Research Project: Ecologically-based Management of Arthropods in the Maize Agroecosystem

Location: Corn Insects and Crop Genetics Research

2021 Annual Report

Objectives
Objective 1: Improve knowledge of the genetics, genomics, ecology, and behavior of key maize insect pests as they affect abundance and pest resistance to insecticidal agents, including those expressed in transgenic maize. Sub-objective 1.A. Determine genomic architecture of phenotypic traits within and among reproductive and ecological variants of European corn borer. Sub-objective 1.B. Determine how insect movement and genetics impact potential for development of resistance to GE insecticidal toxins. Sub-objective 1.C. Develop genomic and computational resources for study of key maize pests. Objective 2: Identify and functionally dissect contributions of maize alleles that confer host plant resistance to lepidopteran pests. Sub-objective 2.A. Identify contributing alleles and specialized metabolites conferring resistance to silk-feeding by corn earworm. Sub-objective 2.B. Characterize resistance and develop doubled haploid inbred lines of maize with leaf activity against fall armyworm. Objective 3: Determine potential impacts of farming practices in maize agro-ecosystems on the ecology and management of both arthropod pests and non-pests such as monarch butterflies and bees. Sub-objective 3.A. Develop a risk-based decision support tool for managing sporadic insect pests of seedling maize. Sub-objective 3.B. Develop strategies for improving monarch butterfly and bee habitat in agricultural landscapes.

Approach
European corn borer, corn rootworm, and western bean cutworm are the most serious pests of maize in the Corn Belt, while corn earworm and fall armyworm are major pests in the southern half of the United States. Genetically-engineered (GE) maize is an important management tool for these insect pests, but they have evolved resistance to GE crops in many areas, seriously threatening their continued effectiveness. This project will take an integrated approach toward developing management strategies and tools to use against these insect pests with emphases on insect resistance management to GE maize, insect ecology, insect genetics and genomics, and native host plant resistance. We will address critical knowledge gaps including maize insect pest population genetic dynamics and genomic function, dispersal behavior, efficacy of insect resistance monitoring, and insect resistance management strategies, including ways to incorporate a diversity of pest suppression tactics. Native host plant resistance to control insect pests can serve the latter function, and provide a cost-efficient sustainable management tool for growers who choose not to use GE maize. This project will study native resistance in maize to insect pests, particularly corn earworm and fall armyworm, so that low-input control options can be developed. Given concerns on the indirect effects of farming practices on non-target arthropods, including bees and monarch butterflies, project scientists will work with stakeholders to develop strategies for increasing habitat for monarch butterflies to counter loss of milkweeds in maize and soybean fields. In addition, researchers will provide growers a decision support tool to allow realistic assessment of when the use of seeds coated with neonicotinoid insecticide is justified in their particular fields to control sporadic seedling pests and when it is not, reducing overall insecticide input. Collectively, this research will result in maize pest management systems that are stable and reliable, cost effective for producers, and safe for growers, consumers and the environment.

Progress Report
Objective 1: Research continued on understanding the genetics and genomics of key maize pests and how they affect population dynamics, ecology, and development of resistance to control tactics. Bt maize is no longer effective at controlling western bean cutworm (WBC). Many pest insects that damage maize, including the western corn rootworm (WCR), European corn borer (ECB), and WBC, are usually managed by genetically engineered (GE) maize varieties, which express one or more insecticidal proteins derived from the bacterium Bacillus thuringiensis (Bt). However, these pests have developed resistance to some Bt maize varieties, threatening economic losses in many locations. Survival was high among WBC from the Midwest to the East Coast when the larvae were fed a diet containing the Bt protein or Bt maize tissue, indicating that Bt maize is no longer very effective in controlling this pest in many areas. This information will be useful to farmers and consultants making WBC management decisions. Mitochondria are organelles in animal cells that contain their own DNA inherited through the female line, and mtDNAs sequences contain useful information for understanding the genetic history of populations. ARS researchers in Ames, Iowa, developed a method to increase the efficiency of generating mtDNA sequence data from ECB, involving enrichment of extracts prior to high-throughput sequencing. Application of the new method revealed previously unknown mutations in the ECB mitochondrial genome, which will be useful for tracking maternal lineages in populations and the contribution of female movement in the landscape to the spread of Bt resistance. Changes in genome structure can affect the evolution of a species, including generation of mutations that lead to Bt resistance. DNA sequences derived from a virus were discoverd integrated into the genomes of WCR and the southern corn rootworm (SCR). This is the first report of new sequences from another organism acquired naturally by WCR and SCR genomes. This information will be important for evaluating how changes in genome structure may have influenced differences in maize host specificity by WCR compared to the broader range of host plants used by SCR. Objective 2: Research continued on dissecting the genetic basis conferring host plant resistance to key moth pests of maize. Field work was conducted to grow, pollinate, and harvest new seed to ensure preservation of breeding lines and other important maize genotypes needed for future research on plant resistance to fall armyworm (FAW) and corn earworm (CEW). Where needed, these seed-increase efforts were conducted under selection pressure from the pest to preserve the integrity of resistance in the maize genotypes. Objective 3: Research continued on the impacts of farming practices in maize agro-ecosystems on non-pests such as monarch butterflies. The eastern North American population of monarch butterflies has declined significantly over the last two decades. Loss of the larval host plant, milkweed, in agricultural landscapes is one of the primary drivers of this decline. Achieving a resilient population of monarchs requires establishing an estimated 1.6 billion additional milkweed stems throughout their summer breeding range. A study was initiated by ARS researchers in Ames, Iowa, to determine best practices for establishing common milkweed in habitats dominated by cool-season smooth brome grass. This type of habitat is very common, particularly on roadsides. Preliminary results suggest establishing common milkweed into smooth brome areas is substantially improved by reducing grass competition through glyphosate application, mowing, and planting milkweed rhizomes. Better understanding of insecticide exposure risk and female monarch behavior could be important in strategic placement of monarch habitat in agricultural landscapes. In choice experiments in laboratory cages, female monarchs did not discriminate between milkweed contaminated by a neonicotinoid insecticide and untreated control milkweed when laying eggs. Tethered flight experiments were conducted by ARS researchers in Ames, Iowa, on directional flight of monarch adults when in the presence of a habitat patch at different distances. Preliminary analyses indicate that monarchs foraging for nectar or milkweed usually fly upwind regardless of direction and distance to habitat. This suggests placing habitat patches along summertime prevailing wind trajectories may facilitate inter-patch detection, movement, and utilization among breeding monarchs.

Accomplishments
1. Determined insecticide risk to monarch butterflies in habitat near crops in Midwest United States. The eastern North American population of monarch butterflies has declined significantly over the last two decades. A variety of seed-treatment and foliar insecticides are used to manage early- and late-season pests in Midwest agricultural landscapes. Thus, there is a need to assess risks of these insecticides to monarch butterfly life stages to inform habitat conservation practices. Dietary and contact toxicity studies were conducted by ARS researchers at Ames, Iowa, in collaboration with researchers from Iowa State University on all monarch developmental stages using representative insecticides from four major classes. The diamide and pyrethroid were generally the most toxic insecticides to all life stages, and the neonicotinoid and organophosphate were generally the least toxic. Impact of an insecticide on a population depends not only on toxicity, but also on the level of exposure. The toxicity results were compared to estimates of insecticide exposure derived from a spray drift model and from data reported in the literature on amounts of insecticide detected on or in milkweed tissue. Results suggest neonicotinoid seed treatments will cause little to no downslope (runoff in soil) mortality or non-lethal adverse effects in larvae and adults. Aerial applications of foliar insecticides could cause high mortality in larvae and eggs located near the field and downwind, with lower mortality predicted for adults and pupae. However, given the predicted levels of exposure, along with the highly mobile behavior of monarch females that lay their eggs in many locations throughout a landscape, these results suggest that benefits of establishing new habitat close to maize and soybean fields in agricultural landscapes outweigh negative effects of insecticides on monarch population growth in the north central United States. This information will be used by regulators and scientists planning monarch habitat restoration.

2. Identification of a gene controlling male European corn borer response to female pheromone. U.S. farmers manage European corn borer (ECB) damage to maize 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 previously developed by ARS researchers at Ames, Iowa, 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.

3. Monarch larvae are not affected by double-stranded RNA for control of Varroa mites in bee hives. Varroa mites are parasites that, combined with other factors, are contributing to high levels of honey bee colony losses. A Varroa-active double-stranded RNA (dsRNA) was recently developed to control Varroa mites in honey bee hives. This dsRNA kills Varroa mites by specifically binding to a region in the mite's calmodulin gene (cam), thus disabling the gene. Because of similarities in the cam gene in monarch butterflies, adverse effects could be possible if monarch larvae are exposed. ARS researchers in Ames, Iowa, in collaboration with researchers from Iowa State University, conducted experiments exposing monarch larva to one- and ten-fold higher concentrations of Varroa-active dsRNA than are used to treat honey bee hives. A previously designed monarch-active dsRNA with a 100% sequence match to a different essential monarch gene was tested for comparison. The Varroa mite and monarch-active dsRNA’s did not cause significant differences in larval mortality, larval or pupal development, pupal weights, or rates of adult emergence from the pupa when compared to untreated controls. The results indicate that dsRNA's, including the Varroa-active dsRNA, eaten by monarch larvae are deactivated before they can interact with the target gene, and do not pose a hazard to monarch larvae. This information will be useful to monarch conservation groups; beekeepers and the honey bee industry; public-sector, industry, and government scientists; and regulatory agencies.

Review Publications
Cheng, Y., Sappington, T.W., Luo, L., Zhang, L., Jiang, X. 2021. Starvation on first or second day of adulthood reverses larval-stage decision to migrate in beet webworm (Lepidoptera: Pyralidae). Environmental Entomology. 50(3):523-531. https://doi.org/10.1093/ee/nvab015.
Liu, S., Sappington, T.W., Coates, B.S., Bonning, B.C. 2021. Nudivirus sequences identified from the southern and western corn rootworms (Coleoptera: Chrysomelidae). Viruses. 13(2). Article 269. https://doi.org/10.3390/v13020269.
Unbehend, M., Kozak, G.M., Koutroumpa, F., Coates, B.S., Dekker, T., Groot, A.T., Heckel, D.G., Dopman, E.B. 2021. Bric à brac controls sex pheromone choice by male European corn borer moths. Nature Communications. 12. Article 2818. https://doi.org/10.1038/s41467-021-23026-x.
Fisher, K.E., Bradbury, S.P., Coates, B.S. 2020. Prediction of mitochondrial genome-wide variation through sequencing of mitochondrion-enriched extracts. Scientific Reports. 10.Article 19123. https://doi.org/10.1038/s41598-020-76088-0.
Addae, P.C., Bruce, Y., Utono, I.M., Abudulai, M., Traore, F., Ishiyaku, M.F., Adamu, R.S., Seidu, A., Batieno, B.J., Nwankwo, O.F., Ba, M.N., Adazebra, G.A., Tignegre, J., Dabire-Binso, C.L., Huesing, J.E., Hellmich II, R.L., Pittendrigh, B.R., Tamo, M. 2021. Distribution and diversity of alternate hosts of Maruca vitrata Fabricius in three West African countries. International Journal of Tropical Insect Science. https://doi.org/10.1007/s42690-021-00470-2.
Krishnan, N., Zhang, Y., Aust, M.E., Hellmich II, R.L., Coats, J.R., Bradbury, S.P. 2021. Monarch butterfly (Danaus plexippus) life-stage risks from foliar and seed-treatment insecticides. Environmental Toxicology and Chemistry. 40(6):1761-1777. https://doi.org/10.1002/etc.5016.
Krishnan, N., Hall, M.J., Hellmich II, R.L., Coats, J.R., Bradbury, S.P. 2021. Evaluating toxicity of varroa mite (Varroa destructor)-active dsRNA to monarch butterfly (Danaus plexippus) larvae. PLoS ONE. 16(6). Article e0251884. https://doi.org/10.1371/journal.pone.0251884.
Yan, M., Zhang, L., Cheng, Y., Sappington, T.W., Pan, W., Jiang, X. 2021. Effect of a near-zero magnetic field on development and flight of oriental armyworm (Mythimna separata). Journal of Integrative Agriculture. 20(5):1336-1345. https://doi.org/10.1016/S2095-3119(20)63287-7.
Roberts, A., Boeckman, C.J., Mühl, M., Romeis, J., Teem, J., Valicente, F.H., Brown, J.K., Edwards, M.G., Levine, S.L., Melnick, R.L., Rodrigues, T.B., Vélez Arango, A., Zhou, X., Hellmich II, R.L. 2021. Sublethal endpoints in non-target organism testing for insect-active GE crops. Frontiers in Bioengineering and Biotechnology. 8. Article 556. https://doi.org/10.3389/fbioe.2020.00556.
Perera, O.P., Fescemyer, H.W., Fleischer, S.J., Abel, C.A. 2020. Temporal variation in genetic composition of migratory Helicoverpa zea in peripheral populations. Insects. 2020(11):463. https://doi.org/10.3390/insects11080463.
Zhang, L., Cheng, L., Chapman, J.W., Sappington, T.W., Liu, J., Cheng, Y., Jiang, X. 2020. Juvenile hormone regulates the shift from migrants to residents in adult oriental armyworm, Mythimna separata. Scientific Reports. 10.Article 11626. https://doi.org/10.1038/s41598-020-66973-z.
Coates, B.S., Abel, C.A., Swoboda, K.A., Palmquist, D.E., Montezano, D.G., Zukoff, S.N., Wang, Y., Bradshaw, J.D., DiFonzo, C.D., Shields, E., Tilmon, K.J., Hunt, T.E., Peterson, J.A. 2020. Geographic distribution of Bacillus thuringiensis Cry1F toxin resistance in western bean cutworm (Lepidoptera: Noctuidae), populations in the United States. Journal of Economic Entomology. 113(5):2465-2472. https://doi.org/10.1093/jee/toaa136.
Coates, B.S., Hohenstein, J.D., Giordano, R., Donthu, R.K., Michel, A.P., Hodgson, E.W., O'Neal, M.E. 2020. Genome scan detection of selective sweeps among biotypes of the soybean aphid, Aphis glycines, with differing virulence to resistance to A. glycines (Rag) traits in soybean, Glycine max. Insect Biochemistry and Molecular Biology. 124. Article 103364. https://doi.org/10.1016/j.ibmb.2020.103364.
Liu, S., Coates, B.S., Bonning, B.C. 2020. Endogenous viral elements integrated into the genome of the soybean aphid, Aphis glycines. Insect Biochemistry and Molecular Biology. 123. Article 103405. https://doi.org/10.1016/j.ibmb.2020.103405.
Seong, K., Coates, B.S., Pittendrigh, B.R. 2020. Post-transcriptional modulation of cytochrome P450s, Cyp6g1 and Cyp6g2, by miR-310s cluster is associated with DDT-resistant Drosophila melanogaster strain 91-R. Scientific Reports. 10.Article 14394. https://doi.org/10.1038/s41598-020-71250-0.
Huang, J., Sun, W., Seong, K.M., Mittapalli, O., Ojo, J., Coates, B.S., Paige, K.N., Clark, J.M., Pittendrigh, B.R. 2020. Dietary antioxidant vitamin C influences the evolutionary path of insecticide resistance in Drosophila melanogaster. Pesticide Biochemistry and Physiology. 168. Article 104631. https://doi.org/10.1016/j.pestbp.2020.104631.
Cheng, Y., Sappington, T.W., Luo, L., Liu, C., Wang, Y., Liu, S., Zhang, Z., Wang, L., Jiang, X. 2021. Key factors involved in reduction of damage to sunflower by the European sunflower moth in China through late planting. PLoS ONE. 16(4). Article e0250209. https://doi.org/10.1371/journal.pone.0250209.
Abel, C.A., Scott, M.P. 2020. Evaluation of 21 Thailand maize germplasms for resistance to leaf feeding spodoptera frugiperda (Lepidoptera: Noctuidae). Journal of Kansas Entomological Society. 93(1):97-102 . https://doi.org/10.2317/0022-8567-93.1.97.
Mullins, A., Bradbury, S., Sappington, T.W., Adelman, J. 2021. Oviposition response of monarch butterfly (Lepidoptera: Nymphalidae) to imidacloprid-treated milkweed. Environmental Entomology. 50(3):541-549. https://doi.org/10.1093/ee/nvab024.