Solar energy harvesting in the epicuticle of the oriental hornet (Vespa orientalis).

The Oriental hornet worker correlates its digging activity with solar insolation. Solar radiation passes through the epicuticle, which exhibits a grating-like structure, and continues to pass through layers of the exo-endocuticle until it is absorbed by the pigment melanin in the brown-colored cuticle or xanthopterin in the yellow-colored cuticle. The correlation between digging activity and the ability of the cuticle to absorb part of the solar radiation implies that the Oriental hornet may harvest parts of the solar radiation. In this study, we explore this intriguing possibility by analyzing the biophysical properties of the cuticle. We use rigorous coupled wave analysis simulations to show that the cuticle surfaces are structured to reduced reflectance and act as diffraction gratings to trap light and increase the amount absorbed in the cuticle. A dye-sensitized solar cell (DSSC) was constructed in order to show the ability of xanthopterin to serve as a light-harvesting molecule.

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.

Temperature distribution and electrical properties along the Oriental hornet body.

The hornet is an endothermic insect. Daily variations in hornet surface temperature were measured. Three peaks were found between 9:30 and 10: 30 a.m., 11 and 12 a.m. and between 2 and 3 p.m. Electrical current and voltage values were highest along the head. Electrical current along the gaster and the head flowed towards the thorax, i.e., from body parts with minimal temperature towards the body part with maximal temperature. Current and voltage values measured across the cuticle of the gaster were about 5nA and 100 mV, respectively, and these were of the same order of magnitude as the current and voltage values along the cuticle. It was found that: 1) temperature regulation most probably originates in the thorax and 2) there is a correlation between the temperature distribution along the hornet body surface and levels of the cuticular electrical signals.

Communication by electrical means in social insects.

Social insects, belonging to the order Hymenoptera, maintain a fixed, optimal temperature in their nest. Thus, in social wasps and hornets, the optimal nest temperature is 29 degrees C, despite the fact that they are distributed in regions of varying climates both in the northern and southern hemispheres of the globe. Since hornets and bees are relatively small insects, determination of their own body temperature as well as that of their nest and the brood was made via thermometers or by the use of infrared (IR) rays. It has been suggested that thermoregulation in social insect colonies is effected primarily by the adult insects via muscle activation, that is, fluttering of their wings, which can raise both their own and the ambient temperature by many degrees centigrade. However, the larval brood can also contribute to the thermoregulation by acting as heat resources and thereby raising the ambient temperature by 1-2 degrees C. To this end, the adult hornets are endowed with a well-developed musculature and their larvae, too, have muscles that enable them to move about. Not so the hornet pupae which are enclosed in a silk envelope (the cocoon), with a rather thick silk cap spun by the pupating larvae, and have rather undeveloped muscles. In the latter instance, it stands to reason that the pupae benefit from the nest warming achieved primarily by the adult hornets, but how is the information regarding their thermal needs relayed from them to the adults? Previously we showed that the adult hornets are attracted to the pupae by pheromones released by the latter, but such chemical compounds can only convey information of a general nature and we are still left with the question as to how the adult hornet can gauge or ascertain the temperature of a single insulated pupa. The present study provides evidence that the hornet pupa can indeed transmit information regarding its body temperature via electrical means.