Urtica dioica, main host plant of the “stolbur” phytoplasma in vineyards of La Rioja and Navarre (Spain)

The “bois noir” disease, associated with ‘Candidatus Phytoplasma solani’ was detected in grapevine areas of La Rioja, Navarre, Aragon and Catalonia (Spain) since long time. The principal insect vector of the phytoplasma to grapevine, Hyalesthes obsoletus, was identified until 2010 in very low populations and always linked to the weed, Convolvulus arvensis. Due to the increase of the disease in Navarre and “La Rioja”, during 2013 and 2014 individual H. obsoletus were captured from both the principal host plants of this insect, C. arvensis and Urtica dioica, in grapevine plots of “La Rioja” and Navarre. The results obtained in 2013 indicated that the populations of H. obsoletus in U. dioica were higher (7–30 individuals per aspiration) than those identified in C. arvensis (0.25–6 individuals per aspiration) in these regions, and that the peak of population occurred in U. dioica in mid-August and later in C. arvensis, in mid-July. The total number of individuals captured in Navarre in 2013 was 80, with 50% of the individuals being carriers of the phytoplasma. Similar results were obtained in 2014. These results indicate that H. obsoletus captured in U. dioica is very likely the main responsible of the disease transmission to the grapevines plots of “La Rioja” and Navarre.