Made available in DSpace on 2014-06-11T19:30:14Z (GMT). No. of bitstreams: 0 Previous issue date: 2009-12-21Bitstream added on 2014-06-13T19:39:35Z : No. of bitstreams: 1 ferreira_b_me_rcla.pdf: 917476 bytes, checksum: ae054d19a346290a51629e619247ffb1 (MD5) / Conselho Nacional de Desenvolvimento Científico e Tecnológico (CNPq) / Coordenação de Aperfeiçoamento de Pessoal de Nível Superior (CAPES) / Os requerimentos de habitat necessários para o estabelecimento e sobrevivências de abelhas e vespas solitárias incluem locais e materiais de nidificação, e recursos para forrageio. Este estudo procurou compreender como os recursos oferecidos pelo habitat e pela paisagem podem influenciar na distribuição desses organismos, ao se estabelecerem e se deslocarem por diferentes tipos de uso e ocupação do solo. Foram utilizados ninhos armadilha como método de amostragem, durante um período de 13 meses, em 24 fragmentos de cerrado na região da Bacia do rio Corumbataí. Simultaneamente as mesmas áreas foram analisadas e descritas pelas métricas da Ecologia da Paisagem. O levantamento dos dados biológicos não permitiu nenhuma conclusão dentro dos objetivos propostos, uma vez que o número amostral de indivíduos adultos foi insatisfatório. Entretanto as análises da paisagem permitiram contextualizar a região de estudo com uma paisagem heterogênea e inadequada para o estabelecimento de uma fauna diversificada de abelhas e vespas. Os fragmentos de estudos são geralmente pequenos, pouco conectados e inseridos em matrizes de baixa permeabilidade, contribuindo com a diminuição da diversidade de fauna. Adicionalmente, foi possível organizar as áreas de estudo em níveis de prioridades de conservação, buscando criar caminhos mais práticos para traçar políticas conservacionistas e concentração de esforços. / Habitat requirements of solitary bees and wasps include nesting sites, food resources and nesting material. This work attempted to understand how those resources, available in different scales, from habitat to landscape, could drive the distribution of bees and wasps populations over a heterogeneous landscape. For solitary bees and wasps sampling it was used trap-nests, during a 13 months period, on 24 cerrado patches scattered over Corumbataí river basin. Meanwhile, those same areas were analyzed by Landscape Ecology metrics. The biological survey could not allow any further analysis, given an unexpected low rate of nesting individuals. However, landscape analysis described Corumbataí river basin as an inappropriate environment for some trap-nesting bee and wasp species; as well the selected patches, which were usually small, with low connectivity, and merged in a hostile matrix. Besides, it was possible to create levels of “priority conservation”, which give decision makers practical choices in environmental policies and efforts.

This study examines the relationship between syntactic and pragmatic language and reticence, solitary-active passive withdrawal, solitary-passive withdrawal, prosocial skills, and likeability. The Children's Communication Checklist (CCC-2), a language checklist, and Teacher Behavior Rating Scale (TBRS), a behavior checklist, were completed by three 2nd-grade teachers and three 4th-grade teachers about each of their students. Factor analysis was used to determine two composite language measures from the CCC-2 scales. The results of two hierarchal regression analyses indicated that social behaviors were significant predictors of pragmatic language, but not structural language. In particular, solitary-passive withdrawal and reticence were significant predictors of pragmatic language deficits.

Vagus nerve stimulation (VNS) treats patients with drug-resistant epilepsy, depression and heart failure, but the mechanisms responsible are uncertain. The mild stimulus intensities used in chronic VNS suggest activation of myelinated primary visceral afferents projecting to the nucleus of the solitary tract (NTS). Here, we monitored the activity of second and higher order NTS neurons in response to peripheral vagal activation using therapeutic VNS criteria. A bipolar stimulating electrode activated the left cervical vagus nerve, and stereotaxically placed single tungsten electrodes recorded unit activity from the left caudomedial NTS of chloralose-anaesthetized rats. High-intensity single electrical stimuli established vagal afferent conduction velocity (myelinated A-type or unmyelinated C-type) as well as synaptic order (second vs. higher order using paired electrical stimuli) for inputs to single NTS neurons. Then, VNS treatment was applied. A mid-collicular knife cut (KC) divided the brainstem from all supramedullary regions to determine their contribution to NTS activity. Our chief findings indicate that the KC reduced basal spontaneous activity of second-order NTS neurons receiving myelinated vagal input by 85%. In these neurons, acute VNS increased activity similarly in Control and KC animals. Interestingly, the KC interrupted VNS activation of higher order NTS neurons and second-order NTS neurons receiving unmyelinated vagal input, indicating that supramedullary descending projections to NTS are needed to amplify the peripheral neuronal signal from VNS. The present study begins to define the pathways activated during VNS and will help to better identify the central nervous system contributions to the therapeutic benefits of VNS therapy. KEY POINTS: Vagus nerve stimulation is routinely used in the clinic to treat epilepsy and depression, despite our uncertainty about how this treatment works. For this study, the connections between the nucleus of the solitary tract (NTS) and the higher brain regions were severed to learn more about their contribution to activity of these neurons during stimulation. Severing these brain connections reduced baseline activity as well as reducing stimulation-induced activation for NTS neurons receiving myelinated vagal input. Higher brain regions play a significant role in maintaining both normal activity in NTS and indirect mechanisms of enhancing NTS neuronal activity during vagus nerve stimulation.

Thesis (MSc)--Stellenbosch University, 2012. / ENGLISH ABSTRACT: Crossing symmetry relates scattering and annihilation processes to each other. Its derivation is straightforward in perturbative approaches to quantum field theory: it merely reflects the exchange of in- and outgoing states in Feynman diagram computations. In soliton models, the situation is much more complicated because the scattering and the annihilation processes concern distinct topological sectors that are not related by any continuous transformation. In this thesis a simple soliton model will be employed to address this problem numerically. First, in the unit topological sector we extract asymptotically the phase shift of the scattering process of a wave packet off the kink-solution. To this end we solve the time-dependent equation of motion of the non-integrable '4 field model in (1+1) spacetime dimensions for two distinct initial conditions: the wave packet in a trivial vacuum background and in the background of the kink-solution. Second, in the topologically trivial sector we present numerical solutions of the kink– antikink interaction in the same model. We find that the final state of this interaction varies dramatically with the impact velocity. As result, we analyze our numerical solutions for the kink–antikink collisions system in two regimes. For the initial velocity of the system less than some critical velocity, vc 0:26, the kink and the antikink either annihilate or inelastically scatter. On the other hand, the kink and the antikink always inelastically scatter when the initial velocity of the system is higher than this critical velocity. However, the scattering processes of the kink–antikink with initial velocity below and above the critical velocity are different. Below the critical velocity the kink and the antikink collide and always undergo n-bounces (n 2) before they depart to infinity. When the initial velocity of the system is higher than vc, the kink and the antikink depart to infinity after only one bounce. We present a qualitative description for these bounce effects between the kink and the antikink motivated by earlier studies as well as our numerical simulations. We utilize collective coordinates to study the dynamics of the kink–antikink system in two degrees of freedom. In this regime, we modify the ansätze of the kink–antikink system from earlier studies to account for relativistic effects. We perform a comparison between this approximation and the full system. We end our discussion of this sector by discussing the scattering data for the inelastic scattering and the annihilation processes of the kink–antikink. Third, we compare the extracted scattering data for the scattering process of a wave packet off the kink-solution and the annihilation process of the kink–antikink to each other. Finally, these studies of different sectors allow us to make a conjecture about the validity of crossing symmetry within the non-integrable '4 field model. / AFRIKAANSE OPSOMMING: Kruising-simmetrie beskryf ’n verband tussen verstrooiings- en vernietigingsprosesse. Die afleiding daarvan binne die raamwerk van steuringsteorie is eenvoudig: dit behels bloot die omruil van ingaande en uitgaande toestande in die Feynman-diagram. In soliton-modelle is die situasie egter meer ingewikkeld aangesien die verstrooiings- en vernietigingsprosesse in verskillende topologiese sektore plaasvind wat nie deur kontinue transformasies aan mekaar gekoppel is nie. In hierdie tesis word daar van ’n eenvoudige soliton-model gebruik gemaak om hierdie probleem numeries te ondersoek. Eerstens word die faseverskuiwing van die verstrooiingsproses van ’n golfpakkie vanaf ’n kinkoplossing asimptoties in die topologiese eenheidssektor bepaal. Vir hierdie doel word die tydafhanklike bewegingsvergelykings van die klassieke, nie-integreerbare 4-veldeteorie in (1+1) dimensionele ruimte-tyd opgelos. Twee beginkondisies word ondersoek: ’n golfpakkie in die triviale vakuum agtergrond asook in die kinkoplossing agtergrond. Tweedens ondersoek ons ook numeriese oplossings vir die kink-antikink wisselwerking binne die triviale topologiese sektor van dieselfde model. Hier vind ons dat die finale toestand van hierdie wisselwerkingsproses op ’n uiters sensitiewe wyse van die impaksnelheid afhang. Ons ondersoek gevolglik die numeriese oplossings vir die kink-antikink botsings in twee gebiede. Vir beginsnelhede onder die kritieke snelheid vc 0:26 sal die kink en antikink mekaar óf vernietig óf nie-elasties verstrooi. In teenstelling hiermee sal die kink-antikink altyd nie-elastiese verstrooiing ondergaan as die beginsnelheid die kritieke snelheid oorskry. Die aard van die verstrooiingsprosesse vir beginsnelhede bo en onder die kritieke snelheid is egter verskillend. Onder die kritieke snelheid sal die kink en antikink ’n n-bots proses (n 2) ondergaan voor hulle finaal van mekaar weg beweeg. Bo die kritieke snelheid sal die kink-antikink egter net ’n enkele botsing ondergaan en dan uitmekaar beweeg. Ons lewer ’n kwalitatiewe beskrywing vir die bons-effek tussen die kink en antikink wat deur vorige studies asook ons numeriese resultate gemotiveer word. Ons maak gebruik van ’n kollektiewe koördinaatstelsel om die dinamika van die kink-antikink in terme van twee vryheidsgrade te bestudeer. In hierdie gebied pas ons ook die ansatz vir die kink-antikink stelsel aan om relatiwistiese effekte in ag te neem. Ons vergelyk dan hierdie benadering met die oplossing van die volle sisteem. Die bespreking van hierdie sektor word afgesluit met ’n analise van die verstrooiingsdata vir die verstrooiing- en vernietingsprosesse van die kink-antikink. Derdens vergelyk ons die verstrooiingsdata vir die verstrooiing van ’n golfpakkie vanaf ’n kinkoplossing met die van die vernietigingsproses van die kink-antikink. Ons studie van die verskillende sektore laat ons dan toe om ’n vermoede te formuleer oor die geldigheid van kruissing-simmetrie binne die nie-integreerbare 4-model.

Abstrakt.Syftet med denna studie är att ta reda på vad som kan göras i trädgårds- och balkongmiljöer för solitära bins överlevnad, då arter redan gått förlorade eller är rödlistade på grund av dåliga förutsättningar i fråga om habitat. Hur kan utformningen av designförslag se ut för trädgård och balkong? Vad innehåller lämpliga habitat samt hur ser hotbilden ut för solitära bin? Målet med denna litteraturstudie var att finna svar på mina frågeställningar. Utifrån de fakta som framkommit från resultaten har sedan designförslag utformats för trädgårds- och balkongmiljöer. Ökad biotopyta från forna tiders mosaiklandskap kan i ny tappning utformas som trädgårds- och balkongmiljöer i form av giftfria och blomrika små ängar, blommande kantzoner, diken och rabatter, krukväxter, blommande träd och buskar. Solitära bin behöver husrum, vatten att dricka och mat att äta i form av nektar- och pollenrika växter. De behöver blommande växter från tidig vår till sen höst för att överleva. Viktigt att sprida kunskap och förståelse för hur solitära bin lever sina liv så att människor kan samarbeta för att nå långsiktiga hållbara habitatlösningar. Solitära bin behöver många blommande växtytor som kan fungera som spridningskorridorer in i de urbana miljöerna där varenda liten kvadratmeter blommande yta har betydelse. Solitära bin ökar i antal med ökad biotopyta är fakta som designförslagen baserats på. Förödande hot för solitära bin är bland annat blombrist i urbana miljöer, besprutning med olika gifter, tambin som sprider sjukdomar, människans rädsla för små kryp samt förändrade livsmiljöer. / Abstract. The purpose of this study is to find out what can be done in gardens and balconies for solitary bees survival, species have already been lost or are red-listed because of poor conditions in terms of habitat. What can design-proposals look like for gardens and balconies? What do suitable habitats contain and what do threats look like for solitary bees?The goal with this literature study was to find answers to my questions. Based on facts that emerged from the results, design proposals have been made for gardens and balconies. Increased biotope-surface from ancient times mosaic-landscape can in modern environments like gardens and balconies be designed as non-toxic and flower-rich meadows, flowering border zones, ditches and flower beds, potted plants, flowering trees and shrubs. Solitary bees need shelter, water to drink and food to eat as in nectar and pollen-rich plants. They need flowering plants from early spring to late autumn to survive. It´s important to spread knowledge and understanding how solitary bees live their lives, that people can cooperate to achieve long-term sustainable habitat solutions. Solitary bees need many flowering plant-surfaces that can act as dispersal corridors in to urban environments, where every single square meter flowering-surface is of importance. Solitary bees increase in number with increasing biotope-surfaces which are facts that design proposals are based on. Devastating threats for solitary bees are floral shortage in urban areas, spraying with various poisons, domestic bees spreading diseases, human fear of small insects and altered habitats.

It is known that there are nonlinear wave equations with localized solitary wave solutions. Some of these solitary waves are stable (with respect to a small perturbation of initial data)and have nonzero spin (nonzero intrinsic angular momentum in the centre of momentum frame). In this paper we consider vector-valued solitary wave solutions to a nonlinear Klein-Gordon equation and investigate the behavior of these spinning solitary waves under the influence of an externally imposed uniform magnetic field. We find that the only stationary spinning solitary wave solutions have spin parallel or antiparallel to the magnetic field direction.

Background: Segregation, within the context of this study, is the removal of a prisoner from the wider prison to an environment that is regimented and controlling, and functions through enforced solitude. There is very little research that explores this environment from the perspective of the prisoners who experience it. By using the voices of the prisoners this study provides rich description of the conceptual understanding of how they and resolved their segregation experiences. Research Aim: The aim of this research was to develop a grounded theory of how prisoners gave meaning to their segregated environment experience. Methodology: This study was guided by a constructivist epistemology and the principles and process of grounded theory (Constructivist Grounded Theory) as described by Glaser, Strauss, and Charmaz. Data was gathered from a participant group of prisoners who were experiencing, or had experienced within the previous two months, time in segregation, from one specific Category A prison, as well as comparable case studies. Data was collected through semi structured interviews, and case study documentary analysis, and analysed using the concurrent processes of constant comparative analysis, data collection, and theoretical sampling. Results: The participants expressed that the main concern of their time in segregation was a desire to survive this experience. They expressed this desire, and the actions and behaviours necessary to achieve it, through a process conceptualised as reframing contextual power. This has three 'subcategories‘ 'Power Posturing', 'Power Positioning', and 'Power Playing', each comprising of further subdivisions of the conceptualisation of the participants main concern. These consisted of 'Knowing Fixed Rules', 'Reading Emergent Rules', 'Relating', 'Resistance', 'Being Bad', 'Being Mad', and 'Being Cool'. Power was the major interlinking concept and this was fundamental to the strategies and actions necessary for the participants to achieve their main concern. While presented as three distinct 'subcategories‘ they are neither independent nor hierarchical, rather they are interconnected and interlinked. The participants were active in the utilisation and enactment of power actions and not passive recipients of power. A theoretical exploration of the power inherent in reframing contextual power demonstrated that no one theory or approach can sufficiently explain power within this context. It is proposed that, drawing from a number of theorists, an integrated approach to viewing and understanding such power is required to allow for a more sophisticated understanding of how the participants reframe contextual power. Conclusions: The findings of this study provide a method of understanding how the participants engaged with, and utilised complex strategies to survive the segregated environment experience. The findings also contribute to how we understand the processes of power within this current (and similar) context(s). I consider that the uniqueness of this thesis is important as it contributes to the extant body of knowledge in this field and thus offers a salient message relating to the (potential) future of segregation and the solitary confinement of prisoners.

Au moyen d'une expérience d'excitation paramétrique d'onde de surface, nous mettons en évidence l'existence de nouveaux types d'ondes solitaires et stationnaires à la surface de l'eau. Ces ondes de grande amplitude sont très non-linéaires et l'étude théorique réalisée ne permet pas de rendre compte de la forme des vagues mais permet de comprendre l'origine du phénomène d'hystérésis observé qui est nécessaire à la compréhension des phénomènes observés. En effet, l'existence de ces ondes (dans notre configuration expérimentale) est conditionnée par la présence d'un domaine de bistabilité dans le plan amplitude d'excitation - amplitude des vagues au coeur duquel nous avons montré qu'il était possible d'avoir coexistence de deux solutions, une d'amplitude nulle et une d'amplitude non nulle. Ces expériences en géométrie Hele-Shaw ont aussi permis de mettre en évidence des ondes enveloppes qui ne sont encore décrit par aucun modèle existant. Il s'agit à notre connaissance de la première onde enveloppe stationnaire observé à la surface de l'eau. Nous mettons aussi en évidence des ondes de gravité de très grande amplitude, qui sont formées alternativement d'étoiles et de polygones. Nous montrons que la symétrie du motif (nombre de branche de l'étoile) est indépendante de la taille et de la forme du récipient vibré. Nous montrons qu'un mécanisme de couplage non-linéaire résonant à trois ondes peut expliquer cette géométrie, bien que cette possibilité fut rejetée pour des ondes purement gravitaire. / By means of the parametric excitation of water waves in a Hele-Shaw cell, we report the existence of two new types of highly localized, standing surface waves of large amplitude. They are respectively of odd and even symmetries. Both solitary waves oscillate subharmonically with the forcing frequency. They are highly nonlinear, and dier strongly from the other types of localized patterns. Moreover, to our knowledge, such a solitary waves of odd symmetry has never been reported hitherto. We report a new type of standing gravity waves of large amplitude, having alternatively the shape of a star and of a polygon. This wave is observed by means of a laboratory experiment by vibrating vertically a tank. The symmetry of the star (i.e. the number of branches) is independent of the container form and size, and can be changed according to the amplitude and frequency of the vibration. We show that this wave geometry results from nonlinear resonant couplings between three waves, although this possibility has been denied for pure gravity waves up to now.

Podium denticulatum é uma espécie de vespa solitária que pertence ao gênero Podium, família Sphecidae, sendo encontrada desde o México o Brasil. As fêmeas desse gênero são caçadoras, capturam e aprovisionam o ninho com baratas paralisadas. As espécies de Podium nidificam em cavidades preexistentes, como ninhos abandonados de outras espécies de vespas, cavidades em troncos e em ninhos-armadilha (NA). O principal objetivo do presente trabalho foi estudar os aspectos comportamentais das atividades realizadas pelas fêmeas de P.denticulatum no processo de nidificação, e a obtenção de dados do tempo de desenvolvimento, número de gerações por ano e novas informações sobre a biologia e fenologia da espécie, permitindo uma análise comparativa com aquelas reportadas por outros autores. O estudo foi realizado no Campus da USP de Ribeirão Preto, SP, onde o clima é tropical quente e úmido. Foram utilizados NA que consistiram de gomos de bambus, fechados em uma das extremidades pelo nó, com comprimentos e diâmetros variados. Esses NA foram inspecionados, frequentemente, de setembro de 2003 a setembro de 2005, para constatação de fêmeas trabalhando e coleta de dados. Com isso, pôde-se constatar que as fêmeas exibem comportamento de inspeção e escolha dos NA antes de começar a captura de presas, as quais são representantes da família Blattellidae. Os ovos são colocados entre o primeiro par de pernas da presa e o desenvolvimento total, ou seja, do ovo até o adulto, foi maior nas fêmeas que nos machos. Uma característica importante observada neste estudo é que as fêmeas fecham a célula ao final do dia caso não tenham completado o aprovisionamento, retornado no dia seguinte. Esse comportamento pode ser interpretado como uma forma de proteção ao alimento larval ou ovo. O material utilizado para fechar as células e o ninho consiste de barro coletado no campo. A parede de fechamento pode ser revestida com uma resina de origem desconhecida. A fêmea pode terminar o aprovisionamento de uma célula em até cinco dias; na conclusão do ninho, ela pode demorar até nove dias, e esse tempo está relacionado à fatores externos. Foram observadas 6 gerações e um período de diapausa e a razão sexual não diferiu significantemente da proporção de 1:1. As fêmeas foram produzidas preferencialmente nas primeiras células de cria, que são dispostas em série linear. Cada ninho continha de 1 a 6 células de cria e, em 43,8% dos ninhos a fêmea construiu uma célula vestibular. Foram encontradas ainda ninhos com célula intercalar e célula vazia de fundo. As paredes de fechamento do ninho foram significantemente mais espessas do que as partições celulares. Os casulos eram de coloração castanho-médio, fusiformes, flexíveis, lisos e mais ou menos brilhantes. Foram encontrados parasitóides da família Chrysididae e Eulophidae (Hymenoptera) e Tachinidae (Díptera) atacando ninhos de P. denticulatum. As atividades de nidificação das fêmeas só foram observadas no período quente e chuvoso. / Podium denticulatum it is a solitary wasp specie which belongs to the Podium class, Sphecidae, found from Mexico to Brazil. The females from this class are hunters, they catch and provide the nest with paralyzed cockroaches that are feed for their lavas. Podium species nesting in preexisting cavities, such as abandoned nests from other species, stem cavities and in nest traps. The major objective in this work it was to study the behavior aspects in detail from the P. denticulatum females, during the nesting process, besides the developing time, generation numbers by year and new information from the biology and phenology from the specie, allowing a comparative analysis from other authors. The study was done at the University of Sao Paulo, Ribeirao Preto Campus, where the weather is tropical, hot and humid showing two seasons will defined. Using trap-nests that were bamboo, tied in one end with a diversity of length and diameters. These trap-nests were inspected frequently, from September 2003 to September 2005, to assure that the females were working and to collect data. With this it was observed that the females show an inspection behavior to choose the nest-traps before the prey capture which are from the Blattellidae family. The eggs are placed between the first pair of legs from the prey and the whole development, from egg to adult, it was bigger among the females than the males. An important characteristic observed in this study is that the females close the cell at the end of the day if they didn?t complete the provision, returning next day. This behavior can be understood as a way to protect the lava feed or the egg. The material used to close the nest is mud collected in the country, which is casted by the female. The closing wall can be coated with a unknown resin. The female can finish the provision from one cell in a day or take up to five days, at the nest conclusion it can take up to nine days, and this time is related to outside factors. It was observed six generations and a period of day pause to the studied specie. The sexual cause wasn?t significantly different from the 1:1 proportion and the females were produced on the first brood cell. The cells are placed on a lineal series and the length and diameter in the trap-nests were diversified. Each nest had from one to six brood cell and in 43,8% of the nests the female built a vestibular cell. It was found nests with intercalary cells and empty space. The nest closing walls were significantly thicker than the cell division, fusiforme, flexible, plain and more less shiny. It was found parasitoids from the Chrysididae and Eulophidae (Hymenoptera) and Tachinidae (Diptera) attacking P. denticulatum nests. The nesting activities from the females were only observed at the hot and rainy days.

Em abelhas, como nos demais himenópteros, a haplodiploidia e o mecanismo de determinação do sexo restringem o tamanho efetivo da população. Ademais, a nidificação próxima ao sítio natal pelas fêmeas das espécies solitárias restringe o fluxo gênico materno e causa alta viscosidade populacional. Centris é um gênero de abelhas solitárias da tribo Centridini, encontradas em distintos locais, como matas contínuas ou fragmentos florestais, bem como em ambientes urbanos; as espécies C. analis e C. tarsata se destacam no gênero pela abundância com que são encontradas nestas localidades. São abelhas poliléticas ou generalistas na coleta de pólen e nidificam em cavidades pré-existentes. Em razão de seu porte médio, presume-se que não apresentem alta capacidade de dispersão. Fêmeas de algumas espécies do gênero apresentam comportamento filopátrico. Estes dados nos levam a supor que espécies com traços biológicos similares tenham suas populações naturalmente estruturadas (subdivididas). Para testar esta hipótese, foram analisadas algumas regiões do genoma mitocondrial (DNAmt) de abelhas Centridini residentes em áreas urbanas. As duas subunidades da citocromo c oxidase (COI e COII), bem como o RNA transportador de leucina (RNAtLeu), apresentaram baixo nível de variação intra-específica, e a dificuldade em amplificar estas regiões para uma das espécies impediu a utilização destas regiões para análises populacionais. Desta forma, foram selecionadas duas regiões gênicas com taxas de variação intra-específicas distintas, o gene citocromo b (cytb) e a subunidade maior do DNA ribossômico (16S). Por ser uma molécula de herança materna, a análise destas regiões gênicas nos permitiu obter informações a respeito de colonização e o número de linhagens maternas. Os resultados deste trabalho sugerem que as populações de Centris tarsata e Centris trigonoides apresentam baixa e moderada estruturação, respectivamente. Para C. analis, a espécie mais bem amostrada, o excesso de picos duplos apresentados nos eletroferogramas dificultou a interpretação dos resultados. Foi possível ainda verificar diferenças na distribuição haplotípica de machos e fêmeas de C. tarsata, sugerindo a ocorrência de uma dispersão enviesada para machos, caracterizando uma dispersão sexo-assimétrica. / In bees, as in other hymenopterans, the haplodiploidy and mechanism of sex determination constrain the effective population size. Moreover, the nesting close to home site by the females of solitary species restricts maternal gene flow and causes high population viscosity. Centris is a genus of solitary bees of the tribe Centridini found in different locations, such as continuous forests or forest fragments, as well as in urban environments; the species C. analis and C. tarsata stand out in the genre for the abundance that are found in these locations. They are polyletics bees, or generalists in collecting pollen, and nest in cavities pre-existing. In reason of its medium size, it is presumed that do not present high dispersal capacity. How some species of the genus are phylopatric, we presume that other also presenting similar behavior. These data lead us to suppose that species with similar traits have their populations naturally structured (subdivided). To test this hypothesis, we analyzed urban populations of four species of Centris for some regions of mitochondrial genome (mtDNA). The two subunits of cytochrome c oxidase (COI and COII) and the tRNA leucine (tRNALeu) showed a low level of intraspecific variation, and the difficulty to amplify those regions for one species prevented the use of these regions to population analysis. Thus, we selected two gene regions with distinct rates of intra-specific variation, the gene cytochrome b (cytb) and the large subunit ribosomal DNA (16S). As a molecule maternally inherited, the analysis of the mitochondrial genes enabled us to obtain informations about colonization through the number of maternal lineages. Our results suggest that Centris tarsata and Centris trigonoides populations exhibit low and moderate genetic structuring, respectively. In C. analis, the species most well sampled, the excess of double peaks showed in the electropherograms difficults the interpretation of results. Also, for the species C. tarsata was possible to verify differences between males and females, suggesting the occurrence of a male skewed dispersion and an asymmetrical dispersion.