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

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.

Live Drosophila melanogaster Larvae Deter Oviposition by Drosophila suzukii

“…Cornmeal media was used as the egg laying substrate in this study. Similar observations were made when fruits were used as the egg laying substrate, where D. suzukii laid fewer eggs on blueberry fruits previously visited and defecated on by D. melanogaster [ 37 ]. Whilst here we exposed the cornmeal media to D. melanogaster for 48 h, Kienzle and Rohlfs [ 37 ] only exposed blueberry fruits to D. melanogaster for 1.5 h, during which time they observed that D. melanogaster visited and defecated on the fruits but did not lay eggs.…”

“…Similar observations were made when fruits were used as the egg laying substrate, where D. suzukii laid fewer eggs on blueberry fruits previously visited and defecated on by D. melanogaster [ 37 ]. Whilst here we exposed the cornmeal media to D. melanogaster for 48 h, Kienzle and Rohlfs [ 37 ] only exposed blueberry fruits to D. melanogaster for 1.5 h, during which time they observed that D. melanogaster visited and defecated on the fruits but did not lay eggs. Further studies using wild-caught D. suzukii and fruit instead of cornmeal media and conducted in horticultural settings such as in glasshouses or polytunnels are planned but these are beyond the scope of this initial study.…”

“…These factors could lead to larvae causing more profound changes to both chemical and physical composition of the egg laying media, including a decrease in the media firmness. Drosophila suzukii tends to prefer firmer and intact substrate to oviposit on which supports this theory [ 7 , 37 ]. Drosophila larval density and their foraging activities are also known to alter the surrounding bacterial community and subsequently affected the phenotypical trait of the emerging flies [ 38 ].…”

“…Drosophila larval density and their foraging activities are also known to alter the surrounding bacterial community and subsequently affected the phenotypical trait of the emerging flies [ 38 ]. These considerations suggest there may be multiple signals at play here, possibly context-dependent, to deter oviposition by D. suzukii [ 37 ].…”

“…Oviposition avoidance by D. suzukii was recorded on apple juice agar inoculated with microbes isolated from D. melanogaster and Drosophila biamirpes, respectively [ 46 ]. Fruits contaminated with faecal matter from non- D. suzukii Drosophila species were avoided by D. suzukii females for oviposition [ 37 ]. In a laboratory choice assay, D. suzukii showed a preference towards Hanseniaspora uvarum, a yeast species commonly associated with D. suzukii [ 47 ], and an acetic acid bacteria strain isolated from D. suzukii [ 48 ].…”