Osservazioni sul vettore del fitoplasma del legno nero della vite, Hyalesthes obsoletus, in Emilia-Romagna.

The Bois noir (BN) is a grapevine yellows of growing economical and epidemiological importance. It is associated to the presence of 16SrXII-A group phytoplasmas (Stolbur) (Lee et al., 1998) and transmitted in Italy by Hyalesthes obsoletus Signoret (Homoptera Cixiidae) (Alma et al., 2002). A monitoring of H. obsoletus populations has been carried out, during 2003 and 2004 vegetative seasons, in vineyards where BN was known to occur. Insects have been captured with entomological nets and then with aspirators. This method resulted to be more efficient than the use of yellow chromotropic traps (Cavallini et al., 2003), moreover various experimental traps are under evaluation such as modified “malaise trap”, simple and omni-directional “window trap”. Data of adults’ flying period in the Emilian area showed to be the same as reported by Alma and Conti (2002). Surveys about adults’ capture have statistically shown that they are mainly present along the perimeter of vineyards than the centre. This distribution is associated to the presence of nettle (Urtica dioica) along vineyards borders. Monitoring of 50 vineyards in which nettle was present have shown that on 47 farms this weed was present at borders, in 3 it was exclusively in the internal area and in 13 its presence was spread. The way nettle is distributed within the vineyards justifies the infection gradient which decreases from borders towards the centre of fields. No matter where nettle is located H. obsoletus has always been found. Molecular analysis carried out by PCR/RFLP revealed that in 2003 the 15,1% of field collected H. obsoletus adults were infected with Stolbur phytoplasmas, while in 2004 the 26,6% of specimens were positive. In 2003 results have then been grouped according to the collection’s dates in order to verify the period into which insects are highly positive to the phytoplasma; this period resulted to be between end of June and beginning of July. Specific studies were performed to verify the possibility that the vector is able to survive and complete its biological cycle on some pluriannual dicotyledon, choosed among the most widespread in the Emilian area, and positive to the BN phytoplasmas (Credi et al., 2004). The species employed were: Cirsium arvense, Convolvolus arvensis, Medicago sativa, Plantago major, Taraxacum officinale and U. dioica. In the studied area nettle is the principal host plant of H. obsoletus, however among the tested weeds, vector has revealed the following characteristics: good survival on P. major, capacity of laying eggs on all weeds, and to achieve nymphs development in C. arvense, C. arvensis, M. sativa, P. major and U. dioica. The cixiid survives only for a few days on grapevine. Results obtained from this research enable us to have more epidemiological information about BN in Emilia region useful to better elaborate a containment strategy of the disease in Lambrusco growing areas.