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An Overview
of Grasshopper Management Research Why we
need new ways to manage grasshoppers Why we need new ways to manage grasshoppers
Grasshopper outbreaks can cause major depletions of range vegetation and result in the migration of grasshoppers to crops. Traditional grasshopper control with insecticides is often not economical; and environmental concerns with insecticide use on rangeland are increasing. New grasshopper management tools are needed. These strategies must be economically and environmentally acceptable and work across large areas. Very little research has been done on preventative grasshopper management to reduce the likelihood or intensity of grasshopper outbreaks. The goal of ARS grasshopper research is to develop sustainable grasshopper management systems that use land management practices and ecological processes in place of nonrenewable resources such as pesticides to reduce grasshopper outbreaks. (Also see - Grasshopper Management: An Integrated Approach) Grazing as a grasshopper management tool
Habitat management has potential to reduce the likelihood or intensity of grasshopper outbreaks. Recent ARS research found that a twice over rotational grazing system reduced grasshopper problems compared to a season long grazing system (Also see - Suppression of grasshoppers in the Great Plains through grazing management). We are examining interactions between grazing management and grasshopper population dynamics to determine how often and what types of grazing management reduce grasshopper outbreaks by maintaining conditions unfavorable to them. In addition to determining what type of grazing systems create unfavorable conditions for grasshoppers, we are also examining the underlying mechanisms responsible for reduced grasshopper populations. Of particular interest is whether certain grazing practices enhance the role of natural pathogens in regulating grasshopper populations. Grasshopper herbivory and rangeland production
Rangeland managers have often viewed grasshoppers as detrimental because grasshoppers consume forage that could be used by livestock and wildlife. However, this ignores the potential long-term benefits that grasshopper consumption might have on plant production by increasing nutrient cycling. This means that under some conditions grasshopper control may be detrimental to rangeland productivity and should be avoided. Under different environmental conditions, grasshoppers may decelerate nutrient cycling and diminish plant production. Therefore, we are examining the ecosystem characteristics that determine when grasshopper herbivory is beneficial or detrimental to plant production. This knowledge will help us determine when grasshopper control is warranted. Microbial biocontrol on rangeland A commercially available microbial insecticide, Nosema locustae, has been shown to reduce overall survival and reproductive potential of key grasshopper species potentially affecting their ecological fitness. While N. locustae is not economically effective at field rates when compared to chemical insecticides, its role in an integrated approach to biocontol of grasshoppers warrants further study. For that reason, we are treating a number of isolated populations of rangeland grasshoppers with N. locustae and will compare changes in population levels over several years with untreated populations. The results will have implications for area-wide management of grasshoppers. Grasshopper-plant interactions
Developing ways to prevent grasshopper outbreaks requires that we understand the ecological interactions underlying these outbreaks and be able to manipulate them accordingly. Unfortunately, the specific mechanisms that produce outbreaks are poorly understood. We know grasshoppers eat plants and their diet affects survival, growth and reproduction. Although we know the early juvenile stages are major periods of grasshopper mortality, the sources of this mortality are largely unknown. We are employing molecular and microscopic techniques to determine if developmental changes in host plant use are widespread among different grasshoppers. If so, we hope to characterize these changes in a number of economically important grasshopper species. A detailed understanding of species-specific ecological interactions may aid the development of long-term cultural and biological control tactics that manipulate critical grasshopper-plant interactions. Dispersal of grasshoppers from rangeland, roadsides, and fallow fields into adjacent crops is a complex and, at times, perplexing component of grasshopper management. For example, information is needed regarding the distance grasshoppers move, the timing of movements, and the species of grasshoppers involved so that we can predict when and where crop protection activities are needed. However, because it is difficult to monitor grasshopper movements and the thick canopy of crops makes sampling of grasshopper densities unreliable, such information is difficult to obtain. Consequently, we are developing methods to study the invasion of crops by grasshoppers. Also, we need to better understand the impacts of grasshopper feeding on crop plants to know when it is economical to treat grasshopper infestations in cropland. We are studying the above- and below-ground responses of small grains and other crops to grasshopper damage to determine how much yield is lost to a given level of grasshopper feeding. A multitude of factors impinge on grasshopper populations at many different levels, from the ecosystem-level (e.g., weather patterns), to the community-level (e.g., plant community characteristics), to the level of interactions among individual grasshoppers (e.g., competitive interactions, nutritional physiology). Recent advances in computers have enabled the development of models that explicitly simulate individuals within a population. In such models, each individual possesses unique attributes, such as location, species, age, or size. By modeling a large population of individuals, we may be able to generate insights into higher-level phenomenon, such as grasshopper outbreaks, from interactions occurring at lower levels. We view modeling efforts as a dialogue between simulation and field studies; models suggest hypotheses to be tested in the field, while field studies provide empirical data to modify the model.
Overwhelming outbreaks of grasshoppers have resulted in severe crop losses in the Delta Junction area of Alaska, but very little research has been conducted on the basic biology and ecology of grasshoppers in sub-arctic regions. Currently we are looking at how grasshopper populations are limited in this area. One hypothesis is that grasshopper populations are contained by the short growing season as opposed to density-dependent factors. If we understand the factors limiting grasshopper populations, we can devise specific methods of control such as habitat management, biological control, or selective baits. Ecological factors affecting the potential of microbial control of grasshopper outbreaks in Delta Junction are also being studied. One question concerns the importance of grasshopper thermoregulation (“behavioral fever”) in their susceptibility to pathogens in the sub-arctic, climate. This thermoregulation often limits the usefulness of microbials at warmer latitudes. Our observations reveal that the cool and cloudy weather in subarctic regions limits the effectiveness of thermoregulation, but also that grasshoppers are generally too cold to support acutely fatal infections of the two commercial microbial agents (Nosema locustae and Beauveria bassiana Strain GHA). However, local indigenous pathogens may have the necessary ecological attributes to succeed where the commercial pathogens fail. Isolates from the indigenous fungal pathogen and microsporida will be assessed for their ability to control grasshopper populations. One or more may become suitable biocontrol agents in the arctic region. Mormon cricket outbreaks produce large migratory bands that can invade and severely damage crop systems. We are investigating the expression of density-dependent phenotypic plasticity in the Mormon cricket, Anabrus simplex, which means simply that the Mormon cricket may change behavior and color when populations reach a critical threshold. If we can establish that the Mormon cricket expresses density-dependent changes in behavior and color, we may be able to identify specific habitats that are conducive to those changes and thus migratory band formation. This approach is based on recent studies of the desert locust, Schistocerca gregaria, which have shown that the distribution of host plants in the habitat mediates the behavioral transition from solitary living individuals to migratory gregarious phase locusts. The identification of habitats that are particularly suitable for the production of migratory Mormon cricket bands will allow us to target monitoring and management efforts on specific sensitive areas. Current USDA-ARS Grasshopper Management Scientists David Branson
Dennis Fielding Stefan Jaronski Greg Sword
USDA-ARS Northern Plains Agricultural Research Laboratory The USDA-ARS Northern Plains Agricultural Research Laboratory (NPARL) was established in 1965 to address agricultural problems in eastern Montana and western North Dakota. The Lab currently consists of two research units: the Agricultural Systems Research Unit (ASRU) and the Pest Management Research Unit (PMRU). The PMRU focuses on weed and insect pest biological control, as well as applied ecology of grasshoppers. Specific targets include leafy spurge, knapweeds, field bindweed, wheat stem sawfly, sugarbeet root maggot, grasshoppers and Mormon crickets. The mission of the ASRU is to increase productivity and economic viability of crops in the northern Great Plains by optimizing use of natural resources and farming inputs. Activities include developing better crop rotations, improving soil and water quality through site-specific farming practices, remote sensing, disease and irrigation management.
Research within the Unit is organized into two projects: (1) ecology and management of grasshoppers and other insect pests and (2) weed biological control. The first project includes research on grasshoppers and Mormon crickets, as well as biological control of wheat stem sawfly and sugarbeet root maggot. This project involves 5 scientists, including one based in Alaska. The Unit’s second project area is weed biological control. Research focuses on identifying and using insect and pathogen natural enemies to reduce the impact and spread of invasive noxious weeds. Weed targets include leafy spurge, knapweeds, and field bindweed. |
