Project Abstract

<p>                     <b>ABSTRACT</b>&nbsp;</p><p> In South Dakota, grasshoppers (Orthoptera Acrididae) are sporadic pests that can cause economic injury to rangeland and crops during outbreaks. It is important to know which grasshopper species are present as not all have the same potential to cause damage. USDA-APHIS conducts annual grasshopper surveys in western South Dakota rangelands, but the last published survey was in 1925. Of the potential biological control agents existing, grasshopper mites feed on grasshopper eggs and the larvae are ectoparasites of nymph and adult grasshoppers. Previous studies suggest that mite larvae reduce grasshopper fecundity and mobility, making them useful for integrated pest management of grasshopper populations. Yet, a study evaluating grasshopper mites in South Dakota has not been conducted since 1944. The purpose of the first study was to determine the abundance and species diversity of grasshoppers and the second study was to determine the density and distribution of grasshopper mites in South Dakota. Data for both studies was obtained by sampling grasshoppers in both 2017 and 2018 using sweep nets with 40 pendulum sweeps. Samples from western South Dakota were collected in rangeland and donated by USDA-APHIS. For eastern South Dakota, 400 sites were sampled once with two samples collected simultaneously from ditches alongside crop and rangeland.<br></p><p> The first study determined that the most abundant species were Melanoplus femurrubrum and Phoetaliotes nebrascensis. For both years, a majority of grasshopper populations did not exceed the recommended thresholds; however, there were localized “hot spots” that greatly exceeded the thresholds. Results of the second study indicated that the most abundant mite (i.e., over 90%) was Eutrombidium spp., which was most commonly found on M. femurrubrum nymphs. For both years, the majority of mite populations were relatively low or absent. However, there were localized, increased populations that were related to increased grasshopper populations. The results from the first study suggest that annual grasshopper surveys are necessary to detect potential outbreaks and forecast “hot spots” in the future, while the results from the second study suggest that annual grasshopper mite surveys could improve the overall understanding of the importance and impact that grasshopper mites could serve for integrated pest management purposes. <br></p>

Project Overview

<p><b>introduction&nbsp;</b></p><p> <b>Thesis Organization&nbsp;</b></p><p>This thesis contains four chapters. The first chapter is an introduction and literature review that covers the main topics of South Dakota rangelands, grasshopper abundance and species diversity, grasshopper pests, general grasshopper biology, grasshopper sampling procedures, abiotic factors that influence grasshopper populations, biotic factors that influence grasshopper populations, grasshopper management, nomenclature and synonymy of grasshopper mites, distribution of grasshopper mites in South Dakota, grasshopper mites life cycle, grasshopper mite larvae effects on grasshoppers and grasshopper mites and integrated pest management. The second chapter evaluates the abundance and species diversity of grasshoppers in South Dakota, separated into eastern and western South Dakota locations. Chapter three investigates common ectoparasitic grasshopper mite species present in South Dakota with attachment site preference, life stages, sex and species of grasshopper hosts of the grasshopper mites, rate of parasitism, and the relationship between grasshopper populations and mite abundance. Chapter four summarizes the general conclusions that were reached regarding the grasshopper abundance and species diversity, as well as the density and distribution of grasshopper mites in South Dakota. <br></p><p> South Dakota Rangeland Hewitt and Onsager (1982), estimated that grasshoppers (Orthoptera: Acrididae) were responsible for the consumption of approximately 21-23% of rangeland in the United States. In 2017, there were approximately 10 million hectares that were classified as rangeland in South Dakota (Davis and Smart 2017). Together the amount of rangeland in South Dakota and the potential negative effects of grasshoppers indicate the need for evaluation of grasshopper populations within South Dakota. Most grasslands in South Dakota are composed of a mixed-grass community with mosaic, plant species, while tallgrass prairie once dominated one-third of the state (Gartner and Sieg 1996). Of the few remnants of tall-grass prairie, the dominant species are big bluestem (Andropogon gerardii Vitman), little bluestem [Schizachyrium scoparium (Michx.) Nash], Indian grass [Sorghastrum nutans (L.) Nash], switchgrass (Panicum virgatum L.), porcupine grass [Hesperostipa spartea (Trin.) Barkworth] and tall dropseed [Sporobolus compositus (Poir.) Merr. var. compositus]. However, much of the area that was originally tall-grass prairie is now cultivated for row crops (Gartner and Sieg 1996). Mixed-grass prairies are made up of dominant species like western wheatgrass [Pascopyrum smithii (Rydb.) Á. Löve], needle and thread [Hesperostipa comata (Trin. &amp; Rupr.) Barkworth ssp. comate], little bluestem (S. scoparium), prairie sandreed [Calamovilfa longifolia (Hook.) Scribn.], green needlegrass [Nassella viridula (Trin.) Barkworth] and stonyhills muhly [Muhlenbergia cuspidata (Torr.) Rydb] (Gartner and Sieg 1996). Species including Kentucky bluegrass (Poa pratensis L.) and leafy spurge (Euphorbia esula L.) are considered invasive species in South Dakota rangelands (Gartner and Sieg 1996). <br></p><p> Annual grasslands have the highest grasshopper populations that are comprised of low species diversity with an increased number of pest species present (Fielding and Brusven 2000).&nbsp;</p><p><b>Grasshopper Abundance and Species&nbsp;</b></p><p>Diversity In the United States, there are 620 species of grasshoppers according to Arnett (2000) with nearly 400 of those species found in 17 states in the western United States (Pfadt 1984, USDA-APHIS 2002). Grasshoppers have been found in several ecosystems including prairies (e.g., short, mixed, tall and desert), mountain meadows, disturbed lands, rangelands and row crops (Pfadt 1994a, Pfadt 2002). However, not every grasshopper species that is observed is necessarily a pest, and many are specialized feeders of particular vegetation types (e.g., grasses and forbs). Of the 400 species, approximately 20 are considered common or serious pests because they are capable of causing economic damage to rangelands and crops (USDA-APHIS 2002). In a given area as many as 45 different grasshopper species may be observed, and of these it is likely that more than one species is capable of causing economic damage alone. The impact on rangeland may be worse when multiple pest species are present simultaneously (USDAAPHIS 2002). <br></p><p> Hebard (1925) conducted the last extensive survey of grasshopper species diversity and abundance in South Dakota. Another more recent study that included species diversity in South Dakota was a multi-state study by Fauske (2007), a project titled “Orthoptera of the Northern Great Plains”. Also, McDaniel (1989) offered a very useful field guide that detailed grasshopper species in South Dakota; however, a large portion of its information was excerpts from of a similar guide by Capinera and Sechrist’s (1982) entitled “Grasshoppers (Acrididae) of Colorado.”&nbsp;</p><p>Annually, USDA-APHIS conducts a survey of grasshopper abundance in western South Dakota. This survey is not species specific, although some samples are collected to examine species composition. These public records do include population density for multiple sites in each county and are used primarily to forecast future outbreaks. This survey data is combined with several western states to examine multi-state trends.</p><p> <b>Grasshopper Pests&nbsp;</b></p><p>Grasshoppers are capable of causing economic damage to crop yields and rangeland tonnage and are classified as pests in South Dakota (Pfadt 1994a). This economic loss occurs during population outbreaks as grasshoppers compete with livestock and humans for resources (Bohls 1982). Although plague level, multi-state outbreaks that were observed during the westward expansion (e.g., 1800’s) and 1900’s are rarely observed today, population outbreaks can still cause significant economic damage in localized “hot spots.” Even with decades of research on grasshoppers, the information that is necessary to accurately predict outbreaks is still being studied (Joern and Gaines 1990, Lockwood 1997, Joern 2000, Branson et al. 2006). Smith (1954) collected and summarized data regarding grasshopper populations for 100 years in Kansas, noting the changes in grasshopper population composition, methods used for&nbsp;management and the biology of species of grasshoppers. Although grasshopper populations rarely reach the severity of those that were noted in the past, they are still one of the most economically damaging pest of rangelands (Hewitt and Onsager 1982). Furthermore, USDA-APHIS historical records in South Dakota indicate that multiple species of grasshoppers are capable of causing yield loss. <br></p><p> Historically in South Dakota, Melanoplus spretus Walsh (Rocky Mountain Locust) was a common pest before becoming extinct (Parker 1939). In 1937, the dominant species were Melanoplus sangunipes Fabricius (migratory grasshopper) and Melanoplus femurrubrum DeGeer (redlegged grasshopper). However, Melanoplos bivittatus Say (twostriped grasshopper) and Melanoplus differentialis Thomas (differential grasshopper) were also common in localized areas (McDaniel 1989). By 1943, the dominant species were M. differentialis, M. bivittatus, M. sangunipes, Melanoplus confuses Scudder (pasture grasshopper) and Melanoplus packardii Scudder (packard grasshopper) (McDaniel 1989). This change in dominant grasshopper species was likely associated with changing ecology as increased cropland brought about plant communities' structures and cultivation practices to prairie grasslands in South Dakota. <br></p><p> In order to better predict similar outbreaks related to changes in which grasshopper species gain dominance in a given area, it is important to understand the changes in grasshopper population abundance and species diversity over time. This is in part because not all grasshopper species reach outbreak levels and not all cause economic loss (Pfadt 1988). Some species even make positive contributions to grassland health (McEwen 1987, Belovsky and Slade 2000, Branson et al. 2006). For example, in South Dakota, Hesperotettix viridis Thomas (snakeweed grasshopper) is considered a beneficial species because it primarily feeds on rangeland plants that provide little to no forage value for livestock (Pfadt 1994a). <br></p><p> As mentioned, the USDA-APHIS conducts an annual survey of grasshopper populations in western South Dakota that is used to forecast where population outbreaks may occur during the following year (Mesman 2016). Although grasshopper populations in eastern South Dakota are not normally surveyed, insecticides are often applied to reduce their populations during outbreak years when serious defoliation is occurring to crops and pastures (Varenhorst and Chirumamilla 2015).&nbsp;</p><p>As mentioned previously, Hebard (1925) was the last extensive grasshopper survey that included the entire state of South Dakota as well as species diversity. Without acknowledging the species that are present in more recent surveys, it is possible that community changes have occurred, or insecticide management may be occurring to reduce large populations of a benign species (Pfadt 1994a). In order to effectively manage grasshopper populations in both rangeland and row crops, both grasshopper abundance and species composition sampling are necessary (Whipple et al. 2010). <br></p><p> Hebard (1925) observed a total of 103 species and races of grasshoppers in South Dakota. The most abundant species were Melanoplus mexicanus Saussure (lesser migratory grasshopper), M. femurrubrum, Trimerotropis pistrinaria Saussure (barren land grasshopper), Trachyrhachys kiowa Thomas (kiowa grasshopper), Orphulella speciosa Scudder (slantfaced pasture grasshopper), Phoetaliotes nebrascensis Thomas (largeheaded grasshopper), Melanoplus keeleri luridus Dodge (keeler grasshopper) and Melanoplus gladstoni Scudder (gladston grasshopper). McDaniel (1989) determined there were 94 species of grasshoppers in South Dakota. The most abundant species were M. sangunipes, M. femurrubrum, Melanoplus dawsoni Scudder (dawson grasshopper), M. bivittatus, Hypochlora alba Dodge (cudweed grasshopper) and H. viridis. Fauske (2007) noted 99 species of grasshoppers in South Dakota but did not evaluate the abundance for each species observed. A species that is typically a pest of one vegetation type (e.g., rangeland) can reach pest levels in another vegetation type (e.g., cropland), but evidence of threshold level defoliation injury should be determined first before selecting a management plan. Table 1 contains a list of the most common grasshopper pests, their potential rangeland and/or crop habitat and whether they are considered major pest, pest or minor pest based on their feeding potential (Pfadt 1994a). Although Pfadt (1994b) categorizes M. sanguinipes as a serious pest, there are reports in recent years that its populations have actually been declining in Arizona, North Dakota and South Dakota (Woller, Jech, Hirsch and Reuter personal communication).&nbsp;</p><p>The cause of the observed declines is unknown but believed to be the result of colder springs that limit early-hatching grasshoppers, including M. sanguinipes. Although outbreaks of the species are still recorded, current populations only account for 1-5% of the total grasshopper populations. However, populations of M. femurrubrum have been increasing, and it is now one of the most observed grasshopper species (Jech personal communication). Other species that are noted as being major pest species include P. nebrascensis, M. bivittatus and M. differentialis. <br></p>