I cixiidi nell'agroecosistema vigneto piemontese: indagini bioetologiche

Bois noir (BN) is a grapevine yellow whose economic importance is fast-growing in Piedmont. The disease is transmitted by Hyalesthes obsoletus Signoret, an insect belonging to the order Hemiptera and the family Cixiidae, currently the only confirmed vector. The planthopper feeds occasionally on grapevine and complete its biological cycle on herbaceous plants like Urtica dioica L. and Convolvulus arvensis L. However the presence of BN in areas where the vector is absent or present in small populations suggests the need to deepen the knowledge about the role of the other cixiid species, potential vectors of BN, in spreading the disease. The aim of this work is to point out new reports on the cixiid fauna in vineyard agro-ecosystem, their role as potential vectors of BN and the relationship between the vector and grapevine in Piedmont in order to plan more efficient control strategies. The survey was carried out in 11 vineyards, selected within the projects VIPLASMI (Regione Piemonte, 2007-2009) and BAYER CropScience, located in the most important Piedmontese viticultural areas. The study on the vector bioethology was performed in 3 vineyards whose rows were divided into blocks alternatively treated with a chemical suckerer. An entomological glue was sprayed onto 9 leaves chose randomly in 3 parts of the plant (high and low canopy and suckerings) collected every 15 days and transferred to the laboratory for being examinated. The cixiids fauna monitoring carried out in the remaining 8 vineyards was performed by a sweep net directly on the host plants. The collected cixiids were used to perform transmission trials on grapevine young plants. They were later identified by the external morphological characters and the male genitalia under a steromicroscope. The survey on relationship between the vector and the vine pointed out the typical erratic feeding activity of H. obsoletus and the scarce vine attractivity towards this planthopper. In fact their captures were limited almost exclusively on sucker-leaves in the blocks not treated. This confirms the preference of the cixiid to fly near the ground where the herbaceous plant, where it feeds on, grow. The obtained results can be an important help to choose more efficient control strategies. The monitoring permitted to verify the presence a spreading of the vector populations in the Piedmontese vineyards and the capability of H. obsoletus to accomplish the whole biological cycle both on nettle and bindweed, preferring anyway the first plant. Concerning the other studied cixiids hardly no information about the biology were available. The samplings showed flying periods similar to H. obsoletus, except for Reptalus cuspidatus (Fieber) which demonstrated to be the earliest one. All the species together cover a flying temporal window of about 4 months, starting from the second half of May till the end of August, this can be considered the critical period when the disease can be transmitted to the grapevine. It was possible for R. cuspidatus to identify the certain host plant, Artemisia verlotiorum Lamotte, for the entire biological cycle.