Western flower thrips (WFT), Frankliniella occidentalis (Pergande) (Thysanoptera: Thripidae), are significant economic pests of crops and ornamental plants because they cause feeding damage and spread plant viruses, in particular, those in the genus Tospovirus. Thrips' small size, behavior, and tendency to develop pesticide resistance also make them difficult to manage. Facultative bacteria have been discovered in the hindgut of WFT and have been found in thrips populations from Europe and Hawaii. These bacteria can be cultured outside thrips and are horizontally transmitted among WFT. We have begun to determine bacterial phylogeny using the highly conserved 16s and 23s rDNA genes, as well as biochemical characteristics. Our initial findings reveal that the bacteria in WFT populations from Hawaii are similar to those found in WFT from the Netherlands. BLAST searches show that the closest relatives to the bacteria found in WFT are plant pathogens in the genus Erwinia. Our phylogenetic characterization will provide a foundation for future experiments designed to understand the role these bacteria play in WFT biology.