The social wasps as a reservoir of non-Saccharomyces yeasts for bio-protection strategies in winemaking

Recent studies on yeast-insect associations demonstrated that social wasps of the genera Polistes and Vespula act as a reservoir for the conservation of yeasts and as vectors capable of transferring such yeasts on the grapes. This work aimed to assess yeast species associated with social wasps and to obtain new strains to be used as bio-protection agents in winemaking. The wine yeast communities present on the exoskeleton, intestine of social wasps, and on the surface of grapes sampled in the vineyards of three Tuscan wineries were determined. Regardless of the wasp species, yeasts were mostly associated with female workers and found mainly in their intestine (up to 7 × 10⁵ CFU/mL). The identification revealed 20 species belonging to 10 genera; Aureobasidium pullulans and Metschnikowia pulcherrima were isolated from wasps of all the wineries, the latter occurring at the highest frequency. Strain-level characterization highlighted that three strains present on grapes were also present in the gut of wasps from the same vineyard. All the isolated M. pulcherrima strains underwent in vitro tests to select the most suitable for use as bio-protective cultures. Three strains showed good inhibitory activity against Kloeckera apiculata and Brettanomyces bruxellensis; hence, they were selected for bio-protection trials on artificially contaminated grapes. Results highlighted the reduction of non-Saccharomyces populations, suggesting the effectiveness of M. pulcherrima as a biocontrol agent. The study confirmed the role of social wasps as yeast vectors in the vineyard and as a reservoir of yeast strains to be exploited for biotechnological applications in oenology. KEY POINTS: • Social wasps can carry yeast strains that are also present on the surface of grapes • Metschnikowia pulcherrima was found within the wasp gut as the prevalent yeast species • M. pulcherrima proved to be a suitable biocontrol agent on grapes.