Potential of fungi of the genus Trichoderma for biocontrol of Philaenus spumarius, the insect vector for the quarantine bacterium Xylella fastidosa

Background: The meadow spittlebug Philaenus spumarius L. is the vector for the bacterium Xylella fastidiosa subspecies pauca, involved in olive quick decline syndrome (OQDS) in Salento (Italy). Control of P. spumarius is key to limiting transmission of the bacterium, and an innovative approach can be based on effective natural compounds and biocontrol agents. Entomopathogenic fungi are an important source of bioactive natural molecules that play a role in the relationship between microorganisms and insects. Results: Pathogenicity bioassays, performed by dipping adults of P. spumarius in either fungal culture suspension (120 mg mL−1) or cell-free culture supernatant of Trichoderma chlorosporum GJS 91-150, showed, respectively, 97% and 87% death within 24 h. The effect was dose-dependent. In laboratory bioassays, the powdered fungal culture of T. chlorosporum GJS 91-150 did not exhibit pathogenic activity when injected into nymph spittle. Conclusions: T. chlorosporum GJS 91-150 affected the survival of P. spumarius adults. The lethal effect was not associated with the development of mycelium on the cuticle, but seems due, at least partly, to fungal metabolites released in the culture medium. The fungus tested here has good potential for the development of effective low-environmental impact control strategies for P. spumarius and suppression of X. fastidiosa.