Diabrotica spp.) nodal injury and yield loss: Early indications of resistance development to Bt-RW traits. Annual meeting of the Entomological Society of America, Vancouver, BC, Nov.
    • Type: Conference Papers and Presentations Status: Published Year Published: 2019 Citation: Benkert III, E.J., and K.R. Ostlie. 2019.Greater-than-expected injury to Bt-RW corn observed in a Minnesota population of northern corn rootworm (Diabrotica barberi Smith and Lawrence). Talk presented at Annual meeting of the North Central Branch of the Entomological Society of America, Cleveland, OH. March
    • Type: Conference Papers and Presentations Status: Published Year Published: 2019 Citation: Foster, BM, M Majeski, EJ Benkert III, and KR Ostlie. 2019. Comparative effects of cage type on adult corn rootworm (Diabrotica spp.) emergence. Poster presented at Annual meeting of the North Central Branch of the Entomological Society of America, Cleveland, OH. March
    • Type: Conference Papers and Presentations Status: Published Year Published: 2019 Citation: Benkert III, E.J., and K.R. Ostlie. 2019. Interspecific competition of corn rootworms (Diabrotica spp.) under field conditions. Talk presented at Annual meeting of the Entomological Society of America, St. Louis, MO, Nov. 18.
    • Type: Conference Papers and Presentations Status: Published Year Published: 2019 Citation: Ostlie, KR and EJ Benkert III. 2019. Performance of Bayer CRWII and III pyramids against Diabrotica spp. In prospective BT-RW resistance situations. Poster presented at Annual meeting of the Entomological Society of America, St. Louis, MO, Nov. 20.
    • Type: Conference Papers and Presentations Status: Published Year Published: 2019 Citation: Ostlie, K. E. Benkert III. 2019. European corn borer and export certification. Invited presentation at Feed Grain Association annual meeting. Willmar, MN. Jan. 21.
    • Type: Conference Papers and Presentations Status: Published Year Published: 2019 Citation: Ostlie, K. and E. Benkert III. 2019. Can we coast on corn insect management in 2019? Research Updates for Agricultural Professionals. Minnesota Extension  Institute for Agricultural Professionals. Rochester, Waseca, Lamberton, Willmar, Morris, and Crookston, MN. Jan. 8-10, 15-17.
    • Type: Conference Papers and Presentations Status: Published Year Published: 2019 Citation: Ostlie, K.R. 2019. Changing northern corn rootworm situation in Minnesota: Status, Bt-RW performance and its management implications. Presentation at Bayer Corn Insect Academic Summit, St. Louis, MO. Feb. 21.
    • Type: Conference Papers and Presentations Status: Published Year Published: 2019 Citation: Koch, R., and Ostlie, K. 2019. Know your enemies and allies: Insect identification in field crops. Presentation and hands-on workshop. Field School for Ag Professionals, St. Paul Campus, University of MN, St. Paul, July 30.
    • Type: Conference Papers and Presentations Status: Published Year Published: 2019 Citation: Ostlie, K.R. 2019. Corn rootworm management updates for 2019. Presentation and field demonstration at 2019 Field School for Ag Professionals. University of Minnesota, St. Paul, MN. July 31.
    • Type: Other Status: Published Year Published: 2019 Citation: Ostlie, KR, EJ Bankert III, HV Vieira, M. Majesk. 2019. Research perspectives: Insect pest management in corn. Lecture in Special Topics in Entomology  Ent 5920. University of Minnesota Entomology, St. Paul, MN Dec. 12.
    • Type: Conference Papers and Presentations Status: Published Year Published: 2019 Citation: Benkert III, EJ. 2019. Evaluating corn rootworm resistance to Bt traits in Minnesota. Invited Talk at 2019 University of Minnesota Production Agriculture Symposium. St. Paul. Mar.
    • Type: Conference Papers and Presentations Status: Published Year Published: 2019 Citation: Ostlie, K. 2018. Adventures with insect management: 2018 insights - 2019 outlook. Presentation at Crop Pest Management Short Course and Minnesota Ag Retail Association Trade Show. Minneapolis, MN. Dec. 12.
    • Type: Other Status: Published Year Published: 2018 Citation: Ostlie, K, D. Nicolai and W. Hutchison. 2018. Update on recent corn rootworm activity and Bt resistance trends in Minnesota. Minnesota Crop News: An IPM Podcast for Field Crops. https://blog-crop-news.extension.umn.edu/2018/06/ipm-podcast-update-on-recent-corn.html. Minnesota Extension  IPM Program, St. Paul, MN. June 7.


    Progress 10/01/17 to 09/30/18

    Outputs
    Target Audience:The target audience for this project included farmers who grow corn, whether they use transgenic corn technology or not, plus the cadre of agricultural professionals, (extension educators, ag management instructors, agronomists, seed/ag chemical dealers, crop consultants) that advise them. In addition, the audience also included peer research scientists and staff at seed companies, agrichemical companies and formulators affected by the changes in insect resistance to transgenic corn. Of course, there is a compelling public interest in the technology, its appropriate use, its effects, and the consequences of insect adaptation. Planning and in-service activities involved faculty from other U of MN departments, IPM specialists, regional extension educators, and support staff from Research and Outreach Centers. Changes/Problems:Corn rootworm resistance to Bt-RW traits is a dynamic situation reflecting ongoing selection for resistance, changes in farmer behavior towards more aggressive management, and impacts of weather and farming practices on corn rootworm populations and trait performance. Over the 2017-2018 winter, bitterly cold winter temperatures and lack of snow cover translated into significant but spotty mortality of western corn rootworm eggs. Combined with saturated soils after hatch began (late June, early July) further reduced the survival of corn rootworm larvae. The result has been a general reduction in corn rootworm abundance and a corresponding decrease in incidence of reported Bt-RW performance problems. In addition, 2018 was a very forgiving year for corn production. This situation may lead some growers and ag professionals to incorrectly conclude that Bt resistance issues have subsided and that further resistance management efforts are not needed. In the face of continued lower crop prices, export restrictions, and reduced corn rootworm populations, growers are looking for opportunities to reduce input costs. However, the frequency of resistance genes has not changed appreciably, and conditions favoring increasing corn rootworm populations could reveal another round of Bt resistance problems. The current Bt-RW resistance situation has expanded to include western corn rootworm resistance to Cry34/35B1 in IA. Northern corn rootworm populations have been increasing over the last three years and extended diapause issues in non-Bt-RW corn have returned to parts of Minnesota. Our research is shifting to explore the performance of these pyramids and building populations of northern corn rootworm. This shift appears justified: root injury and beetle emergence at our site at Litchfield in 2018 suggests that Bt-RW resistance may have developed in northern corn rootworm. Certainly this situation needs to be explored with bioassays. If Bt-RW resistance in northern corn rootworm combines with extended diapause trait, these combined traits would put nearly every corn field in MN in potential jeopardy, especially if favorable weather conditions and agronomic conditions (reduced use of Bt corn, reduced use of soil insecticides) that favor buildup of rootworm populations return. The key management challenge is anticipating Bt-trait performance problems before they occur and generating the research to enable management decisions that mitigate current, or avoid future, resistance problems. What opportunities for training and professional development has the project provided?Opportunities for training and professional development for me, my graduate students and my research staff were provided by academic forums, sponsored by the seed companies (Pioneer, Monsanto) and NC246, to discuss the ongoing Bt-RW resistance situation, progress on understanding traits and resistance, and best management responses. These were complemented by attendance at entomology national and regional meetings, the Commodity Classic and Corn Insect Academic Summit. Our lab also provided extension experiences for 3 graduate students and 6 undergraduate research assistants, and 1 MAST International Program student from Brazil and 2 technicians at several events, such as the Ag Professional Field School, where they helped organize and teach sessions on Insect identification, and a refresher on caterpillar pests of corn. Situations like these also create educational opportunities to cover the basics of resistance, resistance management, and the role of IPM as it relates to corn insects. The Ag Professional Field School sessions were specifically designed to offer hands-on experience in a corn insect management context. How have the results been disseminated to communities of interest?This corn rootworm research was featured in presentations targeting both farmers and their advisory ag professionals via the Crop Pest Management Short Course [1450 attendees], Ag Professional Updates [5 locations - 327 attendees influencing decisions on 9.8 million acres of cropland], Winter Crops Days, Private Pesticide Applicator Training (CRW resistance part of IPM training), extension crop management updates, and industry-sponsored farmer meetings. Hands-on training occurred at the Ag Professional Field School [99 attendees]. Information on resistance status and the management implications of this research continued to be featured in a variety of farm and public press venues, ranging from Corn and Soybean Digest and Successful Farming, to local farm publications (The Land, AgriNews) and various farm radio stations. I was asked to present at a media event on Sicence Behind Insect Control held at the 2018 Commodity Classic and a poster for the MN Corn Growers Association . What do you plan to do during the next reporting period to accomplish the goals?Obj. 1. Impacts of Cultural Practices. Field research is completed. Obj. 2 Transgenic Traits as a Tool to Manage Corn Rootworms. Studies exploring the comparative performance of new traits and trait pyramids, e.g., SmartStax Plus expressing the RNAi DvSnf7 (mCry3A + e.Cry3.1) will continue. Efforts will expand into sites dominated by northern corn rootworm, including the 2018 Litchfield site. Development of a web site providing information on corn rootworm scouting, access to publications, photos and "how-to" videos plus on-line entry of scouting data is underway. Comparative study of scouting data (sticky traps) with root injury, lodging and yield will emphasize sites with mixed northern and western corn rootworm populations to re-evaluate various yellow sticky traps. Follow-up research from 2018 scouting will explore the relationship of beetle captures to corn rootworm injury and Bt-RW trait / soil insecticide performance and the role of soil texture. My graduate student is exploring northern and western competitive interactions under field conditions and impacts of Bt resistance levels on root injury and survivor emergence. Obj. 3. Explore implications of prospective resistance on corn rootworm management. On-farm comparative performance of Bt-traits and soil insecticides will be evaluated under newly developing scenarios as they arise. Specific focus will be on northern corn rootworm and fields with multiple trait problems. The northern corn rootworm population at the 2018 Litchfield site will be sampled to generate eggs for bioassays to determine its resistance profile. We will examine how to combine survey data from ag professionals regarding scouting, user input on yellow sticky traps, and surveys of farmer perceptions regarding risk perceptions into a decision framework that will provide field-specific decisions. Technology will be developed or evaluated to improve assessing field populations of corn rootworms for field-specific management decisions. Obj. 4, Measure efficacy of insecticides against corn rootworm. Research will continue into soil insecticide performance focusing on liquid insecticides in comparison to granular standards.

    Impacts
    What was accomplished under these goals? Impact: As a result of research characterizing Bt resistance in MN and exploring management options, farmer practices continue to shift. 2013 surveys of ag professionals previously indicated ca. 12% of continuous corn acreage had suspected corn rootworm resistance problems. Educational efforts since this problem "blew up" in 2012 by Minnesota Extension and advisory ag professionals have led to changes in grower management. In contrast, only about 4.5% of corn acreage experienced a Bt performance issue in 2018, a 63% reduction since 2013. Asked about their clients' plans for 2018, 155 ag professionals opined that their growers typically invested about $31 per acre in corn rootworm management. Since 2013, over 43% of growers changed their corn rootworm management in response to Bt resistance and reduced corn market prices, primarily through increased crop rotation, decreased Bt trait use, and reduced soil insecticide use. For example, in corn after corn, crop rotation increased from 33 to 58%, use of Bt corn in rotated fields dropped from 76% to 56%, and soil insecticide use dropped from 40 to 21%. Interestingly, before the advent of Bt corn, soil insecticides were used on less than 10% of the corn acreage. Despite claims of the potential for Bt corn to reduce soil insecticide use, it's ironic that Bt resistance has actually increased soil insecticide use. In the face of uncertainty about corn rootworm populations and economic risk, over 27% were planning to scout fields for corn rootworms. Our research on resistance has documented: Bt-RW resistance to all traits (Cry34/35 Ab1 resistance documentation in Minnesota was verified in 2015); confirmed cross-resistance among Cry 3 proteins, (including the newest protein eCry3.1Ab 2016-7), and explored the role of soil insecticides in managing corn rootworm populations or managing injury when Bt-RW traits fail. The dilemma: knowing when population pressure is severe enough to warrant crop rotation, a switch in Bt-RW traits, or an overlay of soil insecticide. For that reason, scouting is critical and a primary focus of our evolving research program. In addition, a dynamic shift in corn rootworm populations may be underway. Relative population magnitude of western and northern corn rootworms have inverted for the first time since Bt resistance appeared in western corn rootworm. Extended diapause issues have returned. While Bt resistance has not been confirmed yet, Bt performance problems have appeared with all available commercial traits with one northern corn rootworm population near Litchfield MN, This development could be a game changer since rotational resistance and Bt resistance have the potential to place all of MN corn at risk. Obj. 1. Impacts of Cultural Practices. No field research was conducted in 2018. Obj. 2 Transgenic Traits as a Tool to Manage Corn Rootworms. Comparative performance of transgenic traits, singly and as pyramids, was evaluated at Rosemount, where previous bioassays indicated susceptible corn rootworms predominate, and three on-farm sites (Litchfield, Hancock, Springfield) with Cry3Bb1 performance problems. Hybrid entries featured all available Bt-RW single traits (mCry3A, Cry 34/35 Ab1, Cry3Bb1) and trait pyramids (mCry3A + Cry34/35 Ab1, Cry3Bb1 + Cry34/35 Ab1, mCry3A + eCry3.1Ab) with corresponding refuge (non-Bt) hybrids plus representative non-Bt-RW and Cry3Bb1 + Cry 34/35Ab1 hybrids with and without a soil insecticide overlay of Aztec 4.67G (tebupirimphos + cyfluthrin). Excessive rainfall during hatch and larval feeding reduced both western and northern corn rootworm populations at Hancock and Springfield with less mortality at Litchfield and Rosemount. Results generally confirmed soil insecticide overlays do not provide consistent yield benefit over the trait(s) alone when they work but rarely provided a benefit when traits fail. Soil insecticides only provided minimal added efficacy (40-60% in drier years) and are unlikely to aid in resistance management. A unique and previously unreported situation occurred at Litchfield where a population of northern corn rootworm caused substantial root injury in all Bt traits and their pyramids. Research in 2017 and 2018 also examininged performance of RNAi technology expressing DvSnf7. The RNAi trait (DvSnf7) functioned well in both prospective Bt-RW resistance situations, achieving 98-99% control. Obj. 3. Explore implications of prospective resistance on corn rootworm management. On-farm comparative performance of Bt traits was evaluated in three prospective Bt-RW resistance sites in 2018 (Litchfield, Hancock, Springfield). Western corn rootworm eggs apparently suffered significant winter mortality with cold air temps, little snow cover and deep frost penetration at the two northern sites (Hancock, Litchfield). Excessive rainfall compromised corn rootworm pressure at all sites with only Litchfield population producing significant root injury (NIR >2.5). Unlike most suspected Bt-RW resistance fields, this field had a long history (approx. 10 years) of Cry3Bb1 + Cry 34/35Ab1 selection (as opposed to Cry3Bb1 alone). The added selection pressure over time resulted in poor performance of Cry34/35Ab1 alone or in pyramids. Meanwhile, cross-resistance was evident. Ironically, root protection with the single trait mCry3A and it's pyramid with eCry3.1Ab, which have never been used at this site, was dismal. This Litchfield site could provide the first evidence of Bt-RW resistance in northern corn rootworm. Research is underway to determine the outcome of western and northern corn rootworms larval competition under field conditions and to explore how resistance ratio (% of Bt-resistance western corn rootworms) affects root injury and beetle emergence. Obj. 4, Measure efficacy of insecticides against corn rootworm. With the corn price squeeze, farmers have reduced reliance on Bt traits in favor of seed treatments alone or soil insecticides, whic has increased their interst in insecticide performance. Eight soil insecticide studies were initiated at Rosemount and two on-farm at Hancock to examine the performance of granular and liquid insecticides, and seed treatments. Results verify that granular formulations generally work better than liquid formulations, which work better than seed treatments. Under the mild, moist conditions in 2018, the liquid insecticides generally worked better than anticipated and,in some cases, approached performance of granular formulations, while seed treatments generally failed under heavier pressure.

    Publications

    • Type: Conference Papers and Presentations Status: Published Year Published: 2018 Citation: Ostlie, K. 2018. Developments in insect issues and management in corn and soybeans. Presentation at Ag Professional Updates. MN Extension - Institute for Ag Professionals. Willmar, MN. Jan.
    • Type: Theses/Dissertations Status: Published Year Published: 2018 Citation: Ludwick, D.C. 2018. Partial characterization of Bt resistance and the bacteriome of western corn rootworm. Ph.D. dissertation. University of Missouri, Columbia, MO. 135 pp.
    • Type: Conference Papers and Presentations Status: Published Year Published: 2018 Citation: Ostlie, K. 2018. Research into managing dynamic corn insect issues for Minnesota growers. Poster displayed at Minnesota Corn Growers Association Meeting. Falcon Heights, MN. Aug. 27.
    • Type: Conference Papers and Presentations Status: Published Year Published: 2018 Citation: Ostlie, K. 2018. Adventures with insect management: 2018 insights - 2019 outlook. Presentation at Crop Pest Management Short Course and Minnesota Ag Retail Association Trade Show. Minneapolis, MN. Dec. 12.
    • Type: Journal Articles Status: Published Year Published: 2017 Citation: Leaf, T., K. Ostlie and D. Kaiser. 2017. Transgenic corn response to nitrogen rates under corn rootworm pressure. Agron. J. 109(4):1632-1641.
    • Type: Conference Papers and Presentations Status: Published Year Published: 2018 Citation: Benkert, E.J., III, and K. Ostlie. 2018. Corn rootworm (Diabrotica spp.) nodal injury and yield loss: Early indications of resistance development to Bt-RW traits. Annual meeting of the Entomological Society of America, Vancouver, BC, Nov.
    • Type: Conference Papers and Presentations Status: Published Year Published: 2018 Citation: Benkert III, E.J., and K.R. Ostlie. 2018. Evaluating nodal injury caused by corn rootworm (Diabrotica spp.) undergoing resistance development to Bt-RW traits. Annual meeting of the North Central Branch of the Entomological Society of America, Madison, WI, March.
    • Type: Conference Papers and Presentations Status: Published Year Published: 2017 Citation: Benkert III, E.J., and K.R. Ostlie. 2017. Detecting corn rootworm (Diabrotica spp.) resistance development to Bt-RW traits: Root injury vs. lodging and yield. Annual meeting of the Entomological Society of America, Denver, CO, November.
    • Type: Conference Papers and Presentations Status: Published Year Published: 2018 Citation: Ostlie, K.R. 2018. Caterpillars in corn: Refresher on pests, Bt and resistance. Presentation at 2018 Field School for Ag Professionals. University of Minnesota, St. Paul, MN. July 26.
    • Type: Conference Papers and Presentations Status: Published Year Published: 2018 Citation: Koch, R., and Ostlie, K. 2018. Identification of insects and the injury they cause in field crops. Presentation and hand-on workshop. Field School for Ag Professionals, St. Paul Campus, University of MN, St. Paul, July 25.
    • Type: Conference Papers and Presentations Status: Published Year Published: 2018 Citation: Ostlie, K., R. Koch, B. Potter and I. MacRae. 2018. Challenges of soybean aphid management. Presentation and Panel Discussion in Science Behind Insect Control. Commodity Classic. Anaheim, CA. Feb. 26
    • Type: Conference Papers and Presentations Status: Published Year Published: 2018 Citation: Ostlie, K.R. 2018. Post-resistance corn rootworm management in MN 2018. Presentation at Corn Insect Academic Summitt, Monsanto, St. Louis, MO. Feb. 21.


    Progress 10/19/16 to 09/30/17

    Outputs
    Target Audience:The target audience for this project includes farmers who grow corn, whether they use transgenic corn technology or not, plus the cadre of agricultural professionals, such as extension educators, ag management instructors, agronomists, seed/ag chemical dealers, and crop consultants, that advise them. In addition, the audience also included peer research scientists and staff at seed companies, agrichemical companies and formulators affected by the changes in insect resistance to transgenic corn. Of course, there is a compelling public interest in the technology, its appropriate use, its effects, and the consequences of insect adaptation. Planning and in-service activities involved faculty from other U of MN departments, IPM specialists, regional extension educators, and support staff from Research and Outreach Centers. Changes/Problems:Corn rootworm resistance to Bt-RW traits is a dynamic situation reflecting ongoing selection for resistance, changes in farmer behavior towards more aggressive management, and impacts of weather and farming practices on corn rootworm populations and trait performance. Over the 2013-2014 winter, bitterly cold winter temperatures and lack of snow cover translated into spotty but significant mortality of western corn rootworm eggs. Combined with the wettest June on record, saturated soils at hatch further reduced the survival of corn rootworm larvae. This wet spring pattern continued in 2015-2017. The result has been a general, but spotty, reduction in corn rootworm abundance and a corresponding decrease in incidence of reported Bt-RW performance problems. In addition, 2017 was a very forgiving year for corn production, except for mid-season drought in western MN. This situation may lead some growers and ag professionals to incorrectly conclude that Bt resistance issues have subsided and that further resistance management efforts are not needed. In the face of continued lower corn prices, growers are looking for opportunities to reduce input costs but may not be anticipating changing corn rootworm pressure. 2017 brought excellent conditions for egg laying and the effects of a "la Niña" winter could enhance egg survival. However, the frequency of resistance genes has not changed appreciably, and conditions favoring increasing corn rootworm populations could reveal another round of Bt resistance problems even to Bt-RW trait pyramids. Cry3Bb1 resistance, cross-resistance with mCry3A and eCry3.1Ab is firmly documented. The development of resistance to Bt-RW traits and the cross-resistance between 3 of 4 traits threatens the long-term viability of Bt-RW trait pyramids, and even the newest products, e.g., SmartStax Pro, build on pyramids of these older traits. Northern corn rootworm populations have been increasing over the last two years and extended diapause issues in non-Bt-RW corn have returned to parts of Minnesota. Our research is shifting to explore the performance of these pyramids and building populations of northern corn rootworm. In particular, is this increase in northern populations related to decreasing susceptibility to Bt-RW proteins? Work on diet and whole-plant bioassays will be needed on this notoriously difficult-to-rear insect. Delayed planting with heavy spring rainfall in previous years coupled with increasing volunteer corn and herbicide-resistance weeds provide late-season pollen sources that are changing the spatial dynamics of corn rootworms. The key management challenge is anticipating Bt-trait performance problems before they occur and generating the research to enable effective management decisions that mitigate current, or avoid future, resistance problems. What opportunities for training and professional development has the project provided?Opportunities for training and professional development for me, my graduate students and my research staff were provided by academic forums, sponsored by the seed companies (Pioneer, Monsanto, and Syngenta) and NC246, to discuss the ongoing Bt-RW resistance situation, progress on understanding traits and resistance, and best management responses. These were complemented by attendance at entomology national and international meetings where my lab gave 4 oral presentations and 1 poster presentation. Our lab also provided extension experiences for 3 graduate students and 6 undergraduate research assistants, and 1 technician, such as the Ag Professional Field School, where they helped organize and teach sessions on Insect identification, and re-acquaintance with European corn borer. Situations like these also create educational opportunities to cover the basics of resistance, resistance management, and the role of IPM as it relates to corn insects. These dimensions have been a standard part of my extension and research presentations to farmers and ag professionals. In addition, the confluence of resistance issues in weed, disease, and insect management create opportunities to discuss similarities and differences in resistance management concepts across disciplines. The majority of the extension activities outlined in the next section have been offered as continuing educations credits for certified crop advisors. The corn rootworm workshop and the Ag Professional Field School were specifically designed to offer hands-on experience in a corn insect management context. How have the results been disseminated to communities of interest?This corn rootworm research was featured in presentations targeting both farmers and their advisory ag professionals via the Crop Pest Management Short Course [628 attendees], Ag Professional Updates [5 locations - 340 attendees influencing decisions on 2.8 million acres of cropland], Winter Crops Days, Private Pesticide Applicator Training (CRW resistance part of IPM training), extension crop management updates, and industry-sponsored farmer meetings. Hands-on training occurred at the Ag Professional Field School [115 attendees - session with greatest improvement in learning scores]. A special Corn Rootworm Scouting Workshop (35 attendees) was held as part of a field day at the Rosemount Research and Outreach Center. Information on resistance status and the management implications of this research continued to be featured in a variety of farm and public press venues, ranging from Corn and Soybean Digest and Successful Farming, to local farm publications (The Land, AgriNews) and various farm radio stations. What do you plan to do during the next reporting period to accomplish the goals?Obj. 1. Impacts of Cultural Practices. Field research is completed. Efforts will focus on incorporating planting date effects into CRW emergence models. Obj. 2 Transgenic Traits as a Tool to Manage Corn Rootworms. Studies exploring the comparative performance of new Bt-RW traits pyramids, e.g., Duracade (mCry3A + e.Cry3.1) will continue. Efforts will expand into sites dominated by northern corn rootworm, including extended diapause situations, to determine their susceptibility to pyramided traits (previous research focused on single traits). Modeling efforts to predict adult emergence will expand beyond 2 pilot studies into the historical database of studies conducted from 2009-2015. Development of web site providing information on corn rootworm scouting, access to publications, photos and "how-to" videos plus on-line entry of scouting data is underway. Comparative study of scouting data (sticky traps) with root injury, lodging and yield will emphasize sites with mixed northern and western corn rootworm populations to re-evaluate various yellow sticky traps. Follow-up research from 2017 scouting will explore the relationship of beetle captures to corn rootworm injury and Bt-RW trait / soil insecticide performance and the role of soil texture. Obj. 3. Explore implications of prospective resistance on corn rootworm management. On-farm comparative performance of Bt-traits and soil insecticides will be evaluated under newly developing scenarios as they arise. Specific focus will be on northern corn rootworm and fields with multiple trait problems. Preliminary bioassays work has identified a western corn rootworm population resistant to Cry34/35 Ab1. We will examine how to combine survey data from ag professionals regarding scouting, user input on yellow sticky traps, and surveys of farmer perceptions regarding risk perceptions into a decision framework that will provide field-specific decisions. Obj. 4, Measure efficacy of insecticides against corn rootworm. Research will continue into soil insecticide performance focusing on liquid insecticides in comparison to granular standards.

    Impacts
    What was accomplished under these goals? Impact: As a result of research characterizing Bt resistance in MN and exploring management options, farmer practices continue to shift. 2013 surveys of ag professionals previously indicated ca. 12% of continuous corn acreage had suspected corn rootworm resistance problems. Educational efforts since this problem "blew up" in 2012 by Minnesota Extension and advisory ag professionals have led to changes in grower management. In contrast, only about 4.5% of corn acreage experienced a Bt performance issue in 2016, a 63% reduction since 2013. Asked about their clients' plans for 2017, 155 ag professionals opined that their growers typically invested about $31 per acre in corn rootworm management. Since 2013, over 43% of growers changed their corn rootworm management in response to Bt resistance and reduced corn market prices, primarily through increased crop rotation, decreased Bt trait use, and reduced soil insecticide use. For example, in corn after corn, crop rotation increased from 33 to 58%, use of Bt corn in rotated fields dropped from 76% to 56%, and soil insecticide use dropped from 40 to 21%. Interestingly, before the advent of Bt corn, soil insecticides were used on less than 10% of the corn acreage. Despite claims of the potential for Bt corn to reduce soil insecticide use, it's ironic that Bt resistance has actually increased soil insecticide use. In the face of uncertainty about corn rootworm populations and economic risk, over 27% were planning to scout fields for corn rootworms. Our research on resistance has documented: Bt-RW resistance to all traits (Cry34/35 Ab1 resistance documentation in Minnesota was verified in 2015); confirmed cross-resistance among Cry 3 proteins, (including the newest protein eCry3.1Ab 2016-7), and explored the role of soil insecticides in managing corn rootworm populations or managing injury when Bt-RW traits fail. As expected with a protective product, soil insecticides don't offer economic (yield) or population management benefits (corn rootworm density) in fields where traits work. While soil insecticides can partially protect yield in a Bt-resistance field, soil insecticides cannot make up for a failing trait ... so they are not as effective as switching to working Bt-RW traits. RIB (refuge-in-bag) products may see an advantage to a soil insecticide overlay under heavy corn rootworm pressure. The dilemma: knowing when population pressure is severe enough to warrant crop rotation, a switch in Bt-RW traits, or an overlay of soil insecticide. For that reason, scouting is critical and a primary focus of our evolving research program. In addition, a dynamic shift in corn rootworm populations may be underway. The causes of increasing northern corn rootworm populations are debatable but extended diapause issues have returned. It's difficult to distinguish whether this observation reflects the direct effects of severe winter temperatures on western corn rootworm versus indirect effects of reduced western corn rootworm competition or, more concerning, prospective signs of Bt resistance developing in northern corn rootworm. Obj. 1. Impacts of Cultural Practices. No field research was conducted in 2017 but planting date effects (3 years of data) are being built into a corn rootworm developmental model to predict scouting windows. Obj. 2 Transgenic Traits as a Tool to Manage Corn Rootworms. Comparative performance of transgenic traits, singly and as pyramids, was evaluated at Rosemount, where previous bioassays indicated susceptible corn rootworms predominated, and two on-farm sites (Chatfield, Rushford) with Cry3Bb1 performance problems. Hybrid entries featured all available Bt-RW single traits (mCry3A, Cry 34/35 Ab1, Cry3Bb1) and trait pyramids (mCry3A + Cry34/35 Ab1, Cry3Bb1 + Cry34/35 Ab1, mCry3A + eCry3.1Ab) with corresponding refuge (non-Bt) hybrids, each appearing with and without a soil insecticide overlay of Aztec 4.67G (tebupirimphos + cyfluthrin). Results generally confirmed previous research indicating soil insecticide overlays did not provide consistent yield benefit over the trait alone when traits are working. Corn rootworm emergence data revealed that the soil insecticide provides minimal added efficacy (40-60%) and is unlikely to aid in resistance management. A comparative study of 4 types of yellow sticky traps provided raw data for establishing calibration curves and determining trap-specific thresholds relative to the Pherocon-AM unbaited sticky trap. While the basic underlying relationship for each species was consistent, fewer traps were required to achieve desired precision with northern (n=6) vs. western corn rootworms (n=8). These sample sizes represent a 33-50% savings in sampling effort, compared to the original recommendation of n=12 traps per field. An ancillary finding that soil texture, (clay content) could improve root injury prediction, suggest further research to establish thresholds is needed. Modeling of corn rootworm emergence was initiated to define scouting windows, based on Bt-RW traits, insecticide overlays and resistance situation. A logistic curve with a local biofix provided the best fit. This preliminary effort verifies Bt-RW trait and resistance effects on emergence and suggest expanding efforts to include historical data sets collected since Bt-RW resistance first appeared with an eye towards developing more robust equations. Obj. 3. Explore implications of prospective resistance on corn rootworm management. On-farm comparative performance of Bt traits was evaluated in two prospective resistance sites in 2017 (Chatfield, Rushford). Both sites experienced significant corn rootworm injury in a year when pressure had generally declined, according to 56% of surveyed ag advisors. Cross- resistance was evident at both sites with Duracade (mCry3A + eCry3.1Ab), a product just receiving clearance for sale (2015), performing poorly. Work is progressing on adult emergence data to determine how resistance translates into increased beetle production. Bt-RW trait resistance unexpectedly showed up in one study site at Rosemount, where the population is generally susceptible in bioassays and trait selection pressure is relatively low. Analyses of root injury, particularly pruning above 7.6cm, may provide a tip-off of developing resistance. Obj. 4, Measure efficacy of insecticides against corn rootworm. Use of seed treatments and soil insecticide aimed at corn rootworm larvae dramatically increased as insurance against the risk of Bt-RW resistance. Ten soil insecticide studies were initiated at Rosemount to examine the performance of granular and liquid insecticides, and seed treatments. A few studies examined rates of seed treatments; other studies focused on liquid insecticide rates when overlaid on seed treatments. Two studies explored liquid & granular insecticide performance on various Bt-RW traits, with one focusing on the efficacy of currently used liquid insecticides, bifenthrin (Capture LFR), and tefluthrin (Force CS). Designs were a randomized complete block w/ 4 replications and all studies were initiated in fields anticipated to have heavy corn rootworm pressure (unprotected nodal injury ratings >2 nodes pruned). Results verify that granular formulations generally work better than liquid formulations which work better than seed treatments. Under the mild, moist conditions in 2017, the liquid insecticides generally worked better than anticipated and approached performance of granular formulations, while seed treatments generally failed under heavier pressure. Where Bt-RW resistance appeared in one study, soil insecticides did not make up for a failing trait and provided little benefit when traits worked.

    Publications

    • Type: Conference Papers and Presentations Status: Published Year Published: 2016 Citation: Ludwick,D., S. Zukoff, L. Miehls, M. Huynh, K. Ostlie, and B. Hibbard. 2016. Does Cry3Bb1 resistance persist following removal from selection? Paper presented at 25th International Congress of Entomology, Orlando, FL. Sept. 27.
    • Type: Conference Papers and Presentations Status: Published Year Published: 2016 Citation: Leaf, T., K. Ostlie. 2016. Revising sticky trap thresholds for corn rootworms (Diabrotica sp.): How long will these thresholds stick? Paper presented at 25th International Congress of Entomology, Orlando, FL. Sept. 27.
    • Type: Conference Papers and Presentations Status: Published Year Published: 2016 Citation: Benkert III, E., T. Leaf, K. Ostlie. 2016. Detecting Corn Rootworm (Diabrotica spp.) Resistance Development to Bt-RW Traits: Root Injury vs. Beetle Emergence. Paper presented at 25th International Congress of Entomology, Orlando, FL. Sept. 27.
    • Type: Conference Papers and Presentations Status: Published Year Published: 2017 Citation: Benkert III, E., K. Ostlie. 2017. Detecting Corn Rootworm (Diabrotica spp.) Resistance Development to Bt-RW Traits: Root Injury vs. Lodging and Yield. Paper presented at Annual Meeting of the Entomological Society of America. Denver, CO. Nov. 5
    • Type: Conference Papers and Presentations Status: Published Year Published: 2016 Citation: Ostlie, K. 2016. Changing role of insecticides in managing crop insects with a special focus on neonics. Presentation at Crop Pest Management Short Course and Minnesota Ag Retail Association Trade Show, Minneapolis, MN. Dec. 7. https://www.extension.umn.edu/agriculture/ag-professionals/cpm/2016/docs/2016-cpm-Ostlie.pdf
    • Type: Conference Papers and Presentations Status: Published Year Published: 2017 Citation: Ostlie, K. 2017. The insecticide option: Changing roles, performance, scouting and decisions. Presentation at Ag Professional Research Update, Willmar, MN. Jan. 10. PDF: http://www.extension.umn.edu/agriculture/ag-professionals/research-updates/presentations/docs/2017-ru-insecticide-option-ostlie.pdf Video: https://www.youtube.com/watch?v=YWlxIbdH6C0&feature=youtube
    • Type: Journal Articles Status: Published Year Published: 2017 Citation: Andow, D.A., R.J. Wright, E,W. Hodgson, T.E. Hunt and K.R. Ostlie. 2017. Farmers perspectives on resistance in western corn rootworm to CRW-Bt corn in Midwest USA. J. Agric. Ext. Rural Dev. 9: 27-38.
    • Type: Journal Articles Status: Published Year Published: 2017 Citation: Ludwick, D.C., L.N. Meihls, K.R. Ostlie, B.D. Potter, L. French and B.E. Hibbard. 2017. Minnesota field population of western corn rootworm (Coleoptera: Chrysomelidae) shows incomplete resistance to Cry34Ab1/Cry35Ab1 and Cry3Bb1. J. Appl. Entomol. 107:2840. DOI: 10.1111/jen.12377
    • Type: Journal Articles Status: Published Year Published: 2016 Citation: Zukoff, S., K. Ostlie, B. Potter, L. Miehls, A. Zukoff, L. French, M. Ellersiek, W. French and B. Hibbard. 2016. Multiple assays indicate varying levels of cross resistance of Cry3Bb1-selected field populations of the western corn rootworm to mCry3A, eCry3.1Ab, and Cry34/35Ab1. J. Econ. Entomol. 109:1387-1398. DOI: 10.1093/jee/tox078
    • Type: Journal Articles Status: Published Year Published: 2017 Citation: Leaf, T., K. Ostlie and D. Kaiser. 2017. Comparative Performance of Transgenic Hybrids and Their Response to Nitrogen Rates. Agron. J. 109:1-10
    • Type: Journal Articles Status: Published Year Published: 2017 Citation: Leaf, T.M., and K.R. Ostlie. 2017. Nitrogen rate effects on Cry3Bb1 and Cry3Bb1 + Cry34/35Ab1 expression in transgenic corn roots: resulting root injury, and corn rootworm beetle emergence. J. Econ. Entomol. 110:1243-1251. DOI: 10.1093/jee/tox078
    • Type: Theses/Dissertations Status: Published Year Published: 2017 Citation: Leaf, T.M. 2017. Utility of scouting with sticky traps for integrated pest management for corn rootworm. Ph.D. dissertation. University of Minnesota, Minneapolis, MN. 94 pp.