Source: PURDUE UNIVERSITY submitted to
MANAGEMENT OF WESTERN CORN ROOTWORM IN INDIANA
Sponsoring Institution
National Institute of Food and Agriculture
Project Status
TERMINATED
Funding Source
HATCH
Reporting Frequency
Annual
Accession No.
0206368
Grant No.
(N/A)
Project No.
IND011477
Proposal No.
(N/A)
Multistate No.
(N/A)
Program Code
(N/A)
Project Start Date
Oct 1, 2010
Project End Date
Sep 30, 2015
Grant Year
(N/A)
Project Director
Krupke, C. H.
Recipient Organization
PURDUE UNIVERSITY
(N/A)
WEST LAFAYETTE,IN 47907
Performing Department
Entomology
Non Technical Summary
Corn and soybean growers in the United States often rotate these crops with one another in consecutive years. In many areas, however, corn is grown without rotation (i.e. continuous corn), either as a result of local market pressures (e.g. biofuels), unfavorable conditions for non-corn crops, or both. Both factors are at play in Indiana, where continuous corn production has increased recently and is forecast to continue to do so (Erickson et al. 2008). A direct-mail survey of 241 Indiana growers conducted by Erickson et al. (2008), found that insect and disease management were the top two concerns expressed by continuous corn growers, with the western corn rootworm (WCR) being the top single concern overall. As a result, there is high demand for Bt corn hybrids developed to combat WCR in continuous corn systems. These insecticidal traits are now usually combined or "stacked" with glyphosate-tolerance leading to no "single-trait" insect control option for growers, amounting to an increase in the adoption of both simultaneously. Adoption of corn hybrids expressing "stacked" or multiple traits has also increased dramatically in the US in recent years; from 29% (9.5 million hectares) in 2004 to 46% (15.1 million hectares) in 2009 (NASS 2009) - driven primarily by the introduction and rapid adoption of hybrids that express toxins active against the rootworm beetle complex that are combined with glyphosate-tolerance genes. This convergence and simplification of pest management practices and the incorporation of transgenic traits in plant breeding has largely benefited producers by contributing to increasing yields. However, the widespread adoption of any pest management strategy carries with it a potential for an increased selection pressure upon the target pests, followed by an increased risk of resistance evolution. This caveat is particularly relevant to the WCR/Bt corn system currently in place. When transgenic corn for rootworm control was registered in 2003, an insect resistance management (IRM) plan, based on mandatory refuges, was required and included with the purchase of the seed. In brief, this strategy hopes to overwhelm the rare adults that survive Bt exposure and carry with them recessive resistant alleles with susceptible alleles when they mate with the more numerous beetles emerging from refuges. The strategy works best when the Bt dose is high, largely because the numbers of heterozygote survivors (and correspondingly, the numbers of resistance alleles) will be reduced. Importantly, none of the currently available Bt toxins for WCR control are considered high dose (Miehls et al. 2008; Tabashnik 2008), a factor that lends even more urgency to research into factors that may hasten resistance development.
Animal Health Component
(N/A)
Research Effort Categories
Basic
30%
Applied
70%
Developmental
(N/A)
Classification

Knowledge Area (KA)Subject of Investigation (SOI)Field of Science (FOS)Percent
2111510113060%
2161510113040%
Knowledge Area
211 - Insects, Mites, and Other Arthropods Affecting Plants; 216 - Integrated Pest Management Systems;

Subject Of Investigation
1510 - Corn;

Field Of Science
1130 - Entomology and acarology;
Goals / Objectives
Indiana corn producers have adopted a new pest management technology for a key insect pest, the western corn rootworm (WCR). Corn plants expressing a rootworm-specific toxin (i.e. B.t. corn) has gained widespread acceptance in the US and abroad. However, there are several challenges associated with managing and maintaining this technology for Indiana agriculture. The goal of the work proposed here is to use tightly-focused studies of natural populations to develop information that will improve our understanding of the response of this adaptable pest to the challenge of current Bt corn varieties. This work will also provide baseline data that will allow for design of better predictive models and management tactics for implementing the next generation of transgenic insect-resistant plants. To address this goal, we propose the following specific objectives: 1) Quantify gene expression in volunteer corn plants in cornfields and document larval damage and beetle emergence from these plants. 2) Analyze the effects of larval survival, adult emergence and sex ratios of WCR moved from volunteer corn plants to commercial Bt corn.
Project Methods
At each location we will flag plots and seed each with volunteer corn seed at a rate of 2 kernel/m2 (for a maximum of 54 plants/plot) on the same day that the rest of the field is planted. Beginning 20 days after planting (emergence will be underway by this time in both the planted crop and volunteer plants), we will count and label each volunteer plant present in the plots. Volunteer plants will be identified as those that do not occur within the planted row. At that time, we will remove a 1 cm2 section of leaf tissue from each volunteer plant and place it in a correspondingly numbered 1.5 ml microcentrifuge tube for transport back to the laboratory and analysis for glyphosate resistance and Bt traits using Quickstix lateral flow qualitative protein expression test strips (Products AS 010 LSS and AS 015 LSS, Envirologix Inc., Portland, ME). The corresponding flags on each plant will then be marked to reflect the results from these tests and identify each plant through the season. Using these plots, we will monitor Bt toxin expression (quantitative and qualitative measures), adult emergence, sex ratios and damage to adjacent plants in each plot. Expected Results: We expect to generate qualitative data on the relative proportions of genetic traits (Bt expression and glyphosate tolerance) that are present in volunteer corn plants. Furthermore, we will document beetle emergence and sex ratios and conduct root damage surveys to determine whether volunteer plants have significant effects upon the adjacent crop plants. This information is important to scientists and producers alike and has the potential to change the way we use these transgenic tools as part of the suite of pest management tools - both in the short and long-term. For example, if we are able to demonstrate that adult beetles emerge from weakly-toxic Cry3Bb1 volunteer plants, modelers can later integrate these partially-exposed WCR adults into deterministic models that endeavor to predict when resistance will occur. Because seed mixes are a viable approach to refuge management that is currently being pursued by the 2 major producers of Bt corn hybrids, it is important to know how volunteer corn affects the system - for example, the 2-5% refuge proposed by Pioneer could be effectively changed by volunteer plants (estimated to comprise up to 11% of plants present) that occur unpredictably throughout the field and either do not express Bt toxins, and do so at a range of rates. We expect to generate data on the relative survival of total adults, males/females, and their relative sizes and dry weights from each of the treatments. Using the volunteer-free plots as a baseline, we will be able to determine whether the addition of a volunteer Bt corn plant contributes significantly to adult emergence. Perhaps more importantly from a long-term stewardship point-of-view, we will be able to test the hypothesis that there are no differences in any of these parameters as a result of exposure to Bt+ vs. Bt- volunteer corn as a potential initial host, including whether adult numbers differ when the volunteer plant is killed early in the season.

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

Outputs
Target Audience:Producers, crop consultants, researchers associated with corn insect pest management. Changes/Problems: Nothing Reported What opportunities for training and professional development has the project provided?One post-doctoral associate led the work completed in 2015 and two undergraduates were integral parts of the day to day data collection. How have the results been disseminated to communities of interest?Through several field days throughout Indiana, audience is primarily farmers and private pesticide applicators. Also disseminated research to fellow scientists via annual Entomological Society meeting in Minneapolis (November 2015). What do you plan to do during the next reporting period to accomplish the goals? Nothing Reported

Impacts
What was accomplished under these goals? Our work strongly indicates that WCR beetles do not mate at random in the field, but instead base their mate preference on size. We discovered that WCR females have a preference for larger and heavier males. We also revealed that males have a preference for larger females. However, most females are mated regardless of their size. This knowledge is critical considering that there are known size differences in beetles that emerge from Bt and refuge corn. It also stresses the importance of understanding factors that influence how often a male beetle mates in the field.

Publications


    Progress 10/01/13 to 09/30/14

    Outputs
    Target Audience: Producers, crop consultants, researchers associated with corn insect pest management. Changes/Problems: Field season of 2014 was not as informative as hoped, partly due to very low insect pressure levels. Updates/changes in 2015 include earlier planting dates and moving the trials to areas where RW pressure is higher. What opportunities for training and professional development has the project provided? One MS student (graduated in summer 2014) and a current post-doctoral fellow (began in May of 2014). 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? Large scale field study is planned for 2015 to expand and increase the power of the conclusions developed by the MS project. The earlier work will also be published during the next reporting period.

    Impacts
    What was accomplished under these goals? Significant progress was made under objective #2. A MAsters student (Steven Smith) completed work analyzing mating rates of WCR in Bt/refuge mixes by using N15 marked plants. This work appeared in his thesis, graduation was August of 2014. A manuscript is in preparation. A new post-doctoral scholar (Ahmed Dirie) is continuing on and expanding this work to a larger field setting.

    Publications


      Progress 10/01/12 to 09/30/13

      Outputs
      Target Audience: Producers, crop consultants, researchers associated with corn insect pest management. Changes/Problems: Nothing Reported What opportunities for training and professional development has the project provided? Paul Marquardt focused upon this for the doctoral research and published 3 papers from this work in 2013. How have the results been disseminated to communities of interest? Primarily in 4 main ways: 1) journal publications (4 total) 2) oral presentations of this work at scientific meetings (ca. 10 total) 3) presentations to grower and extension educator groups at Diagnostic Training sessions and Pesticide Applicator Recertification Training (ca. 10 total). What do you plan to do during the next reporting period to accomplish the goals? The main goals of the project are achieved - volunteer corn can and is being controlled by growers in the Midwest. During the next period we will work more on quantifying emergence from Bt/refuge corn plants and figuring out how these emergence rates impact mating and, ultimately, the durability of Bt proteins.

      Impacts
      What was accomplished under these goals? In collaboration with William Johnson (weed scientist), Dr. Krupke performed a study that has implications for both weed management and for long-term management of resistance in rootworm populations. Volunteer corn is relatively easy to manage in soybeans using grass herbicides. However, because sub-lethal exposure can promote and accelerate the development of resistance, the exposure of WCR larvae to volunteer Bt corn in soybean fields must be seen as a threat to the Bt/refuge system currently in place - this type of non-lethal exposure is precisely the situation that current, structured refuges are designed to avoid (i.e. the goal is to minimize the probability of generating heterozygotic, weakly-resistant individuals). This is another dynamic variable that must be included in current and future models of resistance. During the past year, Dr. Krupke co-supervised a student (Paul Marquardt) who publshed work showing that volunteer corn is a damaging weed in soybeans (this induces producers to control it) and that nitrogen deficit is a driver of low toxin expression in volunteer corn plants growing in soybean fields.

      Publications

      • Type: Journal Articles Status: Awaiting Publication Year Published: 2013 Citation: Marquardt, P.T., C.H. Krupke, J.J. Camberato, and W.G. Johnson. (2013). The effect of nitrogen rate on transgenic corn Bt protein expression. Pest Mgt. Sci.
      • Type: Journal Articles Status: Published Year Published: 2013 Citation: Kang, J.K., C.H. Krupke, A.F. Murphy, J.L. Spencer, M.E. Gray, and D.W. Onstad. 2013. Modeling a western corn rootworm, Diabrotica virgifera virgifera (Coleoptera: Chrysomelidae) maturation delay and resistance evolution in Bt corn. Pest. Mgt. Sci.
      • Type: Journal Articles Status: Published Year Published: 2013 Citation: Marquardt, P.T., R.M. Terry, C. Krupke, and W.G. Johnson. 2013. Competitive effects of volunteer corn on hybrid corn growth and yield. Weed Sci. 60: 537-541
      • Type: Journal Articles Status: Published Year Published: 2013 Citation: Venkata BP, Lauter N, Li X, Chapple C, Krupke C., Johal, G. and S. Moose. (2013) crw1 - A Novel Maize Mutant Highly Susceptible to Foliar Damage by the Western Corn Rootworm Beetle. PLoS ONE 8(8): e71296. doi:10.1371/journal.pone.0071296


      Progress 10/01/11 to 09/30/12

      Outputs
      OUTPUTS: The Corn and Soybean Field Guide, published by Purdue University Extension, typically sells approximately 70,000 copies to a variety of agronomic clientele in Indiana and elsewhere. The Forage Field Guide circulation is approximately 6,000. Dr. Krupke, in cooperation with IPM specialist John Obermeyer, edits and updates the insect pest management sections of these publications yearly. Dr. Krupke will continue to be the entomology lead on this annually-updated publication. We are currently developing a digital version of the pocket guide for smartphone users. This will be rolled out late in 2012. Krupke, C.H. and J.L. Obermeyer. 2011. Corn Insect Pest Management. In: Corn and Soybean Field Guide. 2008 Edition. ID-179 Purdue University Extension Publications. Krupke, C.H. and J.L. Obermeyer. 2011. Soybean Insect Pest Management. In: Corn and Soybean Field Guide. 2008 Edition. ID-179 Purdue University Extension Publications. Krupke, C.H. and J.L. Obermeyer. 2011. Small Grains and Forage Insect Pest Management. In: Forage Field Guide. 2008 Edition. ID-317 Purdue University Extension Publications. Dr. Krupke prepares weekly Pest&Crop newsletter articles during the growing season. Since arriving at Purdue, Dr. Krupke has been primary author on over 90 newsletter articles addressing timely pest management topics. John Obermeyer works with Dr. Krupke on these publications. Generally, 12-15 articles are produced each growing season. Most readers are not farmers, but consultants and pest managers who typically manage large acreages. The newsletter features authors from multiple disciplines, and is one of the most frequently accessed agronomic resources produced by Purdue Extension: C.H. Krupke, V. Willot, P. Marquardt. Volunteer corn: challenges for weed management and insect resistance management. Annual Meeting - Entomological Society of America. Reno, NV. November 2011. Symposium oral presentation. PARTICIPANTS: Not relevant to this project. TARGET AUDIENCES: Primary audiences include field crop growers, consultants and any agri-business individuals that are connected with pest management activities in field crops. Dr. Krupke also interacts with fellow public sector scientists from both academia and USDA. PROJECT MODIFICATIONS: Not relevant to this project.

      Impacts
      The extension recommendation has been to treat this weed with a selective grass herbicide prior to pupation of larvae (i.e. early June). This work was published and featured as the cover story in a multi-disciplinary publication, the Journal of Agronomy, and has been featured in several print media. This information will form a cornerstone of future presentations and research will be extended to answer questions about the more difficult problem of volunteer corn in continuous corn systems. As part of NCCC-46 North Central Region Technical Committee on corn rootworms, Dr. Krupke's work as chair helped shape new bagtag requirements for transgenic field crop seeds. The practical outcome of this is that research can now be conducted by public sector scientists on these crops with much greater freedom.

      Publications

      • Onstad, D., P. Mitchell, Terry Hurley, Jon Lundgren, Pat Porter, Christian Krupke, Joseph Spencer, Christina Difonzo, Tracey Baute, Rick Hellmich, Lawrent Buschmann, William Hutchison and John Tooker. 2011. Seeds of Change: Corn seed mixtures for resistance management and IPM. J. of Economic Entomology. 104: 343-352.
      • Isolated females and limited males: evolution of insect resistance in structured landscapes (pages 38 - 49)Joseph Spencer, David Onstad, Christian Krupke, Sarah Hughson, Zaiqi Pan, Bruce Stanley and Lindsey Flexner Article first published online: 4 DEC 2012 DOI: 10.1111/eea.12022
      • Murphy, Alexzandra, Nicholas Seiter and Christian Krupke. 2011. The impact of Bt maize as a natal host on adult head capsule width in field populations of western corn rootworm. Entomologia experimentalis et applicata. 139: 8-16.


      Progress 10/01/10 to 09/30/11

      Outputs
      OUTPUTS: Talks at annual meetings: P. Marquardt, V. Willot and C.H. Krupke. Quantifying impacts of volunteer transgenic corn in continuous corn systems. Annual Meeting - Entomological Society of America. Reno, NV. November 2011. Field days: Research was also disseminated to producers and consultants over the course of several field days and DTC workshops (5 workshops, approximately 200 participants), Pinney Purdue field day (300 participants) with special focus upon volunteer corn control and the risks of refuge-in-a-bag in Bt corn systems. Many popular press articles (Corn and Soybean Digest, Top Crop Manager) and Purdue press releases (AgAnswers) have featured this work as well, usually in the form of interviews with Krupke. PARTICIPANTS: Dr. William Gordon Johnson, weed scientist, Purdue BTNY TARGET AUDIENCES: Primary audiences are producers, consultants and researchers involved with the implementation and stewardship of Bt corn in agro-ecosystems PROJECT MODIFICATIONS: None to report, other than the shift of primary focus from volunteer corn in soybean plantings to the potentially more problematic issue of volunteer corn in corn.

      Impacts
      On the weed management side, we shifted focus (with W. Johnson, weed scientist) to quantify effects on corn yield. Finding no significant yield reductions indicates that volunteer corn will not be a weed that is prioritized by producers, this is a different situation than in soybeans - where control can be accomplished by June 15. This is a change in knowledge - we know that this is a not a significant yield-limiting weed. However, we also know that volunteer corn in corn causes increased damage to neighboring plants and (more importantly) offers a potential harborage for rootworm larvae and sublethal exposure. Another change in knowledge is the finding that these plants will typically occur in cornfields at a rate of 1/square meter. This can alter the calculations for refuge plants by as much as 10%. In seed mix refuges, where 5% is the desired goal, volunteer corn plants can raise (or lower) that percentage significantly, depending on whether they express the Bt toxin or not. The extension recommendations are still under development, but will include 2 points: 1) growers should calibrate harvest equipment properly to avoid leaving corn in the field during harvest, and 2) in order to minimize opportunities for sublethal exposure of larvae to volunteer plants, proper pre-planting weed control is a priority where continuous corn is expected to include volunteer corn pressure.

      Publications

      • Onstad DW, Mitchell PD, Hurley TM, Lundgren JG, Porter RP, Krupke CH, Spencer JL, DiFonzo CD, Baute TS, Hellmich RL, Buschman LL, Hutchison WD, Tooker JF. 2011. Seeds of change: corn seed mixtures for resistance management and integrated pest management. J Econ Entomol. Apr;104(2):343-52.


      Progress 10/01/09 to 09/30/10

      Outputs
      OUTPUTS: Research was disseminated via several talks, both by Dr. Krupke and his students: C.H. Krupke, P. Marquardt and W. Johnson. Volunteer transgenic corn: assessing potential impacts for rootworm resistance management in continuous and rotational cropping systems. Annual Meeting - Entomological Society of America. Indianapolis, IN. December 2009. Research was also disseminated to producers and consultants over the course of several field days and DTC workshops (7 workshops), with special focus upon volunteer corn control and the risks of refuge-in-a-bag in Bt corn systems. PARTICIPANTS: William Johnson (BTNY - Purdue) has been involved extensively with the volunteer corn project. Steve Weller (HORT - Purdue) also assisted with this work. TARGET AUDIENCES: Primary audiences are producers, consultants and researchers involved with the implementation and stewardship of Bt corn in agro-ecosystems PROJECT MODIFICATIONS: Nothing significant to report during this reporting period.

      Impacts
      Several outcomes from the volunteer Bt corn work (with W. Johnson): first, quantification of corn as a weed led to an understanding that this is the 4th most common weed in soybeans, and densities as low 2 plants/sq. meter can reduce yield. The finding that these plants express Bt and allow larvae to survive to adulthood led to an extension recommendation to treat volunteer corn early (pre June 15), which minimizes yield effects and kills the plant/host before larvae can reach adulthood. The work that is summarized in the Murphy et al., paper was cited by the EPA Science Advisory Panel in assessing whether Bt corn should be incorporated with a refuge in a seed mix form. This was the only peer-reviewed published work available at the time that empirically tested the various Bt/refuge plantings in the field, with natural pest populations.

      Publications

      • Murphy, Alexzandra, Matthew Ginzel and Christian Krupke. 2010. Effect of varying refuge structure upon root damage, emergence and sex ratios of western corn rootworm on transgenic corn. Journal of Econ. Entomol. 103: 147-157.
      • Michel, A.P., C.H. Krupke, T.S. Baute, and C.D. Difonzo. 2010. Ecology and management of the western bean cutworm (Lepidoptera: Noctuidae) in dry beans. 1: 1-10.
      • Seiter, Nick, Jeffrey Holland, Douglas Richmond and Christian Krupke. 2010. A novel method for estimating herbivory in the western corn rootworm. J. Econ. Entomol. 103: 1464-1473.
      • Sappington, Tom, Ken Ostlie, Christina Difonzo, Bruce Hibbard, Christian Krupke, Patrick Porter, Steve Pueppke, Elson Shields and Jon Tollefson. 2010. Conducting public-sector research on commercialized transgenic seed: In search of a paradigm that works. 1: 2, 1-4.


      Progress 10/01/08 to 09/30/09

      Outputs
      OUTPUTS: Research was disseminated via several talks, both by Dr. Krupke and his students: C.H. Krupke, P. Marquardt and W. Johnson. Volunteer transgenic corn: assessing potential impacts for rootworm resistance management in continuous and rotational cropping systems. Annual Meeting - Entomological Society of America. Indianapolis, IN. December 2009. Symposium oral presentation. C.H. Krupke, P. Marquardt and W. Johnson. Emergence of adult western corn rootworm beetles from volunteer corn in soybean fields presents challenges for resistance management. Annual Meeting - Entomological Society of America. Reno, NV. November 2008. Symposium oral presentation. P. Marquardt, W. Johnson and C.H. Krupke. Emergence of adult western corn rootworm beetles from transgenic Bt corn in soybean fields. Annual Meeting - Entomological Society of America. Reno, NV. November 2008. Poster presentation. Seiter, N., D. Richmond and C.H. Krupke. Biological and economic consequences of varying refuge construction in transgenic cornfields. Annual Meeting - Entomological Society of America. Reno, NV. November 2008. McKinnis, A. M. Ginzel and C.H. Krupke. Biological and economic consequences of varying refuge construction in transgenic cornfields. Annual Meeting - Entomological Society of America. Reno, NV. November 2008. Research was also disseminated to producers and consultants over the course of several field days and DTC workshops (7 workshops). One graduate student (Nick Seiter) graduated during the reporting period, earning an MS degree. PARTICIPANTS: William Johnson (BTNY - Purdue) has been involved extensively with the volunteer corn project. Steve Weller (HORT - Purdue) also assisted with this work. Matthew Ginzel (ENTM - Purdue) has assisted with the project, co-supervising PhD student Alex Murphy. Nick Seiter (MS graduate) developed an ELISA and photographic method for determining the risk of variant behavior in western corn rootworms trapped in Indiana. TARGET AUDIENCES: Primary audiences are producers, consultants and researchers involved with the implementation and stewardship of Bt corn in agro-ecosystems. PROJECT MODIFICATIONS: Nothing significant to report during this reporting period.

      Impacts
      Several changes in knowledge resulted from the outputs described above. The primary outcome was development of an understanding that volunteer corn is a concern not just because it is a weed, but also because it expresses sublethal rates of Bt toxin. This has potential to accelerate resistance development. Fortunately, producers may treat volunteer corn early using a graminicide herbicide to kill the weed and eliminate development of WCR larvae on these plants. Another outcome was the use of research into novel implementation of Bt corn into seed mixes by Dr. Krupke's student (Alex Murphy) by an EPA panel commissioned to assess the viability of a Pioneer proposal to alter refuge structure. This data was the only independent data to be reviewed by the panel.

      Publications

      • Marquardt, Paul and Christian Krupke. 2009. Dispersal behavior of western corn rootworms in Bt and refuge cornfield environments. Environmental Entomology. 38: 176-182.
      • Krupke, Christian, William Johnson, Paul Marquardt, Stephen Weller and Shawn Conley. 2009. Volunteer corn presents new challenges for insect resistance management. Agronomy Journal. 101: 797-799. Featured as cover story.
      • Kang, Jungkoo and Christian Krupke. 2009. Influence of weight of male and female western corn rootworm, Diabrotica virgifera virgifera LeConte, on mating behaviours. Annals of the Entomological Society of America. 102: 326-332.


      Progress 10/01/07 to 09/30/08

      Outputs
      OUTPUTS: Activities in the past year including advancing experiments to understand the prevalance of volunteer Bt corn in Indiana, the toxicity of these plants to larval rootworms, and the emergence of adult beetles from these plants. We also continued experiments with alternate methods of planting refuge in transgenic crops (refuge in a bag), to determine the effects of this practice upon yield and beetle damage and emergence. Finally, we continued our project to quantify the degree of soybean feeding in Indiana, to give growers an idea of the degree of risk to first-year corn in their areas. This project has 3 years of beetle data and we are currently analyzing beetle gut contents to develop a risk map. These results were disseminated using crop management workshops (5 throughout the state) during January of 2008, where growers were informed of findings regarding movement of WCR beetles in refuge environments. These included approximately 1000 growers and applicators. Other output methods included summer workshops that reached approximately 500 ag-business reps and consultants. Adoption of Bt crops continues to grow, and with increased combination of Bt and herbicide-tolerance traits into single plants, the issues of weed and insect resistance management have become one issue - this was a focus of 2008 outputs that stressed the importance of managing volunteer Bt corn in the light of it both as a glyphosate-tolerant weed and as a possible alternate development site for larval rootworm larvae. PARTICIPANTS: Collaborator on volunteer transgenic corn project: Dr. William Johnson, Purdue BTNY department TARGET AUDIENCES: 1) growers and private applicators 2) agribusiness (consultants, chemical company reps) 3) other scientists - both public and private sector PROJECT MODIFICATIONS: Nothing significant to report during this reporting period.

      Impacts
      We developed the following changes in knowledge over the past year: 1) we found that Bt volunteer corn in soybeans can act as a larval host for rootworms, and that beetles can survive to adulthood; 2) we found that this is likely due to lower N rates in these cropping systems, which prevent corn from synthesizing Bt protein. These changes resulted in an increase in grower awareness of volunteer corn as more than just a weed, but also a potential host and reservoir for a damaging pest. The change in actions we hope to affect is that growers treat this weed earlier in season with a non-glyphosate grass herbicide. We also developed new knowledge that shows that refuge-in-bag options for rootworm management allow synchrony of emergence peaks while also causing increased damage on adjacent plants. This will allow grower clientele to appreciate that that although refuge-in-bag options offer convenience, they may also carry increased risk of damage to adjacent, non-refuge plants and a risk of exposure to sub-lethal Bt rates. We propose that as a long-term option, this refuge strategy may carry more risk than the existing, structured refugia.

      Publications

      • Diffenbaugh, Noah, Christian Krupke, Michael White and Corinne Alexander. 2008. Global Warming poses challenges for maize pest management. Environmental Res. Letters.


      Progress 10/01/06 to 09/30/07

      Outputs
      OUTPUTS: The primary output was using field days during the 2007 growing season, which included over 500 growers, industry representatives and consultants. Although the research is not yet complete, interest in the questions we are posing in this research was very high. Adoption of transgenic crops for rootworm control is estimated to almost have doubled from 2006 to over 17 million acres in 2007, and is expected to continue to rise. After data summary and analysis are completed in early fall of 2007, these results will be included in our winter extension programming, which includes dozens of presentations to an estimated 1000+ clientele, through pesticide applicator training, crop management workshops (approximately 900 participants annually) and scheduled presentations to certified crop consultants and the Indiana Seed Trade Association. TARGET AUDIENCES: Indiana crop consultants Agro-chemical industry representatives Growers Extension educators

      Impacts
      Work continued towards unravelling interactions between rootworm beetles, Bt corn, and on-farm refuge management. Our data from the past year indicate that the in-field dispersal of male WCR responding to reproductive females is extensive. This may be a key factor in determining the number and type of male beetles (transgenic feeding or refuge feeding) moving into transgenic blocks of cornfields. Based on probabilities alone, the closer a female within a transgenic block of corn is to a refuge/transgenic corn interface, she is more likely to be approached by mates that emerged from the refuge corn, (i.e. refuge-feeding males), yet our data suggest that even females in the center of transgenic cornfields have a 40 to 60% probability that a male that approaches them will be a refuge-feeding individual. Other results indicate that there are differences between how the 3 IRM refuge designs allow for dispersal of refuge-feeding males into transgenic areas of the field, namely that the strip refuge design does a better job of dispersing refuge-feeding males into transgenic areas than the block and adjacent designs. In summary, one of the key findings of the past year is the observation that refuge placement in relation to transgenic corn affects the proportion of refuge males dispersing into transgenic areas of a field to mate. The closer the refuge corn is to transgenic corn, the higher the probability that refuge-feeding males will find transgenic emerging females to mate with. Another key finding is the very high dispersal rate of male WCR beetles, often up to 200 m/d. This high dispersal rate by male beetles had not previously been described. These findings may ultimately help determine the efficacy of current transgenic rootworm-resistant products and current IRM strategies.

      Publications

      • 1. Bledsoe, L.W., Krupke, C. 2007. Corn and soybean insecticide evaluations: 2006 Summary. Dept. of Entomology, Purdue University. 2. Krupke, C.H., Obermeyer, J.L., and Bledsoe, L.W. 2007. Managing corn rootworms. Dept. of Entomology, Purdue University. Publication E-49W.