Research Project: Forecasting, Outbreak Prevention, and Ecology of Grasshoppers and Other Rangeland and Crop Insects in the Great Plains

Location: Pest Management Research

2023 Annual Report

Objectives
OBJECTIVE 1: Determine the role of rangeland insects, particularly grasshoppers, on rangeland ecosystem function and production. OBJECTIVE 2: Identify climatic and biotic ecological drivers of pest population dynamics of wheat stem sawflies, grasshoppers and Mormon crickets. Subobjective 2A: Develop and verify growing degree day models of Mormon cricket embryonic development and hatch. Subobjective 2B: Investigate the duration that Mormon cricket eggs remain in egg beds. Subobjective 2C: Identify causes of Mormon cricket mortality in egg beds, including temperature and desiccation. Subobjective 2D: Identify cues that cause Mormon cricket females to lay eggs that break diapause and hatch after one, two, or several winters to improve applicability of Mormon crickets as high protein component of feed and food. Subobjective 2E: Identify vegetation variables (e.g. increase in invasive grasses) associated with shifts in grasshopper abundance and community structure. Subobjective 2F: Identify forage quality effects on grasshopper performance and spectral bandwidth differences in vegetation. OBJECTIVE 3: Develop predictive models of rangeland and crop insect pest distribution, population growth and impact to allow land managers to address outbreaks at earlier stages and optimize control efforts. Subobjective 3A: Model embryonic development and hatch of Mormon crickets across elevations in the Western U.S. Subobjective 3B: Model centers of endemism in Mormon cricket populations based on multi-annual life cycles and topographic variation in the Western U.S. Subobjective 3C: Investigate the effects of annual to decadal scale weather patterns and spectral vegetation indices on pest insect outbreaks. Subobjective 3D: Model the effect of El Niño Southern Oscillation on plant primary productivity and grasshopper outbreaks in the Western U.S. OBJECTIVE 4: Design sustainable approaches (e.g. roadside and conservation plantings, landscape diversification, rangeland fire and grazing management) to manage key crop and rangeland insects, such as wheat stem sawfly, alfalfa weevil, pea aphids, grasshoppers, and their natural enemies. Subobjective 4A: Examine the impact of rangeland management practices on grasshopper populations. Subobjective 4B: Identify factors enhancing Bracon cephi abundance and efficacy in controlling wheat stem sawfly populations. Subobjective 4C: Identify field and landscape drivers of alfalfa weevil population dynamics and biological control.

Approach
Grasshoppers, Mormon crickets, wheat stem sawfly, and alfalfa weevil significantly damage rangeland and crop productivity in the Central and Western United States. Grasshoppers and Mormon crickets consume ~$1.7 billion of forage annually in the U.S. and wheat stem sawfly causes ~$250-350 million in crop damage annually. These pests are high priority targets for ranchers, farmers and federal and state land managers, since current control strategies are inadequate, costly and/or result in unacceptable environmental impacts due to the historical reliance on broad spectrum insecticides. The long-term goal of this proposed research is to develop innovative, environmentally sound and sustainable management alternatives for control of these pests which currently lack sustainable control measures. To achieve this end, we will pursue research to broaden the ecological knowledge of these pests, improve pest risk assessments, and enhance prevention of pest outbreaks. We will develop a sound understanding of pest impacts on rangeland production and determine climatic and biotic drivers that cause crop and rangeland pests to exceed economic thresholds in the Great Plains. We will design sustainable habitat and landscape approaches to manage these pests and their natural enemies. Pursuing research in ecology, forecasting and prevention will provide the foundational knowledge necessary to achieve the ultimate goal of developing ecologically-based and economically practical management strategies that reduce economic impacts and promote food security, while decreasing environmental impacts of control measures. We will communicate our results through meetings, publications and presentations targeting land management agencies, farmers and ranchers, academic societies, industry and state extension services.

Progress Report
Objective 1. ARS researchers at Sidney, Montana, continued investigating how multi-species grazing practices and fire affect dung beetles, that can speed up nutrient cycling and reduce cattle fly pest issues. Little is known about the role of dung beetles in the northern Great Plains, with stakeholders identifying this area as a priority topic needing additional research. Multi-species grazing practices and mob-grazing (using a large number of cattle grazing on a pasture for a short period of time) are popular with producers, but impacts of these management approaches on rangeland insects such as dung beetles have not been examined. As part of a project with USDA Animal and Plant Health Inspection Service (APHIS) Plant Protection and Quarantine (PPQ) and other collaborators, we investigated how APHIS PPQ grasshopper spray programs on rangeland covering hundreds of thousands of acres in Montana in 2021 are affecting grass production, flowering plant abundance and pollinator abundance over time. APHIS PPQ is the federal agency responsible for managing grasshoppers on federal land, but they lack data on longer term impacts of spray programs on rangeland function. Objective 2. ARS research scientists completed a ten-year study of embryonic development and hatching of Mormon crickets at several seasonal cycles in the lab. This relates to Sub-objective 2A to develop and verify growing degree day models of Mormon cricket embryonic development and hatch. This research shows that embryonic development of Mormon crickets is generally dependent on duration of the growing season rather than chill time or number of annual cycles. The duration of the growing season required for 50% of the embryos to develop was well over one year, ranging from 84 to 144 weeks. ARS researchers conducted experiments on the effects of temperature and desiccation on Mormon cricket embryonic development in the lab. Metabolic rate and water loss were measured on embryos at three stages of diapause. This study relates to Sub-objective 2C to Identify causes of Mormon cricket mortality in egg beds, including temperature and desiccation. During a multi-year grasshopper outbreak causing significant economic damage in the northern Great Plains, ARS researchers in Sidney, Montana, began collaborations with federal agencies, land grant universities, and the Smithsonian Institution to better understand factors leading to grasshopper outbreaks and to examine whether grasshopper spray programs provide multi-year benefits for producers. Large scale spray programs covering millions of acres occur during outbreaks in the western U.S., however information is lacking on whether these spray programs reduce grasshopper populations for multiple years or if spraying leads to enhanced rangeland forage for livestock. Grasshopper abundance, rangeland plant production and forage quality data were collected at over 140 sites in Montana that were either sprayed or not sprayed in 2021 and 2023. The data will assist ranchers, federal agency partners, and land managers in making pest management decisions and determining when it is cost effective to control grasshoppers. Objective 3. ARS researchers monitored soil temperatures, embryonic development and hatching of Mormon crickets at sites in Oregon, Nevada, Utah, and Wyoming. This relates to Sub-objective 3A to model embryonic development and hatch of Mormon crickets across elevations in the Western U.S. This research has shown that the Mormon cricket half-life exceeds 7 years at high elevations with all but the final year in the egg stage, whereas it is only 2 or 3 years at lower elevations in Wyoming. Because the eggs in this study derived from the same genetic stock, this field research verifies the laboratory findings from Objective 2 that accumulated temperature during the growing season (i.e., growing degree days) is of primary importance for embryonic development. ARS researchers in Sidney, Montana, compiled data on Pacific Ocean surface temperature indices of decadal and interannual climatic oscillations (PDO and ENSO, respectively) in conjunction with the drought monitor index, soil pH and organic carbon, temperature and precipitation, vegetation index (NDVI), and areal proportions of cultivated land cover to determine the factors that best determined grasshopper densities over a 40-year period (1982-2021) in the western U.S. This study was particularly novel in its accounting of unavoidable biases in data collection that result from multiple observers sampling temporally and spatially variable grasshopper densities. ARS initiated a collaborative project with the University of Colorado focused on improving forecasting of pest grasshopper and Mormon crickets by merging Geospatial Artificial Intelligence (GeoAI) and deep-learning methods. Despite decades of work, grasshopper and Mormon cricket outbreaks can’t be accurately predicted. Artificial Intelligence and deep-learning methods hold significant promise to improving pest insect management, but these big data methods remain largely untapped. Objective 4. ARS researchers in Sidney, Montana, completed research demonstrating that sugar resources associated with multiple different crop aphid species can significantly enhance longevity of Bracon cephi, the most important biological control agent against the wheat stem sawfly. This research relates to Sub-objective 4B. Researchers initiated field experiments to assess the seasonal availability of honeydew resources for wheat stem sawfly parasitoids in the field, and began collaborative work with university extension partners in Colorado and Nebraska to examine how crop rotation frequency and crop diversity influence wheat stem sawfly infestation intensity and biological control. The first year of field work on a coordinated project to examine wheat stem sawfly pressure across a 6-state area spanning the northern plains was completed. ARS scientists are collaborating with researchers at USDA-ARS in Colorado on two wheat stem sawfly studies: evaluating agronomic practices and crop resistance as strategies for wheat stem sawfly control, examining wheat stem sawfly pressure and biological control in Kernza. ARS scientists completed field work and sample processing on a multi-year landscape study examining the influence of field size and landscape structure on alfalfa weevil population dynamics and biological control. We provided expertise on a funded NIFA postdoctoral fellowship proposal to examine the importance of Conservation Reserve Program grassland habitat for conservation of key biocontrol agents of wheat and alfalfa pests. This research relates to Sub-objective 4C.

Accomplishments
1. Mormon cricket egg banks and outbreak dynamics. By burying eggs from the same genetic stock at high (8,000 ft) and low (4,000 ft) elevations in the Bighorn Mountains, ARS scientists at Sidney, Montana, discovered that Mormon crickets at high elevation will develop and hatch over at least an eight-year period and likely much longer, whereas they require two to three years on average at low elevation. Consequently, soil temperature is a critical factor in determining the persistence of Mormon cricket eggs in egg banks. Because mountains and canyons provide a patchy thermal environment, multiple generations of eggs are likely to be banked in the soil in these regions. Unusual warm events in mountain or canyonlands will rush the development of eggs that have accumulated in egg banks resulting in Mormon cricket outbreaks, banding, and migration from mountain and canyonlands the following spring. This research improves forecasting of Mormon cricket outbreaks to assist land managers in preparations for control efforts. It also points to the need to find new methods to locate and control Mormon cricket populations in egg banks to reduce the risk of synchronous hatching and migration of nymphs to arable lands.

2. Intermediate wheat grass: A potential tool to promote conservation biological control of the wheat stem sawfly. The wheat stem sawfly has been a devastating economic pest of wheat across the northern Great Plains for over a century. In the past decade, economic infestations have been increasing across the central plains resulting in increased urgency to develop integrated and sustainable management solutions. Biological control is a key component of effective management, and increasing the efficacy of Bracon sp. parasitoids, the most important biological control agents of the wheat stem sawfly, is critical to reducing its economic impacts across the region. Using a multi-year manipulative common garden experiment, ARS researchers in Sidney, Montana, demonstrated that parasitoid performance (the number of adults emerging per infested grass stem) was significantly (3-4 times) higher in intermediate wheat grass relative to any other wild grass species tested and also exceeded that observed on two common wheat varieties. In addition, large-scale surveys confirmed that wheat stem sawfly is heavily parasitized in this host grass in the field. The results suggest that incorporating intermediate wheat grass into Conservation Reserve Program grasslands and roadside plantings could significantly benefit parasitoid conservation by increasing their numbers and potential efficacy. The results also present the intriguing possibility that Kernza (an intermediate wheat grass variety gaining traction as a potential perennial grain crop across the region) could similarly provide key conservation habitat for these parasitoids.

3. Grasshoppers are attracted by higher crude protein following prescribed fire. Grasshopper outbreaks can cause significant economic hardships for ranchers by removing most living vegetation, but land managers lack knowledge on how sustainable management approaches including interactions between livestock grazing and fire affect grasshopper populations and vegetation damage. ARS researchers in Sidney and Miles City, Montana, examined how improved forage quality from fire affected grasshopper densities and rangeland grass removal by grasshoppers. Both vegetation removal by grasshoppers and grasshopper densities were significantly higher in burned plots compared to unburned plots, which appeared to result from higher crude protein content in burned plots. These findings showing that fire-grasshopper dynamics may be driven by shifts in protein content between unburned and burned vegetation, suggests that this could be an important driver of grasshopper populations and grass consumption. The research points to the need for additional research to determine how livestock grazing-fire interactions impacts pest grasshopper species outbreaks.

Review Publications
Srygley, R.B. 2022. Temperature effects Mormon cricket Anabrus simplex embryo development, hatching and nymphal growth: Thermal performance curves change with ontogeny. Journal of Thermal Biology. 110. Article 103356. https://doi.org/10.1016/j.jtherbio.2022.103356.
Srygley, R.B., Dudley, R., Hernandez, E.J., Kainz, F., Riveros, A.J., Ellington, C.P. 2023. Quantifying the aerodynamic power required for flight and testing for adaptive wind drift in passion-vine butterflies Heliconius sara (Lepidoptera: Nymphalidae). Insects. 14(2). Article 112. https://doi.org/10.3390/insects14020112.
Holcomb, K.M., Mathis, S., Staples, J.E., Fischer, M., Barker, C.M., Beard, C.B., Nett, R.J., Keyel, A.C., Marcantonio, M., Childs, M.L., Gorris, M.E., Rochlin, I., Hamins-Puertolas, M., Ray, E.L., Uelmen, J.A., Defelice, N., Freedman, A.S., Hollingsworth, B.D., Das, P., Osthus, D., Humphreys Jr, J.M., Nova, N., Mordecai, E.A., Cohnstaedt, L.W., Kirk, D., Kramer, L., Harris, M.J., Kain, M.P., Reed, E.M., Johansson, M.A. 2023. Evaluation of an open forecasting challenge to assess skill of West Nile virus neuroinvasive disease prediction. Parasites & Vectors. 16(1):11. https://doi.org/10.1186/s13071-022-05630-y.
Srygley, R.B., Dixon, J.I., Lorch, P.D. 2023. Microclimate refugia: Comparing modeled to empirical near-surface temperatures on rangeland. Geographies. 3:344-358. https://doi.org/10.3390/geographies3020018.
Humphreys Jr., J.M. 2022. Amplification in time and dilution in space: Partitioning spatiotemporal processes to assess the role of avian host phylodiversity in shaping eastern equine encephalitis virus distribution. Geographies. 2(3):419-434. https://doi.org/10.3390/geographies2030026.
Wilson, E.C., Cousins, S., Etter, D., Humphreys Jr, J.M., Roloff, G., Carter, N.H. 2023. Habitat and climatic associations of climate-sensitive species along a southern range boundary. Ecology and Evolution. 13. Article e100083. https://doi.org/10.1002/ece3.10083.
Rand, T.A., Senior, L. 2023. Honeydew associated with four common crop aphid species increases longevity of the parasitoid wasp, Bracon cephi (Hymenoptera: Braconidae). The Canadian Entomologist. 155:1-8. Article e20. https://doi.org/10.4039/tce.2023.5.
Pellissier, M.E., Rand, T.A., Murphy, M.A., Jabbour, R. 2022. Landscape composition and management history affect alfalfa weevil but not its parasitoid. Environmental Entomology. 51(5):892-900. https://doi.org/10.1093/ee/nvac057.
Srygley, R.B. 2023. Grasshoppers and other orthopteran pests. In: Eigenbrode, S., Rashad, A., editors. Advances in Understanding Insect Pests Affecting Wheat and Other Cereals. Oxford: Burleigh Dodds Science Publishing. p 33-56.
West, N.M., Gaskin, J.F., Milan, J., Rand, T.A. 2022. High genetic diversity in the landscape suggests frequent seedling recruitment by Euphorbia virgata Waldst. & Kit. (leafy spurge) in the northern U.S. Biological Invasions. 25:645-652. https://doi.org/10.1007/s10530-022-02954-9.
Srygley, R.B. 2023. Selective protein self-deprivation by Mormon crickets following fungal attack. Journal of Insect Physiology. 149. Article 104555. https://doi.org/10.1016/j.jinsphys.2023.104555.