Efficient Olfactory Coding in the Pheromone Receptor Neuron of a Moth

The concept of coding efficiency holds that sensory neurons are adapted, through both evolutionary and developmental processes, to the statistical characteristics of their natural stimulus. Encouraged by the successful invocation of this principle to predict how neurons encode natural auditory and visual stimuli, we attempted its application to olfactory neurons. The pheromone receptor neuron of the male moth Antheraea polyphemus, for which quantitative properties of both the natural stimulus and the reception processes are available, was selected. We predicted several characteristics that the pheromone plume should possess under the hypothesis that the receptors perform optimally, i.e., transfer as much information on the stimulus per unit time as possible. Our results demonstrate that the statistical characteristics of the predicted stimulus, e.g., the probability distribution function of the stimulus concentration, the spectral density function of the stimulation course, and the intermittency, are in good agreement with those measured experimentally in the field. These results should stimulate further quantitative studies on the evolutionary adaptation of olfactory nervous systems to odorant plumes and on the plume characteristics that are most informative for the ‘sniffer’. Both aspects are relevant to the design of olfactory sensors for odour-tracking robots

Using a New Odour-Baited Device to Explore Options for Luring and Killing Outdoor-Biting Malaria Vectors: A Report on Design and Field Evaluation of the Mosquito Landing Box.

Mosquitoes that bite people outdoors can sustain malaria transmission even where effective indoor interventions such as bednets or indoor residual spraying are already widely used. Outdoor tools may therefore complement current indoor measures and improve control. We developed and evaluated a prototype mosquito control device, the 'Mosquito Landing Box' (MLB), which is baited with human odours and treated with mosquitocidal agents. The findings are used to explore technical options and challenges relevant to luring and killing outdoor-biting malaria vectors in endemic settings. Field experiments were conducted in Tanzania to assess if wild host-seeking mosquitoes 1) visited the MLBs, 2) stayed long or left shortly after arrival at the device, 3) visited the devices at times when humans were also outdoors, and 4) could be killed by contaminants applied on the devices. Odours suctioned from volunteer-occupied tents were also evaluated as a potential low-cost bait, by comparing baited and unbaited MLBs. There were significantly more Anopheles arabiensis, An. funestus, Culex and Mansonia mosquitoes visiting baited MLB than unbaited controls (P<=0.028). Increasing sampling frequency from every 120 min to 60 and 30 min led to an increase in vector catches of up to 3.6 fold (P<=0.002), indicating that many mosquitoes visited the device but left shortly afterwards. Outdoor host-seeking activity of malaria vectors peaked between 7:30 and 10:30pm, and between 4:30 and 6:00am, matching durations when locals were also outdoors. Maximum mortality of mosquitoes visiting MLBs sprayed or painted with formulations of candidate mosquitocidal agent (pirimiphos-methyl) was 51%. Odours from volunteer occupied tents attracted significantly more mosquitoes to MLBs than controls (P<0.001). While odour-baited devices such as the MLBs clearly have potential against outdoor-biting mosquitoes in communities where LLINs are used, candidate contaminants must be those that are effective at ultra-low doses even after short contact periods, since important vector species such as An. arabiensis make only brief visits to such devices. Natural human odours suctioned from occupied dwellings could constitute affordable sources of attractants to supplement odour baits for the devices. The killing agents used should be environmentally safe, long lasting, and have different modes of action (other than pyrethroids as used on LLINs), to curb the risk of physiological insecticide resistance

The Speed of Smell: Odor-Object Segregation within Milliseconds

Segregating objects from background, and determining which of many concurrent stimuli belong to the same object, remains one of the most challenging unsolved problems both in neuroscience and in technical applications. While this phenomenon has been investigated in depth in vision and audition it has hardly been investigated in olfaction. We found that for honeybees a 6-ms temporal difference in stimulus coherence is sufficient for odor-object segregation, showing that the temporal resolution of the olfactory system is much faster than previously thought

Sugar-fermenting yeast as an organic source of carbon dioxide to attract the malaria mosquito Anopheles gambiae s.s.

<p>Abstract</p> <p>Background</p> <p>Carbon dioxide (CO₂) plays an important role in the host-seeking process of opportunistic, zoophilic and anthropophilic mosquito species and is, therefore, commonly added to mosquito sampling tools. The African malaria vector <it>Anopheles gambiae sensu stricto </it>is attracted to human volatiles augmented by CO₂. This study investigated whether CO₂, usually supplied from gas cylinders acquired from commercial industry, could be replaced by CO₂derived from fermenting yeast (yeast-produced CO₂).</p> <p>Methods</p> <p>Trapping experiments were conducted in the laboratory, semi-field and field, with <it>An. gambiae s.s</it>. as the target species. MM-X traps were baited with volatiles produced by mixtures of yeast, sugar and water, prepared in 1.5, 5 or 25 L bottles. Catches were compared with traps baited with industrial CO₂. The additional effect of human odours was also examined. In the laboratory and semi-field facility dual-choice experiments were conducted. The effect of traps baited with yeast-produced CO₂on the number of mosquitoes entering an African house was studied in the MalariaSphere. Carbon dioxide baited traps, placed outside human dwellings, were also tested in an African village setting. The laboratory and semi-field data were analysed by a χ²-test, the field data by GLM. In addition, CO₂concentrations produced by yeast-sugar solutions were measured over time.</p> <p>Results</p> <p>Traps baited with yeast-produced CO₂caught significantly more mosquitoes than unbaited traps (up to 34 h post mixing the ingredients) and also significantly more than traps baited with industrial CO₂, both in the laboratory and semi-field. Adding yeast-produced CO₂to traps baited with human odour significantly increased trap catches. In the MalariaSphere, outdoor traps baited with yeast-produced or industrial CO₂+ human odour reduced house entry of mosquitoes with a human host sleeping under a bed net indoors. <it>Anopheles gambiae s.s</it>. was not caught during the field trials. However, traps baited with yeast-produced CO₂caught similar numbers of <it>Anopheles arabiensis </it>as traps baited with industrial CO₂. Addition of human odour increased trap catches.</p> <p>Conclusions</p> <p>Yeast-produced CO₂can effectively replace industrial CO₂for sampling of <it>An. gambiae s.s</it>.. This will significantly reduce costs and allow sustainable mass-application of odour-baited devices for mosquito sampling in remote areas.</p

Performance-related pay and the teaching profession: a review of the literature

This is a postprint of an article whose final and definitive form has been published in Research Papers in Education© 2002 Copyright Taylor & Francis; Research Papers in Education is available online at http://www.informaworld.comThis paper examines and summarizes research into performance-related pay. It was undertaken as part of the Teachers' Incentive Pay Project, currently in progress at the University of Exeter, which is a study of the introduction of threshold assessment and performance management for teachers in schools in England and Wales. The paper examines research into the effects of pay on employees' behaviour and considers the claimed benefits and disadvantages of performance-related pay, both generally and with particular reference to the teaching profession. Proponents of performance-related pay claim that it improves the motivation of employees and assists in the recruitment and retention of high quality staff. Disadvantages include: neglect of unrewarded tasks; disagreement about goals; competitiveness; lack of openness about failings; cost and the possibility of demotivating those who are not rewarded. Performance-related pay has long been a feature of teachers' remuneration in the US, where it has usually been promoted in response to national crises perceived to be rooted in educational failure. Traditionally, most US merit pay schemes for teachers have not been long lasting. This paper considers research into a variety of US schemes, including studies of the conditions under which they are found to succeed. Performance-related pay works best in situations in which there are easily measured outcomes, such as in manufacturing, but the outcomes of teaching are many and varied and there have been problems related to measuring teachers' effectiveness. The paper reports claims by Odden (2000) that measuring teachers' performance is now more feasible and that, therefore, the time is right for the introduction of performance-related pay for teachers

Pay at the crossroads

SIGLEAvailable from British Library Document Supply Centre-DSC:96/28298 / BLDSC - British Library Document Supply CentreGBUnited Kingdo