The microbiota associated to grape yellows leafhopper vectors: which potential for symbiotic control?

Europe is the main wine-producing area in the world. Flavescence Dorée (FD), an insect-borne grape yellow disease, is causing economic losses from Portugal to Hungary and is a major cause of concern, among others, in wine production areas in north Spain, south France and north Italy (Angelini et al., 2001, Vitis 40:79–86). Cell wall less bacteria, previously termed mycoplasma-like organisms, and re-named as ‘Candidatus Phytoplasma vitis’, are the causative agents of FD in grapevine (Lefol et al., 1994, J. Invertebr. Pathol. 63:285–293). FD is transmitted by a leafhopper widespread in vineyards, Scaphoideus titanus (Hemiptera: Cicadellidae), which inoculates the phytoplasma into the phloem of healthy plants while feeding on the lymph. FD control is a high priority in European wine producing areas and is currently achieved through the destruction of infected vineyards and by extensive insecticide treatments against S. titanus, while direct control strategies are not yet available. The actual control strategy by chemical treatments has obvious economical and ecological impacts, and insecticide treatments are incompatible with organic production. In recent years there has been an increasing interest in the potential use of biological control microorganisms, which are pathogenic to insect. However this technology, when available, require spraying of the biocontrol agent at each growing season, with consequent economic charge and risk of resistance development.