Friend or foe? Relationship between ‘Candidatus Liberibacter asiaticus’ and Diaphorina citri

Interactions between insects and plant pathogens have been more enthusiastically studied in the recent decade, especially those relationships which takes the insects as vectors. The spectrum of these interactions ranges from mutualistic to pathogenic. The length of the co-evolutionary process will determine whether a microorganism shares a friend or a foe relationship with its host, and a friendship connection is frequently observed if the coexistence is longer. This review updates knowledge about the morphological, physiological and genetic mechanisms that drive the interaction between ‘Candidatus Liberibacter asiaticus’ (Las) and its vector, the Asian citrus psyllid, Diaphorina citri. Las is the predominant causal agent of citrus huanglongbing (HLB) disease, the major constrain to citrus production worldwide. This bacterium is transmitted by D. citri, in a propagative-circulative manner during its feeding from plant host. Understanding of the interactions among vector, plant pathogen and host plant are important for the management of this vector-borne disease complex.