Yeasts play an important role in the life cycle and biology of the insect pest Drosophila suzukii (Matsumura), commonly known as the spotted wing drosophila (SWD). Adult and larvae of this species are known to feed and benefit from yeast in their diet. In addition, yeasts were found to be attractive to SWD and were repeatedly found to be associated with SWD. Among those, Hanseniaspora uvarum is the most commonly mentioned. The present study explores the chemical composition and the effects of three H. uvarum strains and five yeast species (Saccharomyces cerevisiae, Candida sp., Issatchenkia terricola, Metschnikowia pulcherrima and Saccharomycopsis vini) in the diet of SWD adults. The different yeast species used in this study influenced mortality, fecundity and ingestion by SWD females. Hanseniaspora uvarum and S. vini were preferably ingested and increased fecundity of SWD females. The intra-and extracellular concentrations of compounds, such as amino acids, carbohydrates, sugar alcohols and organic acids, produced or consumed by yeasts differed among the species. Knowledge of the interaction of different yeast species with SWD and specific differences in the profile of compounds of yeast can help to improve the development of control strategies against the insect pest by promoting the ingestion of attractand-kill formulations based on the combinations of yeasts and an appropriate insecticide. Keywords Fecundity • Hanseniaspora uvarum • Ingestion • Spotted wing drosophila • Yeast metabolites Key message • Naturally occurring yeasts play an important role in SWD development. • Mortality, fecundity and ingestion by SWD adults are influenced by the yeast species in their diet. • The concentrations of nutritional compounds in the fermentation broth of different yeasts vary due to differences in the methods they produce or consume compounds. • Chemical analysis of selected yeast cultures helps to understand the interaction between SWD and putative associated yeast species.

The production of phagostimulant and attractive volatile organic compounds (VOCs) by yeasts can be exploited to improve the efficacy of attract-and-kill formulations against the spotted wing drosophila (SWD). This study evaluated the persistence over one week of a yeast-based formulation under greenhouse conditions. Potted grape plants were treated with: (i) potato dextrose broth (PDB), (ii) PDB containing spinosad (PDB + S), and (iii) H. uvarum fermentation broth grown on PDB containing spinosad (H. u. + S). Laboratory trials were performed to determine the survival and the oviposition rate of SWD after exposure to treated leaves. Ion-exchange chromatography was performed to measure carbohydrates, sugar alcohols, and organic acids on leaf surfaces, while amino acids were assessed through liquid chromatography–mass-spectrometry. Additionally, the VOCs released by plants treated with H.uvarum were collected via closed-loop-stripping analysis and compared to those emitted by untreated leaves. A higher mortality was observed for adult SWDs in contact with H. uvarum containing spinosad compared to PDB containing spinosad. Generally, a decrease in the amounts of non-volatile compounds was observed over time, though numerous nutrients were still present one week after treatment. The application of the yeast-based formulation induced the emission of VOCs by the treated leaves. The concentration of 2-phenylethanol, one of the main VOCs emitted by yeasts, decreased over time. These findings describe the presence of potential phagostimulants and compounds attractive to SWD in a yeast-based attract-and-kill formulation and demonstrate the efficacy of the formulation over one week.

The impact of two different winemaking practices on the chemical and sensory complexity of Pinot Blanc wines from South Tyrol (Italy), from grape pressing to the bottled wine stored for nine months, was studied. New chemical markers of Pinot blanc were identified: astilbin and trans-caftaric acid differentiated the wines according to the vinification; S-glutathionylcaftaric acid correlated with the temporal trends. Fluorescence analysis displayed strong time-evolution and differentiation of the two wines for gallocatechin and epigallocatechin, respectively. After nine months of storage in bottle, the control wine showed higher amounts of most ethyl esters, acetate esters and octanoic acid, whereas higher alcohols characterized instead the wine obtained with prefermentative cold maceration. The sensory panel found notes of apple and tropical fruit in the control wine and attributed a higher overall quality judgement to it, whereas the cold-macerated wine was described by olfactory intensity, spicy and pear attributes.

BACKGROUND The invasive pest, Drosophila suzukii attacks fresh soft‐skinned fruit. Broad‐spectrum insecticides are implemented for control but there is a need to reduce environmental risks and insecticide residues on fruits. Hanseniaspora uvarum is a yeast frequently found on ripe fruits and associated with D. suzukii. We aim to exploit the ecological association and attraction of D. suzukii to H. uvarum by developing an attract‐and‐kill strategy, with spray‐application on canopy but not fruit. We therefore investigated D. suzukii attraction, egg‐laying and mortality when exposed to insecticidal yeast‐based formulations. RESULTS Hanseniaspora uvarum strongly attracted D. suzukii when applied on leaves of grapevine, Vitis vinifera. Notably, this attractiveness was competitive to ripe grape berries that were susceptible to D. suzukii infestation. Moreover, adding H. uvarum enhanced the efficacy of insecticidal formulations against D. suzukii. Flies exposed to leaves treated with yeast‐insecticide formulations showed higher mortality and laid a lower number of eggs compared to flies exposed to insecticide alone. In a wind tunnel, all treatments containing H. uvarum alone or in combination with insecticides, caused similar upwind flight and landing at the odor source, which provides evidence that the addition of insecticide did not reduce D. suzukii attraction to yeast. CONCLUSION Hanseniaspora uvarum can be used to manipulate the behavior of D. suzukii by attracting flies to insecticide formulations. Yeast attraction is competitive to grape berries and improves insecticide effectiveness, suggesting that sprays covering canopy only, could reduce residues on fruit without compromising management efficacy.

No abstract