Investigation over the life cycle of ST1-C the endosymbiont of Scaphoideus titanus

Scaphoideus titanus Ball (Hemiptera Cicadellidae) is a phloem-feeder leafhopper vector of 'Candidatus Phytoplasma vitis', the phytoplasma responsible of "flavescence doree" (FD), a grape yellows afflicting several wine production areas in Europe. Natural symbionts of the leathopper for symbiotic control of FD transmission could be used. Previous work showed the presence of a CFB bacterium, 'Candidatus Cardinium sp.' (named ST1-C) in several body districts of S. titanus. Our work was aimed to investigate the life cycle of ST1-C endosymbiont inside and outside of insect body. We fed S. titanus individuals on artificial media and tested insects and diets after the treatment for the presence of the ST1-C endosymbiont by qualitative and quantitative PCR, showing the release of the bacterium during feeding. We also performed fluorescent in situ hybridization on the sugar solutions after insect feeding, detecting ST1-C cells that confirmed its release into the medium. We tested by ST1-C-specific PCR DNA extracted from small areas of grape leaves exposed to S. titanus, identifying the bacterium in the majority of pierced leaves. Our experiments suggest that the ST1-C endosymbiont can undergo a horizontal transmission and have a complex life cycle possibly involving more than one host.