Intra-species variation of ovipositor morphology and oviposition preference in Drosophila suzukii (Diptera: Drosophilidae)

Females of Drosophila suzukii have an enlarged and sclerotized ovipositor (oviscapt, hypogynium), which is a key evolutionary trait that enabled D. suzukii to lay eggs through the skin of ripening fruits. We investigated the intra-species variation of D. suzukii in ovipositor morphology and oviposition preference for substrate hardness among 27 strains recently established from local populations in Japan. A significant difference between strains was observed in the length of the ovipositor as well as in the number of bristles on it. Further analysis using representative strains revealed that the ovipositor size variation among strains was independent of the body size variation, suggesting that the proportion between the ovipositor and other body parts was different among the strains. In the two-choice oviposition assay using 2% and 7% agar substrates, four strains preferred the soft substrates, and one strain preferred the hard substrates. Competitive cross-modal assay between substrate hardness and surface curvature revealed that the preference for curvature overrode the preference for hardness in all the tested strains.