Phenological synchrony between Scaphoideus titanus (Hemiptera: Cicadellidae) hatchings and grapevine bud break: could this explain the insect's expansion?

Scaphoideus titanus is the invasive vector of the phytoplasma causing the Flavescence dorée in European vineyards. This epidemic is a serious threat to viticulture that has been increasing for more than 60 years in Europe. We studied the effect of synchrony with the plant phenology and the effect of plant-sap quality on the individual fitness. Thus, we conducted laboratory experiments to determine if insect hatchings were synchronized with grapevine bud break. We used two natural populations: one from a cold winter vineyard and one from a mild winter vineyard. In both cases, egg hatching was synchronized with bud break and leaf appearance. The phloem quality of the young and old leaves as a food source was analysed by high-performance liquid chromatography, and the effects on S. titanus growth were evaluated. Phloem composition varied with the grapevine cutting's age but also varied between leaves of different ages from the same plant. The older leaves were less nutritious because they had the highest carbon-to-nitrogen ratio and the lowest content of essential amino acids. Despite diverse phloem qualities, no fitness difference was observed. We found that the synchronization of egg hatchings with bud break is well regulated. However, the nymphs are not affected by the phloem-sap quality, suggesting that S. titanus may accept different food qualities and that egg hatching synchrony could contribute to population expansion in vineyards.