Abstract
Xylosandrus compactus and X. crassiusculus are two ambrosia beetles originating from Southeastern Asia and invasive on several continents, whose atypical biology and ecology favour invasion. During this thesis, a multidisciplinary approach was used to (i) identify the origin of invasive populations and their invasion routes and (ii) determine the areas in which they could spread and establish. Invasion routes were traced using a mitochondrial marker and genomic markers, and the suitable areas for each species were identified using species distribution models (SDM).Despite their ecological and phylogenetic proximity, the two species have different invasion histories. Two lineages were identified in X. compactus, one originating from India or Vietnam, who invaded Africa, and the other from the Shanghai area, who independently invaded the American-Pacific and Europe. X. crassiusculus comprises two very diverging clusters, mostly allopatric and with different ecological niches. Cluster 1 independently invaded Pacific islands and Africa. Cluster 2 is responsible for the invasion in the Americas, Europe, Africa and Oceania, with several independent introductions from multiple sources (including bridgehead, where an invasion occurs from an area already invaded) followed by intra-continental dispersion. For both species, SDM showed suitable areas where the pests are not present yet and which could be invaded. We expect an impact of climate change on their future potential distributions. Conversely, the recent evolution of climate is not responsible for their recent invasion in Europe, which has already been suitable for decades.