Research Project: Productive Cropping Systems Based on Ecological Principles of Pest Management

Location: Integrated Cropping Systems Research

2019 Annual Report

Objectives
Objective 1. Develop strategies to manage insects in cropping systems, focusing on biology with regards to resistance evolution, insect health and diversity, and the value of these strategies to sustainable crop production. [NP304, Component 3, Problem Statement 3A2]. Subobjective 1a. Assess the risk to susceptible western corn rootworm, and hence insect resistance management, from adult feeding on corn tissue expressing toxic Bacillus thuringiensis (Bt)-proteins. Subobjective 1b. Evaluate neonicotinoid seed treatments for usefulness to U.S. crop production. Subobjective 1c. Compare pest and beneficial insect levels between a soybean pest-management system that uses an aphid-resistant cultivar versus one that relies on conventional insecticides. Subobjective 1d. Compare pest and beneficial insect levels, soil properties, plant growth, yield, and seed composition of soybean when grown alone and with an oilseed relay crop. Subobjective 1e. Evaluate cover-cropping scenarios within crop rotations that encourage ecosystem services from beneficial insects. Subobjective 1f. Develop procedures for hazard assessments of pesticides to non-target organisms. Subobjective 1g. Establish exposure pathways for pesticides and non-target organisms and determine how plant diversity within the farmscape affects these exposure pathways. Objective 2. Develop innovative strategies for managing weeds in dynamic cropping systems, and assess the benefits of these strategies that rely on bottom-up approaches to weed management (such as the use of cover crops) within diverse crop rotations. [NP304, Component 2, Problem Statement 2A2]. Subobjective 2a. Develop a methodology to convert red clover to cropland without tillage. Subobjective 2b. Determine the best annual clovers to use as cover crops to control post-harvest weeds without tillage.

Approach
Pest management is crucial in cropping systems, and strategies to control weeds and insect pests need to be integrated with agronomic and other management goals to achieve sustainable cropping systems. In the northern Great Plains, corn rootworms, soybean aphids, and weeds greatly reduce agricultural productivity and profitability through yield loss and costly control measures. Widely adopted management tactics have initially reduced economic loss from these pests, but their utility needs reassessment in light of herbicide-tolerant weeds, insect adaptation to resistance transgenes, secondary pest outbreaks, and unwitting impacts on pollinators, natural enemies, and soil health. This project plan proposes research to address strategies used against major pests such as corn rootworms and soybean aphid, refine tactics for weed management in organic production systems, and determine the value and drawbacks to pest management and ecosystem services from diversifying crop rotations, incorporating cover crops, and using various plant-incorporated protectants. The research will be instrumental in developing management practices that increase farming efficiency and improve environmental and economic sustainability.

Progress Report
The research project progressed in generating knowledge about resistance of corn rootworms to transgenic, rootworm-resistant corn hybrids, the management of soybean aphid with resistant soybean varieties, and the fate of herbicides in soil, in accordance with the NP 304 Action Plan. Results of the current project may be used to reduce the impacts of insect pests on crops in Northern Plains farming systems and understand the fate of sulfonylurea herbicides, a common class of herbicides used in major crops throughout the world. In accordance with Objective 1 regarding management of corn rootworm, scientists documented the first cases of resistance to corn expressing toxic Bacillus thuringiensis (Bt)-proteins in northern corn rootworm. This adds to reports of field control failures of Bt corn hybrids against western corn rootworms. Investigations conducted in Nebraska showed the importance of local cropping history on the prevalence of resistance to Bt toxins among western corn rootworm populations. Additional research under Objective 1 on the management of soybean aphid concluded with regard to field evaluations on the efficacy and impact of a soybean variety that has been pyramided with two aphid-resistance genes. The resistant variety thwarted aphid infestations across the three years of the study, and there was no yield drag from use of the resistant variety. The plots were also sampled to determine the impact on non-target insects, and the samples are being processed. With regard to Objective 2 and weed management in cropping systems, research using soils from North America and South America provided quantitative information regarding interactions between agricultural soils and the herbicides nicosulfuron and rimsulfuron and their metabolites.

Accomplishments
1. Herbicide behavior after application to soil. Sulfonylurea herbicides are used throughout the world to control a large variety of weeds in major crops. Although these herbicides have low application rates, they can carryover, causing crop injury under some conditions; they have also been detected in groundwater. ARS scientists at Brookings, South Dakota, and St. Paul, Minnesota, and a researcher from Instituto Nacional de Tecnología Agropecuaria, Argentina measured herbicide partitioning between soil and water to evaluate the potential availability of herbicides to plants versus their likelihood to contaminate water resources. Measurements were conducted on two sulfonylurea herbicides and five breakdown products in soils collected from La Pampa, Argentina and Minnesota, U.S. Results demonstrated that quantitative data are required to accurately predict herbicide fate in soils because: (1) behavior of the sulfonylurea parent compounds does not necessarily represent the behavior of similarly-structured metabolites; (2) results from one geographical region cannot be reliably generalized to another region; (3) partitioning determined for surface soils cannot be reliably extrapolated to nearby soils; and (4) sorption values alone do not characterize herbicide availability for leaching or plant uptake. Scientists, extension specialists, and risk assessors can use this information to more accurately predict benefits (weed control) and detriments (crop damage, water contamination) of using sulfonylurea herbicides, and help growers use these herbicides effectively and safely.

2. First documented cases of resistance to Bt corn hybrids in northern corn rootworm. Western corn rootworm (WCR) and northern corn rootworm (NCR) are major economic pests of corn in North America. Corn hybrids expressing specific bacterial proteins known as Bt toxins are commonly planted to manage these pests. Several cases of field resistance to Bacillus thuringiensis (Bt) corn hybrids have been documented in many corn-producing areas of North America, but only for WCR. ARS scientists at Brookings, South Dakota, and researchers at North Dakota State University collected NCR and WCR from five eastern North Dakota corn fields and reared their offspring in the laboratory. Offspring were subjected to plant bioassays to screen for potential resistance to Bt toxins, leading to the first documented cases of resistance in field-derived NCR to Bt corn hybrids. Resistance was also found in one population of WCR. The results inform industry researchers, university scientists, and pest management practitioners that more effective control tools and improved resistance-management strategies are needed to prolong the durability of Bt toxins for managing corn rootworms.

3. Tough enough for soybean aphid biotype 4. Although outbreaks of soybean aphid (SA) are less frequent than in previous years, this insect remains a perennial pest of soybean throughout the Midwest. Economic infestations are generally managed with insecticides, but numerous recent instances of insecticide failure against SA have renewed interest in the development of SA-resistant soybean cultivars with multiple resistance genes. Such cultivars will require a broad repertoire of aphid-resistant sources. Using numerous cultivated and wild soybean lines that were previously categorized with resistance to SA, ARS scientists from Brookings, South Dakota, along with researchers from South Dakota State University, and The Ohio State University challenged these lines against three colonies of SA biotype 4, the most virulent strain of this pest. Several lines were identified with resistance to one or more of the biotype 4 colonies. These results ensure that breeders have the strongest resistant lines for developing durable SA-resistant soybean cultivars for farmers.

4. Local use of corn hybrids with Bt traits in Nebraska are key to explaining resistance in western corn rootworm. Transgenic field-corn hybrids that express insecticidal proteins from the Bacillus thuringiensis (Bt) bacterium have selected for resistant populations of western corn rootworms (WCR) in the Midwest. WCR is a major insect pest of field corn that is planted in successive years at the same location. ARS scientists from Brookings, South Dakota, and researchers from the University of Nebraska characterized planar variation in WCR susceptibility to specific Bt traits among corn fields in two counties of Nebraska and related the variation to pest-management practices used in those counties. Results revealed that neighboring corn fields may support WCR populations with very different susceptibility levels, indicating that gene flow of resistant alleles from high trait-survival sites is not inundating large cropping areas. A method known as sensitivity analysis indicated years of local Bt-trait use was a key driver of WCR susceptibility to one of the Bt traits. Results from this study support current science-based extension recommendations aimed at mitigating the prevalence of resistance in WCR by using a multi-tactic pest management approach in individual fields.

Review Publications
Azcarate, M.P., Papiernik, S.K., Montoya, J.C., Koskinen, W.C. 2018. Sorption-desorption of rimsulfuron, nicosulfuron, and metabolites in soils from Argentina and the USA. Agricultural and Environmental Letters. 3:180048. https://doi.org/10.2134/ael2018.09.0048.
Hesler, L.S., Perreira, W.D., Yee, D., Silva, J. 2019. New records of Coccinellidae (Coleoptera) from Hawaii, U.S.A. The Coleopterists Bulletin. 73:382-383. https://doi.org/10.1649/0010-065X-73.2.382.
Hesler, L.S., Nixon, J.J. 2018. Novel prey record for Scymnus caudalis LeConte and first records of four other species of Coccinellidae (Coleoptera) in Wisconsin, U.S.A. Great Lakes Entomologist. 51:30-33.
Conzemius, S., Hesler, L.S., Varenhorst, A., Tilmon, K. 2019. Resistance of soybean plant introductions to three colonies of soybean aphid (Hemiptera: Aphididae) biotype 4. Journal of Economic Entomology. https://doi.org/10.1093/jee/toz116.
Conzemius, S., Hesler, L.S., Varenhorst, A., Tilmon, K. 2019. Resistance to soybean aphid biotype 4 in plant introductions of Glycine soja. Euphytica. 215:98. https://doi.org/10.1007/s10681-019-2421-6.
Hesler, L.S., Tilmon, K.J. 2019. Identification and characterization of resistance to soybean aphid (Hemiptera: Aphididae) in plant introductions of wild soybean. Journal of Kansas Entomological Society. 91:19-29. https://doi.org/10.2317/0022-8567-91.1.19.
Reinders, J.D., Hitt, B.D., Stroup, W.W., French, B.W., Meinke, L.J. 2018. Spatial variation in western corn rootworm (Coleoptera: Chrysomelidae) susceptibility to Cry3 toxins in Nebraska. PLoS One. 13(11):e0208266. https://doi.org/10.1371/journal.pone.0208266.
Meihls, L., Huynh, M.P., Ludwick, D.C., Coudron, T.A., French, B.W., Shelby, K., Hitchon, A.J., Smith, J.L., Schaafsma, A.W., Pereira, A.E., Hibbard, B.E. 2018. Comparison of six artificial diets for western corn rootworm bioassays and rearing. Journal of Economic Entomology. 111(6):2727-2733. https://doi.org/10.1093/jee/toy268.
Pereira, A.E., Coudron, T.A., Shelby, K., French, B.W., Bernkalu, E.J., Bjostad, L.B., Hibbard, B.E. 2019. Comparative susceptibility of western corn rootworm (Coleoptera: Chrysomelidae) neonates to selected insecticides and Bt proteins in the presence and absence of feeding stimulants. Journal of Economic Entomology. 112(2):842-851. https://doi.org/10.1093/jee/toy415.
Man, H.P., Hibbard, B.E., Lapointe, S.L., Niedz, R.P., French, B.W., Pereira, A.E., Finke, D.L., Shelby, K., Coudron, T.A. 2019. Multidimensional approach to formulating a specialized diet for northern corn rootworm larvae. Scientific Reports. 9:3709. https://doi.org/10.1038/s41598-019-39709-x.
Calles-Torrez, V., Knodel, J.J., Boetel, M.A., French, B.W., Fuller, B.W. 2019. Field-evolved resistance of northern and western corn rootworm (Coleoptera: Chrysomelidae) populations to corn hybrids expressing single and pyramided Cry3Bb1 and Cry34/35Ab1 Bt proteins in North Dakota. Journal of Economic Entomology. https://doi.org/10.1093/jee/toz111.
Hanson, A., Lorenz, A., Hesler, L.S., Bhusal, S., Bansal, R., Michel, A., Jiang, G., Koch, R. 2018. Genome-wide association mapping of host-plant resistance to soybean aphid. The Plant Genome. 11:180011. https://doi.org/doi:10.3835/plantgenome2018.02.0011.