| INTRODUC TI ON'Flavescence dorée' (FD), a quarantine grapevine disease caused by FD phytoplasmas (FDp), was first reported in the 1950s in south-western France (Caudwell, 1957). The spread of FD to an epidemic level within vineyards is caused by the Nearctic leafhopper Scaphoideus titanus (Ball, 1932), which, in Europe, usually accomplishes its whole life cycle on plants of the genus Vitis

The first record of Erasmoneura vulnerata Fitch, 1851 in Switzerland is reported. Specimens were collected in 2019 using yellow sticky traps during a Scaphoideus titanus monitoring campaign in vineyards in Ticino (Southern Switzerland). E. vulnerata is a grapevine pest that has recently been introduced to Europe, whose phytophagy causes detrimental damage to grapevine leaves. Its occurrence in this area has likely been favored by the ongoing suspension of insecticide treatments for the control of the S. titanus population, the vector agent of the “Flavescence dorée” phytoplasma in grapevines.

Anatomical modifications of xylem and phloem tissues of grapevine (Vitis vinifera) stems of shoots infected by the flavescence dorée phytoplasma (FDp) were first observed and described in the 1960s, but never quantified in detail. In this paper, we describe and quantify the impact of FDp on grapevine stem tissues, and relate it to the level of expression of symptoms and to cultivar‐specific FDp susceptibility. For this purpose, we measured and quantified the anatomical parameters of xylem and phloem tissues of a tolerant (Merlot) and a susceptible (Chardonnay) cultivar. For each cultivar, thin sections of eight shoots with symptoms from FDp‐infected grapevines, eight symptomless shoots from the same FDp‐infected grapevines, and eight symptomless shoots from symptomless grapevines (control) were compared. Results showed general inhibition of xylem growth and proliferation of phloem tissues (hyperplasia) with lack or irregular arrangement of the fibre‐sclereids in the axial phloem of the stems from shoots with symptoms, irrespective of the cultivar. Xylem vessels of infected Merlot shoots were partly occluded by tyloses and a higher number of smaller vessels were produced than in control plants. Thus, the anatomical responses confirmed the detrimental effect of FDp on stems of infected grapevine shoots, including impaired stem development and lack of periderm formation. Statistically significant differences were found between the two cultivars with different levels of susceptibility to FDp infection.

Phytoplasma strains were sporadically found in specimens of Hishimonus hamatus, Japananus hyalinus and Graphocephala fennahi caught during an entomological survey conducted in Southern Switzerland on the edges and woods surrounding cultivated vineyards in 2017. The subsequent molecular characterization of the pathogens allowed to identify them as strains strictly associated to Flavescence dorée, a serious European grapevine disease, transmitted from vine to vine by the leafhopper Scaphoideus titanus. In particular, M12 and M50 genotypes were found in H. hamatus and J. hyalinus, respectively, while G. fennahi harboured a mixed infection with at least two different Flavescence dorée phytoplasma genotypes. The potential importance of these findings in the frame of the Flavescence dorée epidemics in Europe is discussed.