Microbiota-Mediated Competition BetweenDrosophilaSpecies

Species that share resources often avoid competition with context-dependent behaviors. This is the case for the invasive insect pest Drosophila suzukii , whose larval ecological niche overlaps with that of Drosophila melanogaster in ripe, but not rotten, fruit. We discovered D. suzukii females prevent costly interspecific larval competition by avoiding oviposition on substrates previously visited by D. melanogaster . More precisely, D. melanogaster association with gut bacteria of the genus Lactobacillus triggers D. suzukii avoidance. However, D. suzukii avoidance behavior is condition-dependent, and D. suzukii females that themselves carry D. melanogaster bacteria stop avoiding sites visited by D. melanogaster . The adaptive significance of avoiding cues from the competitor’s microbiota was revealed by experimentally reproducing in-fruit larval competition: reduced survival of D. suzukii larvae was dependent on the presence of gut bacteria in the competitor. This study unveils a new role for the symbiotic microbiota and plastic behaviors in mediating interspecific competition.