Hornets yellow cuticle microstructure: A photovoltaic system

This paper describes cuticular structures on the abdomen of the Oriental hornet (Vespa orientalis, Vespinae, Hymenoptera) in the region of the yellow stripes. A cross section in this region reveals the cuticle to resemble a notebook with more than 30 pages, the topmost pages (analogous to layers) being the thicker (up to 5 mu m or more in thickness) while the ones underneath are gradually thinner. The exterior of the cuticle displays pores which are dispersed at distances of 10-50 mu m apart. These pores are actually cuticular depressions which frequently possess eaves on their cephalic side whose internal diameter is 1-3 mu m near the surface but further down, in the region of the yellow pigment and the hypocuticle, this internal diameter broadens to about 20-30 mu m. These pores thus extend from the exocuticle down to the hypocuticle. In the spaces between the pores in the endocuticular region there are sinuses. Within these sinuses granules of yellow pigment are located. As for the pores, each of them represents the external outlet of a canal that is perpendicular to the cuticle. The canal walls are composed of the same layers making up the cuticle. Structurally, the canal encasing the pore resembles an upside down arrow. This arrow extends to about 35-40 mu m in depth and is narrow and hollow in its upper part-the shaft-for about 1-3 mu m, broadens into the shape of an onion in its lower head part (some 20-30 mu m in diameter). Down to its tip it becomes slightly sharpened to close at the hypocuticle by forming a concentric, dome shape structure that terminates in a nipple-shaped protuberance. Permeating through all layers of the cuticle are hemolymph, nerve fibers and tracheae. The parallel lamellae associated in the cuticle give the impression of an electrical capacitor. The present article discusses the structure of the cuticle as a photovoltaic system in which the endocuticle-lamellar layer and yellow pigment serves as a solar cell linked to an electrical capacitor. The manner whereby light energy and heat are collected, converted into electric energy, accumulated, transformed and used by the hornet is discussed. We assume that this source of energy is used for their thermoregulation by thermoelectric circuits.