Location: Pest Management Research2011 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
This is the first report for the new project #5436-22000-016-00D, started on January 3, 2011 and replaced bridging project #5436-22000-014-00D “Ecology and Management of Grasshoppers and Other Insect Pests in the Northern Great Plains”, terminated on January 2, 2011. Additional information relevant to the ongoing work associated with this current project is recorded in the old project 5436-22000-014-00D, including thirteen published works. Accomplishments are listed in the new project 5436-22000-016-00D. Grasshopper biological control: ARS researchers at Sidney, MT, along with collaborators, continue to evaluate domestic insect pathogens (fungi) and two commercial pathogens as insecticides for grasshoppers. We acquired 250 fungus specimens for evaluation and started preliminary bioassays. The USDA-APHIS conducted a field trial of four fungi against grasshoppers; we also tested a combination of one commercial fungus with two chemicals that stress the insects to enhance efficacy. One fungus continues to show excellent potential; it has been given to other ARS locations for evaluation against other insects. Mormon cricket ecology: To investigate environmental effects on the survivorship of crop damaging Mormon crickets, we conducted experiments on the effect of soil moisture during summer development. Although soil moisture had significant effects on the probability of eggs developing into embryos, we were surprised to find that many eggs showed normal development with 0% moisture. We also found that 70 days of autumn cooling significantly shortened the time that the embryos required in winter diapause (similar to hibernation). Wheat stem sawfly: We completed quarantine trials to assess the suitability of wheat stem sawfly as a host for a potential biocontrol imported from China in the spring of 2010. Only one parasitoid completed development on the native Chinese host, and none on wheat stem sawfly. A second set of trials with improved methodology is being evaluated. A large scale sampling effort (MT, ND, and SD) is close to completion to look at regional variation in wheat stem sawfly infestation and parasitism. Alfalfa weevil: Initial surveys and predator exclusion experiments have been completed to characterize the important natural enemies of alfalfa weevil in the region. Two larval parasitoids and a fungal pathogen have been identified as potentially important. Grasshopper ecology: Research continued with range ecologists from Oklahoma State University to examine the impact of long term grazing exclusion and fire on grasshopper population dynamics during a period with high grasshopper densities. We also continued examining how winter soil temperatures and fall soil moisture affect grasshopper outbreaks. We planned and initiated collaborative experiments examining the impact of grasshopper herbivory on restoration of exotic grass dominated landscapes, and initiated new research examining how predators influence rangeland forage damage through their impact on economically important grasshopper species.
1. Grasshopper coloration and disease. Grasshoppers are huge problems for producers, eating not only crops, but more forage than cattle eat in the western USA. At higher temperatures, grasshoppers develop lighter coloration to reflect more sunlight and keep their bodies cooler. Because phenoloxidase is a key enzyme affecting both color and disease immunity, ARS researchers at Sidney, MT, explored whether grasshoppers reared at higher temperatures had less disease immunity and were more susceptible to fungal attack. They discovered that phenoloxidase enzyme concentrations in the blood of grasshoppers reared in a hot environment were lower than those reared at a more normal temperature. Consistent with this difference in immunity, grasshoppers reared in the hot environment had greater mortality and shorter survival time following application of a pathogenic fungus. Thus, although the change in body coloration is generally considered beneficial for regulating body temperature, it is also harmful to the grasshopper from the standpoint of combating disease. This research result helps us determine when grasshoppers are easiest to kill with chemical or biological treatments.
2. Wheat stem sawflies more susceptible to attack than previously believed. Wheat stem sawflies attack wheat stems in the northern Great Plains, living inside the stem, lowering seed production and quality, and eventually cutting the stem so that the wheat falls over and is difficult to harvest. It was previously thought that after the stem was cut, few of the sawflies were attacked by parasitic wasps that lay eggs through the wheat stem wall. ARS researchers at Sidney, MT, examined rates of late season parasitism by native species of wasps and found that rates of parasitism in wheat stubble chambers reached a maximum of 46%, exceeding the previously reported maximum of 2.5%. In contrast with previous work, our results demonstrate that larvae of wheat stem sawfly are suitable hosts for parasitic wasps, even after the formation of overwintering chambers in wheat stubble, and suggest that parasitism rates have likely been seriously underestimated when sampling stems prior to harvest, as typically done. This research will help us determine how to improve the efficacy of native wasps in controlling wheat stem sawfly.
3. Plant diversity not a good predictor of grasshopper population density or diversity. Grasshoppers cause significant economic damage during outbreak periods, but not all species are economic problems. ARS researchers in Sidney, MT, demonstrated that in a northern mixed grass prairie with relatively low plant diversity, the number of plant species at a site cannot be used to accurately predict the number of grasshopper species or grasshopper abundance. In a number of grassland ecosystems, grassland insect diversity and abundance has often been linked to plant species composition and habitat structure. However, plant species richness appears to be too variable to lead to accurate predictions of grasshopper abundance or species richness in the northern Great Plains. This research shows how we need to change our outlook to better predict grasshopper population densities and locations of outbreaks that threaten producers and range managers.