1,721,054 research outputs found
Virulence and Evolutionary Ecology in the Entomopathogen Bacillus thuringiensis
Get PDFBacillus thuringiensis is an entomopathogen in the Bacillus cereus species group, and has been used as a biopesticide for over 50 years. Despite extensive use of B. thuringiensis, there remain questions over its specific ecology compared to other members of the B. cereus group which poses problems for its continued applied use. Tying entomopathogenic ecology to a specific clade within the B. cereus group will limit confusion between B. thuringiensis used in agriculture and more harmful strains. Better understanding of B. thuringiensis ecology can also be used to combat resistance in pest species through selective passaging. The ecology of B. thuringiensis was explored through competitions in Plutella xylostella (diamondback moth) larvae, which showed clade 2 B. thuringiensis have improved fitness in insects compared to clade 1 strains. Additionally, growth rates were compared in vitro, giving different thermal profiles for the two clades. Growth media preference was assessed for B. cereus group species with all favouring protein media over soil-based ones. Selective passaging explored the effects of relatedness and host background on virulence evolution. For relatedness, B. thuringiensis subsp. aizawai was passaged for five rounds in P. xylostella larvae with none, one or two bottlenecking events. These treatments failed to produce any increase in virulence. In the second, B. thuringiensis subsp. entomocidus was passaged either in Cry1Ac-resistant, Cry1Ac-susceptible, alternating rounds of each or coevolved P. xylostella, with all containing a mutagenesis step with ethyl methanesulfonate. Virulence increased in the resistant and coevolved treatments, confirming that resistance is best overcome by passaging in harder-to-kill hosts. The ecological and genetic distinctiveness of clade 2 B. thuringiensis suggests the species should be reclassified to solely this clade, which will limit safety concerns. Selective passaging can improve the virulence of strains, even if the underlying interactions are unknown; it can also provide insight into virulence evolution which would be lost when improving only at the protein level.Leverhulme Trus
Developing screening tools to identify novel, resistance breaking pesticides.
Get PDFPesticide resistance is estimated to cost the USA $1.4 billion annually. Not only is there a huge economic cost, but the loss of crop yield and higher doses of pesticides needed to control pests damages the ecosystem 1,2. The development of resistance to chemicals is a universal phenomenon and within insect pests more than 440 species are now resistant to one or more pesticidal compound 3,4. As increasing levels of resistance arise and new molecular tools become available the understanding of resistance mechanisms grows and the limitations of pesticides are clarified 5,6. Understanding resistance is vital to counter it 5,7,8. Still facing high levels of pesticide resistance and the damaging effects of the remaining effective compounds, I here look to identify a novel pesticidal compound to overcome current resistance mechanisms 9. Synthetic compounds made by industrial partner Darr House M.I. were tested for activity against Drosophila melanogaster and Myzus persicae. The first 18 compounds were expected to act on the nicotinic acetylcholine receptor using imidacloprid as a positive control. Four competitively active compounds were found but, following a ban on neonicotinoids in the EU in 2018 and a knock-on lack of interest on the part of major agrochemical companies in novel nAChR compounds, this part of the project was pursued no further 10,11. The next 30 compounds were then tested for activity against the neurotransmitter gamma-aminobutyric acid (GABA) receptor. Here activity was only found against Drosophila not Myzus. Five compounds showed activity against D. melanogaster susceptible strain Canton-S, four then showed activity against metabolic resistant strain Hikone-R with compound 47 being close to resistance breaking. While synthetic compounds are popular, natural sources are not only a source of inspiration for synthetic products but natural products used for pest control have advantages of being environmentally friendly and constantly evolving with their pests. I tested 9 botanical sources for insecticidal and repellent activity against D. melanogaster and the Peach potato aphid M. persicae. Extracts from samples were taken using a methanol extraction technique. Rosemary extract results suggest potential lethal effects on Drosophila but development of this product would be required to concentrate the lethal effects above 40%. All extracts: basil, chilli, garlic, lemongrass, nasturtium leaves, flowers and seeds and rosemary showed repellent activity against Myzus except dill extract which had no effect. An increase in nymph droppings was seen for Myzus treated with basil suggesting possible problems for use of this compound as aphid control. To address the problem of cost and identification of novel active pesticides a Fly-Tox panel was developed using D. melanogaster as a model screening tool containing metabolic P450 resistance genes from multiple economically important pests and pollinator species. In this thesis four lines were developed containing Cyp6cm1, Cyp6bq23, Cyp6bq9 and Cyp337b3 but conferral of resistance was unsuccessful. Alternative lines from the published Fly-Tox panel were used to test the use of the screening tool with novel insecticides from chapter 2 and 3; one nAChR and one GABA targeting compound. These novel compounds were compared against positive controls; imidacloprid and fipronil, and showed a successful test run of a section of the screening tool. No resistance breaking bee-safe compounds were identified in this thesis but there was a successful trial of the Fly-Tox screening tool of transgenic Drosophila showing the value of this new resource in pesticidal discovery science. There were also findings of broad metabolic capabilities of the gene Cyp6er1, known to metabolise neonicotinoids, but also found to be active against suspected GABA targeting novel compound 47.European Commission
BBSR
The ecological genetics of insecticide resistance in Myzus persicae. PhD thesis, Imperial College, University of London
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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
koamabayili/VECTRON-author-checklist: VECTRON author checklist
No full textWe have done our best to complete the author checklist relating to the use of animals in the hut study. Note that the objective for the hut study was to evaluate the IRS treatment applications for residual efficacy against Anopheles mosquitoes, including the local An. coluzzii mosquito population. Cows were only used to attract mosquitoes into the huts and no tests were carried out directly on the cows. The author checklist is intended for use with studies where experiments are carried out on animals, which is why we have had such difficulty in completing this for the hut study, as many of the questions do not relate to how the cows were used
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