Micromorphology of the Yellow Cuticle in Social Wasps: The Presence of Rhabdomeric and Ciliary Peripheral Photoreceptors

Jacob S. Ishay; Marian Plotkin; Reuben Hiller; Stanislav Volynchik; David J. Bergman

Abstract

Social hornets (Hymenoptera, Vespinae) are colorful organisms in that between their segments of brown cuticle there are stripes which outwardly appear of a different color. The Oriental hornet Vespa orientalis bears two yellow stripes on its gastral cuticle and yellow plates on its vertex. In other vespan species the number of yellow stripes varies. Microscopic examination of the so-called yellow cuticle reveals, beneath about 30 layers of transparent cuticle, a relatively thick stratum of yellow pigmented granules. At intervals of 10-50μm apart, one can see extrusions emerging from peripheral photoreceptor cells and proceeding upward to the epicuticular layer. Underneath the mentioned cuticular layers, the photoreceptor cell broadens to contain at its periphery a rhabdom-shaped structure which bears dark pigment granules on its surface. Outside the membrane of the photoreceptor but abutting it are numerous yellow granules which are interconnected by branches. Thus all the photoreceptor cells and all the yellow granules beneath the yellow cuticle in each yellow stripe are bound to one another to form a single tissue. Each photoreceptor cell is synaptically linked with a single nerve extension, which renders it bipolar. These neural extensions, in turn, are interlinked to form a network or rete. The various elements of the photoreceptor, and particularly its extension and the yellow granules, are endowed with a network of contractile fibrils (myoids) that supposedly can regulate the uptake of light. Since the entire structure is comprised of rhabdom-shaped photoreceptors surrounded by numerous interconnected yellow granules that originate from cilia, what we have here basically is an array made up of few villi-shaped photoreceptors and an abundance of cilia (about 10.000). We suspect that this entire array serves to pick up light energy and convert it to readily available energy that is transmitted via neural fibers for use by the hornet.

Keywords: Rhabdomeric and ciliary photoreceptors, Hornets and Wasps, Yellow stripes, Yellow granules, Cuticular structure, Purines and pteridines

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