Electrophysiological and behavioral responses of Philaenus spumarius and Neophilaenus campestris females to host plant volatiles

The spittlebugs, Philaenus spumarius and Neophilaenus campestris (Hemiptera: Aphrophoridae) are xylem-feeder insects that have been identified as main vectors of Xylella fastidiosa in Europe. In the present study we aimed to identify volatile organic compounds (VOCs) that may act as semiochemicals for these species. We collected VOCs from Olea europaea and Polygala myrtifolia, highly susceptible plant species to X. fastidiosa, Pinus halepensis a common plant where N. campestris is found during summer, and from host plant species that are used as cover crops or exist as natural vegetation in olive orchards like, Cistus creticus, Medicago sativa, Cynodon dactylon, Festuca arundinacea, Apium graveolens and Petroselinum crispum using dynamic headspace technique. We tested the response of adults’ antennae on those blends with Gas Chromatography-Electro-Antennographical Detection (GC-EAD). The chemical profile of C. creticus and P. halepensis was rich in terpenes, alcohols, aldehydes, and esters. As for P. myrtifolia, the volatile profile consisted majorly of alkanes and their substitutes. In the volatile profile of M. sativa, C. dactylon and F. arundinacea, common volatile compounds were detected. Petroselinum crispum and Apium graveolens chemical profile was dominated by terpenes. Numerous compounds elicited EAD responses for both species. α–pinene was present in all tested plants and found to stimulate antennae of female P. spumarius in five plants. In addition, antennae of P. spumarius females responded in camphor, limonene, 4-methyl octane and sabinene. These compounds were found in the volatile profile of at least 5 out of 8 examined plant species. The VOCs that triggered the most frequent EAD responses in P. spumarius females' antennae were selected for olfactometer behavioral bioassays depending on availability of synthetic compounds. Behavioral studies with authentic samples, namely (-)-α-pinene, (+)-α-pinene, sabinene, (-)-S-limonene and (1R)-(+)-camphor showed a significant attraction to camphor for P. spumarius females.