Source: IOWA STATE UNIVERSITY submitted to
MANAGEMENT OF WESTERN CORN ROOTWORM AND OTHER INSECT PESTS OF CORN
Sponsoring Institution
National Institute of Food and Agriculture
Project Status
TERMINATED
Funding Source
HATCH
Reporting Frequency
Annual
Accession No.
1007123
Grant No.
(N/A)
Project No.
IOW05443
Proposal No.
(N/A)
Multistate No.
(N/A)
Program Code
(N/A)
Project Start Date
Aug 9, 2015
Project End Date
Jul 31, 2020
Grant Year
(N/A)
Project Director
Gassmann, AA, JO.
Recipient Organization
IOWA STATE UNIVERSITY
2229 Lincoln Way
AMES,IA 50011
Performing Department
Entomology
Non Technical Summary
Iowa produces more corn than any other state in the US. Within Iowa and in neighboring states, referred to collectively as the Corn Belt, western corn rootworm Diabrotica virgifera virgifera LeConte (Coleoptera: Chrysomelidae) is the most serious pest of corn. Yield reductions and management costs associated with western corn rootworm and other pests of corn impose annual economic losses in excess of one billion dollars. Effective management of western corn rootworm and other pests of corn requires the development of sustainable practices for the use of current management tools and the evaluation and development of novel approaches for management.One of the primary tools used in present day management of western corn rootworm is corn that produces insecticidal toxins derived from the bacterium Bacillus thuringiensis (Bt). Beginning in 2009, populations of western corn rootworm were identified in Iowa that had evolved resistance to corn that produces Bt toxin Cry3Bb1. Resistance to Cry3Bb1 corn has persisted in field populations within Iowa and has been identified in neighboring states, including Nebraska, Minnesota and Illinois. Resistance is often associated with severe feeding injury to Bt corn. More recently, cross-resistance has been documented between Cry3Bb1 corn and corn that produces a different Bt toxin, mCry3A. The continued application of Bt corn for management of western corn rootworm requires understanding the scope and severity of Bt resistance. Additionally, monitoring of field populations is needed to detect resistance that may arise to additional Bt toxins such as Cry34/35Ab1 and eCry3.1Ab. Furthermore, with the evolution of resistance to Bt corn by western corn rootworm, farmers have begun using more conventional insecticides to manage this pest. As with Bt corn, use of these products selects for resistance, and it is currently unknown, to what extent resistance to conventional insecticides may be present among populations of western corn rootworm in Iowa, or elsewhere.In addition to understanding the severity and geographic extent of resistance in the field, laboratory research will be conducted to quantify the risk of resistance developing in additional fields, spreading across the landscape, and persisting in populations once selected. This will be achieved by quantifying fitness costs and inheritance of traits that are associated with Bt resistance. Fitness costs of Bt resistance arise in the absence of Bt corn when Bt-resistant individuals have lower fitness than Bt-susceptible individuals. If present, fitness costs can act to delay the evolution of resistance and diminish the level of resistance within a population if a management option is used less intensively. However, if fitness costs are minimal or absent, resistance may develop rapidly and persist once selected. Using laboratory strains of Bt-resistant western corn rootworm that were generated from populations with field-evolved resistance, I will test for the presence of fitness costs associated with Bt resistance in western corn rootworm. Additionally, these strains will be used to measure the inheritance of resistance. Past computer modeling has shown that resistance develops more quickly when it is inherited in a non-recessive manner. By quantifying the inheritance and fitness costs of Bt resistance in western corn rootworm, this research will determine the risks of resistance developing to novel Bt toxins, and persisting and spreading within the landscape once present.
Animal Health Component
0%
Research Effort Categories
Basic
40%
Applied
60%
Developmental
(N/A)
Classification

Knowledge Area (KA)Subject of Investigation (SOI)Field of Science (FOS)Percent
2111510113050%
2113110113050%
Knowledge Area
211 - Insects, Mites, and Other Arthropods Affecting Plants;

Subject Of Investigation
1510 - Corn; 3110 - Insects;

Field Of Science
1130 - Entomology and acarology;
Goals / Objectives
The goals of this project are to improve integrated pest management and insect resistance management for insect pests of corn. Improvements to integrated pest management will be achieved through field and laboratory research that studies various management tools to prevent yield loss caused by insect pests of corn. Improvements to insect resistance management will focus on understanding the factors affecting resistance of insects to both transgenic technologies and convention chemistries used for pest management in corn cropping systems. These goals will be achieved by completing the following objectives.Evaluate current and emerging management strategies for western corn rootworm and other pests of cornQuantify resistance to Bt corn and conventional insecticides among field populations of western corn rootwormConduct laboratory research to measure inheritance, fitness costs and patterns of cross-resistance as it pertains to resistance to Bt corn by western corn rootworm
Project Methods
The general experimental design to evaluate management options for corn rootworm and other pests of corn in the field (e.g., soil insecticides and transgenic corn) will be a randomized complete block design with four blocks and two rows per treatment within each block. However, the number of blocks and size of treatments within a block may be modified depending on the specific pest and management approach being studied, the available space and the desired statistical power. Feeding injury by western corn rootworm will be quantified by digging roots, washing away soil, and scoring feeding injury on a 0 to 3 node injury scale. Data will be analyzed with an analysis of variance based on a general linear model.To quantify resistance of western corn rootworm to Bt corn and conventional insecticides, populations of rootworm will be sampled either at random throughout the landscape or in response to reports of injury to Bt corn. Methods for conducting bioassays with Bt corn use single plants held in a growth chamber. For conventional insecticides, topical assays are used in addition to soil-based assays. Experimental controls include rootworm populations taken into culture before the commercialization of Bt corn in 2003 and available through USDA ARS Northern Central Agricultural Research Laboratory (NCARL). Each rootworm population will be tested against as many insecticides and types of Bt corn as possible to provide the most complete understanding about levels of resistance to Bt corn and conventional insecticides, and possible cross-resistance.Laboratory studies to test for fitness costs and inheritance of Bt resistance in western corn rootworm will use both diapausing and non-diapausing strains. Diapausing strains will be collected from fields with a history of injury to Bt corn and confirmed resistance through plant-based bioassays. Susceptible strains will be diapausing strains from NCARL that were brought into laboratory culture before the commercialization of Bt corn. Diapausing resistant and susceptible strains will be paired at random and crossed reciprocally to generate heterozygous stains. Eggs for parental strains and crosses will be collected and placed at 4°C for 6 months to break diapause. Resistance will be measured for each strain and cross using single-plant bioassays and inheritance values then calculated. Additionally, studies will be conducted with non-diapausing strains that have been generated by crossing populations with field-evolved Bt resistance into a non-diapausing background and then reselecting for resistance. The same general approach applied with diapausing strains will be applied with non-diapausing resistant and susceptible strains. Fitness costs of Bt resistance will be measured with the same diapausing and non-diapausing strains used to test the inheritance of resistance. To measure fitness costs affecting specific life-history characteristics, strains will be reared on non-Bt corn in the greenhouse. The base of each plant will be enclosed in mesh to collect adult insects as they emerge and plants will be checked three times per week for adult emergence. Adults will be placed in small cages that are held within an incubator and data will be collected on adult longevity, fecundity and size. Additionally, the number of adults emerging from each plant will provide a measure of survival to adulthood. Fitness costs also will be measured by propagating resistant strains in the absence of Bt corn for several generations and measuring the level of resistance at each generation. If fitness costs of resistance are present, the magnitude of resistance should decrease over time.

Progress 08/09/15 to 07/31/20

Outputs
Target Audience:The target audience included agricultural companies, biotechnology companies, extension specialists, farmers, members of the scientific community, regional agronomists, regulators, and the general public. Changes/Problems: Nothing Reported What opportunities for training and professional development has the project provided?Work conducted as part of this project has provided training for two postdoctoral scientists, who have since gone on to careers in agricultural, either in the private sector or with the USDA.Additionally, two M.S. degrees and three Ph.D. degrees were completed during the course of this project, and research training has been provided to an additional four Ph.D. students, who are currently progressing towards graduation.These graduate students and postdoctoral scientists had opportunities to present their research at scientific conferences, and to publish research results in peer-reviewed journals.Numerous undergraduate students gained research experience by participating in laboratory and field research projects that were conducted as part of this project. How have the results been disseminated to communities of interest?Research results were disseminated through the publication of research papers in peer-reviewed scientific journals, through the publication of meeting abstracts and online reports.Additionally, information was disseminated through numerous presentations were given at scientific meetings, interviews with news media, and presentations to stakeholder groups.Slides were made available to the department's extension entomologist, Dr. Erin Hodgson, and to Iowa State University field agronomists for use in meetings with clientele. What do you plan to do during the next reporting period to accomplish the goals? Nothing Reported

Impacts
What was accomplished under these goals? Overall impact statement: Each year, US farmers suffer billions of dollars in economic losses due to insect pests of corn, with these losses arising as a result of both management costs and lost yield.One of the most serious pests of corn in the US Corn Belt is the western corn rootworm. The challenges associated with management of western corn rootworm have increased over time due to the evolution of resistance to various management practices including crop rotation, conventional insecticides, and corn that produces insecticidal proteins derived from the bacterium Bacillus thuringiensis (Bt). Research conducted as part of this project has provided farmers with timely information on the effectiveness of current management tools for corn rootworm and other insect pests of corn, policy makers and biotechnology companies with data on the long-term durability of Bt technologies for management of corn rootworm, and scientists with new information on interactions between corn and one of its associated agricultural pests.As part of this project, extensive research has been conducted on resistance to Bt corn by western corn rootworm, using both laboratory-selected strains and strains with field-evolved resistance.Research on Bt resistance has included monitoring field populations for the development of resistance, and measuring features associated with resistance, specifically the inheritance of resistance and the extent to which resistance has accompanying fitness costs.These data have enabled scientists and regulators to better understand the spread and persistence of resistance in the landscape, and to improve the long-term viability of Bt corn as a management tool for rootworm. Objective 1) Evaluate current and emerging management strategies for western corn rootworm and other pests of corn. During each year of this study, field evaluations were conducted at multiple locations in Iowa to quantify the effectiveness of commercially available insecticides and Bt corn in preventing feeding injury to corn from western corn rootworm and other pests of corn.The data generated from this research provided farmers with an unbiased assessment of the performance of various management options they can use on their farm to manage insect pests.Additionally, data were collected on patterns of feeding injury to Bt corn by Bt-resistant western corn rootworm, and the prevalence of Bt resistance within local and regional landscapes.This included assessing how resistance was affected by farming practices such as continuous corn cultivation and continuous use of the same Bt trait.These data have been presented at both regional and national scientific conferences, and provide scientists from industry and the public sector, as well as regulators, with a better understanding of the current scope and consequences of Bt resistance, and actions farmers are taking to mitigate the effects of pest resistance in their fields. Objective 2) Quantify resistance to Bt corn and conventional insecticides among field populations of western corn rootworm. Multiple studies were conducted to quantify resistance to Bt corn by western corn rootworm within the agricultural landscape.One part of this work was visiting fields that experience high levels of feeding injury to Bt corn by western corn rootworm. Within these fields, corn roots were sampled to quantifyroot injury to Bt corn and adult corn rootworm were collected for use in bioassays.The other part of this work consisted of conducting bioassays of rootworm populations to measure resistance. These research results represent a change in knowledge concerning the geographic distribution of resistant genotypes and the occurrence of resistance to multiple Bt traits within rootworm populations.These data will make it possible for public sector scientist and scientists from industry to understand the scope and severity of Bt resistance by western corn rootworm within the agricultural landscape.This in turn will enable scientific strategies to be developed to manage resistance and to develop new technologies that can be applied to manage resistant populations.Furthermore, through outreach and extension presentations, these data have made available to farmers and other in the agricultural community so that farmers can adjust their management approaches before they suffer severe yield losses from Bt-resistant western corn rootworm. Objective 3) Conduct laboratory research to measure inheritance, fitness costs and patterns of cross-resistance as it pertains to resistance to Bt corn by western corn rootworm. Understanding fitness costs and inheritance of Bt resistance is important because these are key factors affecting how quickly pest populations will adapt to Bt crops.During the course of this project, multiple studies were published that characterized the inheritance of Bt resistance by western corn rootworm, and the extent to which such traits have accompanying fitness costs. This research found that, in general, Bt resistance by western corn rootworm is inherited in a non-recessive manner and that few fitness costs accompanied resistance. Both results indicate a heighted risk of western corn rootworm evolving resistance to Bt corn, and are important to biotech companies, regulators and other scientist as they develop plans for managing resistance.The change in knowledge that resulted from this research will help improve the sustainability of Bt corn for management of western corn rootworm by enabling the development of scientifically sound approaches to delay resistance.

Publications

  • Type: Conference Papers and Presentations Status: Published Year Published: 2020 Citation: McCulloch, J. and Gassmann, A. J. 2020. Density-dependent mortality of larval western corn rootworm on Bt and non-Bt corn. North Central Branch Meeting, Entomological Society of America. Virtual Meeting (talk)
  • Type: Journal Articles Status: Published Year Published: 2020 Citation: Shrestha, R. B. and Gassmann, A. J. 2020. Inheritance and fitness costs of Cry3Bb1 resistance in diapausing field strains of western corn rootworm (Coleoptera: Chrysomelidae). Journal of Economic Entomology 113:2873-2882
  • Type: Journal Articles Status: Published Year Published: 2020 Citation: St. Clair, C. R., Clifton, E. H., Dunbar, M. W., Masloski, K. E., Paolino, A. R., Shrestha, R. B., Gassmann, A. J. 2020. Applying a selection experiment to test for fitness costs of Bt resistance in western corn rootworm and the effect of density on fitness costs. Journal of Economic Entomology 113:2473-2479
  • Type: Journal Articles Status: Published Year Published: 2020 Citation: St. Clair, C. R., Head, G. P., Gassmann, A. J. 2020. Comparing populations of western corn rootworm in regions with and without a history of injury to Cry3 corn. Journal of Economic Entomology 113:1839-1849
  • Type: Journal Articles Status: Published Year Published: 2020 Citation: St. Clair, C. R., Norris, E. J., Masloski, K. E., Coats, J. R., Gassmann, A. J. 2020. Evaluation of pyrethroids and organophosphates in insecticide mixtures for management of western corn rootworm larvae. Pest Management Science 76:3871-3878
  • Type: Journal Articles Status: Published Year Published: 2020 Citation: St. Clair, C. R., Head, G. P., Gassmann, A. J. 2020. Western corn rootworm abundance, injury to corn, and resistance to Cry3Bb1 in the local landscape of previous problem fields. PLoS ONE 15(7): e0237094. doi.org/10.1371/journal.pone.0237094
  • Type: Journal Articles Status: Published Year Published: 2020 Citation: Gassmann, A. J., Shrestha, R. B., Kropf, A. L., St. Clair, C. R. and Brenizer, B. D. 2020. Field-evolved resistance by western corn rootworm to Cry34/35Ab1 and other Bacillus thuringiensis traits in transgenic maize. Pest Management Science 76:268-276
  • Type: Other Status: Published Year Published: 2020 Citation: Hodgson, E., Gassmann, A. and Dean, A. 2020. Current challenges in managing corn rootworm. Iowa State University Extension and Outreach, Publication 3169.
  • Type: Other Status: Published Year Published: 2020 Citation: Gassmann, A. and Brenizer, B. 2020. 2019 Iowa evaluation of insecticides and plant-incorporated protectants. Iowa State University, Department of Entomology. File number 306-19.
  • Type: Other Status: Published Year Published: 2020 Citation: Gassmann, A. and Brenizer, B. 2020. Evaluation of soil-applied insecticide and Bt corn for management of corn rootworm in central Iowa. Central Iowa Research and Demonstration Farm Progress Report, Iowa State University.


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

Outputs
Target Audience:The target audience included agricultural companies, biotechnology companies, extension specialists, farmers, members of the scientific community, regional agronomists, regulators, and the general public. Changes/Problems: Nothing Reported What opportunities for training and professional development has the project provided?Research conducted as part of this project has provided training for twelve undergraduate students, and four Ph.D. students. Undergraduate students participated in laboratory and field research on agricultural pest insects of corn. Graduate students were engaged in original research to characterize resistance by insect pests to transgenic crops within the agricultural landscape. They studied how farmers can effectively manage insect pests of corn and delay the development of pest resistance to management practices. Graduate students conducted investigations on the community of naturally occurring insect pathogens found within agricultural soils. In addition to conducting experiments, the project's graduate students have given research presentations at regional and national meetings, and contributed to data analysis and writing of peer-reviewed publications. How have the results been disseminated to communities of interest?Research results were disseminated through the publication of peer-reviewed papers, abstracts, on-line reports, presentations at scientific meetings, and presentations to stakeholder groups. Slides were made available to the Iowa State University extension entomologist, and to field agronomists, for use in meetings with clientele. What do you plan to do during the next reporting period to accomplish the goals?Research will be conducted to quantify the contribution of Bt traits and soil-applied insecticide to rootworm mortality in the field, and the potential for these approaches to be pyramided for resistance management. Laboratory experiments will be conducted to understand interactions between naturally occurring insect pathogens and western corn rootworm larvae. Field studies will be conducted to evaluate the effectiveness of commercial and pre-commercial products for management of western and northern corn rootworm.Studies of western corn rootworm with laboratory-selected resistance to Cry34/35Ab1 will be conducted to measure the inheritance and fitness costs that accompany Cry34/35Ab1 resistance. We will visit fields with rootworm feeding injury to Bt corn and quantify root injury. We will also sample adult corn rootworm from these fields for subsequent use in laboratory bioassays. Plant-based bioassays will be conducted to measure resistance to Bt corn by western corn rootworm.

Impacts
What was accomplished under these goals? Overall impact statement: Western corn rootworm is the most serious pests of corn in the United States Corn Belt. Each year US farmers suffer economic losses in excess of one billion dollars, as a result of yield losses and management costs associated with corn rootworm. The challenges associated with management of this pest have increased over time due to the evolution of resistance to various management practices including crop rotation, conventional insecticides, and corn that produces insecticidal proteins derived from the bacterium Bacillus thuringiensis (Bt). This project period, field evaluations were conducted at multiple locations in Iowa to quantify the effectiveness of current and pre-commercial insecticides and Bt corn for preventing root injury from western corn rootworm. Results from this research will make it possible for public sector scientists and scientists from industry to understand changes in Bt resistance by western corn rootworm that are taking place across the agricultural landscape. Research conducted as part of this project has provided farmers with timely information on the effectiveness of current management tools for corn rootworm, policy makers and biotechnology companies with data on the long-term durability of Bt technologies for management of corn rootworm, and scientists with new information on interactions between corn and one of its primary agricultural pests.This in turn will enable farmers to adjust their management approaches before they suffer severe yield losses. Objective 1... Evaluate current and emerging management strategies for western corn rootworm and other pests of corn. Field evaluations were conducted at multiple locations in Iowa to quantify the effectiveness of current and pre-commercial insecticides and Bt corn for preventing root injury from western corn rootworm. These data provide farmers with an unbiased assessment of the performance of various management options they can use on their farms to manage western corn rootworm. Research was conducted to characterize resistance to Bt corn by western corn rootworm, including patterns of resistance within local and regional landscapes, and how resistance is affected by farming practices such as continuous corn cultivation and continuous use of the same Bt trait. Additionally, we concluded work on a study that evaluated the effectiveness of various types of Bt corn, both in terms of managing western corn rootworm and preventing feeding injury to roots, among multiple field populations of western corn rootworm that differed in the level of Bt resistance. These data have been presented at regional, national and international scientific conferences, and provide scientists from industry and the public sector, as well as regulators, with a better understanding of the current scope and consequences of Bt resistance, and how the effects of resistance may be mitigated to preserve corn yield. Objective 2... Quantify resistance to Bt corn and conventional insecticides among field populations of western corn rootworm. We continue to monitor susceptibility of western corn rootworm to Bt corn. One part of this work was visiting fields that experience high levels of feeding injury to Bt corn by western corn rootworm. Within these fields corn roots were sampled to quantifying root injury to Bt corn and sampling adult corn rootworm to use in bioassays. The other part of this work consists of conducting bioassays of rootworm populations to measure resistance. These research results represent a change in knowledge concerning the geographic distribution of resistant genotypes and the occurrence of resistance to multiple Bt traits within a rootworm population. These data will make it possible for public sector scientist and scientists from industry to understand changes in Bt resistance by western corn rootworm that are taking place across the agricultural landscape. This in turn will enable farmers to adjust their management approaches before they suffer severe yield losses. Objective 3... Conduct laboratory research to measure inheritance, fitness costs and patterns of cross-resistance as it pertains to resistance to Bt corn by western corn rootworm. Understanding fitness costs and inheritance of Bt resistance is important because these are key factors affecting how quickly pest populations will adapt to Bt crops. One new area of concern in the US Corn Belt is the development of resistance by western corn rootworm to corn producing Bt toxin Cry34/35Ab1. Laboratory-selected strains of western corn rootworm with resistance to Cry34/35Ab1 were developed to quantify inheritance and fitness costs of resistance. These data will be useful in quantifying the risk of Cry34/35Ab1 resistance developing and spreading in the agricultural landscape.

Publications

  • Type: Conference Papers and Presentations Status: Published Year Published: 2019 Citation: Shrestha, R. B and Gassmann, A. J. 2019. Characterization of field populations: a key to sustainable management of western corn rootworm. North Central Branch Meeting, Entomological Society of America. Cincinnati, Ohio, USA (symposium talk)
  • Type: Conference Papers and Presentations Status: Published Year Published: 2019 Citation: Shrestha, R. B., Gassmann, A. J. 2019. Inheritance and fitness costs of field-evolved resistance to Cry3Bb1 corn by western corn rootworm. Entomological Society of America. St. Louis, Missouri (talk)
  • Type: Conference Papers and Presentations Status: Published Year Published: 2019 Citation: Kropf, A. and Gassmann, A. J. 2019. Quantifying the susceptibility of western corn rootworm larvae to entomopathogenic fungi. Entomological Society of America. St. Louis, Missouri (talk)
  • Type: Conference Papers and Presentations Status: Published Year Published: 2019 Citation: McCulloch, J. and Gassmann, A. J. 2019. Evaluating the use of a soil-applied insecticide as a pyramid with Bt corn for western corn rootworm management. Entomological Society of America. St. Louis, Missouri (talk)
  • Type: Conference Papers and Presentations Status: Published Year Published: 2019 Citation: Smith, E., Coates, B., and Gassmann, A. J. 2019. Evaluating resistance to Cry34/35Ab1 by western corn rootworm. Entomological Society of America. St. Louis, Missouri (poster)
  • Type: Journal Articles Status: Published Year Published: 2019 Citation: Yu, E. Y., Gassmann, A. J. and Sappington, T. W. 2019. Using flight mills to measure flight propensity and performance of western corn rootworm Diabrotica virgifera virgifera LeConte (Coleoptera: Chrysomelidae). JoVE (152), e59196, doi:10.3791/59196
  • Type: Journal Articles Status: Published Year Published: 2019 Citation: Shrestha, R. B. and Gassmann, A. J. 2019. Field and laboratory studies of resistance to Bt corn by western corn rootworm (Coleoptera: Chrysomelidae). Journal of Economic Entomology 112:2324-2334
  • Type: Journal Articles Status: Published Year Published: 2019 Citation: Yu, E. Y., Gassmann, A. J. and Sappington, T. W. 2019. Effects of larval density on dispersal and fecundity and western corn rootworm Diabrotica virgifera virgifera LeConte (Coleoptera: Chrysomelidae). PLoS ONE 14(3): e0212696. doi.org/10.1371/journal.pone.0212696
  • Type: Other Status: Published Year Published: 2019 Citation: Gassmann A. and Brenizer, B. 2019. 2018 Iowa evaluation of insecticides and plant-incorporated protectants. Iowa State University, Department of Entomology. File number 305-18.
  • Type: Other Status: Published Year Published: 2019 Citation: Gassmann, A. and Brenizer, B. 2019. Evaluation of soil-applied insecticide and Bt corn for management of larval corn rootworm in central Iowa. Central Iowa Research and Demonstration Farm Progress Report, Iowa State University.
  • Type: Other Status: Published Year Published: 2019 Citation: North Carolina State University. Department of Entomology and Plant Pathology 2019. Western corn rootworm and Bt corn: a model system for understanding interactions between insect pests and Bt crops. (invited research presentation)
  • Type: Conference Papers and Presentations Status: Published Year Published: 2019 Citation: Gassmann, A. J. 2019. Bt resistance by western corn rootworm and the potential for IPM to delay resistance. Entomological Society of America. St. Louis, Missouri, USA. (symposium talk)
  • Type: Conference Papers and Presentations Status: Published Year Published: 2019 Citation: Gassmann, A. J. 2019. Field-evolved resistance to Bt maize by western corn rootworm: patterns of resistance, potential causes and management approaches. Resistance '19. Rothamsted Research, Harpenden, England. (invited presentation)
  • Type: Conference Papers and Presentations Status: Published Year Published: 2019 Citation: St. Clair, C., Head, G. P. and Gassmann, A. J. 2019. Western corn rootworm in agricultural landscapes in Iowa: testing for patterns in root injury to corn, rootworm abundance and Bt resistance. North Central Branch Meeting, Entomological Society of America. Cincinnati, Ohio, USA (symposium talk)


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

Outputs
Target Audience:The target audience included agricultural companies, biotechnology companies, extension specialists, farmers, members of the scientific community, regional agronomists, regulators, and the general public. Changes/Problems: Nothing Reported What opportunities for training and professional development has the project provided?Research conducted as part of this project has provided training for twelve undergraduate students, one M.S. student, four Ph.D. students and one postdoctoral scientist. Undergraduate students have participated in laboratory and field research on agricultural pest insects of corn. Graduate students and the postdoctoral scientist have been engaged in original research to characterize resistance by insect pests to transgenic crops within the agricultural landscape. They have studied how farmers can effectively manage insect pests of corn and investigated the community of naturally occurring insect pathogens found within agricultural soils. In addition to conducting experiments, the project's graduate students and postdoctoral scientist have given research presentations at regional, national and international meetings, and contributed to data analysis and writing of peer-reviewed publications. How have the results been disseminated to communities of interest?Research results were disseminated through the publication of peer-reviewed papers, abstracts, on-line reports, presentations at scientific meetings, and presentations to stakeholder groups. Slides were made available to Iowa State University field agronomists for use in meetings with clientele, and a video presentation was produced and has been used in the annual continuing education course for pesticide applicators in Iowa. What do you plan to do during the next reporting period to accomplish the goals?Research will be conducted on field-evolved resistance to Bt corn by western corn rootworm. This includes visiting fields with injury to Bt corn to quantify root injury and to sample adult corn rootworm for subsequent use in laboratory bioassays. Plant-based bioassays will be conducted to measure resistance to Bt corn by western corn rootworm. We will analyze a multi-year data set on abundance of western corn rootworm in cornfields and patterns of resistance to Bt corn within the agricultural landscape. We will develop laboratory strains of western corn rootworm with field-derived genes for Bt resistance, for subsequent experiments to measure the inheritance and fitness costs of resistance. Research will be conducted to quantify the contribution of Bt traits and soil-applied insecticide to rootworm mortality in the field, and the potential for these approaches to be pyramided for resistance management. Laboratory experiments will be conducted to understand interactions between naturally occurring insect pathogens and western corn rootworm larvae. Field studies will be conducted to evaluate the effectiveness of commercial and pre-commercial products for management of western and northern corn rootworm.

Impacts
What was accomplished under these goals? Overall impact statement: Western corn rootworm is the most serious pest of corn in the United States Corn Belt. Each year US farmers suffer economic losses in excess of one billion dollars, as a result of yield losses and management costs associated with corn rootworm. The challenges associated with management of this pest have increased over time due to the evolution of resistance to various management practices including crop rotation, conventional insecticides, and corn that produces insecticidal proteins derived from the bacterium Bacillus thuringiensis (Bt).As part of this project, research has been conducted on resistance to Bt corn by western corn rootworm, using both laboratory-selected strains and strains with field-evolved resistance.Research on Bt resistance has included monitoring field populations to characterize Bt resistance within the agricultural landscape, which will enable scientists and regulators to estimate the spread and persistence of resistance.Research conducted as part of this project has provided farmers with timely information on the effectiveness of current management tools for corn rootworm, policy makers and biotechnology companies with data on the long-term durability of Bt technologies for management of corn rootworm, and scientists with new information on interactions between corn and one of its primary agricultural pests. Objective 1... Evaluate current and emerging management strategies for western corn rootworm and other pests of corn Field evaluations were conducted at multiple locations in Iowa to quantify effectiveness of commercially available insecticides and Bt corn in preventing root injury from western corn rootworm. These data will provide farmers with an unbiased assessment of the performance of various management options they can use on their farm to manage western corn rootworm. I continue to conduct research to characterize resistance and root injury in fields with a history of high levels of rootworm injury to Bt corn. This project involves sampling fields with a history of injury and neighboring fields to quantify rootworm abundance, root injury and resistance within the agricultural landscape, to understand how resistance in a single field affects neighboring fields. These data have been presented at both regional and national scientific conferences, and provide scientists from industry and the public sector, as well as regulators, with a better understanding of the current scope and consequences of Bt resistance, and actions farmers are taking to mitigate the effects of pest resistance in their fields. Objective 2... Quantify resistance to Bt corn and conventional insecticides among field populations of western corn rootworm We continue to monitor susceptibility of western corn rootworm to Bt corn. One part of this work involves visiting fields that had high levels of feeding injury, quantifying root injury to Bt corn and sampling adult corn rootworm to use in bioassays. The other part of this work consists of conducting bioassays of rootworm populations to measure resistance. These research results represent a change in knowledge concerning the geographic distribution of resistant genotypes. Data will make it possible for public sector scientist and scientists from industry to monitor populations of western corn rootworm in Iowa for changes in Bt resistance. Thus, allowing farmers to adjust their management approaches before they suffer severe yield losses. Objective 3... Conduct laboratory research to measure inheritance, fitness costs and patterns of cross-resistance as it pertains to resistance to Bt corn by western corn rootworm Understanding fitness costs and inheritance of Bt resistance is important because these are key factors affecting how quickly pest populations will adapt to Bt crops. One new area of concern in the US Corn Belt is the development of resistance by western corn rootworm to corn producing Bt toxin Cry34/35Ab1. Previously developed strains with laboratory-selected resistance to Cry34/35Ab1 are being used to quantify inheritance and fitness costs of resistance. These data will be useful in assessing the risk of Cry34/35Ab1 resistance developing and spreading within field populations.

Publications

  • Type: Journal Articles Status: Published Year Published: 2018 Citation: Shrestha, R. B., Dunbar, M. W., French, B. W., and Gassmann, A. J. 2018. Effects of field history on resistance to Bt maize by western corn rootworm, Diabrotica virgifera virgifera LeConte (Coleoptera: Chrysomelidae). PLoS ONE 13(7): e0200156. doi.org/10.1371/journal.pone.0200156
  • Type: Journal Articles Status: Published Year Published: 2018 Citation: Shrestha, R. B., Jakka, S. R. K. and Gassmann, A. J. 2018. Response of Cry3Bb1-resistant western corn rootworm (Coleoptera: Chrysomelidae) to Bt maize and soil insecticide. Journal of Applied Entomology 142:937-946
  • Type: Journal Articles Status: Published Year Published: 2018 Citation: Rault, L. C., Siegfried, B. D., Gassmann, A. J., Wang, H., Brewer, G. J., Miller, N. J. 2018. Investigation of Cry3Bb1 resistance and intoxication in western corn rootworm by RNA sequencing. Journal of Applied Entomology 142:921-936
  • Type: Journal Articles Status: Published Year Published: 2018 Citation: Rovnyak, A. M., Burks, C. S., Gassmann, A. J. and Sappington, T. W. 2018. Interrelation of mating, flight, and fecundity in navel orangeworm (Lepidoptera: Pyralidae) females. Entomologia Experimentalis et Applicata 166:304-315
  • Type: Journal Articles Status: Published Year Published: 2018 Citation: Clifton, E. H., Tylka, G. L., Gassmann A. J., and Hodgson, E. W. 2018. Interaction of effects of host plant resistance and seed treatments on soybean aphid (Aphis glycines Matsumura), soybean cyst nematode (Heterodera glycines Ichinohe), and soybean yield. Pest Management Science 74:992-1000
  • Type: Journal Articles Status: Published Year Published: 2018 Citation: Clifton, E. H., Jaronski, S. T., Coates, B. S., Hodgson, E. W., Gassmann, A. J. 2018. Effects of endophytic entomopathogenic fungi on soybean aphid and identification of Metarhizium isolates from agricultural fields. PLoS ONE 13(3): e0194815 doi.org/10.1371/journal.pone.0194815
  • Type: Other Status: Published Year Published: 2018 Citation: Gassmann A. J. and Weber, P. J. 2018. 2017 Iowa evaluation of insecticides and plant-incorporated protectants. Iowa State University, Department of Entomology. File number 303-17.
  • Type: Other Status: Published Year Published: 2018 Citation: Gassmann A. J. and Weber, P. J. 2018. Evaluating of various technologies for management of larval corn rootworm in central Iowa. Central Iowa Research and Demonstration Farm Progress Report, Iowa State University.
  • Type: Other Status: Published Year Published: 2018 Citation: Gassmann A. J. and Weber, P. J. 2018. Evaluating soil-applied insecticides for management of corn rootworm larvae in southeastern Iowa. Southeast Iowa Research and Demonstration Farm Progress Report, Iowa State University.
  • Type: Other Status: Published Year Published: 2018 Citation: Gassmann A. J. and Weber, P. J. 2018. Evaluation of management approaches for corn rootworm larvae. Northeast Iowa Research and Demonstration Farm Progress Report, Iowa State University.
  • Type: Conference Papers and Presentations Status: Published Year Published: 2018 Citation: Gassmann, A. J. 2018. Perspectives from the midwestern United States on pest adaptation to Bt crops. Research symposium talk presented at Entomological Society of America. Vancouver, British Columbia, Canada
  • Type: Conference Papers and Presentations Status: Published Year Published: 2018 Citation: Coates, B. S., Gassmann, A. J., Guillemaud, T. and Robertson, H. M. 2018. Genomics of western corn rootworm response to insecticidal toxins. Research symposium talk presented at Entomological Society of America. Vancouver, British Columbia, Canada
  • Type: Other Status: Published Year Published: 2018 Citation: Gassmann, A. J. 2018. Insect adaptation in a transgenic landscape. Dr. Douglas Futuyma Retirement Symposium. Research symposium talk presented at State University of New York at Stony Brook, New York, USA.
  • Type: Conference Papers and Presentations Status: Published Year Published: 2018 Citation: Kropf, A. and Gassmann, A. J. 2018. Tritrophic interactions among corn, Diabrotica virgifera virgifera and entomopathogenic fungi. Poster presented at Entomological Society of America. Vancouver, British Columbia, Canada
  • Type: Conference Papers and Presentations Status: Published Year Published: 2018 Citation: St. Clair, C, Head, G. P., Gassmann, A. J. 2018. Western corn rootworm abundance, injury to maize, and resistance to Cry3Bb1 in the local landscape of previous problem fields. Talk presented at Entomological Society of America. Vancouver, British Columbia, Canada
  • Type: Conference Papers and Presentations Status: Published Year Published: 2018 Citation: Gassmann, A. J. 2018. Western corn rootworm resistance to Bt maize within agricultural landscapes. Talk presented at European Congress of Entomology. Naples, Italy
  • Type: Conference Papers and Presentations Status: Published Year Published: 2018 Citation: St. Clair, C, Head, G. P., Gassmann, A. J. 2018. Western corn rootworm abundance, injury to maize, and resistance to Cry3Bb1 in the local landscape of previous problem fields. Poster presented at European Congress of Entomology. Naples, Italy
  • Type: Conference Papers and Presentations Status: Published Year Published: 2018 Citation: Yu, E., Gassmann, A. J., Sappington, T. W. 2018. Effects of larval density on dispersal and fecundity of Diabrotica virgifera virgifera. Talk presented at North Central Branch Meeting, Entomological Society of America. Madison, Wisconsin
  • Type: Conference Papers and Presentations Status: Published Year Published: 2018 Citation: St. Clair, C, Head, G. P., Gassmann, A. J. 2018. The effect of proximity to past problem fields on western corn rootworm abundance, injury to corn, and resistance to Cry3Bb1. Talk presented at North Central Branch Meeting, Entomological Society of America. Madison, Wisconsin
  • Type: Conference Papers and Presentations Status: Published Year Published: 2018 Citation: Shrestha, R. B., Gassmann, A. J. 2018. Field and laboratory studies of Bt resistance by western corn rootworm. Talk presented at North Central Branch Meeting, Entomological Society of America. Madison, Wisconsin


Progress 10/01/16 to 09/30/17

Outputs
Target Audience:The target audience included agricultural companies, biotechnology companies, extension specialists, farmers, members of the scientific community, regional agronomists, regulators, and the general public. Changes/Problems: Nothing Reported What opportunities for training and professional development has the project provided?Research conducted as part of this project has provided training for twelve undergraduate students, one M.S. students, five Ph.D. students and one postdoctoral scientist. Undergraduate students have participated in laboratory and field research on agricultural pest insects of corn. Graduate students and the postdoctoral scientist have been engaged in original research to characterize resistance by insect pests to transgenic crops and convention insecticides within the agricultural landscape. They have studied how farmers can effectively manage insect pests of corn and investigated the community of naturally occurring insect pathogens found within agricultural soils. In addition to conducting experiments, the project's graduate students and postdoctoral scientist have given research presentations at regional and national meetings, and contributed to data analysis and writing of peer-reviewed publications. How have the results been disseminated to communities of interest?Research results were disseminated through the publication of peer-reviewed papers, abstracts, on-line reports, presentations at scientific meetings, and presentations to stakeholder groups. Slides were made available to the department's extension entomologist, Dr. Erin Hodgson, and to Iowa State University field agronomists for use in meetings with clientele. What do you plan to do during the next reporting period to accomplish the goals?Laboratory bioassays will be conducted to measure resistance to Bt corn by western corn rootworm. Work will begin to build a computer-based model to test how various farming practices affect the evolution of resistance by agricultural pest insects. We will analyze a multi-year data set on abundance of western corn rootworm in cornfields and patterns of resistance to Bt corn. Laboratory experiments will be conducted to understand interactions between naturally occurring insect pathogens and western corn rootworm. Field studies will be conducted to evaluate the effectiveness of commercial and pre-commercial products for management of western and northern corn rootworm.

Impacts
What was accomplished under these goals? Overall impact statement: Western corn rootworm is the most serious pests of corn in the United States Corn Belt. Each year US farmers suffer economic losses in excess of one billion dollars, as a result of yield losses and management costs associated with corn rootworm. The challenges associated with management of this pest have increased over time due to the evolution of resistance to various management practices including crop rotation, conventional insecticides, and corn that produces insecticidal proteins derived from the bacterium Bacillus thuringiensis (Bt). Research conducted as part of this project has provided farmers with timely information on the effectiveness of current management tools for corn rootworm, policy makers and biotechnology companies with data on the long-term durability of Bt technologies for management of corn rootworm, and scientists with new information on interactions between corn and one of its primary agricultural pests. As part of this project, extensive research has been conducted on resistance to Bt corn by western corn rootworm, using both laboratory-selected strains and strains with field-evolved resistance. Research on Bt resistance has included monitoring field populations for the development of resistance and measuring features associated with resistance, specifically inheritance and fitness costs, which enable scientists and regulators to estimate the spread and persistence of resistance in the landscape. Objective 1... Evaluate current and emerging management strategies for western corn rootworm and other pests of corn Field evaluations were conducted at multiple locations in Iowa to quantify effectiveness of commercially available insecticides and Bt corn in preventing root injury from western corn rootworm.These data will provide farmers with an unbiased assessment of the performance of various management options they can use on their farm to manage western corn rootworm. I continue to conduct research to characterize resistance and root injury in fields with a history of high levels of rootworm injury to Bt corn. This project involves sampling fields with a history of injury and neighboring fields to quantify rootworm abundance, root injury and resistance within the agricultural landscape, to understand how resistance in a single field affects neighboring fields.These data have been presented at both regional and national scientific conferences, and provide scientists from industry and the public sector, as well as regulators, with a better understanding of the current scope and consequences of Bt resistance, and actions farmers are taking to mitigate the effects of pest resistance in their fields. I published a book chapter that reviewed the use of biopesticides, including Bt corn, for management of insect pests of corn. This book chapter will serve as a valuable reference for current and future scientists studying the application of biopesticides in corn and other crops. Also, I coauthored a peer-reviewed synthesis paper outlining strategies to proactively delay resistance to Bt corn by western corn rootworm.This paper is written for scientists, regulators and members of the biotech industry, and describes strategies to preserve the efficacy of Bt traits, crop yield, and income for farmers. Objective 2... Quantify resistance to Bt corn and conventional insecticides among field populations of western corn rootworm We completed a two-year study quantifying baseline susceptibility to conventional insecticides by western corn rootworm. The results of this work represent a change in knowledge concerning landscape-level patterns in pest susceptibility to commonly used insecticides. These data will make it possible for public sector scientist and scientists from industry to monitor populations of western corn rootworm in Iowa and elsewhere, for changes in susceptibility to insecticides.Thus, allowing farmers to adjust their management approaches before they suffer severe yield losses. Objective 3... Conduct laboratory research to measure inheritance, fitness costs and patterns of cross-resistance as it pertains to resistance to Bt corn by western corn rootworm Understanding fitness costs and inheritance of Bt resistance is important because these are key factors affecting how quickly pest populations will adapt to Bt crops. This year I published two studies that provide new information about the extent to which fitness costs accompany resistance to Bt corn in both the western coron rootworm and the European corn borer, both key pests of corn in the United States. Experiments with western corn rootworm found that the inheritance of resistance was non-recessive and that few fitness costs accompanied resistance. Both results indicate a heighted risk of resistance Bt corn, and are important to biotech companies and regulators as they develop plans for managing resistance. By contrast, European corn borer was found to suffer a fitness cost of Bt resistance, with resistant individuals suffering reduced fecundity compared with Bt-susceptible individuals. These contrasting results provide a change in knowledge about why, more than two decades after it was introduced, Bt corn continues to provide a highly effective management tool against European corn borer, but western corn rootworm has develop Bt resistance in less than 10 years. This knowledge will be useful to biotech companies, regulators and other scientist as they develop risk assessments for Bt crops that target agricultural pest insects.

Publications

  • Type: Journal Articles Status: Published Year Published: 2017 Citation: Paolino, A. R. and Gassmann, A. J. 2017. Assessment of inheritance and fitness costs associated with field-evolved resistance to Cry3Bb1 maize by western corn rootworm. Toxins 9(5):159; doi:10.3390/toxins9050159
  • Type: Journal Articles Status: Published Year Published: 2017 Citation: Dunbar, M. W., Gassmann A. J. and ONeal, M. E. 2017. Impacts of rye cover crop on beneficial arthropods. Environmental Entomology 46:284-290
  • Type: Journal Articles Status: Published Year Published: 2017 Citation: Petzold-Maxwell, J. L., Siegfried, B. D., Hellmich, R. L., Abel, C. A., Coates, B. S., Spencer, T. A., Horikoshi, R. J. and Gassmann, A. J. 2017. Fitness costs associated with Cry1F resistance in the European corn borer. Journal of Applied Entomology 141:67-79
  • Type: Journal Articles Status: Published Year Published: 2017 Citation: Schrader, P. M., Estes, R. E., Tinsley, N. A., Gassmann, A. J. and Gray, M. E. 2017. Evaluation of adult emergence and larval root injury for Cry3Bb1-resistant populations of the western corn rootworm. Journal of Applied Entomology 141:41-52
  • Type: Journal Articles Status: Published Year Published: 2017 Citation: Gressel, J., Gassmann, A. J., and Owen, M. D. K. 2017. How well will stacked transgenic pest/herbicide resistances delay pests from evolving resistance? Pest Management Science 73:22-34
  • Type: Book Chapters Status: Published Year Published: 2017 Citation: Gassmann, A. J. and Clifton, E. H. 2017. Current and potential applications of biopesticides to manage insect pests of maize. pp. 173 - 184 In Lacey, L. A. (ed). Microbial Control of Insect and Mite Pests: From Theory to Practice. 1st edition. Elsevier, London.
  • Type: Other Status: Published Year Published: 2017 Citation: Gassmann A. J. and Weber, P. J. 2017. Evaluation of various technologies for management of larval corn rootworm. Central Iowa Research and Demonstration Farm Progress Report, Iowa State University.
  • Type: Other Status: Published Year Published: 2017 Citation: Gassmann A. J. and Weber, P. J. 2017. Field test for effects of cross-resistance on root injury to Bt corn by western corn rootworm. Northeast Iowa Research and Demonstration Farm Progress Report, Iowa State University.
  • Type: Other Status: Published Year Published: 2017 Citation: Gassmann A. J. and Weber, P. J. 2017. Evaluation of Ampex insecticide for management of rootworm larvae. Southeast Iowa Research and Demonstration Farm Progress Report, Iowa State University.
  • Type: Other Status: Published Year Published: 2017 Citation: Gassmann, A. J., and Weber, P. J. 2017. 2016 Iowa evaluation of insecticides and plant-incorporated protectants. Iowa State University, Department of Entomology. File number 301-16.
  • Type: Conference Papers and Presentations Status: Published Year Published: 2017 Citation: Gassmann, A. J. 2017. Resistance to Bt maize by western corn rootworm. 26th International Working Group on Ostrinia Conference, Beijing, China.
  • Type: Theses/Dissertations Status: Published Year Published: 2017 Citation: Clifton, E. H. 2017. Pest management of soybean aphid and soybean cyst nematode: Host-plant resistance, entomopathogens, and seed-applied pesticides. Ph.D. Dissertation in Entomology. Iowa State University.
  • Type: Conference Papers and Presentations Status: Published Year Published: 2017 Citation: Shrestha, R. B. and Gassmann, A. J. 2017. The opportunities for management of Bt-resistant western corn rootworm: an experience from Iowa cornfields. Entomological Society of America. Denver, Colorado
  • Type: Conference Papers and Presentations Status: Published Year Published: 2017 Citation: Gassmann, A. J. 2017. Inheritance and fitness costs of Bt resistance in western corn rootworm. Entomological Society of America. Denver, Colorado
  • Type: Conference Papers and Presentations Status: Published Year Published: 2017 Citation: Coates, B., Gassmann, A. Siegfried, B. 2017. Quantitative trait locus mapping of Bacillus thuringiensis (Bt) toxin resistance traits using high density genotyping-by-sequencing markers. Entomological Society of America. Denver, Colorado
  • Type: Conference Papers and Presentations Status: Published Year Published: 2017 Citation: St. Clair, C., Gassmann, A. J., and Head, G. P., 2017. Western corn rootworm abundance, injury to corn and Bt resistance in landscapes near previous problem fields. Entomological Society of America. Denver, Colorado
  • Type: Conference Papers and Presentations Status: Published Year Published: 2017 Citation: Yu, E., Gassmann, A. J., and Sappington, T. 2017. Understanding dispersal by Diabrotica virgifera virgifera: effects of larval density on flight and effects of flight on female reproduction. Entomological Society of America. Denver, Colorado
  • Type: Conference Papers and Presentations Status: Published Year Published: 2017 Citation: French, B., Gassmann, A. J. and Hibbard, B. E. 2017. Offspring survivorship of diapausing and non-diapausing western corn rootworm under field and laboratory conditions. Entomological Society of America. Denver, Colorado
  • Type: Conference Papers and Presentations Status: Published Year Published: 2017 Citation: Clifton, E. H., Jaronski, S. T., Coates, B. S., Hodgson, E. W., Gassmann, A. J. 2017. Effects of endophytic entomopathogenic fungi on soybean aphid, Aphis glycines. Annual Meeting of the Society for Invertebrate Pathology. San Diego, California


Progress 10/01/15 to 09/30/16

Outputs
Target Audience:The target audience included agricultural companies, biotechnology companies, extension specialists, farmers, members of the scientific community, regional agronomists, regulators, and the general public. Changes/Problems: Nothing Reported What opportunities for training and professional development has the project provided?Participation in this project has provided training for twelve undergraduate students, two M.S. students, three Ph.D. students and two postdoctoral scientists. In addition to conducting experiments, graduate students and postdoctoral scientists gave research presentations at the North Central Branch meeting of the Entomological Society of America and at the International Congress of Entomology. Graduate students and postdoctoral scientists also contributed to data analysis and writing of peer-reviewed publications. How have the results been disseminated to communities of interest?Research results were disseminated through the publication of peer-reviewed papers, abstracts, on-line reports, presentations at scientific meetings, interviews with news media, and presentations to stakeholder groups. Slides were made available to the department's extension entomologist, Dr. Erin Hodgson, and to Iowa State University field agronomists for use in meetings with clientele. What do you plan to do during the next reporting period to accomplish the goals?Field studies will be conducted to evaluate the effectiveness of commercial and pre-commercial products for management of western and northern corn rootworm. Experiments will be conducted to compare the utility of measuring Bt resistance in western corn rootworm with diet-based and plant-based bioassays. Field populations will be evaluated in bioassays to measure susceptibility to conventional insecticides and Bt corn.

Impacts
What was accomplished under these goals? IMPACT: Western corn rootworm is the most serious pest of corn in the United States Corn Belt. Each year US farmers suffer economic losses in excess of one billion dollars, as a result of yield losses and management costs associated with western corn rootworm. The challenges associated with management of this pest have increased over time due to the evolution of resistance to various management practices including crop rotation, conventional insecticides, and corn that produces insecticidal proteins derived from the bacterium Bacillus thuringiensis (Bt). Research conducted as part of this project have provided farmers with timely information on the effectiveness of current management tools for corn rootworm, policy makers and biotechnology companies with data on the long-term durability of Bt technologies for management of corn rootworm, and scientists with new information on interactions between corn and one of its primary agricultural pests. As part of this project, extensive research has been conducted on resistance to Bt corn by western corn rootworm, using both laboratory-selected strains and strains with field-evolved resistance. Research on Bt resistance has included monitoring field populations for the development of resistance and measuring features associated with resistance, specifically inheritance and fitness costs, which enable scientists and regulators to estimate the spread and persistence of resistance in the landscape. Objective 1) Evaluate current and emerging management strategies for western corn rootworm and other pests of corn. Field evaluations were conducted at multiple locations in Iowa to quantify effectiveness of commercially available insecticides and Bt corn in preventing root injury from western corn rootworm. These data will provide farmers with an unbiased assessment of the performance of various management options they can use on their farm to manage western corn rootworm. A paper was published that examined the effects of Bt corn and soil-applied insecticide on root injury and survival of western corn rootworm. Results of this work provide information to farmers on how to manage western corn rootworm populations that are resistant to Bt corn. These data are also of value to scientists and regulators because it provides a detailed characterization of how Bt-resistant populations interact with current management practices. Results from two years of on-farm research summarized patterns of root injury and rootworm abundance from across a range of farming practices. The study found that farmers could adjust their management of western corn rootworm to mitigate the effects of historically high levels of root injury and population size by western corn rootworm. The results of this study provide scientists, regulators and farmers with insights into how the effects of Bt resistance can be mitigated and yields preserved. I am conducting additional work to characterize resistance and root injury in fields with a history of high levels of rootworm injury to Bt corn. This project involves sampling fields with a history of injury and neighboring fields to quantify rootworm abundance, root injury and resistance within the agricultural landscape, to understand how resistance in a single field affects neighboring fields. Multiple studies were published looking at effects of crop rotation and cover crops on the abundance of pest and biological control agents. Cover crops are an emerging practice to conserve soil and prevent nutrient run-off. I found that cover crops can also increase the abundance of early season pests in corn, and that farmers should scout for pests and be ready to manage these pests if a cover crop is grown. I found that both cover crops and extended rotations may benefit farmers by increasing the abundance of some biological control agents in their fields. I published a book chapter that reviewed the use of biopesticides, including Bt corn, for management of insect pests of corn. The book chapter will serve as a valuable reference for current and future scientists studying the application of biopesticides in corn and other crops. In a laboratory study, I demonstrated that non-Bt refuges can delay resistance to Bt corn by western corn rootworm in some cases but not others. Consequently, combining the refuge strategy with pyramids of multiple Bt toxins and applying other pest management strategies will likely be necessary to delay resistance of western corn rootworm to Bt corn. Also, I coauthored a peer-reviewed synthesis paper outlining strategies to proactively delay resistance to Bt corn by western corn rootworm. This paper is written for scientists, regulators and members of the biotech industry, and describes strategies to preserve the efficacy of Bt traits, crop yield, and income for farmers. Objective 2) Quantify resistance to Bt corn and conventional insecticides among field populations of western corn rootworm. Field populations of western corn rootworm were sampled and screened for resistance to conventional soil-applied insecticides. Data will provide a base-line for understanding geographic variability of susceptibility to soil-applied insecticides targeting western corn rootworm, and will make it possible to monitor populations in Iowa for changes in susceptibility to insecticides and allow farmers to adjust their management approaches before they suffer severe yield losses. Western corn rootworm populations also were sampled from fields with a history of feeding injury to Bt corn and from neighboring fields. These populations were screened for resistance to Bt corn, with the goal of quantifying the extent to which Bt resistance exists within the landscape, which will be of value to farmers, regulators, biotech companies, and agricultural scientists. Additionally, for corn rootworm population sampled from fields with a diversity of management practices, diet-based and plant-based bioassays were conducted to quantify Bt resistance. This work will help members of the agricultural community understand how field history and pest-management decisions affect the development of Bt resistance within a farmer's field. Objective 3) Conduct laboratory research to measure inheritance, fitness costs and patterns of cross-resistance as it pertains to resistance to Bt corn by western corn rootworm. Fitness costs and inheritance of resistance to Bt corn was determined for two strains of western corn rootworm with field-evolved Bt resistance. These experiments found that the inheritance of resistance was non-recessive and that few fitness costs accompanied resistance. Both results indicate a heighted risk of resistance Bt corn, and are important to biotech companies and regulators as they develop plans for managing resistance. I conducted two studies to test for Bt resistance and cross-resistance in field populations of western corn rootworm. One study found that western corn rootworm has evolved resistance to three of the four Bt traits in corn (Cry3Bb1, mCry3A and eCry3.1Ab) through the presence of cross-resistance among these Bt toxins. A second study documented the presence of resistance to Cry34/35Ab1 in some populations of western corn rootworm in the Corn Belt. This information will help farmers develop strategies to effectively manage this pest, by avoiding those insecticidal traits in areas where they have been compromised by resistance. These results highlight the potential vulnerability of all Bt traits to resistance by western corn rootworm. Such findings are relevant to farmers, regulators and biotech companies because they emphasize the need to use Bt traits judiciously and with sound integrated pest management and resistance management. I also published a review paper that synthesizes current knowledge around resistance to Bt corn by western corn rootworm.

Publications

  • Type: Theses/Dissertations Status: Published Year Published: 2016 Citation: Paolino, A. R. 2016. Inheritance and Fitness Costs of Field-Derived Resistance to Cry3Bb1 Corn by Western Corn Rootworm. MS Thesis in Entomology, Iowa State University.
  • Type: Journal Articles Status: Published Year Published: 2016 Citation: Dunbar, M. W., ONeal, M. E. and Gassmann A. J. 2016. Effects of field history on corn root injury and adult abundance of northern and western corn rootworm (Coleoptera: Chrysomelidae). Journal of Economic Entomology 109:2096-2104
  • Type: Journal Articles Status: Published Year Published: 2016 Citation: Dunbar, M. W., Gassmann A. J. and ONeal, M. E. 2016. Impacts of rotation schemes on ground-dwelling beneficial arthropods. Environmental Entomology 45:1154-1160
  • Type: Journal Articles Status: Published Year Published: 2016 Citation: Gassmann, A. J., Shrestha, R. B., Jakka, S. R. K., Dunbar, M. W., Clifton, E. H., Paolino, A. R., Ingber, D. A., French, B. W., Masloski, K. E., Doudna, J. W. and St. Clair, C. R. 2016. Evidence of resistance to Cry34/35Ab1 corn by western corn rootworm (Coleoptera: Chrysomelidae): root injury in the field and larval survival in plant-based bioassays. Journal of Economic Entomology 109:1872-1880
  • Type: Journal Articles Status: Published Year Published: 2016 Citation: Dunbar, M. W., ONeal, M. E. and Gassmann A. J. 2016. Increased risk of insect injury to corn following rye cover crop. Journal of Economic Entomology 109:1691-1697
  • Type: Journal Articles Status: Published Year Published: 2016 Citation: Shrestha, R. B., Jakka, S. R. K., French, B. W. and Gassmann, A. J. 2016. Field-based assessment of resistance to Bt corn by western corn rootworm (Coleoptera: Chrysomelidae). Journal of Economic Entomology 109:1399-1409
  • Type: Journal Articles Status: Published Year Published: 2016 Citation: Gassmann, A. J. 2016. Resistance to Bt maize by western corn rootworm: insights from the laboratory and the field. Current Opinion in Insect Science 15:111-115
  • Type: Journal Articles Status: Published Year Published: 2016 Citation: Jakka, S. R. K., Shrestha, R. B. and Gassmann, A. J. 2016. Broad-spectrum resistance to Bacillus thuringiensis toxins by western corn rootworm (Diabrotica virgifera virgifera). Scientific Reports 6, 27860; doi: 10.1038/srep27860
  • Type: Journal Articles Status: Published Year Published: 2016 Citation: Andow, D. A., Pueppke, S. G., Schaafsma, A. W., Gassmann, A. J., Sappington, T. W., Meinke, L. J., Mitchell, P. D., Hurley, T. M., Hellmich, R. L. and Porter, R. P. 2016. Early detection and mitigation of resistance to Bt maize by western corn rootworm (Coleoptera: Chrysomelidae). Journal of Economic Entomology 109: 1-12
  • Type: Journal Articles Status: Published Year Published: 2016 Citation: Deitloff, J., Dunbar, M. W., Ingber, D. A., Hibbard, B. E., and Gassmann, A. J. 2016. Effects of refuges on the evolution of resistance to transgenic corn by western corn rootworm. Pest Management Science 72: 190-198
  • Type: Book Chapters Status: Published Year Published: 2016 Citation: Gassmann, A. J. and Clifton, E. H. 2016. Current and potential applications of biopesticides to manage insect pests of maize. pp. 173 - 184 In Lacey, L. A. (ed). Microbial Control of Insect and Mite Pests: From Theory to Practice. 1st edition. Elsevier, London.
  • Type: Other Status: Published Year Published: 2016 Citation: Hodgson, E. and Gassmann, A. 2016. Guidelines for using sticky traps to assess corn rootworm activity. Integrated Crops Management News. Iowa State University.
  • Type: Other Status: Published Year Published: 2016 Citation: Gassmann A. J. and Weber, P. J. 2016. Comparison among various tactics for management of corn rootworm larvae. Central Iowa Research and Demonstration Farm Progress Report, Iowa State University.
  • Type: Other Status: Published Year Published: 2016 Citation: Hodgson, E. and Gassmann, A. 2016. Approaches for managing corn rootworm in Iowa. Integrated Crops Management News. Iowa State University.
  • Type: Other Status: Published Year Published: 2016 Citation: Gassmann, A. J., and Weber, P. J. 2016. 2015 Iowa evaluation of insecticides and plant-incorporated protectants. Iowa State University, Department of Entomology. File number 299-15.
  • Type: Other Status: Published Year Published: 2016 Citation: Hodgson, E., Clifton, E. Tylka, G., and Gassmann, A. 2016. Managing two soybean pests to optimize yield. Integrated Crops Management News. Iowa State University.
  • Type: Other Status: Published Year Published: 2016 Citation: Gassmann A. J. and Weber, P. J. 2016. Evaluation of Bt corn and soil-applied insecticides for management of corn rootworm larvae. Northeast Research and Demonstration Farm Progress Report, Iowa State University.
  • Type: Conference Papers and Presentations Status: Published Year Published: 2016 Citation: Shrestha, R. and Gassmann, A. 2016. IPM vs. IRM: The experiences from western corn rootworm management. International Congress of Entomology. Orlando, Florida, USA
  • Type: Conference Papers and Presentations Status: Published Year Published: 2016 Citation: Hellmich, R., Gassmann, A., Omoto, C. and van den Berg, J. 2016. Role of Bt maize in global IPM. International Congress of Entomology. Orlando, Florida, USA
  • Type: Conference Papers and Presentations Status: Published Year Published: 2016 Citation: Miller, N., Bermond, G, Rault, L., Wang, H., Siegfried, B., Meinke, L., Baxter, B., Gassmann, A. J., and Hibbard, B. 2016. Evolution and mechanisms of rootworm resistance to Cry3Bb1 maize. International Congress of Entomology. Orlando, Florida, USA
  • Type: Conference Papers and Presentations Status: Published Year Published: 2016 Citation: Gassmann, A. J., Clifton, E. H., Doudna, J., Dunbar, M. W., Hoffmann, A., Ingber, D. A., Jakka, S. R. K., Keweshan, R. S., Masloski, K. E., Paolino, A., Petzold-Maxwell, J. L. Shrestha, R. and St. Clair, C. 2016. Field-evolved resistance to Bt maize by western corn rootworm. International Congress of Entomology. Orlando, Florida, USA
  • Type: Conference Papers and Presentations Status: Published Year Published: 2016 Citation: Hibbard, B., Ludwick, D., Meihls, L., Dietloff, J. and Gassmann, A. 2016. Selection of resistance in western corn rootworm to Cry3Bb1, mCry3a, eCry3.1Ab, and Cry34/35Ab1 transgenic corn: variations in traits in the laboratory and the field. International Congress of Entomology. Orlando, Florida, USA
  • Type: Conference Papers and Presentations Status: Published Year Published: 2016 Citation: Masloski, K. E., Coats, J. R. and Gassmann, A. J. 2016. Testing western corn rootworm (Coleoptera: Chrysomelidae) for cross-resistance between Cry toxins and soil insecticides. International Congress of Entomology. Orlando, Florida
  • Type: Conference Papers and Presentations Status: Published Year Published: 2016 Citation: St. Clair, C., Head, G. P., and Gassmann, A. J. 2016. Abundance of western corn rootworm, injury to corn, and Bt resistance in local landscapes. International Congress of Entomology. Orlando, Florida
  • Type: Conference Papers and Presentations Status: Published Year Published: 2016 Citation: Clifton, E. H., Hodgson, E. W., Gassmann, A. J. 2016. Can entomopathogenic fungi induce plant defenses to suppress soybean aphid? International Congress of Entomology. Orlando, Florida
  • Type: Conference Papers and Presentations Status: Published Year Published: 2016 Citation: Gassmann, A. 2016. Resistance to Bt maize by western corn rootworm: inheritance, fitness costs and cross-resistance. International Congress on Invertebrate Pathology and Microbial Control and Annual Meeting of the Society for Invertebrate Pathology. Tours, France
  • Type: Conference Papers and Presentations Status: Published Year Published: 2016 Citation: Clifton, E., Jaronski, S., Hodgson, E., and Gassmann, A. 2016. Impacts of conventional and organic agriculture on soil-borne entomopathogenic fungi. International Congress on Invertebrate Pathology and Microbial Control and Annual Meeting of the Society for Invertebrate Pathology. Tours, France
  • Type: Conference Papers and Presentations Status: Published Year Published: 2016 Citation: Shrestha, R. B. and Gassmann, A. J. 2016. Inheritance and fitness costs associated with field-evolved Cry3Bb1 resistance by western corn rootworm. North Central Branch Meeting, Entomological Society of America. Cleveland, Ohio
  • Type: Conference Papers and Presentations Status: Published Year Published: 2016 Citation: Masloski, K. E. and Coats, J. R. and Gassmann, A. J. 2016. Testing western corn rootworm (Coleoptera: Chrysomelidae) for cross-resistance between Cry toxins and soil insecticides. North Central Branch Meeting, Entomological Society of America. Cleveland, Ohio


Progress 08/09/15 to 09/30/15

Outputs
Target Audience:The target audience included agricultural companies, biotechnology companies, extension specialists, farmers, members of the scientific community, regional agronomists, regulators, and the general public. Changes/Problems: Nothing Reported 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?Objective 1) Evaluate current and emerging management strategies for western corn rootworm and other pests of corn. Field trials will be conducted at various Iowa State University Research Farms to evaluate current and pre-commercial products for management of western corn rootworm and other insect pests of corn. Objective 2) Quantify resistance to Bt corn and conventional insecticides among field populations of western corn rootworm Laboratory bioassays will be conducted using populations of western corn rootworm that were collected throughout Iowa during 2015. Assays will measure susceptibility of populations to both Bt corn and soil-applied insecticides. Objective 3) Conduct laboratory research to measure inheritance, fitness costs and patterns of cross-resistance as it pertains to resistance to Bt corn by western corn rootworm Data will be analyzed from recent experiments measuring inheritance of resistance to Bt corn in both field and laboratory strains of western corn rootworm. Fitness costs of Bt resistance will be tested with field-collected strains using greenhouse experiments. Patterns of cross-resistance among Bt toxins and conventional insecticides will be tested with field populations sampled throughout Iowa.

Impacts
What was accomplished under these goals? The goals of this project are to improve integrated pest management and insect resistance management for insect pests of corn. Corn is attacked by a variety of insect pests, and research work conducted here will improve the ability of famers to reduce yield losses caused by insects. Among the most serious insect pests of corn in the United States is the western corn rootworm. Each year farmers in the US suffer over a billion dollars in crop losses and management costs associated with western corn rootworm. Research conducted under this project will improve management of western corn rootworm by helping regulators, biotech companies, farmers and others in the agricultural community more effectively and delay resistance of western corn rootworm to pest management approaches. Additionally, this research will aid in the development of improved pest management approaches for western corn rootworm. Objective 1) Evaluate current and emerging management strategies for western corn rootworm and other pests of corn Data were analyzed for various field experiments that were conducted during the summer of 2015. These data will be used in presentations at scientific conferences, and in extension and outreach presentations and publications. Objective 2) Quantify resistance to Bt corn and conventional insecticides among field populations of western corn rootworm Eggs were collected from populations of western corn rootworm during the summer of 2015. These eggs will be held in a cold room for 5 months to break diapause and then will be used in various laboratory bioassays to measure resistance to conventional insecticides and Bt corn. Objective 3) Conduct laboratory research to measure inheritance, fitness costs and patterns of cross-resistance as it pertains to resistance to Bt corn by western corn rootworm Using laboratory strains of western corn rootworm with field-derived Bt resistance, plant-based and diet-based bioassays were conducted to measure inheritance of resistance. Data were analyzed for experiments conducted earlier in the year that quantified fitness costs of Bt resistance.

Publications