138 research outputs found
The fitness of African malaria vectors in the presence and limitation of host behaviour
No full text<p>Background
Host responses are important sources of selection upon the host species range of ectoparasites and phytophagous insects. However little is known about the role of host responses in defining the host species range of malaria vectors. This study aimed to estimate the relative importance of host behaviour to the feeding success and fitness of African malaria vectors, and assess its ability to predict their known host species preferences in nature.</p>
<p>Methods
Paired evaluations of the feeding success and fitness of African vectors Anopheles arabiensis and Anopheles gambiae s.s in the presence and limitation of host behaviour were conducted in a semi-field system (SFS) at Ifakara Health Institute, Tanzania. In one set of trials, mosquitoes were released within the SFS and allowed to forage overnight on a host that was free to exhibit natural behaviour in response to insect biting. In the other, mosquitoes were allowed to feed directly on from the skin surface of immobile hosts. The feeding success and subsequent fitness of vectors under these conditions were investigated on 6 host types (humans, calves, chickens, cows, dogs and goats) to assess whether physical movements of preferred host species (cattle for An. arabiensis, humans for An. gambiae s.s.) were less effective at preventing mosquito bites than those of common alternatives.</p>
<p>Results
Anopheles arabiensis generally had greater feeding success when applied directly to host skin than when foraging on unrestricted hosts (in five of six host species). However, An. gambiae s.s obtained blood meals from free and restrained hosts with similar success from most host types (four out of six). Overall, the blood meal size, oviposition rate, fecundity and post-feeding survival of mosquito vectors were significantly higher after feeding on hosts free to exhibit behaviour, than those who were immobilized during feeding trials.</p>
<p>Conclusions
Allowing hosts to move freely during exposure to mosquitoes was associated with moderate reductions in mosquito feeding success, but no detrimental impact to the subsequent fitness of mosquitoes that were able to feed upon them. This suggests that physical defensive behaviours exhibited by common host species including humans do not impose substantial fitness costs on African malaria vectors.</p>
Polyphony and the anxiety of influence in the fiction of Henry James
No full textJames's fiction, especially in the Middle Phase, centres
on the figure of the artist and is characterized by, the two
interrelated aspects which previous criticism has largely
overlooked: the Bakhtinian 'polyphonic' -creation of
'author-thinkers'; and the conflict between ephebes and
precursors, for which Harold-Bloom's concept of 'the-anxiety of
influence' is the most illuminating model. Polyphony is the
narrative mode, and influence is the intra-artistic, theme.
These, as the Introduction to the thesis makes clear, are
rehearsed in James's inaugural novel, Roderick Hudson. Rowland
Mallet is an author-thinker, and his failure is caused by
authorial limitations. His monologism -is impaired by his
mistaking empathy for the authorial sympathy. Likewise,
Hudson's failure does not arise from a mercurial temperament,
but from a polyphonic shortcoming: not possessing the power of
fiction to contain the fiction of power in, his mentor. And the
relationships among the three artists - Gloriani, Hudson and
Singleton - perfectly exemplify the Bloomian-theme. It is these
two concepts, polyphony and influence, which are the major
preoccupation in the Middle Phase; as, the works chosen
demonstrate. These are a novella, a novel, and a number of
short stories all of which have been unjustifiably neglected.
Chapter One, on The Aspern Papers, argues that Tina Bordereau,
far from being, the artless victim seen by many critics,
actually challenges and defeats the narrator by the very form
of her narrative. Her 'realist' discourse undermines his
language of 'romance', and shows up its internal unstability.
Chapter Two is an extensive study of the critical reception of
The Tragic Muse. The most common areas of critical attention
have been its contemporary topicality, its relation to previous
novels on similar themes, and the possible genealogy of Gabriel
Nash. Those have all missed the core of the work. - Chapter Three
demonstrates how polyphony and the anxiety of influence make
the novel what it really is. Influence arises from the
juxtaposition of, and the wrestling between, artistic ephebes
and their precursors (Nick and Nash,, Miriam and Madame Carre).
The dialogic quality defined by Bakhtin is crucial to the
proper, and even-handed, characterization of all, the conflicts
in the novel. And since most of James's tales in the eighties
and nineties -are about 'masters - and acolytes, the anxiety of
influence remains central. Chapter Four is a study of 'The
Author of Beltraffiol' and 'The Lesson of the Master'. Again the
characters' manipulations are a crucial focus in a way that
G6rard Genette's terminology helps to illuminate. The fact that
the ephebe is the author-thinker emphasizes the inextricability
of the Bakhtinian and the Bloomian in James. Just as
polyphony offers a different focus for explicating the poetics
of James's fiction; so the ephebal conflict provides the basis
for a fresh perception of James's own artistic struggle
Entomopathogenic fungi, Metarhizium anisopliae and Beauveria bassiana reduce the survival of Xenopsylla brasiliensis larvae (Siphonaptera: Pulicidae).
No full textEntomopathogenic fungi, particularly those belonging to the genera Metarhizium and Beauveria have shown great promise as arthropod vector control tools. These agents, however, have not been evaluated against flea vectors of plague. A 3-h exposure to the fungi coated paper at a concentration of 2 × 108 conidia m-2 infected >90% of flea larvae cadavers in the treatment groups. The infection reduced the survival of larvae that had been exposed to fungus relative to controls. The daily risk of dying was four- and over three-fold greater in larvae exposed to M. anisopliae (HR = 4, p<0.001) and B. bassiana (HR = 3.5, p<0.001) respectively. Both fungi can successfully infect and kill larvae of X. brasiliensis with a pooled median survival time (MST±SE) of 2±0.31 days post-exposure. These findings justify further research to investigate the bio-control potential of entomopathogenic fungi against fleas.\ud
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Selection of mosquito life-histories: a hidden weapon against malaria?
No full textBackground
There has recently been a substantial decline in malaria incidence in much of Africa. While the decline can clearly be linked to increasing coverage of mosquito vector control interventions and effective drug treatment in most settings, the ubiquity of reduction raises the possibility that additional ecological and associated evolutionary changes may be reinforcing the effectiveness of current vector control strategies in previously unanticipated ways.
Presentation of hypothesis
Here it is hypothesized that the increasing coverage of insecticide-treated bed nets and other vector control methods may be driving selection for a shift in mosquito life history that reduces their ability to transmit malaria parasites. Specifically it is hypothesized that by substantially increasing the extrinsic rate of mortality experienced in vector populations, these interventions are creating a fitness incentive for mosquitoes to re-allocate their resources towards greater short-term reproduction at the expense of longer-term survival. As malaria transmission is fundamentally dependent on mosquito survival, a life history shift in this direction would greatly benefit control.
Testing the hypothesis
At present, direct evaluation of this hypothesis within natural vector populations presents several logistical and methodological challenges. In the meantime, many insights can be gained from research previously conducted on wild Drosophila populations. Long-term selection experiments on these organisms suggest that increasing extrinsic mortality by a magnitude similar to that anticipated from the up-scaling of vector control measures generated an increase in their intrinsic mortality rate. Although this increase was small, an change of similar magnitude in Anopheles vector populations would be predicted to reduce malaria transmission by 80%.
Implications of hypothesis
The hypothesis presented here provides a reminder that evolutionary processes induced by interventions against disease vectors may not always act to neutralize intervention effectiveness. In the search for new intervention strategies, consideration should be given to both the potential disadvantages and advantages of evolutionary processes resulting from their implementation, and attempts made to exploit those with greatest potential to enhance control
Securities clearance and settlement systems - a guide to best practices
No full textAs an essential part of a nation's financial sector infrastructure, securities clearance, and settlement systems must be closely integrated with national payment systems, so that safety, soundness, certainty, and efficiency can be achieved at a cost acceptable to all participants. Central banks have paid considerable attention to payment systems, but securities clearance, and settlement systems have only recently been subjected to rigorous assessment. The Western Hemisphere Payments and Securities Clearance and Settlement Initiative (WHI), led by the World Bank, and in cooperation with the Centro de Estudios Monetarios Latinoamericanos (CEMLA), gave the authors a unique opportunity to observe how various countries in Latin America, and the Caribbean undertake securities clearance, and settlement. To do so, the authors developed a practical, and implementable assessment methodology, covering key issues that affect the quality of such systems. In this paper they discuss the objectives, scope, and content of a typical securities system, identify the elements that influence the system's quality, and show how their assessment methodology works. They focus on the development of core principles, and minimum standards for integrated systems of payments, and securities clearance and settlement. Their paper fills a gap by providing an evaluation tool for assessors of such systems, especially those who must assess evolving systems in developing, and transition economies. Essentially, an assessment involves a structured analysis to answer four related questions: 1) What are the objective, and scope of a securities clearance and settlement system? 2) Who are the participants, what roles do they play, and what expectations do they have? 3) What procedures are required to satisfy the participants'needs? 4) What inherent risks are involved, and how can they be mitigated at an acceptable cost?Environmental Economics&Policies,Payment Systems&Infrastructure,Financial Intermediation,International Terrorism&Counterterrorism,Securities Markets Policy&Regulation,Financial Intermediation,Environmental Economics&Policies,Settlement of Investment Disputes,Payment Systems&Infrastructure,Insurance&Risk Mitigation
Dragging the History Behind in Brackets. Intervista A Ivan Vladislavic
No full textIn this interview, South African author Ivan Vladislavic explores the relationship to his translators and the issues concerning the complexity and allusiveness of his language. He speaks about his history as a writer and editor in Post-apartheid South Africa and how to cope with social pressures for artists to present positive ‘nation-building’ images of the country. The interview examines one of his most recent work, Portrait with Keys – which has brought him more prominently to the attention of the European public – with particular reference to one of the postmodernist authors who influenced him the most, Italo Calvino. He talks about the importance of expanding fiction from its traditional forms and how he manages to weaves his work as a writer into his interest for architecture and visual art
Exploiting the behaviour of wild malaria vectors to achieve high infection with fungal biocontrol agents
No full textBackground
Control of mosquitoes that transmit malaria has been the mainstay in the fight against the disease, but alternative methods are required in view of emerging insecticide resistance. Entomopathogenic fungi are candidate alternatives, but to date, few trials have translated the use of these agents to field-based evaluations of their actual impact on mosquito survival and malaria risk. Mineral oil-formulations of the entomopathogenic fungi Metarhizium anisopliae and Beauveria bassiana were applied using five different techniques that each exploited the behaviour of malaria mosquitoes when entering, host-seeking or resting in experimental huts in a malaria endemic area of rural Tanzania.
Results
Survival of mosquitoes was reduced by 39-57% relative to controls after forcing upward house-entry of mosquitoes through fungus treated baffles attached to the eaves or after application of fungus-treated surfaces around an occupied bed net (bed net strip design). Moreover, 68 to 76% of the treatment mosquitoes showed fungal growth and thus had sufficient contact with fungus treated surfaces. A population dynamic model of malaria-mosquito interactions shows that these infection rates reduce malaria transmission by 75-80% due to the effect of fungal infection on adult mortality alone. The model also demonstrated that even if a high proportion of the mosquitoes exhibits outdoor biting behaviour, malaria transmission was still significantly reduced.
Conclusions
Entomopathogenic fungi strongly affect mosquito survival and have a high predicted impact on malaria transmission. These entomopathogens represent a viable alternative for malaria control, especially if they are used as part of an integrated vector management strategy
Poor people in rich countries : the roles of global governance
No full textConnections between global governance and poverty are usually made in relation to what are loosely called ‘poor countries’ of the ‘global south’. However, global governance also significantly shapes dynamics of impoverishment in ‘rich countries’ of the ‘global north’. These impacts become the more apparent when global governance is understood to involve not only well-known intergovernmental agencies such as the United Nations and the World Trade Organisation, but also additional institutional forms such as transgovernmental networks and private regulatory mechanisms. This broad complex of global governance has often exacerbated poverty in the global north: e.g., through neglect of the issue; through marginalisation of the people affected; and through the promotion of neoliberal policy frames. At the same time, global governance has in other ways also promoted poverty alleviation in ‘high-income countries’: e.g., with rules that work in their structural favour; with policy learning; with rights discourses; and with some promotion of global-scale social democracy. Thus the challenge for efforts to reduce poverty in the global north is, on the one hand, to counter the negative implications of global governance and, on the other hand, to nurture the positive forces. Global coalitions of anti-poverty campaigners – in particular across north-south lines – could especially serve these politics
Implementing the market approach to enterprise support - an evaluation of ten matching grant schemes
No full textDeveloping viable new business is critical to recovery, and long-term growth, especially in transition economies. There has been a long history of public support of enterprise development, starting with centralized state agency initiatives, but moving more recently to decentralized instruments for development of the business services market. The window of time during which the benefits of intervention are likely to be greatest: when a market is in its infancy, and its development is constrained by uncertainty, and lack of information. Interventions for enterprise support should be demand-responsive, and flexibly organized. In some circumstances, centralized assistance may still be effective, but it is generally better to use competitive private service providers responding to enterprises'changing needs. The main task is to stimulate the private services sector, improving its capacity to respond to the demands of new, and expanding private enterprises. Support for enterprises has tended to be either free, or heavily subsidized. But such subsidies can be justified only if interventions efficiently supply goods. Providing technical, and management know-how can be a public good if it generates externalities- if, for example, know-how benefits can be disseminated at proportionately low additional cost. Any subsidy for an intervention should be temporary, and should be phased out when the main objective of intervention is achieved - that is, when the market takes off. Grants should generally be for know-how, not for equipment. There may be a case for unbundling the know-how component of loans (including feasibility studies, and follow-up expert services) for grant funding. A package combining loans and grants - through a single financial institution, or through separate institutions - may work provided safeguards can be put in place to prevent perverse use of grants. The matching grant model, which is used increasingly in the World Bank, and elsewhere, is one solution - but it must be justified, and carefully designed. After evaluating ten matching grant funds, the author concludes that performance is mixed. Best practice models are needed. Ensuring economic benefits requires proactive management, with clear objectives of market facilitation ("making a market"). And it requires a balance between rapid grant approval procedures, and careful selection of services for grants.Economic Theory&Research,Decentralization,Enterprise Development&Reform,Environmental Economics&Policies,Banks&Banking Reform,Health Economics&Finance,Banks&Banking Reform,Economic Theory&Research,Environmental Economics&Policies,ICT Policy and Strategies
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