Location: Pest Management Research2018 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: New research was initiated that examines the interactions between pest grasshoppers and Mormon crickets and how they impact rangeland plants, as grasshoppers remove over $1 billion in rangeland forage annually. Grasshopper and insect identification efforts were completed on separate multiple researcher experiments examining the impact of energy development and Russian olive removal on insect communities. Objective 2: Research continued examining how drought and food quality affect rangeland sustainability where ARS researchers in Sidney, Montana conducted an experiment manipulating drought and nitrogen availability to examine how grasshoppers and belowground organisms affect rangeland production. Long-term grasshopper sampling continued at 25 sites, with the goal of better predicting grasshopper outbreaks, since detailed long-term data is highly uncommon. Processed samples and carried out initial analysis of data from precipitation manipulation experiments to assess drought effects on wheat stem sawfly infestation and efficacy of biocontrol parasitoids. Investigated a population of Mormon crickets at high elevation in Wyoming that is reportedly biennial with egg diapause prolonged to the second summer. To test whether parental photoperiod is typical of the end of the growing season serves as a cue for parents to prolong egg diapause, mating pairs set in the same daily temperature and humidity profiles with 20 pairs on short daylength (12:12h) and 20 pairs on long daylength (15:9h). Although females in short daylength were not more likely to have eggs with a biennial life cycle, they were more likely than those in long daylength to lay eggs with multi-annual life cycles. The multi-annual life cycle probably constitutes a bet-hedging strategy in an unpredictable, montane environment. Objective 3: Carried out greenhouse studies to examine the use of floral resources by wheat stem sawfly and its parasitoids, and the impacts of sugar feeding on performance (crop infestation and parasitism levels). Conducted common garden experiment 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. Carried out a literature review of the influence of resistance traits in wheat (i.e. stem solidity) on sawfly life history traits to be integrated into a population model projecting the influence of crop resistance and biological control on sawfly population growth. Objective 4: Demonstrated field efficacy of a bait formulation to deliver insect pathogenic fungi to grasshoppers and Mormon crickets, lowering the cost of control. Demonstrated efficacy of a fungus formulation for grasshoppers. In developing a practical approach to deliver insect pathogenic fungi to wheat in order to establish them as wheat symbionts for attack of invading sawfly larvae, demonstrated success in seed treatment, as well as developed an improved formulation for foliar sprays. Successfully demonstrated the establishment of these fungi outdoors in wheat, and documented that a number of the common wheat fungicides have no effect on our fungi.
1. Outdoor establishment of sawfly-derived fungi by foliar spray successfully demonstrated. 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. There is almost no effective control measure because the larva lives protected inside the plant. Researchers at ARS in Sidney, Montana had speculated the insect could be managed using a fungus that was discovered naturally attacking sawflies, by first getting the fungus to establish harmlessly in the wheat plant, subsequently infecting an invading sawfly larva and killing it. Until now all the experiments were conducted in the greenhouse environment. This year ARS scientists demonstrated successful establishment of these fungi in wheat following a foliar spray, outdoors, in the field. Wheat fungicides also could present a significant barrier to using the sawfly fungus. ARS determined that some of the leading candidate sawfly-attacking fungi were generally unaffected by most of the eight popular crop fungicides, dispelling concerns about this obstacle. A farmer could judiciously use a fungicide to protect his crop from head blight without affecting the fungal attack on the sawfly.
2. Flower nectar benefits wheat stem sawfly enemies much more than it benefits the pest sawfly. Adding flowers to agricultural landscapes, for example in cover crop mixes, roadside plantings or Conservation Reserve Program, has been gaining attention as an important means of increasing the efficacy of biological control. While sugar resources associated with flowering plants can significantly benefit parasitoid wasps, important natural enemies of many crop pests, they can also in some cases benefit the crop pest. Thus, an important first step in developing flowering plant resources to promote biological control, is determining the extent to which crop pests potentially benefit from these same resources. Researchers at ARS in Sidney, Montana tested the benefits of various flower species for the wheat stem sawfly, the most important insect pest of wheat in Montana, and its dominant natural enemy, a parasitoid wasp. Greenhouse work demonstrated for the first time that the wheat stem sawfly benefits from sugars associated with flowering plants, in this case buckwheat (a common cover crop). However, preliminary results indicate that these benefits are minor relative to the benefits to parasitoids; thus, adding appropriate floral resources to agricultural landscapes is predicted to be a net benefit for biological control.
3. Successful demonstration of a fungus bait for Mormon cricket and grasshoppers. A limitation to using insect pathogenic fungi against grasshoppers and Mormon crickets as ground or aerial sprays is the extremely large numbers of spores needed per acre. Concentrating the spores in an attractive bait would greatly concentrate the dose of fungus, decreasing the quantity needed per acre and thus the cost of treatment. ARS scientists in Sidney, Montana demonstrated efficacy of a bait laced with insect pathogenic fungus in replicated field trials against both grasshoppers and Mormon crickets. This success opens the way to economic application rates of such fungi against these insects.
4. Pest grasshoppers increase in reclaimed oil development sites. Over 50,000 new wells have been installed annually in the central plains of North America since the year 2000, with total productivity losses estimated at 10 Tg dry plant biomass. ARS researchers in Sidney Montana, sampled insects in areas of undisturbed rangeland and in reclaimed oil development sites in western North Dakota to examine how insect communities respond to disturbance and subsequent revegetation of oil pads. The dramatic increase in the abundance of a crop pest grasshopper on reclaimed oil production sites suggests that these reclaimed oil and gas pads may increase pest problems into adjacent crop areas. There was no evidence that the insect communities in reclamations would eventually resemble native communities, therefore, the effects of development and reclamation may irreversibly change the insect communities, harming agriculture. This also informs that there is an opportunity to improve the reclamation process on these lands.
5. Protein deficiency lowers resistance of Mormon crickets to a pathogenic fungus. Little is known about the effects of dietary macronutrients on the capacity of insects to ward off a fungal pathogen. In a laboratory study, ARS researchers at Sidney, Montana found that Mormon crickets fed restricted protein diets have lower immunity, slower encapsulation of foreign bodies, and greater mortality from Beauveria bassiana infection than those fed high protein diets. This research informs pest managers that B. bassiana is a more efficacious microbial control agent when Mormon crickets are on a forced march in search of protein.
Srygley, R.B., Jaronski, S. 2018. Protein deficiency lowers resistance of Mormon crickets to the pathogenic fungus Beauveria bassiana. Journal of Insect Physiology. 105:40-45. doi:10.1016/j.jinsphys.2018.01.00.
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Clifton, E.H., Jaronski, S., Coates, B.S., Hodgson, E.W., Gassmann, A.J. 2018. Effects of endophytic entomopathogenic fungi on soybean aphid and identification of Metarhizium isolates from agricultural fields. PLoS One. 13(3):e0194815. https://doi.org/10.1371/journal.pone.0194815.
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Greco, E., Wright, M., Burgueño, J., Jaronski, S. 2018. Efficacy of Beauveria Bassiana applications on Coffee Berry Borer across an elevation gradient in Hawaii. Biocontrol Science and Technology. https://doi.org/10.1080/09583157.2018.1493088.