Diagnostics of Xylella fastidiosa vectors: how biometric traits in nymphs and adults play a role in identifying Philaenus italosignus and Philaenus spumarius in Tuscany (Italy)

The accurate identification of Philaenus Stål, 1964 species is essential for effective monitoring of Xylella fastidiosa Wells et al., 1987 (Xf) vectors in Europe. Although Philaenus spumarius (Linnaeus, 1753) is the primary vector of X. fastidiosa subsp. pauca ST53 in Apulia (Italy), the Mediterranean-restricted Philaenus italosignus Drosopoulos & Remane, 2000 also exhibits transmission capability, though its role in field epidemiology remains poorly defined. To date, discrimination between P. italosignus and P. spumarius has relied exclusively on adult male genitalia examination or molecular analyses. Here, we investigated biometric features of both adults and nymphs from sympatric populations in southern Tuscany to evaluate their potential use as practical diagnostic characters. Our study shows that adult female body length is clearly different between species: females of P. italosignus were consistently longer than 7.0 mm, while those of P. spumarius never exceeded this threshold. Nymphal head capsule width also differed significantly between species across instars. In fact, P. italosignus nymphs collected on Asphodelus ramosus Linnaeus, 1753 were consistently larger than those of P. spumarius from other host plants. The integration of size-based criteria into monitoring programs may enhance vector surveillance and support early measures against Xf spread in areas where the two species coexist.