Thesis (Ph. D., Entomology and Agroforestry Systems)--University of Idaho and Centro Agronómico Tropical de Investigación y Enseñanza, May 2008. / Major professor: Nilsa A. Bosque-Pérez. Includes bibliographical references. Also available online (PDF file) by subscription or by purchasing the individual file.

Thesis (M.S.)--University of Wisconsin--Madison, 1982. / Typescript. eContent provider-neutral record in process. Description based on print version record. Includes bibliographical references (leaves 186-199).

Leafhoppers (Homoptera: Cicadellidae) were surveyed in Western Oregon vineyards in 1999. Four sites were sampled for leafhoppers using a sticky trap method, and 29 vineyards were sampled for leafhoppers using a sweep net method in the summer of 1999. The sticky trap and sweep net methods were chosen based on cost, ease of use, and the fact that they are commonly used tools available for growers and IPM programs. Populations varied according to sample method, date, location, height, agricultural practices, and growing region. Each method resulted in the capture of different leafhopper species. Sticky traps attracted, and caught mobile insects such as the winged adults. The sweep net captured leafhoppers of all stadia from the vegetation. There was seasonal variation seen for each leafhopper group. Greatest numbers of leafhoppers were caught on the border and edges of the vineyard, presumably because of the surrounding vegetation providing refuge and food. The height of catch was dependent upon the preferred host plant of the leafhopper. Species that feed on the grapevine were generally found in the canopy from 90 to 150 cm above the soil surface. Vineyard management influenced abundance and diversity within the sites. Those vineyards using the least input had the highest diversity and lowest overall abundance of leafhoppers. Chemical use, irrigation, and cover crop choice influenced the species composition of the vineyard. The sites to the south of the Willamette Valley had a higher abundance of the species Psamotettix sp. The community structure of leafhoppers appeared to be more similar in the southern sites to California. The vineyards that had a diverse mix of plants in the cover crop had a more diverse population of leafhoppers. Most species found in this study feed on herbaceous plants that are common as vineyard ground cover. The cover crop that most low input management sites use may increase the number of leafhoppers that feed on the vine, but the presence of a cover crop has many advantages in the vineyard system. / Graduation date: 2001

No description available.

Typescript. Thesis (Ph. D.)--University of Hawaii, 1954. Bibliography: leaves [156]-159.

Thesis (M.S.)--Virginia Polytechnic Institute and State University. / Vita. Abstract. Includes bibliographical references (leaves 66-72). Also available via the Internet.

No description available.

Thesis (Ph. D.)--University of Adelaide, Department of Plant Pathology, 1985. / Includes bibliographical references (leaves 62-64).

No description available.

Thesis (PhD)--Stellenbosch University, 2015. / ENGLISH ABSTRACT: Understanding how divergent selection results in the evolution of reproductive isolation (i.e. speciation) is an important goal in evolutionary biology. Populations of herbivorous insects using different host plant species can experience divergent selection from multiple selective pressures which can rapidly lead to speciation. Restio leafhoppers are a group of herbivorous insect species occurring within the Cape Floristic Region (CFR) of South Africa. They are specialised on different plant species in the Restionaceae family. Throughout my thesis I investigated how bottom-up (i.e. plant chemistry/morphology of host plant species) and top-down (i.e. predation and competition) factors drive specialisation and divergence in restio leafhoppers. I also investigated interspecific competition as an important determinant of restio leafhopper community structure. In chapter 2 I quantified host specificity of restio leafhopper species within a local community for 24 months. I found that restio leafhopper species are highly host specific and potentially synchronised with the growth phases of their host plants. In chapter 3 I used a network metric, modularity, to determine whether host plant partitioning in a restio leafhopper community is non-random (i.e. driven by a deterministic process). This metric allows the identification of the components underlying host plant partitioning (modules). I then performed experiments to show that modules, and therefore host plant partitioning, can mostly be explained by preference and performance relationships (i.e. bottom-up factors). In chapter 4 I used null models to test whether niche partitioning in restio leafhopper communities is a general pattern across the landscape. I found non-random niche partitioning, which results from strong host specificity, in all investigated restio leafhopper communities. In addition, I performed binary host choice experiments in the presence and absence of interspecific competition, but found no evidence that interspecific competition narrows host preferences. These findings suggest that host specificity, the cause of niche partitioning, is likely shaped over evolutionary time. Sampling multiple interaction networks across the CFR, in chapter 5, I tested whether restio leafhopper populations are more host specific in species rich communities and regions in the CFR than in species poor communities and regions. I found no positive relationship between restio leafhopper species richness and host specificity at any scale. These findings suggest that specialisation is not driven by interspecific competition. In chapter 6 I investigated host shifts in Cephalelus uncinatus. C. uncinatus has a broader distribution than any single restio species that it can use; suggesting that host plant related divergence may result from geographic range expansion. I found that allopatric and parapatric populations, but not sympatric individuals, using different host plants have divergent host preferences. I also found evidence for morphological divergence in traits related to predator avoidance in population pairs that exhibit divergent host preferences. My findings emphasise the importance of both bottom-up and top-down factors, with the exception of interspecific competition, as determinants of specialisation and divergence in restio leafhoppers. I find no evidence that interspecific competition is an important force structuring restio leafhopper communities. Instead, strongly niche partitioned community structure appears to emerge from the speciation process. / AFRIKAANSE OPSOMMING: Die wyse waarop uiteenlopende seleksie lei tot die evolusie van seksuele isolasie (n.l. spesiasie) is ‘n belangrike vraag in evolutionêre biologie. Plantetende insekpopulasieses wat verskillende gasheerplante gebruik kan onder uinteenlopende veelvoudige seleksie wees en vinnig spesiasie ondergaan. Restio-blaarspringers is ‘n groep plantetende insekspesies wat gespesialiseerd is op verskillende plantspesies in die restio familie. In my tesis ondersoek ek die onder-op (n.l. plantchemie en morfologie) en bo-af seleksiekragte (n.l. predasie en kompetisie) wat lei tot gasheerspesialisasie en -spesiasie in restio-blaarspringers. Ek ondersoek ook die belangrikheid van tussen-spesieskompetisie in gemeenskapsorganisasie. In hoofstuk 2 het ek gasheerspesialisasie gekwantifiseer in ‘n klein restio-blaarspringergemeenskap oor 24 maande. Ek het gevind dat restio-blaarspringers hoogs gasheerspesifiek is en moontlik met die groeifase van hul hoofgasheerplante gesinchroniseerd is. Ek het in hoofstuk 3 ‘n netwerkmetriek, modulariteit, gebruik om te bepaal of restio-blaarspringers se gasheerverdeling nie-stokasties is (n.l. deur deterministiese prosesse veroorsaak is). Hierdie metriek laat ‘n mens toe om die komponente van gasheerverdeling (modules) te identifiseer. Deur middel van eksperimente het ek bepaal dat modules, en dus gasheerverdeling, deur gasheervoorkeur en prestasie (onder-op prossesse) verduidelik kan word. In hoofstuk 4 het ek ondersoek of gasheerverdeling algemeen is. Ek het deur middel van nulmodelle gewys dat gasheerverdeling algemeen is en veroorsaak is deur sterk gasheerspesifiekheid. Ek het ook voorkeureksperimente uitgevoer in die teenwoordigheid en afwesigheid van tussen-spesies kompetisie. Hier het ek geen teken gevind dat huidige tussen-spesies kompetisie gasheervoorkeur beïnvloed nie. My bevindinge in hierdie hoofstuk stel dus voor dat spesialisasie, die oorsaak van gasheerverdeling, oor evolutionêre tyd gevorm word. In hoofstuk 5 het ek ondersoek of populasies van restio-blaarspringers meer gasheerspesifiek is in restio-blaarspringerspesies ryke gemeenskappe en streke as populasies in spesies-arm gemeenskappe en streke. Ek het geen positiewe korrelasie tussen spesiesrykheid en gasheerspesialisasie gevind nie. Dit dui daarop aan dat gasheerspesialisasie, en dus gasheerverdeling, nie deur tussen-spesies kompetisie veroorsaak word nie. In hoofstuk 6 het ek gasheerplantgekoppelde divergensie ondersoek in Cephalelus uncinatus. C. uncinatus se verspreiding is breër as enige restio-spesies wat dit kan gebruik. Dit stel voor dat verspreidingvergroting gasheerverskuiwing mag veroorsaak. Ek het gevind dat populasies wat verskillende plante in allopatrie en parapatrie gebruik uiteenlopende gasheerkeuses maak, maar insekte wat verskillende plante in sympatrie gebruik wys nie ontwrigtende gasheerkeuses nie. Die populasies wat uiteenlopende gasheerkeuses getoon het, het ook verskillende morfologiese teen-predasie eienskappe getoon. Dit dui daarop aan dat predasie belangrik mag wees vir spesiasie in restio-blaarspringers. Die bevindinge van my tesis dui daarop aan dat beide onder-op en bo-af seleksie belangrik is vir gasheer-spesialisasie in divergensie. Nietemin, tussen-spesies kompetisie is nie ‘n belangrike bron vir spesialisasie, divergensie of gemeenskapsorganisasie nie. Gemeenskapsorganisasie is klaarblyklik slegs ‘n gevolg van die spesiasie proses.