Mind the Wound!-Fruit Injury Ranks Higher than, and Interacts with, Heterospecific Cues for Drosophila suzukii Oviposition.

Drosophila suzukii is a globally distributed insect that infests many economically important fruit varieties by ovipositing into ripening fruits. The mechanisms underlying host selection, in particular the fly's preference for fresh, intact, and competitor-free fruits, are only partially understood. We hypothesize that D. suzukii females use cues of different fruit properties to rank potential host fruits in a hierarchical manner. We created four naturally occurring fruit (blueberries) categories: (1) intact; (2) artificially wounded; (3) wounded + containing eggs of different Drosophila species; and (4) intact + exposed to D. melanogaster. Individual D. suzukii females were offered several fruits in different two-way combinations of the fruit categories. Females showed a robust oviposition preference for intact vs. wounded + infested fruits, which was even stronger compared to the intact-wounded combination. Females preferred ovipositing into intact vs. intact + exposed blueberries; however, they preferred intact + exposed over wounded blueberries. This implies a hierarchical host preference in D. suzukii, which is determined by heterospecific cues (possibly fecal matter components) and an unknown "wounding factor" of fruits.

Resource use by individual Drosophila suzukii reveals a flexible preference for oviposition into healthy fruits.

The invasive pest fruit fly Drosophila suzukii is thought to be a specialist on healthy, i.e. unwounded, non-fermenting fruits. Morphological (sharp ovipositor) and neurophysiological/behavioural adaptations have been suggested to contribute to distinct adult feeding (wounded/microbe-laden fruits) and reproductive (healthy fruits) sites. We tested whether (1) variation in the overall availability of fruits, (2) variation in fruit type (healthy, wounded, fermenting), and (3) the relative abundance of different fruit types are ecological determinants of D. suzukii egg-laying decisions. Even though individual flies reduced their reproductive output when resource availability (blueberries) was low, a significantly higher proportion of eggs was allocated to healthy fruits, relative to wounded and fermenting fruits. However, the preference for healthy over wounded fruits declined continuously with a decrease in the relative abundance of healthy fruits and the overall reproductive output did not change. Under laboratory conditions, D. suzukii larvae achieved a higher developmental success on wounded than on healthy blueberries, but suffered less from density-dependent competition in healthy fruits. These data suggest that D. suzukii, despite showing an egg-laying preference for healthy fruits, also uses wounded/fermenting fruits as egg-laying sites, and that it may thrive well in windfall fruits.