[Thesis defence] 25/11/2025 - Margaux Darnis: "Identifying the likely trajectories of dissemination of insect vectors of plant pathogens for better prophylaxis" (INRAE - PV)

Ms Margaux DARNIS will publicly defend her thesis entitled "Identifying the probable trajectories of dissemination of insect vectors of plant pathogens for better prophylaxis", directed by Ms Cindy MORRIS and Mr Nicolas SAUVION, on Tuesday 25 November 2025 at 2:00 pm.

Laboratory

UPR 407 - PV - Plant pathology

Composition of the jury

Ms Cindy MORRIS	INRAE Plant Pathology	Thesis supervisor
Ms Karine CHALVET-MONFRAY	UMR EPIA, INRAE, VetAgro Sup Lyon	Rapporteur
Mr Jean PECCOUD	EES team University of Poitier	Rapporteur
Nicolas SAUVION	UMR PHIM, INRAE	Thesis co-director
Ms Alexandra SCHOENY	INRAE, Plant Pathology	Thesis co-supervisor
Ms Christine MEYNARD	CBGP, INRAE	Examiner
Mr Manuel PLANTEGENEST	IGEPP, INRAE, Institut Agro Rennes	Examiner

Summary

French agriculture is currently facing a twofold challenge: coping with the ever-increasing phytosanitary problems that threaten yields and crop quality, and the need to reduce the use of pesticides for environmental and public health reasons. Epidemics caused by plant pathogens are particularly difficult to manage when curative methods are lacking. In the case of plant pathogens transmitted by insect vectors, one of the major levers for action is vector control, the effectiveness of which depends on a good match between the methods used and the ecology of the vectors. In particular, understanding and predicting the dispersal patterns of these insect vectors is the cornerstone of vector control, enabling surveillance to be optimised, risks to be assessed and appropriate prophylactic measures to be put in place.

This thesis therefore addresses two central questions: (1) What are the main determinants (local or distant, wind transport, etc.) influencing vector dispersal, and what is their relative importance? and (2) How can this knowledge be integrated into modelling tools for plant health monitoring? To answer these questions, we studied two contrasting biological models: psyllids Cacopsylla pruni, the vector of the phytoplasma responsible for apricot chlorotic leafroll (ACL) in Prunus, and several species of aphid vectors of viruses (CABYV and WMV) in melon. Our methodology is based on an integrative approach combining population and landscape genetics, statistical analysis, modelling of atmospheric trajectories and connectivity (HYSPLIT-Tropolink model), and vector population dynamics. This approach enabled us to assess the relative influence of various factors - local climate, atmospheric connectivity and wind dispersal, landscape, host distribution and geography - on vector dispersal and to identify the likely sources and patterns of dispersal to fields and orchards. Our results reveal that vector dispersal cannot be explained by a single factor, but emerges from the interaction between local abiotic factors (e.g. winter temperature, contemporary climate), atmospheric connectivity (i.e. wind dispersal), landscape (e.g. host availability, physical barriers), geographical distances (limiting possible flights), and the biology and ecology of the insect studied. In addition, the modelling of flight paths has made it possible to identify the likely source regions of each vector species studied, and to improve predictive models of their abundance at the start of the growing season.

Our approach thus offers a transferable methodological framework for studying the dispersal of vectors in other systems (e.g. culicoides, mosquitoes), provided that the method is adapted to the specific features of the model. This thesis therefore contributes to providing new fundamental information on the movements of insect vectors, and the role of atmospheric connectivity in these movements. It also provides a methodological basis that can be adapted to other pathosystems, enabling the study of these dispersions and the development of earlier and better applied monitoring and warning systems for improved management of vector-borne diseases.

Keywords epidemiology, surveillance, plant pathogens, insect vectors, prophylaxis, atmospheric connectivity