Xylella fastidiosa has been reported in 2018 in a Belgian nursery in West Flanders. Even before this event, the need to explore scientifically the threat to the country presented by the bacterium has been recognized, and investigation started in 2016. Based on a first screening of the Xylella host plants, three model tree species were selected: Prunus domestica cv Opal, Quercus petraea, and Salix alba. The susceptibility to the bacterium of these plant species is investigated in two different ways. The first way, known as “Sentinel plantation”, is the establishment of these plant species in areas contaminated by the bacteria to evaluate their susceptibility under natural conditions. Based on the presence of the largest number of Xylella subspecies and STs in EU, the area selected was the campus of the University of the Balearic Islands (UIB). In total, 27 plants of each targeted species were brought from Belgium and planted in the UIB campus in a repeated randomized fashion. Additionally, 32 Rosmarinus officinalis plants were used as known susceptible host plant controls. A floristic inventory was carried out to survey host plants in the vicinity. Field surveys have been done regularly in the plantation and in the surrounding monitored area. Molecular methods including several PCR (Minsavage et al., 1994, Harper et al., 2010 and Cruaud et al., 2018) were used for the bacterial detection in collected insects and investigated plants. The second complementary way consists in inoculating mechanically different strains of X. fastidiosa into the plant xylem under biosafety quarantine controlled glasshouses. The presence and the progression of the bacterium into the plants is monitored by PCR as well as by confocal microscopy with the use of a GFP-marked strain kindly provided by S. Lindow (Newman et al., 2003). Both approaches of investigating susceptibility will be discussed.