All wasps in the superfamily Ceraphronoidea have pairs of translucent patches on the metasoma—two on the top and two on the bottom. The translucent patches on the bottom are also flanked by rows of bristles. But what are these structures for, and why are they important?
The translucent patches (stp) and setiferous patches (smp) in two different species of Conostigmus. A Conostigmus sp. C7A (identifier: CLEV 22741) B Conostigmus sp. C7B (identifier: PSUC_FEM 83781). The species notations given are not issued for purposes of zoological nomenclature, and are not published within the meaning of the International Code of Zoological Nomenclature. These images represent an early version of a figure created for publication. The final version of this figure was published in the Journal of Hymenoptera Research and can be viewed in the paper cited below. Photo by Carolyn Trietsch (CC BY 2.0). Click for source.
Ceraphronoidea are some of the most common parasitoid wasps in the world, but their lack of distinguishing features between species and small size (think sesame seeds and smaller) make them difficult to study. However, we noticed that the sizes and shapes of the translucent patches and the rows of bristles accompanying them were specific to each species, making it possible to distinguish between them.
So why are these patches different in different species? It could be related to their functions, but these were never investigated until now. In our study, titled “Translucent cuticle and setiferous patches in Megaspilidae (Hymenoptera: Ceraphronoidea)”, we used state-of-the-art techniques like serial block-face scanning electron microscopy (SBFSEM) to build three-dimensional models of the patches and corresponding internal structures.
Through this work, we showed that there are glands underneath the patches of bristles—the bristles probably increase the surface area for the evaporation of gland products. The substances secrete by these glands are probably for chemical communication (for example, producing pheromones related to courtship).
We’re still not sure what the function of the translucent cuticle is, but we did find unique cells called lamellar bodies underneath them. These cells are sometimes associated with glands, but they can also be associated with photoreceptors. It’s possible that light could shine through the patches and activate photoreceptors in the body that regulate circadian rhythms.
We looked to see if there were translucent patches of cuticle in other groups of wasps, and found similar structures in Orussidae and Ichneumonoidea. Since the relationships between different groups of wasps are still unclear, further studies on these patches could help uncover how different groups of wasps evolved.
Trietsch C, Mikó I, Ulmer JM, Deans AR (2017) Translucent cuticle and setiferous patches in Megaspilidae (Hymenoptera, Ceraphronoidea). Journal of Hymenoptera Research 60: 135-156. https://doi.org/10.3897/jhr.60.13692
This material is based upon work supported by the U. S. National Science Foundation, under Grant Numbers DBI-1356381 and DEB-1353252. Any opinions, findings, and conclusions or recommendations expressed in this material are those of the authors and do not necessarily reflect the views of the National Science Foundation.