Research Project: Ecology and Management of Grasshoppers and Other Rangeland and Crop Insects in the Great Plains

Location: Pest Management Research

2019 Annual Report

Objectives
Objective 1: Determine the role of rangeland insects, particularly grasshoppers and Mormon crickets, on rangeland ecosystem function and production. [NP304, Component 3, Problem Statements 3B1, 3B2] Subobjective 1.A: Identify the impacts of grasshopper herbivory and drought on rangeland function and nutrient cycling. Subobjective 1.B: Identify the competitive and predatory interactions between Mormon crickets and grasshoppers, their impacts on plant community composition and nutrient cycling on rangeland, and the effect of grasshopper abundance on Mormon cricket immunity to disease. Objective 2: Identify climatic and biotic ecological drivers of pest population dynamics (such as wheat stem sawflies, grasshoppers, and Mormon crickets) in order to develop practical predictive models of when these key pests will exceed economic thresholds. [NP304, Component 3, Problem Statements 3A1, 3B1, 3B2] Subobjective 2.A: Using long-term monitoring data, identify climatic and vegetation/landscape components that are associated with population shifts and variability of individual grasshopper species and grasshopper species diversity. Subobjective 2.B: Determine whether Mormon crickets have annual, biennial, and plurennial populations, and identify cues that cause females to lay eggs that break diapause and hatch after one, two, or several winters. Subobjective 2.C: Identify the role of moisture stress in breaking diapause and triggering Mormon cricket embryonic development. Subobjective 2.D: Identify climatic correlates of wheat stem sawfly and parasitoid wasp abundance and quantify the effects of precipitation on pest pressure, biological control and crop yield. Objective 3: 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, grasshoppers, and their natural enemies. [NP304, Component 3, Problem Statements 3A2, 3B2] Subobjective 3.A: Identify components of native vegetation that provide sugar resources for beneficial natural enemies, and assess the potential influence of these resources on natural enemy longevity and biological control. Subobjective 3.B: Identify components of rangeland management practices that can be used to sustainably manage grasshopper populations. Objective 4: Develop microbial control agents as tools for control of key rangeland and wheat pests [NP304, Component 3, Problem Statement 3A2, 3B2] Subobjective 4.A: Develop microbial control agents for grasshoppers and Mormon crickets. Subobjective 4.B: Determine the biological significance of endophytic Beauveria affecting wheat stem sawfly.

Approach
Grasshoppers, Mormon crickets and wheat stem sawfly are key constraints on rangeland and crop productivity. Grasshoppers and Mormon crickets consume ~$1.5 billion of forage annually and wheat stem sawfly causes ~$250-350 million in crop damage annually. Current control strategies for these major pests are inadequate, costly and/or result in unacceptable environmental impacts due to the historical reliance on broad spectrum insecticides. The goal of this proposed project is to acquire the knowledge needed 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 our ecological foundation, enhance prevention of pest outbreaks, and develop microbial intervention tools. We will develop a sound understanding of pest impacts on rangeland function and determine climatic and biotic drivers that cause these pervasive Great Plains pests to exceed economic thresholds. We will design sustainable habitat and landscape approaches to manage these pests and their natural enemies. We will develop microbial control agents to provide critically needed alternatives to pesticide-based control. Pursuing research along these themes of ecology, prevention and intervention 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 on-going relationships with land management agencies, farmers and ranchers, academic societies, industry and state extension services.

Progress Report
At the request of USDA-Animal and Plant Health Inspection Service-Plant Protection and Quarantine, new research was initiated to more accurately determine grasshopper density economic thresholds, as grasshoppers remove over $1 billion in rangeland forage annually. New collaborative research with ARS researchers in Mandan, North Dakota, was initiated examining how grazing and fire management treatments can be used to reduce dominance of the exotic grass Kentucky bluegrass and simultaneously manage grasshopper populations. New research was initiated and a multi-year experiment continued examining interactions between the pest rangeland grasshoppers and Mormon crickets. Long-term grasshopper sampling continued at 25 sites, with the goal of better predicting grasshopper outbreaks, since detailed long-term data is highly uncommon yet valuable. Data set integrity checks and error checking on the 20 year dataset was largely completed. Objectives 1, 2 and 3. In order to understand the duration of embryonic development in Mormon cricket egg beds, ARS scientists initiated a population comparison of the dependence of egg development on temperature. Although embryos developed quickly at high temperature, they arrested development before reaching the overwintering stage. As a result, the optimum temperature for initial development is higher than the optimum temperature for the final development stages. Because preliminary results suggest that there are differences among populations in the lower critical temperature for development, degree day models specific to elevation of the population will improve forecasting. Objective 2. Completed bioassays of three USDA-discovered fungi against wheat stem sawfly. These resulted in significant levels of infection and insect mortality. Furthermore, colonization of wheat by these fungi, presence, or exposure of plants to foliar sprays of fungus spores, decreased the susceptibility of treated wheat to Fusarium head blight. These results give promise to using USDA fungi to manage both insect pest and disease. Completed data analysis for experiments to assess drought effects on wheat stem sawfly infestation and efficacy of biocontrol parasitoids. Initiated greenhouse studies examining floral resource use by wheat stem sawfly parasitoids; results from similar studies of sugar resource impacts on Cephus cinctus completed and published. Completing final data collection on experiments to assess the relative benefits of various native and introduced grasses, as well as resistant (solid-stem) and susceptible (hollow-stemmed) wheat varieties, on sawfly and parasitoid performance. Completed population model projecting the influence of crop resistance and biological control on sawfly population growth. Started two new collaborative field studies in alfalfa: 1) Effects of harvest timing on alfalfa weevil population dynamics and biological control, and 2) Variation in weevil phenology and natural history across a three state region (Montana, Wyoming, Utah). Participated in (conducting sampling and uploading survey data) a new alfalfa weevil web-based monitoring tool (PestWeb) being developed by Montana State University. Objectives 3 and 4.

Accomplishments
1. Mormon crickets can delay hatching for years to cope with drought. Most insects lay eggs that hatch the following year. ARS scientists in Sidney, Montana, were first to determine that Mormon crickets delayed embryonic development to avoid drought until favorable conditions for growth and hatching were restored. In general, more severe drought delayed development of Mormon cricket embryos, but populations differed in susceptibility to drought. Although drought did not concentrate development and hatching into one year, variability in the insects allowed them to cope and await more favorable conditions. State entomologists report that knowledge of the effects of climate on egg bed longevity improves forecasting and reduces the cost and impact of management of this pest.

2. Farmers must combine crop resistance and biological control to curb wheat stem sawfly populations over time. Wheat stem sawfly is a major pest of wheat in the Northern Great Plains of North America. Researchers at ARS in Sidney, Montana, carried out a comprehensive literature review to extract data which was incorporated into a matrix model to evaluate the potential efficacy of crop resistance, both alone and in combination with biological control, for managing this pest. Model results illustrate that crop resistance alone reduces, but does not halt, wheat stem sawfly population growth. Model simulations further suggests that the levels of biological control needed are much lower in resistant solid-stemmed compared with hollow-stemmed lines. Wheat farmers will benefit by effectively combining these approaches to affect overwintering larval survival and reduce pest numbers over the longer-term.

3. Grasshopper herbivory interacts with drought and nitrogen to affect belowground soil communities. Climate variability has resulted in increased variation in precipitation and shifts in nitrogen deposition, but it remains unknown how these changes interact with grasshopper herbivory, particularly during outbreaks, to affect belowground processes and rangeland production. ARS researchers in Sidney, Montana, manipulated grasshopper abundance, nitrogen and water availability to examine how feeding by grasshoppers reduced rangeland production for livestock and indirectly affected belowground organisms. Grasshopper survival and reproduction declined with drought, while reproduction was higher with added nitrogen. Drought and nitrogen both affected belowground communities, while grasshoppers had stronger impacts on belowground fungal and bacterial communities in the year following the experiment. The novel finding that grasshopper feeding impacts on belowground communities persist for more than one year has implications for USDA-APHIS grasshopper control economic thresholds and predicting grasshopper impacts on rangeland production.

Review Publications
Riveros, A.J., Srygley, R.B. 2019. Magnetic compasses in insects. In: Choe, J.C., editor. Encyclopedia of Animal Behavior. 2nd edition. Elsevier/Academic Press. p. 588–597. https://doi.org/10.1016/B978-0-12-809633-8.01251-6.
Rand, T.A., Lundgren, J.G. 2018. Quantifying temporal variation in the benefits of aphid honeydew for biological control of alfalfa weevil (Coleoptera: Curculionidae). Environmental Entomology. 48(1):141–146. https://doi.org/10.1093/ee/nvy165.
Sylvain, Z.A., Espeland, E.K., Rand, T.A., West, N.M., Branson, D.H. 2019. Oilfield reclamation recovers productivity but not composition of arthropod herbivores and predators. Environmental Entomology. 48(2):299-308. https://doi.org/10.1093/ee/nvz012.
Dakhel, W., Latchininsky, A., Jaronski, S. 2019. Efficacy of two entomopathogenic fungi, Metarhizium brunneum, strain F52 alone and combined with paranosema locustae against the migratory grasshopper, Melanoplus sanguinipes, under laboratory and greenhouse conditions. Insects. https://doi.org/10.3390/insects10040094.
Srygley, R.B. 2018. Experimental manipulation of dispersal ability in Neotropical butterfly Anartia fatima (Lepidoptera: Nymphalidae). Insects. https://doi.org/10.3390/insects9030107.
Laws, A.N., Prather, C.M., Branson, D.H., Pennings, S. 2018. Effects of grasshoppers on prairies: Herbivore composition matters more than richness in three grassland ecosystems. Journal of Animal Ecology. 87(6):1727–1737. https://doi.org/10.1111/1365-2656.12897.
Portman, S.L., Jaronski, S., Weaver, D.K., Reddy, G.V. 2018. Advancing biological control of the wheat stem sawfly (Cephus cinctus) – new strategies in a 100 year struggle to manage a costly pest in the Northern Great Plains. Biological Control. 111(3):85-91. https://doi.org/10.1093/aesa/say002.
Sylvain, Z.A., Branson, D.H., Rand, T.A., West, N.M., Espeland, E.K. 2019. Decoupled recovery of ecological communities after reclamation. PeerJ. https://doi.org/10.7717/peerj.7038.
Rand, T.A., Titus, E.F., Waters, D.K. 2019. Do floral resources benefit the herbivorous sawfly, Cephus cinctus, a major pest of wheat in North America? Journal of Economic Entomology. 112(2):565-570. https://doi.org/10.1093/jee/toy408.