Data to: Single and combined effects of Drosophila suzukii and D. melanogaster on sour rot development in viticulture

Sour rot is a disease complex that causes serious damage in viticulture. The common vinegar fly Drosophila melanogaster (Diptera: Drosophilidae) is associated with sour rot in overripe or otherwise damaged grapes. Drosophila suzukii (Diptera: Drosophilidae) is an invasive species, which is suspected to induce sour rot in previously undamaged grapes due to the flies’ ability to infest healthy, undamaged soft fruits with its serrated ovipositor. As a consequence, infection of healthy grapes by D. suzukii may facilitate the colonization by D. melanogaster. The aim of this study was to investigate the single and combined influence of D. suzukii and D. melanogaster on sour rot development under near-natural conditions in the vineyard, along with laboratory experiments under controlled climate. For that, manipulative experiments with gauze-bagged grapes comprising four different treatments: 1) D. suzukii, 2) D. melanogaster, 3) both Drosophila species combined and 4) without flies as control were performed in 2017 and 2018. Subsequently, sour rot development was determined by measuring the volatile acidity levels. All experiments were performed around the harvest, started with the adding of the flies and ended with the determination of the volatile acid levels (as an indicator for sour rot). Field experiments were set up in a randomized block design: Blocks comprised four different treatments and were repeated 10 times and randomly distributed over the vineyard. For the laboratory experiments, the same experimental set up was chosen with four treatments repeated 10 times and randomly distributed in the climatic chamber. Therefore, one grape cluster per sample was placed in a plastic box. For all experiments n = 40 samples (4 treatments x 10 replicates) were used to check for differences in volatile acidity levels between the treatments performing variance analyses followed by post hoc tests. The raw data supporting the results in the paper are presented in three datasets referring to the five figures in the publication. A legend, explaining the different variables used in the datasets is given in a separate document. Dataset 1 is from the semi-field experiments in 2017 and underlies figure 1, 2 and 3 and related analyses. In two experimental repetitions starting at 30.8.2017 and 6.9.2017 and ending three weeks later at 20.9.2017 and 25.9.2017, grapes were exposed to the four different treatments in gauze sleeves in the field, followed by an incubation in the laboratory. In this experiment, additionally to the volatile acidity of the grape clusters, the fly emergence rates and grape cluster weight were determined. Dataset 2 is from the field experiments in 2018 and underlies figure 4 and related analyses. The experimental setup was same as in dataset 1, but the experiment took place completely in the vineyard. Again, two experimental repetitions were performed starting at 24.8.2018 and 31.8.2018 and ending with the determination of volatile acidity at 13.9.2018 and 20.9.2018. Dataset 3 is from the laboratory experiments in 2018 and underlies figure 5 and related analyses. For that, two laboratory repetitions were performed starting at 29.8.2018 and 4.9.2018 by placing one grape cluster per sample in a plastic box. The experimental setup was the same as in the field experiments with four treatments repeated 10 times and distributed randomly in the climatic chamber. The experiment ended after two weeks with the determination of volatile acidity of the grape cluster at 12.9.2018 and 29.9.2018 respectively.