Location: Pest Management Research2017 Annual Report
1a. Objectives (from AD-416):
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.
1b. Approach (from AD-416):
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.
3. Progress Report:
Objective 1: ARS researchers from Sidney, Montana initiated new research examining how drought and food quality affect rangeland sustainability, production and interactions between grasshoppers and belowground organisms. Grasshoppers remove over $1 billion in rangeland forage annually and compete with livestock. It is unknown if interactions between aboveground feeding by grasshoppers and belowground organisms affect grazing sustainability, particularly during droughts when grasshopper problems are most severe. Currently conducting an experiment manipulating drought and nitrogen availability. Objective 2: Long-term grasshopper sampling continued at 25 sites, with the goal of better predicting grasshopper outbreaks, since detailed long-term data is highly uncommon. ARS researchers from Sidney, Montana initiated new research on Mormon crickets, which are well known for their carnivory, which can effectively drive their migration. In addition to feeding on plants, Mormon crickets eat invertebrates, and we hypothesized that invertebrate prey availability determines the amount of protein in their diet. Because Mormon crickets commonly occur with grasshoppers that feed on the same plants, we investigated interactions between grasshoppers and Mormon crickets. In a field setting, both grasshopper and Mormon cricket survivorship declined with Mormon cricket density. Mormon cricket predation on grasshoppers and cannibalism were frequently observed. As predicted, diet preference shifted from protein to carbohydrates as grasshopper density increased. Grasshoppers can be an important source of dietary protein for Mormon crickets, with grasshopper availability affecting Mormon cricket immunity to disease. Collaborated with researchers from Colorado State University to collate data on host plants (grasses) used by the wheat stem sawfly. Completed a precipitation manipulation experiment to assess drought effects on wheat stem sawfly infestation and efficacy of biocontrol parasitoids. Initiated field and greenhouse studies to examine use of floral resources by sawfly and parasitoids. Completed a collaborative cross-state survey assessing the long-term persistence of parasitoids of adult alfalfa weevils, which were found to be currently absent from counties in which they initially established across Montana, Wyoming and South Dakota. Objective 3: Validated the efficacy and ultraviolet (UV) resistance of a new fungus formulation for killing grasshoppers developed by a U.S. industrial partner. The fungus showed applicability to other chewing insects. Additionally, validated the field efficacy of a bait formulation of a fungus developed in the ARS Sidney, Montana lab to kill grasshoppers. Wheat stem sawfly: Regarding wheat stem sawfly management with microbial agents, we evaluated additional wheat varieties, further identifying inter-variety receptiveness to being colonized by the candidate fungi, demonstrated the extreme infectivity and pathogenicity of the original and several subsequent fungus strains for the insect, and identified important application variables affecting successful within-plant establishment by the fungi.
1. Management of wheat stem sawfly using a fungus that grows into the plant. Wheat stem sawfly is the most important insect pest of wheat on the Northern Plains, extending now into the winter wheat of Nebraska and Kansas, with almost no effective control measures since it lives protected inside the plant. Researchers at ARS in Sidney, Montana indicated that the insect could be managed using a fungus that was unexpectedly discovered attacking the sawflies, by first getting the fungus to establish harmlessly in the wheat plant, where it will lay in wait for an invading sawfly larva, then infect and kill it. A patent application for use of this fungus to control wheat stem sawfly was submitted jointly with Montana State University. ARS is currently negotiating a license of the technology with a private U.S. company and creation of a cooperative research agreement to further develop this approach to a practical, commercial level. The invention could provide a major tool for managing this very important pest in wheat.
2. Extreme early summer drought may be required to strongly reduce grasshopper densities. Grasshopper outbreaks frequently lead to large scale chemical control efforts, but ranchers’ and land managers’ abilities to proactively manage grasshopper problems are constrained by an inability to predict population responses to weather variation. Drought timing could be more important than drought intensity in how it affects grasshopper populations, but it is poorly understood. ARS researchers in Sidney, Montana modified patterns of rainfall and grasshopper abundance to examine how drought timing affected rangeland production and grasshopper populations. Moderate early summer drought positively affected grasshopper survival by improving protein content of vegetation. Combined with previous work by ARS researchers in Sidney, Montana, the results indicate that extreme early summer drought conditions are likely required to strongly reduce forage availability and lead to lower grasshopper populations in the following year. The results confirm that a better understanding of the timing of drought is critical to allow managers to predict both the beginning and end of grasshopper outbreaks.
3. Mormon cricket egg banks contribute to pest outbreaks. Mormon crickets are a major pest of crops in the western USA that often form huge groups and march in search of food. Conventionally, Mormon crickets are thought to complete their life cycle annually. In a laboratory study, ARS researchers at Sidney, Montana were the first to discover that Mormon cricket eggs can remain in the soil and still hatch more than five years after being laid. Delayed hatching is more prevalent in high altitude populations than populations at low elevations, but all populations thus far examined exhibit the potential to bank some eggs for multiple years. This research informs farmers and pest managers that Mormon crickets may remain in the soil in a location and life stage for which current insecticidal practices may not be effective.
4. Using population models to inform biocontrol management of the wheat stem sawfly. Wheat stem sawfly is the most damaging insect pest of wheat in the northern Great Plains. The lack of information on which pest life stages should be targeted (egg or larva), and how many pest individuals need to be killed to get effective control, hampers the development of effective sustainable pest management approaches. ARS researchers at Sidney, Montana used mathematical population models to identify the most vulnerable sawfly life stages to be targeted by management. Models indicate that killing larvae in the overwintering stage will contribute most to sawfly population suppression, and that parasitism levels must exceed 60% to exert significant control. Results suggest that effective biological control management of sawfly will require adoption of farming practices to increase parasitoid numbers (such as additional flower resources nearby to feed sawfly enemies) and the development of new biological approaches to killing overwintering larvae (such as fungal pathogens). This model represents a critical first step in developing better targeted biological control management of wheat stem sawfly.
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