There are conflicting statements in the literature concerning the effects of phytophagous insects on rangeland grass yields. This preliminary study was intended to asses the use of range forage by insects, especially grasshoppers. The study areas were two south-facing slopes at about 5500 feet elevation in the Ashnola Resources Management Area in South Central British Columbia. A plant community analysis was made to determine which grasses and forbs were most numerous and which provided most ground-cover in selected areas. The communities under study were characterized by various combinations of four prominent grass species: Bluebunch Wheatgrass (Agropyron spicatum), Junegrass (Koeleria cristata), Kentucky Bluegrass (Poa pratensis), and Columbia Needlegrass (Stipa columbiana). Insect grazing damage to grasses was estimated by random sampling of individual grass blades. The "preferred" (most-utilized) species were Koeleria cristata, Poa pratensis, Poa secunda, and Stipa columbiana, in that order. Agropyron spicatum was not visibly utilized. Grasshopper numbers were estimated in several ways; the most common species were Camnula pellucida, C. xanthippus, and Melanoplus sanguinipes. Grasshoppers were least numerous on the climax Agropyron spicatum community where only 21% of the total grass was of the four preferred species, and where only 32% of the ground was covered by vegetation. Highest numbers of grasshoppers were found on a "disclimax" Poa community, where 90% of the grass was of a preferred species, and where the ground was 62% covered. Experiments to determine the effects of grasshoppers on grass yields used exclosure cages placed on three different communities (Stipa - Agropyron, Poa - Stipa, and Poa) in 1969 and 1970. In all areas the mean grass yields were higher inside the cages, but the differences were not statistically significant. This result is similar to those of other workers who have attempted to demonstrate effects of grasshoppers on rangeland grass yields; while grasshoppers consume a fairly large amount of grass, they appear to have little effect on the total standing yield of grass, as determined by an end-of-season clip of vegetation. Grasshoppers may be attracted to moist areas, for example plant communities dominated by succulent grasses, where they congregate on spots which have been clipped, trampled, grazed by livestock, or otherwise disturbed. In the absence of overgrazing by livestock, even high numbers of grasshoppers probably can do little permanent damage, since their grazing is distributed over a large number of healthy, intact plants. The mature grassland, dominated by Agropyron spicatum, seems to be relatively immune to dramatic developments in insect populations. / Land and Food Systems, Faculty of / Graduate

Field collections of grasshoppers (Orthoptera: Acrididae, Tetrigidae, and Tettigoniidae) from twenty hayfield and pasture sites in twelve counties in Virginia were made in 1979 and 1980. Fifteen Acrididae, two Tetrigidae, and six Tettigoniidae species were found among the 20,793 grasshoppers collected. Melanoplus femurrubrum femurrubrum (DeGeer) dominated the acridid fauna in both years, comprising 76.0 and 86.97 in 1979 and 1980, respectively. Two collection methods, sweepnetting and drop trapping, were used. It was assumed that the drop trap gave an absolute estimate of population densities and that discrepancies between the two collections were due to failure of sweepnetting to reliably sample the complex. Sweepnetting was found to bias against Acrididae in favor of the tettigoniidae in the complex studied. With species grouped by feeding preferences (quilds), sweepnetting sampled head (inflorescence) feeders above mixed-forb feeders, and mixed-forb feeders above grass feeders. Compared with other Acrididae, M.f. femurrubrum was over-represented in sweepnet samples above the composite of the other acridids. Within its quild its representation did not differ from the drop trap samples. Differences in the composition of the species complex from site to site were examined according to quilds based on diet, and were correlated with measurable properties or the vegetation. The proportion of head feeders was positively correlated with the plant height. Mixed-forb feeders were negatively correlated. Other vegetation properties (grass/forb ratio and percent of ground cover) were themselves highly correlated with plant height, and yielded no patterns that were as strong as those with plant height. / Master of Science

Thesis (Ph. D.)--Ohio State University, 2006. / Title from first page of PDF file. Includes bibliographical references (p. 413-447).

Typescript, etc. / Digitized by Kansas State University Libraries

Call number: LD2668 .T4 1962 J36

The understanding of the motion of animal groups, such as birds, fish and insects, has been greatly advanced by applying principles of self-organisation – the emergence of global patterns from simple, local, interactions between individuals. The desert locust, Schistocerca gregaria, provides a useful model system for the experimental study of collective behaviour. During plague years, the desert locust can form aggregations extending over hundreds of km. Before developing wings, juvenile locusts form marching ‘bands’ which can maintain group cohesion as they migrate over large distances. In this thesis I investigate locust aggregation, group motion and individual interactions. I also apply the same principles to a study of human behaviour. In Chapter 2, I describe the automated tracking methods that I developed and used to collect the data for the rest of the thesis. In the experiments described in Chapter 3, the relative strengths of the attraction to conspecifics and environmental heterogeneities were explored by presenting groups of locusts with two aggregation sites. I found that locusts had a preference to enter the site with the higher population. The locusts formed dynamic aggregations on the sites; no site was consistently more populated than the other, but individuals were significantly more attracted to the site with the higher current population. In Chapter 4, I consider the effect of marching experience on locust behaviour. Groups of locusts that had experience of directed marching, followed by a sudden reduction in density, behaved indistinguishably from those that had only experienced the lower density throughout, indicating a lack of hysteresis effects in collective responses to change in local population density. In Chapter 5, I investigate a locust’s response to its nearest neighbour. I quantified a locust’s propensity to start or stop moving according to the relative position, orientation and movement of its nearest neighbour. In Chapter 6 the techniques developed studying the locusts were applied to human groups. The response of people to different sized groups was quantified, replicating an earlier study in New York. The response was weaker in Oxford but had the same characteristics of the previous study, showing an initially linear response which saturated. The spatial distribution of gaze copying was anisotropic, tending to occur behind the group.

This dissertation examines how states and international organizations respond to complex ecological problems that are mismatched to their management capacity. The study concentrates on effort by scientific advisors, technicians, and bureaucrats to manage the population dynamics of the desert locust, Schistocerca gegaria in Western and Northern Africa. Desert locusts periodically invade crops and pastures, where they cause massive depredations that undermine agricultural productivity and food security, often in extremely impoverished regions. The immensely complex and bio-geographically stochastic breeding and gregarization dynamics of the desert locust put the insect at odds with the conventional spatiality of the state. This make it difficult for managers to precisely predict and effectively control locust outbreaks and invasions. To better understand the factors shaping institutional responses to this insect, I address three interrelated questions primarily informed by political ecology, political geography, and critical development studies: (1) What historical trajectory yielded the contemporary configuration of locust control? (2) Why do some approaches to locust management become selected over others amongst experts and organizations? (3) What is the relationship between the spatial dynamics of locust outbreaks and invasions, on the one hand, and the spatial logic and imperatives of the state? Analysis of interviews, field observations, and archival records indicates that the ability of the desert locust to evade and exceed the conventional spatiality of the state has made this pest problem an appealing field to innovate and enact new regimes of governance that operate transnationally. This has embedded locust control in the historical arc spanning from formal colonialism to the current configuration of independent states supported by international programs of foreign aid and technical assistance. In this context, concerns for the professional viability of locust expertise within state agencies and international organizations favor the selection of strategies that best fit the modalities of access to development aid and resources. This motivates state-mandated locust managers to favor the adoption of locust control strategies that are best aligned with capacity building goals of these programs, and that incorporate locust management in broader interventions of social and environmental improvement.

A method is described for the preparation of an everted rectal sac of the desert locust. Water and solute absorption by the rectum was determined by measuring changes in hemocoel fluid and rectal tissue. Initial absorption rates of Na, K, Cl, water and trans-rectal potential are comparable to those in vivo under similar conditions. After an initial transient period (1 hour), transport activity of the in vitro rectum remained in a steady state for at least 4- hours. The relationship between osmotic gradient and steady state rate of net water movement across the rectal wall was determined. Absorption of water is partially inhibited by anoxia, malonate (10־² M), dinitrophenol (10־³M), potassium cyanide (10־³ M) plus iodoacetate (10־³ M) and ouabain (10־³ M). Tissue ions and water are secreted into the hemocoel compartment when the rectal sac is incubated in isosmotic pure sucrose solution. Dependence of water movement on solute transport is indicated by the requirement of lumen ions for prolonged maintenance of water absorption. Effects of different ions (Na, K and Cl) in bathing media on absorption rate of water and ions, absorbate concentrations, trans-epithelial electro-potential differences, and tissue compositions were determined. Observed properties of water and solute movement in vitro are discussed and evaluated in relation to possible mechanisms for active absorption of water. Possible locations of transport sites are suggested in a hypothetical scheme based on the ultrastructure of rectal epithelium. / Science, Faculty of / Zoology, Department of / Graduate

Statement Qf the problem. The green valley grasshopper, Schistoceroa venusta Scudder, is one of the most common grasshoppers to be found in the San Joaquin Valley and environs. Despite the fact that the insect is commonplace, very little work has been done on its biology. It was the purpose of this study, therefore, to learn by field and laboratory observations of the life cycle and habits of Schistoceroa venusta.

<p>Social learning, defined as learning from other individuals, has been well studied in vertebrates and social insect species. In order to promote further understanding of the evolution of social learning, I tested a non-social insect for social learning and socially influenced behaviour. The desert locust (Schistocerca gregaria) is a gregarious insect which has the opportunity for social learning and can benefit from such ability. Locusts showed rapid individual learning, preferring a diet they have experienced over another of equal nutritional quality. Adult locusts also showed socially influenced behaviour, preferring to eat and lay eggs in the vicinity of other locusts over doing so alone. Fifth instar locusts did not show the same socially influenced behaviours. Neither adult nor nymphs showed social learning after interacting with previously fed models or after observing models feed through a screen. These results provide evidence for socially influenced behaviour in locusts and for a difference in social behaviour between nymphs and adults. Further research utilizing locusts as a model system may help us gain a better understanding of the evolution of social learning.</p> / Master of Science (MS)