Biology of Hyalesthes obsoletus, vector of grapevine bois noir phytoplasma
Hyalesthes obsoletus (Homoptera: Cixiidae) is a vector of stolbur phytoplasma and the main vector of grapevine bois noir phytoplasma. H. obsoletus is present around the Mediterranean Basin, it can be found from coastal areas up to an altitude of 1000 m. In France, it is essentially present south of a line going from Angers to Dijon. But it is likely to be present further north, as it occurs in Germany, and bois noir disease is observed in Alsace. H. obsoletus is a polyphagous species (more than 50 host plants), but grapevine is not a preferred host (adults can feed on it, but the insect cannot complete its life cycle). In France, it has been observed on Convolvulus arvensis and Cardaria draba which are common weeds in vineyards, and also on Lavandula. The insect's habitat is essentially non-cultivated areas (abandoned land, weeded field borders, grass cover in orchards) and fields where young plants of Lavandula are growing. H. obsoletus has one generation per year, including 5 larval stages. In summer, females lay their eggs on the stems of host plants near the soil surface. Larvae hatch and migrate into the soil, along the roots. In spring, L4 and L5 migrate towards the soil surface, and adults emerge in the soil. Adults are good flyers and they leave their host plants to explore the environment and find sexual partners. During these flights (which occur in France from June to August), insects can enter vineyards, feed on grapevine sap by making several test punctures, and on this occasion transmit bois noir phytoplasma (if they had acquired it before). Direct control of H. obsoletus is not envisaged, as grapevine is not a host for the insect. However, weed control (chemical and mechanical control) in the vineyards and their vicinity appears as a possibility to control the disease. Many aspects of the biology of H. obsoletus remain to be studied, for example the acquisition and inoculation periods, the attractiveness of grapevine cultivars to the insect, and possibilities of biological control.
Sources
Sforza, R.; Boudon-Padieu, E. (1998) Le principal vecteur de la maladie du Bois noir - Faisons connaissance avec cet insecte fulguromorphe, Hyalesthes obsoletus, depuis le vignoble jusqu'au laboratoire.
Phytoma - La Défense des Végétaux, no. 510, 33-37.