Degree of specificity among the psyllid-phytoplasma interactions and consequences in epidemiology
Résumé
Psyllid vectors often show close association with the pathogens they transmit. In par-ticular, the eight known vectors of the genus Cacopsylla transmit only one phytoplas-ma species, and in contrast a single phytoplasma species may be transmitted by only one or no more than two psyllid species. When two species are described they are generally very closely related from a taxonomic point of view, such as for the vectors of Candidatus Phytoplasma pyri’. Recent results confirmed this degree of specificity of the vector-psyllid interaction (C. pruni species complex) or suggested that this could be even more specific (different populations of the same species would be able to have a distinct transmission efficiency against ‘Ca.P. mali’). On the other hand, other reports suggest that several species living on the same host plant may transmit the same phytoplasma (‘Ca. P. mali’ and the psyllids on hawthorn). We discuss why these new results have important consequences for the investigation and the risk assessment of the role of a specific psyllid species in the spread of a phytoplasma disease.