Correlation between ovipositor structure and functional categories of fig wasps in Ficus semicordata

The ovipositor of parasitic Hymenoptera is a specific organ for depositing eggs by piercing into host's tissues, holding significance for understanding the competition, cooperation, and multitrophic cascades among coexisting species.

In this study, we used light and scanning electron microscopy to observe the ovipositors of one pollinating fig wasp Ceratosolen gravelyi and four species of non-pollinating fig wasp Philotrypesis dunia, Sycophaga cunia, Apocrypta sp., and Sycoscapter trifemmensis, which are endosymbiosis with the fig syconia of Ficus semicordata. By analyzing data on their syconium visitation sequence, oviposition timing, and syconium wall thickness, we explored the correlation between the functional traits of ovipositors and the dietary habits of these five wasps.

The results showed that the sclerotization degree of the ovipositor tip gradually increased with delayed oviposition timing. The pollinator C. gravelyi, laying eggs inside the syconium, possessed one ovipositor tooth at the tip, two types of campaniform sensilla and one type of shallow pit sensillum. In contrast, four non-pollinators, depositing eggs outside, had multiple teeth and diverse sensilla types at the same location of ovipositor. Furthermore, the number and diversity of ovipositor teeth and sensilla increased from gall-makers to parasitoids. There was a positive correlation between the length of the toothed area of the ovipositor and syconium wall thickness. Hierarchical cluster analysis using ovipositor traits mirrored the functional categories of fig wasp in F. semicordata.

The results contribute to understanding the dietary habits and coexistence mechanisms in the fig wasp community. Additionally, the detailed knowledge of ovipositor structure may predict the function categories of parasites in other communities.