Location: Pest Management Research2022 Annual Report
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.
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.
Objective 1. Researchers at Sidney, Montana, investigated if multi-species grazing practices and fire can increase the abundance of dung beetles that can speed up dung decomposition and increase nutrient availability for rangeland plants. Impacts of multi-species grazing practices and mob-grazing (a high number of cattle grazing a pasture for a short period of time) are popular with producers, but impacts of these management approaches on dung beetles have not been examined. Dung beetle samples were collected in five different rangeland management treatments. Objective 2. Researchers investigated how variation in micronutrient availability in rangeland grasses across a 23 year data set was associated with grasshopper population densities at 25 sites. Researchers are also examining if variation in plant micronutrient composition across 20 sites in a single year explains grasshopper community differences. Relationships between plant nutrient content and grasshopper population dynamics remain poorly understood and can contribute needed information for grasshopper forecasting models. Researchers have found that a parasitic wasp is a principal source of mortality for Mormon cricket eggs in the Bighorn Basin of Wyoming. This relates to the sub-objective to identify causes of Mormon cricket mortality in egg beds. ARS scientists have also reared Mormon crickets on diets rich in nitrogen or phosphorus to determine whether the females lay eggs that develop directly as opposed to delaying development for multiple growing seasons. This relates to the sub-objective to identify cues that cause Mormon crickets to lay eggs that break diapause and hatch after one, two, or several winters to improve the applicability of Mormon crickets as a high protein component of feed and food. Objective 3. ARS scientists monitored soil temperatures, embryonic development and hatching of Mormon crickets at sites in Oregon, Nevada, Utah, and Wyoming. This relates to the sub-objective to model embryonic development and hatch of Mormon crickets across elevations in the Western U.S. Some eggs buried in bags in the soil have remained dormant for over 6 years at high elevation in Wyoming and for 5 years near sea-level in Oregon. ARS investigated the effects of annual to decadal scale El Nino/La Nina Southern Oscillation (ENSO) and Pacific Decadal Oscillation (PDO) patterns in relation to grasshopper outbreaks in the Western U.S. Key aspects of this study included the development of new statistical methods that allowed climate-grasshopper relationships to be estimated based on location specific temperature, precipitation, and vegetative characteristics. Results from the research indicated that grasshoppers located in the Northern Great Plains, the Southern Great Plains, and in other portions of the West do not respond uniformly to changes in the ENSO or PDO. This research represents a major step towards achieving future project goals and has been published in the peer-reviewed literature. ARS scientists developed population models for the migratory grasshopper (Melanoplus sanguinipes) that improved future forecasts of the species’ abundance in Wyoming. The migratory grasshopper is one of the foremost pest grasshopper species in the West and can negatively impact rangeland vegetation and crops when species populations exceed normal densities. Statistical models developed by scientists incorporated information from prior year grasshopper densities to better predict how the species might respond to future climate conditions. The research has been published in the peer-review literature and has been adapted to aid in vegetative biomass estimation by the USDA Forest Service, Rangeland Production Monitoring Service. ARS scientists established new partnerships, collaborations, and funding for the development of Artificial Intelligence for insect distribution modeling. Geospatial Artificial Intelligence (GeoAI) and deep-learning methods hold significant promise to revolutionize how agricultural problems are addressed, however these methods remain largely untapped and require massive quantities of multi-scale, multi-source data (Big Data) that frequently exhibit complex spatiotemporal structure. To better utilize existing GeoAI tools and to improve on these methods, ARS scientists at Sidney, Montana, have secured approximately $500,000 during this year to fund new partnerships with university cooperators and ARS scientists from across the country. Research funds will be used to sponsor multiple postdoctoral researchers with the goal of better forecasting agriculturally significant insect species abundances over the entirety of the U.S. Objective 4. ARS scientists completed experiments demonstrating that sugar resources associated with multiple crop aphid species can significantly enhance the longevity of Bracon cephi, the most important biological control agent against the wheat stem sawfly. ARS scientists completed the final year of field work on a three-year collaborative study examining whether early harvest is an effective management tool for alfalfa weevil. While early harvest is touted in the extension literature as an effective approach, scientific evaluation was previously lacking. ARS scientists continued 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. ARS scientists initiated work examining how crop rotation frequency influences wheat stem sawfly infestation intensity and biological control.
1. Forecasting grasshopper outbreaks in response to density dependence, future climate, and long-term climate oscillations. Grasshoppers are preeminent herbivores and major rangeland pests in the U.S. Despite the important ecosystem functions they provide, grasshopper populations often obtain densities that cause significant economic harm to grazing operations and agricultural production. ARS researchers at Sidney, Montana, developed new statistical methods that enabled location specific estimation of how population density, climate, and vegetation characteristics shape grasshopper abundance in the Western U.S. Results from the research indicated that grasshopper numbers during prior years can be used in conjunction with local weather and long-term climate oscillations to predict future grasshopper outbreaks. These findings will economically benefit ranchers and farmers by providing tools to prioritize grasshopper monitoring and treatments in advance of future outbreaks.
2. Assessing the influence of long-term climate oscillations on grasshopper density. Climate change may alter the spatial and temporal stationarity of the El Nino Southern Oscillation (ENSO) and the Pacific Decadal Oscillation (PDO) and their relative importance to ecosystems globally. For the Western United States, seasonal warming and increased climate variability are likely to accelerate the frequency and intensity of extreme drought, flooding, and wildfire events. To understand how these changes may influence future grasshopper densities, ARS researchers at Sidney, Montana, modeled ENSO and PDO effects on grasshopper density over the historic period 1982-2021. Outcomes of the study demonstrated that changes to the ENSO and PDO will affect grasshoppers differently depending on the specific geographic region where grasshoppers were located. The study also showed that increased grasshopper densities in the Northern Great Plains may occur at different times than those seen in the Southern Great Plains.
3. Crop aphid honeydew: A key performance enhancing resource for parasitoids of the wheat stem sawfly. The absence of sugar resources in simplified agricultural landscapes is thought to be a major factor limiting the success of biological control of crop pests. Restoring vegetation complexity within these landscapes has thus become a major focus of conservation biological control efforts, with a traditional emphasis on bolstering floral resources. However, aphid honeydew can also provide sugar resources that are seldom considered in the context of conservation biological control. ARS researchers at Sidney, Montana, demonstrated that feeding on honeydew produced by common crop aphids (in wheat, pea and canola) dramatically increases the longevity (2-3 fold) of biocontrol wasps attacking the wheat stem sawfly. The results suggest that aphids occurring in crops at sub-economic levels may provide critical sugar resources to sawfly parasitoids, enhancing their potential efficacy, and re-enforcing integrated pest management recommendations regarding the avoidance prophylactic pesticide applications. More generally, the results suggest that honeydew provisioning is likely an important mechanism underlying the benefits of crop diversification to support biological control that merits further research. Increasing the efficacy of biological control of the wheat stem sawfly is critical to reducing the economic impacts of this pest for wheat producers in the Northern Plains.
4. Temperature effects on the Mormon cricket life cycle. Some pesticides can only be applied at specific developmental stages of the target insect. Hence advance knowledge of changes in the life history of the pest saves land managers time and money. ARS researchers in Sidney, Montana, measured rates of embryonic development and hatch of Mormon crickets across a broad range of ambient temperatures. Focusing on a population from 9000 feet elevation in the Bighorn Mountains, these data represent the first complete analysis of temperature effects on the development rate of Mormon crickets. The optimal temperature for development changes from 80 °F in the early embryonic stages to 75 °F in the latter stages, which causes the embryos to enter summer diapause when half grown. Final maturation occurs when temperatures cool again in autumn prior to the obligate winter diapause. In the spring, hatching rate is maximized at 71 °F, which is much cooler than the temperature of maximal nymphal development (96 °F). This study economically benefits farmers and ranchers of the western United States by contributing to population modeling by the USDA to inform state entomologists of the potential for economically damaging outbreaks and critical timing for pesticide application.
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Humphreys Jr., J.M., Srygley, R.B., Lawton, D., Hudson, A.R., Branson, D.H. 2022. Grasshoppers exhibit asynchrony and spatial non-stationarity in response to the El Niño/Southern and Pacific Decadal Oscillations. Ecological Modeling. 471. Article 110043. https://doi.org/10.1016/j.ecolmodel.2022.110043.
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