Figure 6.

Propionic acid does not promote feeding behaviors in Drosophila suzukii. (a) Schematic drawing illustrating the differences on ecological niche occupied by Drosophila melanogaster and D. suzukii. D. melanogaster adults have a preference for overripe, rotten, and fermenting fruit, where the levels of propionic acid are higher. In contrast, D. suzukii adults attack fresh fruit which present lower levels of fermentation products as propionic acid. (b) Rate of mouth hook contractions of early D. suzukii foraging larvae in the context of a poor medium (0.4% yeast). Contrary to what was observed in D. melanogaster, propionic acid did not trigger an increase of mouth hooks contractions in D. suzukii larvae (t-TEST, n = 15 independent replicates). (c) Pupariation rate (graph in the left) and pupal volume (graph in the right) for D. suzukii larvae in a normal medium (6.5% yeast) or a poor medium (0.4% yeast) supplemented or not with 1% propionic acid. D. suzukii larvae survived and grew significantly less in a poor medium compared to a normal medium, and this effect was not reversed by the addition of propionic acid (One-way ANOVA followed by a Tukey post-hoc test, p < 0.05, n = 6–12 independent tubes with an average of 50 initial larvae). (d) Preference index for 1% propionic acid in a chemotaxis assay. D. suzukii larvae showed a reduce attraction to the smell of propionic acid compare to w ¹¹¹⁸ D. melanogaster larvae (*p = 0.0189 t-TEST, n = 21). (e) Mean larval velocity of w ¹¹¹⁸ (D. melanogaster) and wild type D. suzukii in the absence of odorants. D. suzukii foraging larvae were statistically significant faster than D. melanogaster (*p = 0.0258 t-TEST, n = 20). In all graphs orange and empty bars indicate presence and absence of 1% propionic acid, respectively. Striped bars represent data from D. suzukii.