Life cycle, population dynamics

• Scaphoideus titanus seems to specialize in the genus Vitis : in Europe, it is enfeoffed to the only cultivated vine species ( Vitis vinifera ), while in North America it is found in abundance on V. riparia .

• The larvae are mainly localized on the underside of young leaves at the base of the vines and on the suckers. S. titanus feeds preferentially on the content of the phloem but can also feed on the xylem, or the parenchyma and excretes a large amount of honeydew.

• S. titanus has only one sexual generation per year. In Europe, fertilized females lay several eggs during summer and early autumn in crevices in the bark of disintegrating vine wood. The eggs, arranged individually or aligned one after the other in small groups, spend the winter in diapause (slowed down state of life) and hatch the following spring. Outbreaks begin in early May and last 6 to 12 weeks.

• The development cycle  larval has 5 stages, which follow one another on average every 10 days.

• The adults appear between mid-July and early August and remain in the vineyard until September. The lifespan of the imagos is approximately 1 month, the sexual maturity being acquired 10 days after the imaginal moult. Males emerge before females and die first.

• Many environmental factors, in particular temperature, can influence the onset and duration of outbreaks as well as that of the various stages of development. Consequently, the different stages of the life cycle (Figure 1) are likely to vary between sites and years.

• The transmission of the phytoplasma of Flavescence dorée is carried out according to the persistent, circulating and multiplying mode. The acquired phytoplasma is passively during food intake by the insect. When feeding on a contaminated plant, phytoplasmas can be absorbed through the ingestion of sap. The phytoplasmas are drawn into the phloem by the stylet, actively multiply in the cells of the intestine, pass into the hemolymph, reach the salivary glands and multiply there (latency period of about one month). The phytoplasmas are excreted with the saliva in the phloem during food intake. The leafhopper that has become infectious will remain so throughout its life but will not transmit phytoplasmas to its offspring.
  As soon as an outbreak of disease is present, the spread of the disease within the plot takes place step by step from these diseased stocks during the movement of the infectious larvae. The adults, moving by their ability to fly, can infect more distant plants. The vines at the edge of the plot are the most exposed to the arrival of infectious adult leafhoppers because they constitute an obstacle to their movements.
  Furthermore, it should be noted that the contaminated plant material intended for the production of scions or rootstocks plays a major role in the long-distance dispersion of the disease. In this case, new primary foci can be introduced into the vineyard even before the vectors are installed.