Project : USDA ARS

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

Location: Integrated Cropping Systems Research

2021 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 nontarget 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 continued to generate knowledge about insect pest management approaches and weed management tactics applicable to sustainable cropping systems in the northern Great Plains. The project includes studies of how pest and weed management practices impact beneficial organisms such as insect predators, pollinators and soil invertebrates, but also how these organisms influence plant health and crop production in the Northern Plains. Results of the current project may be used to reduce the impacts of insect pests and weeds and to determine how particular practices promote ecosystem services that are valuable for sustainable crop production in the Northern Plains. Research was extended on Objective 1: “Develop strategies to manage insects in cropping systems, focusing on biology with regards to resistance evolution, insect health and diversity, and the usefulness of these strategies to sustainable crop production.” Specifically, research continued on the biology of corn rootworm to understand the development of their resistance to toxic Bacillus thuringiensis (Bt) proteins. Data analysis was completed for a non-diapausing colony of northern corn rootworm developed at NCARL. This colony has the potential to be an important research tool in the future. We completed data analysis for an experiment in which rootworms were collected from the field and subjected to bioassays to evaluate the susceptibility of Nebraska WCR populations to a rootworm-Bt pyramid in areas with a history of Cry3Bb1 and Cry34/35Ab1 cultivation. Most WCR populations were highly resistant to Cry3Bb1 and exhibited similar larval development when feeding on Cry3Bb1 and non-Bt corn, as indicated by head capsule width and fresh weight metrics. In contrast, most WCR populations exhibited a lower level of resistance to Cry3Bb1 + Cry34/35Ab1 corn and sublethal exposure to the rootworm-Bt pyramid resulted in more variable results in larval development compared to non-Bt corn. The results document a neighborhood WCR Cry3Bb1 resistance pattern and confirm the first cases of field-evolved resistance to Cry3Bb1 + Cry34/35Ab1 corn in Nebraska. Some research activities related to Objective 1 were concluded. Specifically, a subobjective on the management of soybean aphid led to publication of a scientific journal article about a 3-year field study in eastern South Dakota that evaluated an insecticide seed treatment, foliar spray application of insecticide, and a soybean cultivar containing two aphid-resistance genes. Soybean aphid infestations had sustained, economically injurious levels in 2015, but not the other two years. The three management tactics independently reduced soybean aphid population densities. Seed treatment and the resistant cultivar suppressed cumulative aphid-days (CAD) in all three years, whereas the foliar spray decreased CAD in 2015 and 2017. By far, the resistant cultivar had the greatest impact on soybean aphid populations, reducing CAD by 28- to 150-fold per year, with mean numbers of aphids much less than 100 soybean aphids per plant. Seed treatment reduced CAD by 1.7- to 3.5-fold per year, and foliar spray reduced it 2.0- to 5.6-fold per year. Soybean yield was not affected by treatments in 2015, and yield was greater for the susceptible than for the resistant cultivar in 2016 and greater for plots without foliar insecticide in 2017. The study demonstrated the comparative strength of the resistant cultivar in suppressing soybean aphid and its viability as an alternative to insecticides as an aphid-management tactic. Our current project is a bridging project, so no new objectives or milestones are documented therein. However, significant progress was made in establishing pilot studies to evaluate the impact of management practices on the structure and activity of terrestrial insect communities. These studies included: (1) evaluations of insect activity and predation in till and no till systems, (2) evaluation of artificial sentinel prey to quantify the potential for biological control of pest species via predation, and (3) surveys of insects in various cropping systems and grassland areas to inform future research objectives. Additional progress was made on ancillary research projects. One is a part of a multi-location, 3-year study to evaluate termination dates of a rye cover crop and the impact on early season pest and beneficial insects. Another study has been evaluating a new soybean aphid biotype known as ‘Accrue,’ which has a novel virulence pattern against known aphid-resistance genes in soybean. Follow-up studies have evaluated wild soybean, or soja, as a new source of resistance against the Accrue biotype and another highly virulent biotype in order to find durable, broad-spectrum resistance against soybean aphid biotypes.

Accomplishments
1. Managing soybean aphid with a resistant cultivar is highly effective and precludes the downsides of insecticides. The soybean aphid remains an important pest of soybean in the Midwestern U.S. and southern Canada. The predominant management strategy includes a combination of planting soybean seed treated prophylactically with insecticide and applying a late-season foliar insecticide. However, this strategy increases production costs, selects for insecticide-resistant aphids, and escalates the chances of detrimental side effects from insecticides. ARS scientists in Brookings, South Dakota, conducted a three-year field study from 2015 thru 2017 that evaluated insecticide seed treatment, foliar insecticide spray, and use of an aphid-resistant soybean cultivar containing aphid-resistance genes. Each of these three management tactics independently reduced soybean aphid population densities. By far, the resistant cultivar had the greatest impact on soybean aphid populations, reducing them by 28- to 150-fold per year, whereas insecticide seed treatment reduced aphid populations 1.7- to 3.5 fold per year, and foliar insecticide spray reduced it from 2.0- to 5.6-fold per year. The study’s results demonstrated the viability of a soybean cultivar with two aphid-resistance genes as an alternative to the common strategy of using insecticides to manage this pest.

2. Best to base management decisions about corn rootworms at the local level. The western corn rootworm is a significant pest of field corn across the United States Corn Belt. Farmers in Nebraska have seen greater than expected crop injury from western corn rootworm despite widespread use of transgenic corn hybrids that express a particular protein known as Cry3Bb1 to manage the pest. ARS scientists in Brookings, South Dakota, and in Nebraska determined that the pattern of crop injury is due to varying levels of resistance to Cry3Bb1 in rootworm populations among various Nebraska counties. Larval development metrics, including rate of development, head capsule width and fresh weight, were associated with western corn rootworm corrected survival on Cry3Bb1 corn. These metrics are important in understanding the ways that resistant rootworms adapt to Cry3bB1. Overall, the findings increase our insight of western corn rootworm population dynamics among field locations within the transgenic corn landscape and reinforce the importance of making corn rootworm management decisions based on information collected at the local level.

3. Wild soybean enhances the arsenal of aphid resistance genes. A particular type of wild soybean known as soja has many useful traits that can be bred into modern soybean cultivars, and these include insect resistance. A study by ARS researchers in Brookings, South Dakota, and Raleigh, North Carolina, evaluated 76 selected soja accessions and 14 soybean accessions for resistance against two virulent colonies of soybean aphid in experiment growth chambers. The two colonies included a new soybean aphid biotype known as ‘Accrue,’ which has a novel virulence pattern against known aphid-resistance genes, and another highly virulent biotype, known as ‘Volga16.’ Soja line PI 507624 showed strong resistance against the Accrue colony, whereas PI 597458 C showed strong resistance to Volga16. Based on results from these tests, follow-up studies are warranted to determine the genetic basis of aphid resistance in these two soja lines in order to inform breeding programs that are developing aphid-resistant soybean cultivars.

4. Feeding strategies of ants indicate higher biodiversity in particular bioenergy landscapes. A dominant trend in global land use has been increased acreage for bioenergy plants grown as an alternative to fossil fuels. This major shift in land use may impact how organisms that share these production lands obtain their nutrients and energy. Ants are ideal organisms for understanding how feeding strategies respond to changing land use patterns. Researchers in Brookings, South Dakota, and Michigan conducted long-term and large-scale experiments on plantings of corn, switchgrass, and restored prairie to understand how ants’ nutritional requirements and the availability of food resources interacted to shape their feeding strategies within each habitat. Ants responded by altering their feeding on plants vs. feeding on insect prey. In corn and switchgrass monocultures, ants became top predators, whereas in restored prairie they consumed a mix of animal prey and plant-based resources and thus increased the complexity of their associated food webs. The extended food webs of ants within restored prairie showed that this land use supports a broader mix of biodiversity than corn or switchgrass monoculture while providing a viable resource of bioenergy plants.

5. Behavior of the herbicide bicyclopyrone in soil is highly variable. Bicyclopyrone is an herbicide that is marketed for the control of herbicide-resistant weeds. However, there is a lack of extensive data on its interactions with soil that determine its weed-control efficacy and tendency to contaminate soil and water resources. Researchers at Brookings, South Dakota, in collaboration with scientists at St. Paul, Minnesota, and elsewhere, evaluated the behavior of bicyclopyrone in 25 different soils with a variety of properties. Retention of bicyclopyrone by soil varied by a factor of 70 and was not related to soil properties that are commonly observed to influence pesticide behavior, including soil organic carbon, cation exchange capacity, and clay content. Additional research is needed to better predict the conditions that present an increased risk of environmental contamination by bicylopyrone.

6. Imported gall midge thrives on invasive sow thistles in the Upper Midwest. Land managers must balance effective control of invasive weeds with minimizing the impact of large-scale herbicide sprays across range, pasture, and natural grasslands. As an alternative to herbicides, various insect species have been imported to North America and released for biological control of invasive weeds. A gall midge known as Cystiphora sonchi was released in Canada in the 1980s to control invasive sow thistles. ARS researchers in Brookings, South Dakota, and Washington, D.C., discovered the gall midge infesting sow thistles in Minnesota, North Dakota, and South Dakota in 2017 and 2018, and many of the sow thistles were heavily galled. The findings documented the gall midge’s establishment in the U.S., which represents a significant southward extension of its known geographic range. The instances of heavy galling suggest the gall midge’s potential to impact sow thistles at lower latitudes in North America. Further research is needed to determine the geographic extent of Cystiphora sonchi in the U.S., its impact on weeds, and the benefits to landowners.

7. Ant thermal traits predict the winners and losers under climate change. Current temperatures are predicted to increase with consequences for many organisms including insects, whose body temperature tracks the environment. From warm deserts to cold tundra, scientists at Brookings, South Dakota, and in Oklahoma documented how 33 ant communities across North America have changed over 20 years to test theoretical predictions that ants with higher thermal tolerance have increased at the expense of less thermally tolerant groups. Consistent with our predictions, we found a positive relationship between CTmax, the temperature at which muscle control is lost, and the proportion of sites in which an ant genus’ incidence had increased. However, this was not the case for CTmin, the low temperatures at which ants first become inactive. We suggest additional working hypotheses for why particular genera have increased, decreased, or remained constant through time and why mean annual temperatures and evolutionary history explained little of this pattern. We suggest that functional traits like CTmax are useful in predicting how ants will respond to rising temperatures and the impacts on their biodiversity.

U.S. DEPARTMENT OF AGRICULTURE

Integrated Cropping Systems Research: Brookings, SD