Animal species have to make important choices throughout their lives. One of them, for females, is to decide where to put their eggs. The vast majority of Drosophila species (more than 3000 species have been described) lay their eggs in rotting or decaying substrates -fruits, plants, cactus, or flowers, depending on species. One noticeable exception is Drosophila suzukii, an invasive species recently arrived in Europe (less than 10 years ago), which lay eggs both in rotten but also in fresh, ripening fruits. This species targets a large range of fruits, in particular strawberries, cherries, raspberries, grapes and more. By laying eggs inside the fruits, D. suzukii is responsible for substantial damages and economical loss to the fruit industry, wherever it is present.
We are studying the phenotypic modifications that enabled or accompanied the shift in the ecological niche of D. suzukii from rotten to ripening fruits. Among these modifications, the serrated ovipositor (the egg laying organ) has doubled in size compared to closely related species, allowing the flies to pierce through the stiff skin of ripening fruits. Such enlargement of the ovipositor is a fairly common on agricultural pest species targeting fresh fruits (the medfly Ceratitis capitata, or the olive fruit fly Batrocera olea are other famous examples), in which it has happened independently.
In addition to the enlargement of the ovipositor, the egg laying behavior of D. suzukii has changed compared to other species, as D. suzukii female are strongly stimulated to lay eggs on ripening fruits. We are studying the egg laying site choice and oviposition in D. suzukii using an interspecies comparative approach. We want to identify the cues that attract or stimulate egg laying in D. suzukii, and the sensory apparatus that respond to these cues.
Ultimately, we hope to better understand the genetic and neuronal changes responsible for innate behavior evolution, and how these changes drive or enable shift in the ecological niche that a particular species occupies.