Host-plant association and host-shifting of nymphs and adults of Philaenus spumarius L. in Italian olive orchards

The spittlebug Philaenus spumarius is by far the most abundant xylem-sap feeder insect in the Italian olive agroecosystems and is the proven vector of Xylella fastidiosa CoDIRO strain to olive in Apulia. This highly polyphagous species has one generation per year, nymphs develop in late winter-early spring, and adults are present over an extended period from spring onwards. Four olive orchards of one ha in size were chosen in the Liguria (North-Western Italy) and in Apulia (South-Eastern Italy) regions. Host-plant association of nymphal stages on the herbaceous cover was investigated while, for the adults, the presence on herbaceous and woody hosts was recorded all through the season. Within 30 sample units of 0.25 m2 randomly distributed in each olive orchard, all nymphs were counted and their host-plants identified. Adults were sampled with sweep net on 10-30 random sample units of different vegetation compartments: grass cover, olive trees, and spontaneous shrubs. Nymphs were mainly associated to species of the families Asteraceae, Fabaceae, Umbelliferae. Host-plant shifting and a different location on the plant was recorded between early and late nymphal stages, suggesting that nymphs are rather mobile. Adult population moved from grass cover to woody plants in late spring and summer and moved back to grass cover in late summer-early autumn, thus showing a clear host-shifting during the season. This information is relevant for the development of control strategies of the vector in the X. fastidiosa infected area, based on both insecticide application and agronomic measures, as well as for risk assessment in non-infected areas.