Yellow pigment granules in hornets: their origin and development

The present article discusses the yellow pigment in the cuticle of the Oriental hornet Vespa orientalis (Vespinae, Hymenoptera). This insect possesses, both in its gaster region and its head plates, yellow pigment granules that are located underneath the upper layers of the cuticle. All other regions of its body are endowed with a colour ranging from brown to black. As for the yellow granules, some occur within cells while others bud off from the cells inside tubular extensions that interpenetrate the cuticular layers and create accumulations of pigment. Whichever the case, the yellow granules invariably are approximately 0.5 microm in diameter and arranged in three longitudinally extending concentric cylinders, with the innermost cylinder comprising a string that interconnects between the various granules. Our paper discusses the physical properties of these yellow granules and their possible role in everyday hornet life.