• Basic Information
• Additional Info

Basic Information

• Project No. and Title: NC246 : Ecology and Management of Arthropods in Corn
• Period Covered: 01/01/2024 to 12/31/2024
• Date of Report: 03/14/2025
• Annual Meeting Dates: 01/21/2025 to 01/23/2025

Participants

Accomplishments

Impacts

1. Entomopathogenic nematodes for corn rootworm control Issue. Corn rootworms, which make up the most economically important pest complex of corn in the U.S., are becoming increasingly difficult to control due to resistance development to Bt traits. Novel control methods are needed to provide farmers with effective tools to complement available biotech traits and insecticides. Actions. During the 2021 NC246 meeting, committee member Elson Shields presented work on persistent entomopathogenic nematodes (EPNs) for control of soil-borne insect pests (particularly corn rootworm) in New York and Texas. These naturally occurring organisms suppress pest populations and remain in the soil for years after an initial inoculation. Several multi-state research projects have been initiated by NC246 members in the years since to evaluate the potential of EPNs as a biological control agent. Later in 2021, a multi-state collaboration among members in Iowa, Illinois, and Nebraska was funded by Corteva with cooperation from Persistent Biocontrol (a private company spun off from Dr. Shields’s work) to examine the potential for EPNs along with cover crops and advanced scouting tools for rootworm management. Fields were inoculated with EPNs in these three states beginning in 2022 and have been assessed each year for EPN activity and rootworm injury. An additional multi-state collaboration among committee members in Texas, Nebraska, and Illinois began in 2023 to assess the impact of EPNs on non-target pest and beneficial insects. Impact. These multi-state collaborations, initiated through NC246, are equipping U.S. farmers to better utilize a sustainable tool for control of a pest that costs over $2 billion each year. Research Grant, Corteva. 2021-2025. “Evaluating diverse approaches to enhance the sustainability of rootworm management.” $316,000. PI: Aaron J. Gassmann. Co-PIs: Erin W. Hodgson and Marshall D. McDaniel Peterson J, R Anderson, H Blanco & T Powers. Corteva Agriscience. “Corteva Innovation Farms: Biological Control & Cover Crops for Corn Rootworm Management.” 2021-2025 ($315,991) ($100,503 in supplemental funding provided by Nebraska Corn Bord) PI: J. Spencer; Co-PI N. Seiter. Corteva Agriscience. 2021-2025. On-farm assessment of innovative approaches to corn rootworm management and monitoring. Project total: $313,500 2023 “Do Persistent Entomopathogenic Nematodes Applied For Western Corn Rootworm Control Negatively Affect The Non-Target Soil Fauna In Cornfields”. USDA-NIFA. D. Ludwick, A. Helms, J. Peterson, T. Powers, N. Seiter, & J. Spencer. NIFA. 1/1/2023-12/31/2025. $748,083.00
2. Corn earworm/bollworm yield impacts in Bt corn Issue. The corn earworm/bollworm, Helicoverpa zea, is the most common ear-feeding pest in corn in the southeastern U.S. While this insect is one of the most important pests of cotton, its effect on field corn yield is often minimal. Bt traits are the primary tool used for control of this insect in both crops, and selection in corn contributes to resistance issues in cotton. Furthermore, these traits increase seed costs. Independent evaluations of their efficacy and effects on yield in corn can assist farmers in making an informed decision of whether or not to use them, improving farm profitability and reducing unnecessary selection pressure for resistance. Actions. Multi-state research in North Carolina, South Carolina, and Georgia has characterized the impacts of Bt traits used to control corn earworm on corn yield and quality. A two-year project in North Carolina and South Carolina did not show any difference in yield among timely-planted Bt and non-Bt hybrids even when corn earworm feeding injury was extensive. Comparisons of 12 years of evaluations that included Georgia, North Carolina, and South Carolina, showed that Bt corn was more likely to provide a yield benefit relative to non-Bt corn when corn was planted late. In addition, this work showed that efficacy of Cry Bt proteins for earworm control has declined since 2015, highlighting the challenges posed by resistance in this species. A USDA NIFA CPPM grant (2021-2024) and a USDA NIFA CARE grant (2021-2024) funded Extension efforts to increase adoption of non-Bt hybrids. These results have been published in scientific journals and translated into best management practice recommendations for farmers in the southeastern U.S. Impacts. Based on recent surveys 16% of farmers were more likely to plant some non-Bt corn and 20% were more likely to plant sufficient non-Bt corn after encountering the results of this work. Reduction of Bt corn acres where it is not likely to provide an economic return improves farmer profitability and reduces selection for resistance, benefiting pest management in cotton and other crops in addition to corn. USDA-NIFA Crop Protection and Pest Management Competitive Grants Program. Improving Bt resistance management through yield comparison of Bt and non-Bt hybrids. (PI: D. Reisig, CoPIs: S. Taylor, Z. Brown, N. Piggott, R. Rejesus, R. Heiniger). 2021-2024. $325,000 USDA-NIFA Foundational and Applied Science Program. Critical Agricultural Research and Extension Program. Exploring conditional cooperation to increase non-Bt refuge corn compliance. (PI: D. Reisig, Co-PI: Z. Brown). 2021-2024. $300,000.
3. Informing the EPA’s regulatory framework for managing Bt-resistance in caterpillar pests Issue: The EPA released a proposal in 2020 to modify the regulation of Bt crops (PIPs = Plant Incorporated Protectants) in response to caterpillar pest resistance, particularly Helicoverpa zea, a key pest of corn and cotton. The initial proposal was poorly aligned with real-world field conditions and allowed the agricultural seed industry to sidestep critical resistance management measures. Actions: Corn and cotton extension entomologists (led by Reisig, NC) drafted a comprehensive letter of recommendations for the EPA informed by ongoing and previous research. This 28-page letter, endorsed by the National Cotton States Arthropod Pest Management Working Group and the NC246 multistate research project, was published in 2022 as a forum article in the Journal of Economic Entomology. The EPA made revisions based on multiple studies authored by NC246 members, ensuring that the regulations better reflected field realities and scientific rigor. Impacts: Corn and cotton growers in the southern U.S. benefited from these efforts through regulatory improvements that help delay resistance to Bt crops. Our forum paper directly influenced several key EPA proposals, such as heightened risk assessments for non-high-dose pests, improved refuge compliance measures, and the prioritization of independent lab results in resistance monitoring. Publications by NC246 members demonstrated that blended refuge should not be an approved tactic to delay refuge for H. zea. Additional research showed that non-Bt hybrids can yield as effectively as Bt hybrids when planted on time, providing growers with cost-effective, sustainable management options. The revised EPA proposal released in 2024 promotes agricultural sustainability by extending the efficacy of Bt crops, saving U.S. growers hundreds of millions of dollars annually. Additionally, reduced reliance on foliar insecticides to manage resistant pests decreases environmental impact and supports biodiversity. These changes exemplify how science-based regulatory frameworks can drive both economic and environmental benefits. Peterson J, B Coates, A Schaafsma, J Smith & M Caprio. USDA-NIFA Biotechnology Risk-Assessment Grant. “Insect Resistance Management: Evaluating the Impact of Blended Refuges and the VIP3A Bacillus thuringiensis Toxin on Western Bean Cutworm.” 2022-2025. ($499,998). USDA-NIFA Biotechnology Risk Assessment Grants Program. Dispersal and reproductive potential of Helicoverpa zea in Bt and non-Bt crops and implications for insecticide resistance management regulations. (PI: S. V. Paula-Moraes, Co-PIs: F.P.F. Reay-Jones, D. Reisig). 2021-2025. $500,000 USDA-NIFA Biotechnology Risk Assessment Grants Program. Impact of blended and structured refuge management tactics on Helicoverpa zea mating behavior and resistance risk implications for Bt crops. (PI: D. Reisig, Co-PIs: A. Huseth, C. Schal, F.P.F. Reay-Jones, M. Caprio). 2023-2027. $617,159
4. Documenting and mitigating resistance to Bt traits in European corn borer Issue: European corn borer, Ostrinia nubilalis, has been kept mostly in check by Bt traits since they were first introduced for commercial use in 1996, dramatically reducing the impact of what once was the most damaging insect pest of corn in the U.S. Beginning in 2018 in Nova Scotia, Canada, several populations of European corn borer with resistance to one or more Bt traits have been identified in small, isolated “pockets” of corn production. In 2023, the first known example of elevated injury by European corn borer to Bt sweet corn in the U.S. was observed in Connecticut in a sentinel plot. Actions: International and multi-state collaborations were initiated by NC246 members to understand the extent, genetic basis, and potential commercial impact of Bt resistance in European corn borer. NC246 members from Ontario identified 6 molecular markers (single nucleotide polymorphisms and a deletion) that were associated with resistance to Cry1F in European corn borer collected in Canada. These polymorphisms caused amino acid changes in the ABCC2 gene, including a deletion that causes a premature stop codon. These were published in Farhan et al. 2023. In 2022, European corn borers were collected from several areas in the northeastern US (3 populations from New York and 1 population from New Hampshire). These samples were sent to the Michel Lab (NC246 member, Ohio) for genotyping with the Cry1F molecular markers. We found alleles associated with resistance, but none of the over 250 samples carried the mutation that led to a premature stop. As resistance to Cry1F has not been detected in the US, our data supports the hypothesis that the deletion is the causal mutation. Similar collections were performed in 2023, including an additional site in Ohio. These collections included both adult insects and live larvae, which will be used to establish laboratory populations. The Jurat-Fuentes lab (NC246 member, Tennessee) has developed a highly multiplexed targeted sequencing approach to facilitate detection of mutations associated with Cry1F resistance, providing a test for early warning of resistance emergence in the U.S. At the 2024 NC246 meeting in Savannah, GA, information on the status of resistance to Cry proteins in Canada and Connecticut led to the initiation of several multi-state projects. European corn borer stalk injury assessments were added to the ongoing Sweet Corn Sentinel Plot Network to provide an early indication of reduced susceptibility. A pheromone and light-trapping network was established to monitor adult populations throughout the U.S. and Canada. Multi-site field experiments were established to examine the impact of corn borer injury on yield of modern hybrids and the potential for stalk destruction to suppress resistant European corn borer larvae as they overwinter. Impact: The international and multi-state collaboration facilitated by this committee was critical to promote early action to identify, understand, and mitigate the potential impacts of Bt-resistant European corn borer at a time when it has not yet been widely observed. As a direct result, farmers (including those in the U.S. corn belt) will have advanced warning if resistant populations of this insect (which they have not dealt with in a meaningful way in the last 25 years) expand and threaten North American corn production more broadly.
5. Managing resistance to insecticides and Bt corn in corn rootworm Issue: Western (WCR) and northern (NCR) corn rootworms have developed resistance to many of the biotech traits available for their control, as well as some insecticides. As the most economically important pest complex of corn in the U.S., corn rootworms account for over $2 billion in control costs and yield losses annually. Actions: A Corn Rootworm Trap Network was established in 2021, which has monitored adult WCR and NCR at 1,782 trap sites in 19 states and provinces. Researchers in Iowa conducted bioassays to monitor local populations for resistance to Cry34/35Ab1 and to determine the inheritance characteristics and fitness costs imposed by resistance traits. Researchers in Nebraska documented high levels of resistance to pyrethroid insecticides in the northeastern portion of the state and confirmed that WCR survival to adulthood and egg production were dramatically reduced by the use of RNAi. A large-plot test in Nebraska resulted in an economic evaluation of the use of Bt traits in combination with insecticides, a common practice on some farms. Researchers in Illinois conducted annual bioassays which detected resistance to Cry3Bb1/mCry3A/eCry3.1Ab and to Cry34/35Ab1 throughout much of the state, publishing these in an annual report to Extension clientele since 2020. Impacts: Farmers throughout the U.S. Corn Belt were better equipped to understand the likelihood of control failures with Bt corn or insecticides in their area, resulting in more effective rootworm control decisions and ultimately protecting crop yields. Information on WCR and NCR resistance status and inheritance of resistance traits will inform more effective Bt resistance management and regulatory strategies for industry registrants and US EPA.
6. Sweet corn sentinel monitoring network Sweet corn sentinel monitoring has been conducted annually since 2017, primarily timed and targeted to track changes in corn earworm (Helicoverpa zea) susceptibility to Cry and Vip3A toxins expressed in Bt corn and cotton. However, activity and damage of western bean cutworm (Striacosta albicosta), European corn borer (Ostrinia nubilalis), and fall armyworm (Spodoptera frugiperda) are also recorded. This network contributed valuable data and alternative methods for monitoring Bt resistance that have changed practices and policy within industry and the EPA. It also facilitated detection of Cry1Ab resistant European corn borer in Connecticut in 2023 and has provided a wealth of valuable data and information that has advanced Bt resistance management and our understanding of Bt resistance mechanisms as well as genetic adaption in insect pests. Two publications have directly resulted from the network team in this project period, with many others leveraging the data and/or specimens for other work.
7. Identified gene controlling male European corn borer response to female pheromone. European corn borer (ECB) damage to maize is usually managed by U.S. farmers by planting varieties that express one or more insecticidal Bacillus thuringiensis (Bt) proteins. Bt-resistant ECB populations have recently been detected in Canada, which is of great concern to the United States due to its potential for spread. Two naturally occurring ECB strains with different pheromone (sex-attractant) communication systems can inter-mate if located in the same geographic region, and the resulting genetic exchange between strains can affect how fast and how far Bt resistance spreads once it develops. Most mating occurs between individuals of the same strain where the genes controlling female pheromone production and corresponding male response are complementary. A genetic marker was developed previously by ARS researchers at Ames, Iowa that indicates which type of pheromone is produced by the female. Now an ARS researcher in Ames, Iowa along with a team of domestic and international collaborators discovered the gene that controls how ECB males specifically respond to different female pheromones, the first time this has been accomplished for any species of moth. This accomplishment opens the door to develop a genetic marker identifying the pheromone strain of ECB males collected in the field, which is crucial in estimating rates of gene exchange between strains and potential for the spread of Bt resistance among ECB populations. This information will be used by regulators, and scientists modeling development and spread of Bt resistance and potential ways to mitigate resistance problems.
8. H. Zea migration A study led by Florida and in a multistate collaborative effort, including Canada, documented the H. zea migration on a continental scale in North America. The study used a novel application of stable hydrogen isotopic ratios (δ2H) in wing tissues as a biogeochemical marker, which can also be used to study other migratory species of moths in the continental U.S. and worldwide. The results offer compelling evidence for novel source regions that support the well-known south-north migration each summer and the first documentation of a reverse migration for H. zea during autumn. This is the first report of the year-round H. zea continental migration, including validation of the isotopic ratio method. This work has implications for predicting large-scale movement and the occurrence of outbreaks and, combined with region-specific information, can refine predictions of arrival and annual colonization of crops in areas where this pest does not survive to the winter. The ultimate impact is to guide environmentally sound and sustainable integrated pest management (IPM) strategies for several economically important crops.
9. H. armigera insecticide resistance Helicoverpa armigera, a quarantine pest in the U.S., has been reported in South America since the crop season of 2012/2013. Since the 2017 crop season, in collaboration with the APHIS/USDA, a year-round pheromone trapping at West Florida Research and Education Center/IFAS/UF, and pest sampling of noctuids during the row crop season has been performed in commercial and experimental fields, in the Florida Panhandle. This species has not been detected. However, recent reports of introgressed populations of H. zea to a single genomic region containing the gene CYP337B3 from H. armigera. This gene is related to encoding the metabolization of several pyrethroid insecticides, and insecticide failures and outbreaks of H. zea in a sweet corn production region in Colorado were reported in 2023. In this scenario, a multistate collaborative work was led by Florida to document the susceptibility of H. zea populations collected in sweet corn production regions in Minnesota and Maryland, besides Florida. Migratory flights of moths of H. zea may further dispersion of populations introgressed with H. armigera genes associated with insecticide resistance. The monitoring system based on insecticide bioassays represents a proactive approach to support an alert system considering the risk of pest outbreaks in corn.

Publications