Transmission characteristics of Xylella fastidiosa subsp. pauca (ST53) by Philaenus spumarius and Cicadella viridis

For insect-borne plant pathogens, transmission biology is of major importance in outlining the disease epidemiology. The characteristics of acquisition, persistence and transmission of X. fastidiosa ST53 by the spittlebug Philaenus spumarius, the main vector in Apulia, are not yet described; similarly, transmission competence of the potential vector Cicadella viridis, the most common sharpshooter in Europe, is unknown. In this perspective, two sets of experiments were performed in 2017 and 2018 to study: i) the kinetics of bacterial multiplication and persistence in P. spumarius and C. viridis; ii) the influence of temperature, season and age of P. spumarius adults on simulated epidemic progression on olive plants under indoor and outdoor conditions.
For the kinetics experiments, following the acquisition, insects were serially transferred in groups of five to olive or periwinkle test plants. In simulated epidemic progression experiments, after the acquisition, groups of insects were isolated in cages with 16 olive seedlings for different inoculation periods. Acquisition and transmission rates were assessed by testing individual insects after inoculation and by testing recipient plants 6 and 10 months post-inoculation. Furthermore, acquisition and transmission of X. fastidiosa ST53 by C. viridis were tested through an in vitro acquisition system. Overall, about 900 insects and 170 plants were tested in kinetics experiments, while about 800 spittlebugs and 1,500 plants were studied in simulated epidemic progression experiments.
Preliminary results for P. spumarius indicate: a) a higher acquisition efficiency in September than July; b) a lower acquisition efficiency from periwinkle compared with olive as source plants, but higher transmission efficiency to periwinkle compared with olive as recipient plants. Cicadella viridis was able to acquire and transmit X. fastidiosa following acquisition on artificial diet or periwinkle, although with low efficiency.