Efficacy of entomopathogenic fungi against Philaenus spumarius, the vector of Xylella fastidosa

BACKGROUND: Xylella fastidiosa is an important causative agent of Olive Quick Decline Syndrome in the Apulia region of Italy. The current study evaluated the bioefficacy of three entomopathogenic fungal strains: Beauveria bassiana SGB7004, Metarhizium robertsii SGB1K, and Akanthomyces lecanii SGB4711 against Philaenus spumarius the main vector of this pathogen, under laboratory conditions. Pathogenicity bioassays were performed by dipping nymphs and adults of P. spumarius in an aqueous suspension of powdered fungal culture (PFC) or conidial suspension (CS) of the three fungal strains. RESULTS: Both B. bassiana SGB7004 and M. robertsii SGB1K affected the viability of nymphs, resulting in more than 80% mortality at 48 h post treatment, while the effect of A. lecanii SGB4711 was not statistically significant. On adults, all three biocontrol strains were effective in a time- and concentration-dependent manner. The PFCs of B. bassiana SGB7004, M. robertsii SGB1K, and A. lecanii SGB4711 at the highest concentration tested (120 mg mL−1) resulted in 97%, 83% and 27% mortality at the trial endpoint (120 h), respectively. Mycelial growth was observed on 38.5%, 37.0% and 61.5% of dead insects treated with B. bassiana SGB7004 (2.3 × 108 CFU mL−1), M. robertsii SGB1K (3.8 × 106 CFU mL−1) and A. lecanii SGB4711 (5.4 × 108 CFU mL−1), respectively. None of the PFCs of the tested strains was pathogenic when injected into nymph spittle. CONCLUSIONS: Beauveria bassiana SGB7004 and M. robertsii SGB1K significantly affected the survival of P. spumarius nymphs and adults, while A. lecanii SGB4711 was not effective on nymphs and only slightly effective against adults.