Population dynamics, host plants and infection rate with Stolbur phytoplasma of Hyalesthes obsoletus Signoret in north-western Italy

The planthopper Hyalesthes obsoletus, is the vector of grapevine bois noir disease, caused by stolbur phytoplasma. This hopper is widespread in Europe and the Middle East but it is not a grapevine specialist, and its host range is still controversial. This paper reports on the population dynamics, host range and infectivity of H. obsoletus in northwestern Italy. Field sampling of adults was done with yellow sticky traps and sweep nets on grapevines and in nettle beds, whereas nymphs were sought on nettle and bindweed roots. PCR and dot-blot analyses were used to detect stolbur phytoplasma. The life span of the planthopper was tested in the laboratory on broadbean, periwinkle, nettle and grapevine. Nymphs were found only on roots of Urtica dioica L., and many more adults were captured in nettle beds than on grapevine. Flight activity started in the middle of June and ended middle of September, with a flight peak at the end of July. In the laboratory, the longest life span was observed on nettle whereas broadbean and grapevine were not suitable for survival. Natural infectivity was 6-8% for nymphs and 9-50% for adults. These results confirm the strong links between H. obsoletus, Bois Noir, and U. dioica in northwestern Italy.