Fitness and feeding behavior of Scaphoideus titanus reared on different grapevine cultivars

Flavescence dorée of grapevine (FD) is a phytoplasma-associated disease present in several European countries and transmitted by the nearctic leafhopper Scaphoideus titanus among plants of the genus Vitis. The leafhopper spreads FD through primary infections (from gone-wild vines surrounding the vineyard to cultivated grapevines) and secondary infections (from vine to vine within the vineyard). FD transmission experiments to the main Piedmontese grapevine cultivars (cvs) were carried out with the vector S. titanus, in order to screen for different levels of cv susceptibility to FD phytoplasmas. We made the hypotheses that tolerance could be due to plant response to phytoplasmas or could be mediated by vector-plant interaction. To test this latter hypothesis, based on the results of the transmission experiments, S. titanus fitness and feeding behavior were studied on three cvs with different susceptibility to FD: Barbera (susceptible), Brachetto and Moscato (tolerant). Survival tests revealed a higher mortality rate on Moscato compared to Barbera and Brachetto, while no major differences were highlighted in developmental time measured on the three cvs. Feeding behavior of the vector was investigated with the electropenetrography (EPG) technique. Hemipteran insects insert the stylets inside the leaf to feed in different plant tissues, and this technology allows studying feeding behavior as different electric waveforms and the association with different feeding phases. The EPG experiments on S. titanus allowed a precise description of feeding behavior on the above mentioned grapevine cvs, thus shedding light on the mechanisms of susceptibility/tolerance of grapevine to FD eventually mediated by the vector.