Abstract
The bacterium Xylella fastidiosa is the quarantine pest with potential socio-economic and environmental impact considered to be the most serious in Europe. It is transmitted by polyphagous insect vectors. Understanding host plant - insect vector - bacterium interaction networks is an essential prerequisite to implement prophylactic and control measures. This thesis proposes a transdisciplinary approach with the study of insect vectors in ecology and an analysis of the issues around the mobilization of this knowledge for the preparation for a possible crisis. In ecology, the study of insect vectors of the bacterium is carried out both in contaminated areas (Corsica) and in unscathed areas (mainly New Aquitaine). In contaminated areas, research work will make it possible to highlight the bacterium in insect vectors, with the detection of Xylella fastidiosa across the Corsican territory. In free areas, the objective is to study potential and proven insect vectors of the bacterium and plant-insect trophic interactions in crops (mainly vines) and adjacent semi-natural environments. Finally, the mobilization of sociological tools (participant observation and semi-structured interviews) in the field of the study of science and methods will shed light on the production of scientific knowledge and its mobilization or not in regulatory and monitoring systems of the disease. The study of the bacterium in contaminated areas has led to the development of a high-throughput method to detect Xylella fastidiosa in its insect vectors. The application of this method on insects collected in Corsica between 2016 and 2020 makes it possible to demonstrate that the bacterium is present throughout the island. In addition, the results of statistical models show the influence of temperature on bacterial populations with a significant prevalence when winter temperatures are milder. From the perspective of global changes, climate projections up to 2100 were used and showed that the areas favorable to the bacterium and its main insect vector would remain significant in Corsica and largely superimposed with possible movements of the pathosystem at altitude and therefore that the risk of an epidemic would remain present. Studies in free areas have shown that Philaenus spumarius, Neophilaenus capestris, Neophilaenus lineatus and Cicadella viridis are the four vector insect species mainly found on the mainland in France. These species are mainly collected in herbaceous strata of meadows and on the edges of crops (vineyards) in relation to the inter-rows. These observations show that semi-natural environments and the edges of plots are more favorable to the spread of the bacterium and the risk of transmission of the bacterium to cultivated plants seems more moderate because few insects were collected in the plots. The results from academic research are used in other contexts, including the regulatory context. In the case of the bacterium Xylella fastidiosa, the results show that global research is shared by the entire scientific community although it is grouped according to the discipline and the disease studied. In France, this research is dissociated according to the disciplines and the institutes and it is also impacted by the media coverage of this quarantine bacterium which must be controlled. Finally, the epidemio-surveillance system concerning Xylella fastidiosa in France and supported by the plant health epidemio-surveillance platform results from arrangements between research and the risk manager. Thus, this thesis proposes a transdisciplinary approach in order to shed light on the integrated management of pathogenic organisms within the framework of preparedness with the production of results in ecology and the analysis of the epidemio-surveillance system of the bacterium in France.