1,721,648 research outputs found
De geurtocht van Marcel Dicke.
No full textInterview with Marcel Dicke who is involved in research on the relationship between phytophagous insects and mites, their predators and the host plants. Plants produce attractants, mostly terpenes, to attrack the predators. Possible applications of this mechanism for pest control are discusse
Interview with Marcel Dicke: the Droste effect in science
No full textMarcel Dicke grew up at the outskirts of Rotterdam, The Netherlands. He enjoyed strolling through the meadows and jumping over ditches to observe animals and plants. He was interested in life in general and his interest in biology, and especially ecology, was aroused by his inspiring high school teacher Piet Groeneboom. Marcel enrolled in the biology curriculum at Leiden University because of its reputation in ecology and obtained his MSc degree cum laude. One of his thesis projects addressed the chemical ecology of parasitoid-host interactions, supervised by Joop van Lenteren
The role of skin microbiota in the attractiveness of humans to the malaria mosquito Anopheles gambiae Giles
No full textMalaria is one of the most serious infectious diseases in the world. The African mosquito Anopheles gambiae sensu stricto (henceforth termed An. gambiae) is highly competent for malaria parasites and preferably feeds on humans inside houses, which make it one of the most effective vectors of the disease. Human body odours are presumably the most important cues that enable An. gambiae to find its host. Knowledge on the odours that mediate the host-seeking behaviour of malaria vectors is expected to contribute to novel intervention methods for disease control. The skin microbiota plays an important role in the production of human body odours and the human microbial and chemical signature displays a qualitative and quantitative correlation. Several studies have indicated a possible role of skin bacteria in the production of volatiles attractive to mosquitoes. The principle goal of this thesis was to understand the role of the human skin microbiota in mosquito-host interactions and to identify which compounds produced by these micro-organisms are involved in the attraction of An. gambiae to humans. Skin bacteria isolated from human feet and grown in vitro on agar plates attracted An. gambiae and this attraction was affected by incubation time and dilution of the skin microbiota. Semi-field experiments showed similar results and field experiments in Kenya suggested that skin bacterial volatiles also attract other disease vectors. Volatiles produced by five bacterial species common on the human skin showed that volatile blends produced by some species, including Staphylococcus epidermidis, were more attractive than blends produced by other species. Volatiles produced by Pseudomonas aeruginosa did not affect the behaviour of An. gambiae. Analysis of the volatiles produced by human skin microbiota grown in vitro led to the identification of 16 compounds, the majority of which had an effect on An. gambiae behaviour. 3-Methyl-1-butanol enhanced the attractiveness of a synthetic blend by a factor of three, and could be used to increase mosquito trap catches for monitoring or vector control purposes. 2-Phenylethanol decreased mosquito catches of a synthetic blend and may act as a spatial repellent. In order to examine the interaction between the microbiota on the skin and human attractiveness to mosquitoes, skin emanation and skin microbiota samples were taken from 48 individuals. The skin emanations from the individuals varied significantly in attractiveness to An. gambiae and several compounds originating from the skin were associated with individuals that were highly attractive or less attractive to mosquitoes. Individuals with a higher abundance of bacteria on their skin were more attractive to An. gambiae, whereas individuals with a higher diversity of skin microbiota were less attractive. Staphylococcus spp. were associated with individuals that were highly attractive and Pseudomonas spp. with individuals that were less attractive to mosquitoes. Human Leukocyte Antigens (HLA) genes are considered to influence the human body odour profile and HLA profile analysis of the 48 human individuals indicated that these genes may also affect the attractiveness of humans to mosquitoes. The studies described in this thesis show that volatiles produced by the human skin microbiota play an important role in the host-seeking behaviour of An. gambiae and the abundance and composition of the skin microbiota determine an individual’s attractiveness to mosquitoes. Optimised blends of the compounds identified can be used in push-pull strategies for the manipulation of mosquitoes, thereby reducing the number of malaria mosquitoes, the human-biting frequency, and the intensity of Plasmodium transmission. Research on the role of skin microbiota in the host-seeking behaviour and host preference of biting insects may lead to a better understanding of vector-host interactions and contribute to the fight against vector-borne diseases. <br/
Going Beyond Counting First Authors in Author Co-citation Analysis
Get PDFThe present study examines one of the fundamental aspects of author co-citation analysis (ACA) - the way co-citation
counts are defined. Co-citation counting provides the data on which all subsequent statistical analyses and mappings
are based, and we compare ACA results based on two different types of co-citation counting - the traditional type that
only counts the first one among a cited work's authors on the one hand and a non-traditional type that takes into
account the first 5 authors of a cited work on the other hand. Results indicate that the picture produced through this non-traditional author co-citation counting contains more coherent author groups and is therefore considerably clearer. However, this picture represents fewer specialties in the research field being studied than that produced through the traditional first-author co-citation counting when the same number of top-ranked authors is selected and analyzed. Reasons for these effects are discussed
Variations on the Author
Get PDF“Variations on the Author” discusses two of Eduardo Coutinho’s recent films (Um Dia na Vida, from 2010, and Últimas Conversas, posthumously released in 2015) and their contribution to the general question of documentary authorship. The director’s filmography is characterized by a consistent yet self-effacing form of authorial self-inscription: Coutinho often features as an interviewer that rather than express opinions propels discourses; an interviewer that is good at listening. This mode of self-inscription characterizes him as an author who is not expressive but who is nonetheless markedly present on the screen. In Um Dia na Vida, however, Coutinho is completely absent form the image, while Últimas Conversas, on the contrary, includes a confessional prologue that moves the director from the margins to the center of his films. This article examines the ways in which these works stand out in the filmography of a director who offers new insights into the notion of cinematic authorship
Appropriate Similarity Measures for Author Cocitation Analysis
Get PDFWe provide a number of new insights into the methodological discussion about author cocitation analysis. We first argue that the use of the Pearson correlation for measuring the similarity between authors’ cocitation profiles is not very satisfactory. We then discuss what kind of similarity measures may be used as an alternative to the Pearson correlation. We consider three similarity measures in particular. One is the well-known cosine. The other two similarity measures have not been used before in the bibliometric literature. Finally, we show by means of an example that our findings have a high practical relevance.information science;Pearson correlation;cosine;similarity measure;author cocitation analysis
Dispelling the Myths Behind First-author Citation Counts
Get PDFWe conducted a full-scale evaluative citation analysis study of scholars in the XML research field to explore just how different from each other author rankings resulting from different citation counting methods actually are, and to demonstrate the capability of emerging data and tools on the Web in supporting more realistic citation counting methods. Our results contest some common arguments for the continued
use of first-author citation counts in the evaluation of scholars, such as high correlations between author rankings by first-author citation counts and other citation
counting methods, and high costs of using more realistic citation counting methods that are not well-supported by the ISI databases. It is argued that increasingly available digital full text research papers make it possible for citation analysis studies to go beyond what the ISI databases have directly supported and to employ more
sophisticated methods
Herbivore-induced indirect defense of Arabidopsis : ecogenomic approach to the role of infochemicals in parasitoid attraction
No full textPlants defend themselves against herbivorous insects with the induced production of volatiles that attract the enemies of the herbivores. In this thesis I used an ecogenomic approach to study the role of signal-transduction pathways that regulate the induction of herbivore-induced plant volatiles (HIPV) and the effects of HIPVs on parasitoid host-finding behavior. To this end, I have combined transcriptomics, metabolite analyses and insect behavioral analyses. Nine Arabidopsis thaliana accessions were screened for the emission of HIPVs. The accessions varied in the emission rate of Pieris rapae–induced volatiles after folivory or treatment with the herbivory-mimicking plant hormone jasmonic acid (JA). The relevance of this observed variation in the emission of JA-induced volatiles for host location was tested with Diadegma semiclausum parasitoids. Furthermore, the accessions also varied in transcript levels of genes that are (putatively) involved in the production of some of the recorded HIPV-compounds. The oxylipin JA is the key plant hormone involved in the induction of the HIPV-blend emitted in response to caterpillar folivory. Mutant plants affected in the oxylipin signal-transduction pathway were studied to assess the effects of JA and its oxylipin intermediates 12-oxo-phytodienoate (OPDA) and dinor-OPDA (dnOPDA) on HIPV emission and attraction of the parasitoid D. semiclausum. In contrast to the effect of JA on the induced production of HIPVs, dnOPDA and OPDA were found to have no and little effect, respectively. The HIPV-compound methyl salicylate was shown to be JA-regulated and its abundance in the headspace varied among accessions. The contribution of methyl salicylate to parasitoid attraction was investigated. Bioassays with P. rapae-infested transgenic plants, lacking MeSA production, showed that MeSA negatively influenced D. semiclausum host-finding behavior. Mutant plants were also studied to assess whether JA and its intermediates affected the induction of genes potentially involved in defense. The different oxylipins were shown to have distinct roles in induced defense signaling. Jasmonic acid had the strongest effect on transcript levels of defense-related genes from the oxylipin- and shikimate signal-transduction pathway. Minor roles were observed for OPDA and dnOPDA in the induction of one of these genes. Utilizing an ecogenomic approach has provided new insight into the mechanisms underlying insect-plant interactions and holds promising opportunities. <br/
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