Phytoplasmas interact with their insect vectors in a very intimate way . In order to deepen this relationship, with many unknown aspects, we performed an RNA seq project on the leafhopper Euscelidius variegatus, which is a well-known natural vector of aster yellows phytoplasmas, including chrysanthemum yellows phytoplasma (CY) and an efficient laboratory vector of Flavescence dorée phytoplasma (FD), as already mentioned in a previous post, see Phytoplasma and their vectors: more than just data flirting.
The RNAseq project originally aimed at investigating the interactions between the insect and the two phytoplasmas, exploiting the fact that the same species could transmit two phylogenetically distant phytoplasmas (competition of the two phytoplasmas in E. variegatus has also been investigated ). Main purposes were to provide clues on the insect response to phytoplasma infection and new insights on the molecular mechanisms used by phytoplasmas during insect colonization. However, valuable additional information about the composition of bacterial and virus population in E. variegatus was also obtained, perfectly in line with a recently discussed topic on this blog, see NGS-derived thought.
Among viruses we focused on a picorna-like virus, because we assembled and obtained a very long contig that probably represents the whole viral genome with a good read coverage. Infection was confirmed by RT-PCR in all the tested insects, so it can be considered endemic in the leafhopper colony. This finding was unexpected as the infection was apparently asymptomatic: insect fitness does not seem to be altered, at least in terms of longevity and prolificity. Although we have no experimental clues yet, the virus could be transmitted either transovarially or by a oro-fecal route, in accordance with the literature on other phylogenetically related arboviruses .
Interestingly, the virus was detected in both phytoplasma-exposed and not exposed insects and the cross-talk among plant pathogens, arbovirus and endosymbiont bacteria will be certainly very interesting to explore. In the very distant, but very well studied, case of honeybee colony collapse disorder induced by Varroa destructor and the associated deformed wing virus (DWV), it is worth to know that, in the absence of the parasitic mite V. destructor, DWV infection is asymptomatic and no apparent negative impact on honeybee fitness is reported . A mutualistic symbiosis between V. destructor and DWV has been recently demonstrated : the mite acts as vector of the viral pathogen, whereas DWV modulates the honeybee humoral immune response, facilitating mite feeding and reproduction.
How can vector-associated viruses affect insect behavior, plant pathogen transmission efficiency and, ultimately, plant response to infection when they are co-transmitted with plant pathogens to the plant? This is really a fascinating and largely unexplored field of investigation.
 Marcone C., 2014. Molecular Biology and pathogenicity of phytoplasmas. Annals of Applied Biology 165: 199-221
 Rashidi M., D’Amelio R., Galetto L., Marzachì C., & Bosco D. 2014. Interactive transmission of two phytoplasmas by the vector insect. Annals of Applied Biology 165: 404-413
 Van Oers M. M., 2010. Genomics and biology of Iflaviruses. Insect Virology Caister Academic Press, Norfolk, 231-250
 de Miranda J. R. & Genersch E., 2010. Deformed wing virus. Journal of Invertebrate Pathology 103: Supplement, S48-S61
 Di Prisco G., Annoscia D., Margiotta M., Ferrara R., Varricchio P., Zanni V., Caprio E., Nazzi F. & Pennacchio F., 2016. A mutualistic symbiosis between a parasitic mite and a pathogenic virus undermines honey bee immunity and health. PNAS 113: 3203-3208