Location: Pest Management Research2012 Annual Report
1a. Objectives (from AD-416):
Objective 1: Clarify how grasshoppers influence interactions between exotic and native grassland plants and the sustainability of grazing systems. Objective 2: Define factors that influence grasshopper outbreaks and Mormon cricket migration to enhance predictions of when outbreaks and migration occur, and identify management techniques that impact population densities. Subobjective 2a: Define the impact climate conditions have on grasshopper and Mormon cricket egg survival to further understand population dynamics and outbreaks. Subobjective 2b: Examine the effectiveness and underlying mechanisms of grassland management practices, such as fire and livestock grazing, to sustainably manage grasshopper populations. Objective 3: Identify ecological factors underlying variability in populations of key crop insect pests and their natural enemies, and identify factors and/or management approaches that augment natural enemies and maximize control of key insect pests. Subobjective 3a: Quantify the effects of semi-natural habitat (grasslands) on grass feeding herbivore-parasitoid food web dynamics and pest pressure in small grains. Subobjective 3b: Determine the effects of landscape structure on the diversity and abundance of natural enemy communities associated with alfalfa pests and how this ultimately influences key interaction-based ecosystem services (i.e. biological control of pests by parasitoids, predators and pathogens). Objective 4: Define biological factors and mechanisms that regulate locomotion, reproduction, and immunity to enhance grasshopper and Mormon cricket management. Subobjective 4a: Identify intake target of Mormon crickets in last nymphal instar and first 8 days of adult life, during which reproductive and immune systems are maturing, and determine if dietary deficiencies alter the efficacy of fungal control. Subobjective 4b: Determine if dietary deficiencies exhibited by migratory Mormon crickets in the field alter their ability to escalate their immune responses. Objective 5: Develop commercializable microbial control agents and methods for their use in managing pest insects such as grasshoppers and Mormon crickets. Objective 6: Assess the suitability and potential effectiveness of classical biocontrol agents against wheat stem sawfly.
1b. Approach (from AD-416):
Insects are key constraints in crops and rangelands. Rangeland is a fundamental resource for the beef industry, with grasshoppers frequently affecting food security on all inhabited continents. Wheat and alfalfa rank as the third and fourth most important crops grown in the U.S. ARS stakeholders have identified grasshoppers and Mormon crickets in rangeland, and wheat stem sawfly and alfalfa weevil in cropping systems as high priority pests. Current control strategies for these pests are inadequate, costly and result in unacceptable environmental impacts. Pest management in the modern era has generally focused on suppressive tactics, primarily via chemical means. However, the increasing reliance on agrochemical inputs in modern agriculture has led to public concerns over safety and environmental impacts. Ecologically based pest management approaches attempt to address these concerns by moving beyond the chemical paradigm, to develop safer and more sustainable control. This project focuses on generating the biological and ecological knowledge necessary to achieve the ultimate goal of developing ecologically-based and economically practical management strategies that maintain pest populations at sub-economic levels via biological and cultural means. A sound understanding of insect pest ecology will form the basis for predicting when an insect will be a pest, understanding pest impacts, and determining whether prevention or intervention will be necessary and/or effective. Long-term sustainable solutions to pest problems will only be achieved by restructuring and managing agricultural and rangeland systems in innovative and novel ways that maximize built-in preventive strengths or negatively affect pest population dynamics. In situations where preventive strategies are overcome or consistently ineffective, developing novel biological intervention tools becomes paramount to provide critically needed alternatives to pesticide-based control. In order to increase predictability of grasshopper and Mormon cricket outbreaks and assess their ecological impacts, we will investigate responses to changing climate conditions, and evaluate the effects of grasshoppers on competition between exotic and native rangeland plants. We will also develop novel, preventive strategies that either work against pest fitness in rangeland or render cropping systems less vulnerable to pest problems via the augmentation of natural enemies. Finally, we will develop innovative ways to intervene and control pests when preventive barriers are overcome, including investigations of Mormon cricket and grasshopper susceptibility to pathogens to enhance the efficacy of these natural enemies, and to identify new biocontrol agents to expand the biological arsenal to disrupt growth of wheat stem sawfly, grasshopper, and Mormon cricket populations. This research will fundamentally expand the knowledge base necessary to develop effective, ecologically-based pest management solutions, promoting food security while decreasing energy inputs and environmental impacts.
3. Progress Report:
ARS researchers in Sidney, MT examined the impact of patch burning and grazing on grasshopper populations in multi-year experiments in shortgrass and mixed grass prairie. We initiated new research examining how predators (ex. spiders) can reduce rangeland forage damage and grasshopper outbreaks through negative direct and indirect impacts on pest grasshopper species. To better understand the impact of grasshopper outbreaks, new collaborative research was initiated in three grassland ecosystems (TX, KS, MT) examining the effects of geography and grasshopper diversity on grassland ecosystem processes. Additional research was initiated examining how severe drought affects overwintering egg survival and grasshopper outbreaks. We continued evaluating domestic fungi and five commercial fungi for controlling grasshoppers. We assessed heat tolerances of 393 fungal strains. We tested 20 candidate fungal strains for ability to kill grasshoppers in the lab, finding several potential candidates. An ARS-APHIS team conducted a grasshopper field trial of four of these fungi, plus two commercial ones; results pending. ARS completed two outdoor persistence tests of Green Muscle, a fungus used to control grasshoppers in Africa. The fungus failed to survive more than two months in the fall and one month in late spring, indicating that it may be useful as a short term, localized control method, which is our objective. Mormon crickets are pests in the western USA and can be deficient in either protein or carbohydrates when they migrate, depending on the population. These two nutritional deficiencies have distinct effects on immune systems that might lead to susceptibility to fungi or bacteria used for population control. By limiting access to proteins or carbohydrates in the last nymphal and early adult stages in the lab, we were able to produce adults with similar weaknesses in immunities to those we observe in migrating populations in the field. The next step is to test these nutrient-deprived adults for susceptibility to fungi and bacteria as potential control agents. We completed sample processing from a large scale effort in MT aimed at examining grassland influences and regional variation in wheat stem sawfly infestation and parasitism. The results suggest that nearby grasslands (rangeland and Conservation Reserve Program (CRP)) are not important sources of either the wheat stem sawfly or its native parasitoids moving into wheat. We performed predator exclusion experiments to characterize the important natural enemies (parasitoids, pathogens and predators) of alfalfa weevil in the MT/ND region. Results indicate that neither ground dwelling nor aerial predators significantly impact weevil survivorship. In larger scale surveys, carried out in 2010 and 2011, two larval parasitoids have been identified as potentially important (with parasitism rates often exceeding 50%). Weevil surveys were competed again in 2012, an outbreak year for this pest. Initial results suggest lower parasitism, compared with previous years, but the same two parasitoids predominate as the most important enemies.
1. Effects of climate change on agricultural insect pests. ARS researchers at Sidney, MT summarized the literature on climate change effects on insect pests for the National Climate Assessment for Agriculture. Rising air temperatures affect all aspects of the insect life cycle and generally result in larger insect populations as a result of earlier emergence with advancing spring, range expansion, and more generations per year. Under elevated CO2, plants shift their defenses from toxins to tougher, less digestible leaves. Beetles and aphids generally perform better under elevated CO2 to the detriment of plants. Information will be used in a status report on the impacts of climate on sectors of the United States for the U.S. Congress and the President of the United States.
2. Egg depth and vegetation abundance determine when pest grasshoppers can be controlled by rangeland fire. Although fire has potential for use as a preventative pest management tool, little information exists on how rangeland fire can be used by land managers to reduce population outbreaks of economically important pest grasshoppers. ARS researchers in Sidney, MT demonstrated that a major pest grasshopper species that lays egg pods deeper below ground than other grasshopper species whose egg pods are vulnerable to fire, is also vulnerable to egg mortality during rangeland fires. Rangeland fire is a common naturally occurring event and is a useful range management tool. This information will help rangeland managers make effective decisions regarding fire and grasshopper control.
3. Development of microbial control agents for Mormon cricket and grasshopper control. USDA ARS and APHIS are jointly searching for environmentally safe, effective microbial agents to manage outbreaks of Mormon crickets and grasshoppers in the Western United States. These would replace existing insecticides, the future of which is uncertain. ARS researchers in Sidney, MT evaluated the spore production and thermal tolerances of 185 Beauveria isolates (new, collected from dead grasshoppers) and 108 Metarhizium isolates (obtained from Utah State University), and initiated bioassays of these fungi, with completion for 20 isolates. ARS, with APHIS, also evaluated several commercial fungi in 10-acre grasshopper field trials. As a result USDA is closer to developing a satisfactory microbial control agent to substitute for the broad-spectrum chemical insecticides currently in use on rangelands.
Foster, N.R., Jaronski, S., Reuter, K.C., Harper, J.D., Schlothauer, R.J., Black, L.R. 2011. Simulated aerial sprays for field cage evaluation of Beauveria bassiana and Metarhizium brunneum (Ascomycetes: Hypocreales) against Anabrus simplex (Orthoptera: Tettigoniidae) in Montana. Biocontrol Science and Technology. 21(11): 1331-1350.