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

Abstract

Simple Summary By using information from the environment, insects make decisions about where to lay eggs. If we know the environmental cues used by insects, we can help in controlling insect pests. The fruit fly Drosophila suzukii is one such pest that attacks numerous fruit varieties and causes great economic damage worldwide. In this study, we investigated which fruit characteristics the flies prefer for egg laying. In laboratory experiments we gave D. suzukii females the choice between different types of blueberries: (1) intact; (2) artificially wounded; (3) wounded and infested with eggs of other fruit-fly species; and (4) intact but exposed to another fruit fly species that had not laid eggs but had defecated on the fruits. The D. suzukii females preferred the different fruit types for egg laying in the following order: (1) > (4) > (2) > (3). The cues of other fly species (4) have already been suspected to deter egg laying in D. suzukii. Here we identified a new cue—the “wounding factor” of injured fruits (2)—that deterred egg laying even more than the cues of other fly species. Knowing the chemical or physical properties of this factor could help manipulate the behavior of the flies to protect fruit from this pest. Abstract 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.