Scaphoideus titanus performs a dual-meaning, sharpshooter-style EPG X wave in xylem and phloem: Could S. titanus be a potential vector of Xylella fastidiosa in European vineyards?

In phytophagous hemipterans, salivary sheath-feeding species are described as xylem or phloemsap-ingesting specialists. Because these two food sources have very different characteristics, two different feeding tactics are associated with this supposed specialization. Study of feeding behavior is crucial to elucidate transmission abilities of vectors of plant pathogens. In a recently published DC-EPG study, results showed that the leafhopper Scaphoideus titanus (subfamily Deltocephalinae) ingests significantly from both phloem and xylem. S. titanus is an invasive species originally from North America that is now common in French vineyards. Until now, this insect hasbeen considered a phloem-feeder; however, this attribute was solely based on its role as a vector of the Flavescence doree phytoplasma. More importantly from a vector standpoint, S. titanus recordings revealed the first dual-meaning X wave, containing two different-appearing ingestion waveforms that were correlated with phloem and xylem ingestion, respectively. In addition, the S.titanus X wave strongly resembled that of sharpshooter leafhoppers (subfamily Cicadellinae),vectors of Xylella fastidiosa ssp. fastidiosa, the xylem-inhabiting bacterium that causes lethal Pierce’s disease of grape. Recent research has shown that the sharpshooter X wave represents the essential feeding behaviors responsible for inoculation of X. fastidiosa into grape xylem cells. Although many hemipterans ingest from xylem, probably only those few species that perform asharp shooter-style X wave can be X. fastidiosa vectors. Therefore, is it possible that S. titanus could also become a vector of Xylella fastidiosa? Until now, no deltocephaline leafhopper has been formally proven to be a vector of X. fastidiosa. Also, North American X. fastidiosa ssp.fastidiosa has not yet been introduced to Europe. However, if this subspecies were introduced into European vineyards, could S. titanus (already present in the vineyards) be a potential vector?