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The yellow granules in the gastral cuticle of the Oriental hornet Vespa orientalis (Hymenoptera, Vespinae) are located in yellow stripes. In the present study, we focus on the micromorphology and formation of the yellow granules from their inception to their spread in the regions which are destined to acquire a yellow color. The cuticle was observed with several methods of electron microscopy. The results showed that the yellow granules comprise a layer which is 20-25 μm thick, within the total cuticular thickness of 40-45 μm. In the mentioned regions one can see, from above, many apertures of about 0.5 μm in diameter which extends into a peripheral photoreceptor cell. In each yellow granule, one discerns a myoid envelope inside which there are 9 fibrils arranged in a circle. Yellow granules maturation process involves infiltration of canals that give rise to the incipient ball-shaped primary granules which increase in number (as a result of continues budding off the walls of a canal) as the cuticle matures and transform into secondary barrel shaped granules, becoming elongated and then splitting into shorter barrels that fill up the entire area. Preliminary examinations have suggested liver-like function activity within the layer of yellow granules.

The present study describes the daily activities of the Oriental hornet (Vespa orientalis) workers older than 48 hours as observed in an Artificial Breeding Box (ABB) in our laboratory at the peak of the active season. These workers were picked randomly from a population of a single nest that was enabled to free egress into the field. The study points to the existence of polyethism in the nest of V. orientalis with the adult worker hornets, separating them into three groups in accordance with the frequency and nature of their exits from the nest, and the tasks which they perform. This polyethism was not age-dependent. Recordings were made of the following vespine activities: the frequency of exits to the field during various hours of the day and the various roles undertaken by the hornets. Also investigated was the assignment of tasks among the hornets and the preference given to some tasks over others. The general organization of traffic and other movements in the colony is discussed.

Social wasps and hornets maintain their nest in the dark. The building of the combs by all Vespinae is always in the direction of the gravitational force of Earth, and in each cell's ceiling, at least one 'keystone' is embedded and fastened by saliva. The sensory mechanisms that enable both building of sizeable symmetrical combs and nursing of the brood in the darkness merit investigation, and the aim of the present study was to identify and characterize the 'keystones' that exist in the ceiling and in the walls of the social wasp comb cells. Bio-ferrography was used to isolate magnetic particles on slides. These slides, as well as original cells, were analyzed in an environmental scanning electron microscope by a variety of analytical tools. It was found that both the roof and the walls of each comb cell bear minerals, like ferrites, as well as Ti and Zr. The latter two elements are less abundant in the soil around the nest. Ti and Zr are known to reflect infrared (IR) light. IR imaging showed a thermoregulatory center in the dorsal thorax of the adult Oriental hornet. It is not known yet whether these insects can sense IR light.

In the Oriental hornet, a thermogenic center is located in its prothorax. The present study attempted to elucidate the development of this organ with age, that is, by following the development of the thermogenic center in the hornet from its pupal stage until several days after eclosion of the imago. To this end, use was made of an infrared camera, with which pictures were taken of the prothorax in hornets at various ages, i.e., several days prior eclosion, 24 h after eclosion, and 48-h posteclosion. The photographic findings established that prior to 48-h posteclosion there was no thermally distinct region or spot in the prothorax, but at about 48 h, such a “hot spot,” namely, a point whose temperature is greater than that of the rest of the prothorax, does appear, and its appearance coincides with certain specific nest activities like warming of the pupae. Next, an attempt was made to transplant by allograft the region in the prothorax housing the hot spot. Accordingly, several pupae at 2 days prior to eclosion were subjected to the following procedure; their future prothoracic thermogenic center was excised and so also an equally sized piece of cuticle from the dorsal region of their abdomen, and the two now allografted in exchange, i.e., the piece from the prothorax replacing the abdominal piece and vice versa. The result of this exchange-transplant was studied 48 h after eclosion of the operated hornets and showed disruption of heat formation in the prothoracic site coupled with nonappearance of a hot spot in the abdominal site. As for the functional, intact hot spot in the adult hornet, it is characterized by a high concentration of tracheae, with numerous mitochondria in between them that probably contribute to the heat generation. Microsc. Res. Tech., 2007. © 2007 Wiley-Liss, Inc.

In both the large carpenter bee (Xylocopa pubescens) and the bumblebee (Bombus terrestris), a hot spot was detected in the center of the prothorax on its dorsal-external aspect. In both cases, the temperature in this hot spot was found to be greater than the ambient temperature and that at the tip of the gaster. In B. terrestris, it was higher by 9–10°C from that at the gaster tip and by 15–16°C from the ambient temperature, while in X. pubescens the corresponding differences were 11–20°C and 18–19°C, respectively. The recorded thermal differences were not fixed but were rather variable, temporally as well as individually, but invariably all individuals measured showed these temperature differences. Furthermore, in none of the studied specimens was a hot spot detected in any part of the body other than the prothorax. From this hot spot in the prothorax, there is a cascade of temperatures in both directions, that is, anteriorly towards the head and posteriorly towards the gaster, with a graded drop in temperature in either direction. This article discusses possible reasons for the existence of such a hot spot in this particular location (the prothorax), its role or function, and its mode of operation. The authors speculate that it is a thermoregulatory center (for heating or cooling) that might be present in possibly all Hymenoptera that spend a considerable part of their life flying, regardless of whether they are social, parasocial, or solitary. Microsc. Res. Tech., 2006. © 2006 Wiley-Liss, Inc.

In social hornets of sub-family Vespinae there are stripes or areas in the cuticle which are endowed with a bright color (yellow, orange, green) that is different from the customary native brown color. In these brightly colored areas, the middle and bottom layers of the cuticle contain a yellow-colored filling material instead of the ordinary lamellae of which the cuticle is comprised. At high magnification, most of the yellow matter is seen to be made up of yellow granules interlinked by string-like threads. Apart from yellow granules, hemolymph and a surrounding cuticle, these areas are also found to contain glucose, iron and triglycerides as well as enzymes like GOT, GPT, CPK and LDH, in high concentrations that vary considerably from those in vespan hemolymph and whose levels are different under illumination than in the dark. Such high levels of enzymes suggest first an association with liver function activities, and secondly, that the difference in their levels when exposed to light and when subjected to darkness is indicative of the influence of the energy of light upon them.

The Oriental hornet bears both brown and yellow colors on its cuticle. The brown component is contributed by the pigment melanin, which is dispersed in the brown cuticle and provides protection against insolation, while the yellow-colored part contains within pockets in the cuticle granules possessing a yellow pigment. These yellow granules (YG) are formed about 2 days prior to eclosion of the imago, and their production continues for about 3 days posteclosion. Xanthopterin is the main component of the granule and lends it its yellow color. Xanthopterin produces a characteristic excitation/emission maximum at 386/456 nm. Characterization by use of mass spectrometry showed the compound to have a molecular ion of 179, as expected from xanthopterin. Spectroscopic examination of the absorption of an entire stripe of yellow cuticle in the course of its metamorphosis revealed that the absorption steadily increases throughout the process to a maximal level of absorption about 3 days posteclosion. In the absence of the YG, the cuticle is permeable to the passage of all wavelengths within the visible range and to the UV range (290-750 nm) in all age groups of hornets. The newly ecloded hornets depart the nest to engage in activities requiring exposure to insolation only as the process of granule formation terminates, namely, when the layer of YG in the cuticle suffices to absorb all the harmful UV radiation.

The Oriental hornet Vespa orientalis (Hymenoptera, Vespinae) coordinates its daily activities (e.g. flights out of the nest associated with digging activities and removal of the dug soil from the nest) with the amount of insolation. Thus, the stronger the insolation, the more intense the flight activity and vise versa. The hornet's cuticle bears a few yellow stripes interposed among brown parts of the gastral cuticle. These yellow stripes are composed of two elements, namely, a transparent cuticle and underneath it a layer of yellow granules. When the hornets are exposed to UV light, the layer containing the yellow granules is less active than in hornets kept in the dark. This diminished activity entails a lower production of glucose as well as of several enzymes prevalent also in the liver of mammals, like creatine kinase, alanine aminotransferase, aspartate transaminase. Thus solar irradiation stimulates and produces a change in the metabolic activities of the hornet. The fact that hornets link their flight activity with the insolation leads us to speculate that the sun contributes energetically to the hornet's activity.

Oriental hornet workers, kept in an Artificial Breeding Box (ABB) without a queen, construct within a few days brood combs of hexagonal cells with apertures facing down. These combs possess stems that fasten the former to the roof of the ABB. In an ABB with adult workers (more than 24 h after eclosion), exposed to an AC (50 Hz) magnetic field of a magnitude of B = 50-70 mGauss, the combs and cells are built differently from those of a control ABB, subjected only to the natural terrestrial magnetic field. The effects of the additional magnetic field consist of (a) 35-55% smaller number of cells and fewer eggs in each comb, (b) disrupted symmetry of building, with many deformed and imperfectly hexagonal cells, and (c) more delicate and slender comb stems.

During the active season, extending from June to October, hornets emerge from their nest in the field in all the daytime hours. In the beginning of the season, when the number of workers is relatively small, the number of exits from the nest is fairly uniform numerically throughout the day. However, with the increase in hornet population from July onwards, the number of workers emerging from the nest entrance around noon (1100-1300 h) is by 1-2 orders of magnitude greater than the number of those emerging in the morning or evening hours. This disparity persists till September or October, at which time the workers revert to behave as in the beginning of the season. It appears, therefore, that in this period hornet activities outside the nest are coordinated with the meteorological conditions, and in this regard, the highest correlation is with the ultra violet B (UVB) radiation level and to a lesser extent with the temperature. Presumably, also, the greater noon-hour activity in the nests of hornets in the field stems from the digging hornets benefiting from the greater availability of solar energy at noon, mainly that of UVB radiation. We assume that the hornets are able to utilize the UVB radiation, but what part of their body is "absorbing" the UVB energy is still a matter of further investigation.

The head of the Oriental hornet in situ, detached from a live sample was imaged using Magnetic Resonance Imaging (MRI). This non-invasive method enabled us to visualize the three-dimensional structure of the hornet's brain and intracerebral organs, as based on cubic voxels of 23 microm3. From these images, we could identify various cephalic structures in both supra-esophageal and sub-esophageal locations. In the former location, we identified and visualized the ocelli, ommatidia, mushroom body, lobula, medulla and the compound eyes in the protocerebrum, as well as the olfactory lobe and bases of the antenna in the deutocerebrum, while in the sub-esophageal region we visualized organs such as the mouthparts, the esophagus, the gnathal pouch and the salivary ducts that empty into the region. Additionally, we identified various muscles, the aorta, cuticular thickenings lending support to the interior of the head and also the cuticular skeleton providing support on the outside. All the mentioned structures and organs were visualized in their relative, normal proportions, without touching or dislocating them.

Wasps apparently develop normally even under extreme thermal conditions, including deserts. We deemed it worthwhile to set up an experiment wherein wasp brood combs containing a full gamut of brood ranging from eggs up to pupae and a few adults were kept in an incubator whose temperature was gradually raised to 45 degrees C, and the response of the disparate brood to such warming was photographed via Infra Red camera. The finding of this experiment showed that for open brood (i.e., eggs, larvae at various instars, and empty cells) the temperature was close to the ambient temperature, but in the silk coated pupae, the temperature was lower than the ambient by up to 4 degrees C. This lower temperature was retained for at least 90 min of incubation. For comparison we evaluated the relative contribution of the pupae to the phenomenon, by warming also a vacant, (i.e., a broodless and silkless comb) in parallel to a comb from which the pupae had been extricated but the silk weave retained and left behind. We found that the totally empty comb heated up under these conditions to nearly 110 degrees C, whereas the silk-containing vacant cells only heated up to about 40 degrees C. These finding are discussed from two aspects, namely the importance for wasps to maintain a constant temperature throughout the pupating process, and the manner in which the silk weave contributes to such a goal.

In silk from the larval silk caps of the Oriental hornet Vespa orientalis (Hymenoptera, Vespinae), temperature-dependent changes in the electric voltage have been recorded, with rise in the voltage occurring mainly upon rise in the temperature between 10–36°C. The peak voltage was measured between 32–38°C and attained 240–360 mV, but with further increase in temperature, the voltage decreased, dropping to 0 mV at about 45–50°C. Upon second measurement (of same silk specimen), the voltage peak usually occurred later (by 8–9°C) and at higher temperature than in the first measurement. Continuous measurements during warming up to 30°C followed by cooling down to 15°C yielded an hysteresis between the warming “line” and the cooling “line”, the former often straight and the latter usually curved. Maintaining the silk specimen at a fixed temperature for a prolonged period (hours) initially causes the voltage to rise, then remain steady, and finally drop. Boiling the silk caps in tap water for 7–10 min exerts some changes in the silk properties, mainly a decrease in voltage level. The general behavior of the silk suggests that it is a polymer endowed with the qualities of an organic semiconductor. The various properties of the larval silk are discussed in great detail. Microsc. Res. Tech., 2006. © 2006 Wiley-Liss, Inc.

In the social wasps Vespa orientalis and Paravespula germanica (Hymenoptera, Vespinae), a thermogenic center has been found in the dorsal part of the first thoracic segment. The temperature in this region of the prothorax is higher by 6-9 degrees C than that at the tip of the abdomen, and this in actively flying hornets outside the nest (workers, males or queens) as well as in hornets inside the nest that attend to the brood in the combs. On viewing the region from the outside, one discerns a canal or rather a fissure in the cuticle, which commences at the center of the dorsal surface of the prothorax and extends till the mesothorax. Thus the length of this canal or fissure is approximately 5-7 mm and it is seen to contain numerous thin hairs whose shape varies from that of the hairs alongside the structure. Beneath the cuticle in this region there are dorsoventral as well as longitudinal muscles in abundance, much the same as the musculature in the remaining thoracic segments (i.e. the meso- and metathorax), which activate the two pairs of wings. The canal-bearing segment is of course devoid of wings, and its dorsoventral muscles are attached to the cuticle, which in this region resembles a bowl harboring several layers of epithelium that boasts numerous butterfly-shaped tracheal branches. Additionally there are layers that display lymph-filled spaces and also perforated layers and depressions, and beneath all these is a lace-like layer that also coats the cuticle's hollows. Underneath the cuticle proper, there are numerous large mitochondria and tracheae, which occupy a considerable part of the cuticular epithelium surface. These abundant mitochondria are, most probably, the main element of heat production in the thermogenic center.

In the Oriental hornet Vespa orientalis (Hymenoptera, Vespinae), there is on the dorsal side of the thorax, beneath the mesoscutum plate of the prothorax and around the median notal suture, a lump that, in the course of hornet activity, is warmer by 9 degrees C from the surrounding milieu and by up to 6 degrees C from other body parts of the hornet. This lump is about 1 mm in diameter, butterfly-shaped, and its upper, posterior border abuts the base of the forewings. During hornet activity and via Infra Red photography one can observe heat extensions stemming from the center of the lump and proceeding forward in the direction of the head, downward toward the legs and backwards toward the bases of the wings. The warmest region is the center of the lump, with its margins showing a lower temperature. As for the legs of the hornet, their upper part is warmer than the other parts. The temperature gradients along the hornet's body are dependent on the extent and nature of hornet activity. Thus, during flight or ventilation activity, the thorax is the warmest part of the body, while the wings, legs, and antennae, as well as the posterior part of the gaster are colder, yet all these body parts are still warmer to varying degrees than the surrounding milieu. Thus, at night, when sentry worker hornets stand guard around the nest entrance and remain practically motionless, the temperature differences between the various body parts are retained unchanged. We conjecture that the described butterfly-shaped lump is a thermoregulatory center (TC), which is neurogenically activated, since the changes occurring in it are rapid, a matter of one to several seconds and do not appear to be directly dependent on the hemolymph supply. The thermoregulatory center keeps a high constant temperature apparently related to hornet activity and the environmental conditions. The temperature cascade is most probably regulated via the tracheal system. Apparently another system activated by a heat pump mechanism keeps the gaster at a lower temperature than the environment.