Thermophotovoltaic (TPV) properties of hornet cuticle as dependent on relative humidity

This paper deals with the thermophotovoltaic (TPV) properties of the cuticle of the Oriental hornet as assessed over time under different regimens of relative humidity (RH). The tests were run at two levels of RH, namely, 30% vs. 90%. Each experiment entailed measuring the cuticular voltage and current in the dark as compared to under illumination (white light = 700 Lux), and at a temperature range of 20-30 degrees C. It was found that increase in the RH level boosts the current values by 2-3 orders of magnitude; contrariwise, the voltage values rise by about three times with drop in the RH. At high RH, the changes in current become rhythmical and each cycle of warming-cooling assumes a distinctly cyclic pattern. Under illumination, the current decreases, the polarity reverses and the resistance increases. The obtained results are describable by a model of electric conductance upon a surface, in this case the hornet cuticle; the findings are also discussed and compared with similar phenomena recorded from other substances possessing the properties of organic semiconductors.

Subcuticular microstructure of the hornet's gaster: Its possible function in thermoregulation

The present study set out to elucidate the structure and function of the large subcuticular air sacs encountered in the gaster of the Oriental hornet Vespa orientalis (Hymenoptera, Vespinae). Gastral segments I, II, III, together with the anterior portion of segment IV, comprise the greater volume of the gaster, and inside them, beneath the cuticle, are contained not only structures that extend throughout their entire length, like the alimentary canal, and the nerve cord with its paired abdominal ganglia, situated near the cuticle in the ventral side, but also the heart, which is actually a muscular and dorsally located blood vessel that pumps blood anteriorly, toward the head of the hornet. The mentioned structures take up only a small volume of the gaster, while the rest is occupied by air sacs and tracheal ducts that also extend longitudinally. Interposed between the two air sacs, there is a hard partition and above it, at the center - a paired tracheal duct that extends the entire length of the air sacs. The endothelium of the air sacs is very anfractuous, thereby enlarging and strengthening the surface area. In each gastral segment there is an aperture for the entry of air, namely, a spiracle. Additionally, in each segment, in the antero-lateral aspect of its tergum and situated between two successive segments, there is an intersegmental conjunctive bearing parallel slits of 1-2 microM in width and 10-30 microM in length. The latter are arranged concentrically around bundles of tracheae that traverse the cuticle from segment to segment. From the upper rims of the slits are suspended downward fringe-like structures or "shutters" ranging between 3-10 microM in length. We discuss the possibility that the Oriental hornet resorts to internal circulation of air, along with a thermoelectric heat pump mechanism, in order to achieve cooling and thermoregulation of its body.

The thermoelectric properties of hornet cuticle: correlation with measuring body sites and activity status

Our study focused on the thermoelectric properties of hornet cuticle at different body compartments and under varying states of awakeness. We also measured the temperature alteration patterns in various body parts of the hornet. Electric voltage and current were dependent on: a) the state of wakefulness; b) the part of the body. The current was lowest in dead hornet cuticle, somewhat higher in narcotized hornet cuticle, considerably higher in the cuticle of hornets awakening from anesthesia and highest in fully awake hornets. Voltage values were of the same order for dead and narcotized hornets, but considerably higher in unanesthetized awake hornets and highest in the cuticle of hornets awakening from anesthesia. At optimal temperature (29 degrees C) the hornet body temperature was higher on the abdominal cuticle than on other body parts. At an ambient temperature of 20 degrees C, the highest temperatures were recorded on the head and thorax, and the lowest on the abdomen. Body temperatures of live hornets were higher than the cooler ambient temperature outside the nest at night. The results suggest that the hornets possess an intrinsic biological heat pump mechanism, which can be used to achieve active thermoregulation.

Light Modulates Electric Phenomena in Hornet Cuticle¶

In the cuticle of live social hornets, such as Vespa orientalis (Hymenoptera, Vespinae), endogenous electric effects are encountered, i.e. voltages of 100-200 mV under illumination and currents amounting to several microamperes on its subjection to darkness-clearly a process of charging and discharging. Of the various wavelengths of sunlight, UV was found to be the most contributory to the active cuticular voltage generation. Throughout the warm season of the year--the active period in colonies of social hornets and wasps--colony members exit from the dark nest during the daytime and fly to the field under the hot sun for various foraging purposes, ultimately returning to the nest. Thus, each hornet, be it queen, worker or drone, probably undergoes daily cyclical process of electric charge and discharge in the exterior part of their integument, cuticle, which lasts up to 30-40 min. Such photoelectric phenomenon was detected in both live, ether-anaesthetized hornets and dead hornets, albeit in the latter the electric values recorded were lower. The present study addresses the possible impact of the phenomenon on vespan daily life and also compares it with a parallel occurrence in electric fish.

Ontogenesis of peripheral electromagnetic receptors in hornets

This article traces the ontogenesis of peripheral electromagnetic receptors (PER) in the cuticle of the Oriental hornet (Vespa orientalis). In the abdominal cuticle of adult hornets, the PERs are densely distributed throughout, but there are even more than 30 at the margins of the segments. These organelles develop as a network in the hornet cuticle immediately upon its completion. Briefly, from each basic cell of a PER grows a bulge towards the exterior, that is, towards the illuminated region of the cuticle. This bulge develops rapidly and as it grows it starts to push out and lift up the various layers of the cuticle, the while pressing them together. By a spiraling movement, the bulge insinuates itself between the layers, whereupon it dissolves and punctures its way through all the layers of the hypocuticle, via the endocuticle up to the exocuticle. The only cuticular layer that remains intact is the epicuticle, but even that undergoes change, assuming the shape of a smooth surface with a depression at its center. The indented part in the epicuticle is circular, approximately 2.5 microm in diameter and enables the entry of radiation (illumination) from the outside into the PER, which is located half-way down the cuticle, with the distance from the exterior to the base of the PER being approximately 25 microm. The numerous lamellae of the cuticle run parallel to one another, but in the region of the bulge they are either perpendicular or directed upwards. This ontogeny of the PERs lends the cuticle a sandwich-like shape, being radically perforated by the PERs bulges, yet covered at the top by the epicuticle and at the bottom by basal cells. The PERs also extend shoots into the cuticular layer and these further perforate the cuticle but also interlink the various PERs. From all the above, it is clear that the cuticle forms first and only subsequently does the network of PERs develop and interpenetrate its various layers.

Hornet peak flight activity is correlated with solar UV radiation: a multi-annual survey

This study deals with the effect which solar irradiation of short wavelength, particularly ultraviolet (UV), exerts on the activities of hornets. The findings are based on multi-annual observations carried out during the years 1985, 1989 and 1998 on hornet nests in the field. At the peak of UV radiation, which occurs at noon, hornet activity is greater by 1-2 orders of magnitude than that during the morning or evening hours. The main visible hornet activity appears to be the removal of soil particles from the nest so as to enlarge its volume, enable the building of additional combs and also increase the size of existing combs. Hornet flight during peak insolation hours is characterized by its briefness (5-20 seconds only) and brevity (to distances of 5-10 meters only) as compared to flights at other hours of the day. These prolonged, multi-annual observations lead to the conclusion that hornets are capable of converting the energy of UV radiation into a form amenable to metabolic usage. In this respect the hornet cuticle behaves as a thermophotovoltaic device, i.e., a semiconductor diode that converts photons radiating from the sunlight into electrical energy.

Hornet cuticle: effects of short-term UV irradiation

Effects of short-term UV irradiation were investigated on various cuticular parts of workers and queens of the Oriental hornet, to wit: brown strip, yellow strip and wing. On each preparation of the afore-mentioned, a reading of the relative optical density (ROD) was taken prior to, immediately following, and 15-30 minutes after its irradiation as compared to white light irradiation. The results showed that brief UV irradiation causes changes in the ROD of hornet cuticle, and that these changes in ROD are different in brown than in yellow cuticle. Those in yellow strip are induced by the presence or absence of the active yellow pigment, whose quantity in worker cuticle is different than in queen cuticle, probably due to the various activities in which they are involved during the active season.

Natural thermoelectric heat pump in social wasps

Photographs of wasps or hornets, taken with different temperature sensitive infrared cameras, reveal body temperatures that are sometimes significantly lower than the ambient temperature. This suggests that the hornets possess an intrinsic biological heat pump mechanism which can be used to achieve such cooling. Evidence is presented to substantiate this novel suggestion and to argue that the heat pump is most likely implemented by exploiting a thermoelectric effect in the hornet cuticle. Such a natural heat pump can conceivably also serve to cool the active hornet, engaged in daytime activities outside the nest at ambient temperatures exceeding 40 degrees C, to a body temperature that is low enough to allow its survival in extreme thermal conditions. It might also function as a means of raising the body temperature up to a level that enables the hornet to remain active even when the ambient temperature is as low as 10 degrees C.

Symbiotic bacteria in hornet pupal silk

The silk weave spun by hornet larvae before undergoing pupal metamorphosis is composed of fibers and sheets, both containing symbiotic bacteria. The bacteria are secreted from the silk gland and are glued to the secreted silk, which is made up of amino-acid polymers. In the dark, it possesses at first an electric current amounting to several hundred nanoamperes (nA) (i.e., a thermoelectric property), and a high electric capacitance of up to several milliFarads (mF). This electrical charge is used gradually by the developing pupa. The symbiotic bacteria penetrate through slits in the coat of the silk fibers to the core or into pockets in the sheets, where they gradually digest parts of the silk weave, thereby nullifying its mechanical properties and facilitating in due time the egress of the imago from the puparium.

Photo-induced arousal response by hornets

When an Oriental hornet Vespa orientalis is subjected to ether anesthesia and then exposed to ultraviolet A light (UVAL) (at a wavelength of 366 nm), it commences showing signs of awakening by starting to move its limbs. While in the process of waking the voltage on its body surface surges sharply from 17-180 mV (median = 71.0) to a level of 93-570 mV (median = 327.5). This elevated level is maintained for several minutes but subsequently drops sharply to starting level. The increase in voltage is throughout accompanied by fluttering of the wings and movements of the legs, as well as attempts to extricate itself from the bindings to the electrodes. These movements by the awakening hornet persist for several minutes even after the irradiation source is turned off but shortly after the switch-off the hornet lapses into sleep again. The described scenario is generally similar in worker, queen and drone hornets, and may even occur in decapitated specimens. The same type of awakening can be repeated in the same fashion after a while, but then the increase in voltage will be smaller than the first time. Continuous UV irradiation of an anesthetized hornet results in a generalized and protracted awakening which, however, is significantly shorter than in a hornet left anesthetized in the dark.

The thermo-photoelectric (TPE) properties of the hornet cuticle: correlation with the morphological structure

The present study investigated thermoelectric phenomena in the cuticle of the Oriental hornet Vespa orientalis (Hymenoptera, Vespinae). This was done in dependence on the pigment extant at various cuticular region, that is, the brown cuticle in which the primary pigment is melanin and embedded within the cuticle, and the yellow stripes in which the yellow pigment is comprised of purines and pteridines that are located in special pockets between the upper part of the cuticle and the basement membrane. The yellow pigment could be separated from the cuticle proper, but the brown pigment was not thus separable. We found that all cuticular regions of the gaster evinced a thermoelectric response, in that with rise in temperature there was a rise in the thermoelectric current, and vice versa. Additionally, the intact hornet displayed a negative photoelectric response in each of its yellow segments, so that upon illumination with UV light, the maximal current dropped by about 40-50%. Measurements taken on individual stripes in the gaster segments revealed that the photoelectric response is elicited only in the yellow stripes. In all the latter the photoelectric response persists but the maximal current level is lower than in the intact whole hornet. If the yellow pigment is detached mechanically or by bacterial incubation, the photoelectric property of the cuticle is abrogated. Likewise the photoelectric property is abrogated upon immersion of the cuticle in alcohol, even though the yellow pigment is still retained. The specific heat of the yellow stripes in the cuticle is about twice as high as that of the same stripes that had been depleted of their yellow pigment, amounting to 1.8-1.9 J/g.K vs. 0.8 J/g.K.

Navigation and thermophotovoltaic activity by hornets at different light conditions: the influence of UVB blockers

The aim of the present investigation was two-fold: a) to observe the homing of the Oriental hornet, Vespa orientalis (Hymenoptera, Vespinae) from different distances; and b) to study the photothermoelectric activity of hornet cuticle obtained from the subjects of goal (a) and kept frozen for a number of days prior to its testing. In both the above mentioned phases of the investigation, an attempt was made to assess how the covering of the hornets' cuticle with Ultra Violet B (UVB) blockers affects their activity as compared to the control. Flying hornets were observed to return to the nest from distances of up to 7 km, once they had learned the way back. However, covering of the cuticle with UVB blockers increases the percentage of 'non-returners' to nearly 100%. Covering the cuticle completely or partly with a number of UVB blockers (except for Sisley) proves lethal for the hornets within 24 hours. A statistical model on homing is proposed of the effect of range, of covering with UVB blockers and covering ocelli with Tippex. In the wing of the hornet there is increase in the electric current with rise in the temperature and decrease in the current upon drop of the temperature, but light has no effect on this alar (wing) current. Contrariwise, the body cuticle of the hornet responds to both temperature and illumination in terms of its electric current. Coating of the cuticle with UVB blockers causes in the wing (under all conditions of illumination) and in the cuticle (only in the dark) a moderation in the amplitude of the photothermoelectric current.

Sub-micromorphology of the epicuticle of hornets: AFM studies

The upper part of the hornet cuticle in the abdominal region reveals several structures. First, situated at intervals of 10 microm or more apart, there are depressions housing a peripheral photoreceptor (PP) and between every two of these, there are horizontal flats resembling an irregular polygon which are mostly elongated and about 100 microm2 in area. Upon each such terrace-like flat there are tile-shaped protuberances up to several micrometres in length and mostly running parallel to one another, covering the entire surface. Between every two such terraces there is a 'step' of up to 1.4 microm in height. Both the 'tiles' and 'steps' terminate in front of the distal part of each PP, which is a recessed and smooth region. Secondly, in other regions of the cuticle one can note other surface configurations such as: (a) a paucity of 'tiles'; (b) no 'tiles' at all but a chessboard-like pattern, the 'squares' of which contain rectangles recessed to various depths, interspersed among 'plaques' that are not recessed and may even protrude; and (c) anfractuous (characterized by windings and turnings) flats that are intermittently criss-crossed by grooves. In addition to the above, most of the cuticle also displays numerous setae (i.e. small hairs). We suppose that all the described structures and configurations either contribute to enlargement of the cuticular surface, or act as an optical grid, thereby enhancing the absorption of light. We further speculate that for hornets in flight, situations may arise where part of the above mentioned structures orientates perpendicular to the sunlight and this entire orientation acts to direct the solar energy toward and into the PP so as to enable greater utilization of light as an energy source.

The specific heat of the cuticle and the morphological differences between the brown and yellow cuticles of hornets

The morphology and thermophysical properties of stripes of brown and yellow cuticle collected from specimens of the Oriental hornet, Vespa orientalis (Hymenoptera, Vespinae), were analysed and compared by scanning and transmission electron microscopy. In the brown cuticle the colour stems from incrustation of the pigment melanin. In the yellow cuticle the yellow coloured pigment is concentrated in pockets between two layers of cuticle and its colour shows through the transparent cuticle. Both brown and yellow cuticles are composed of more than 30 layers. The upper layers are about 1-4 microm thick and as we proceed inwards, they become thinner so that the deepest ones that can still be discerned are thinner than the upper-most layer by one or two orders of magnitude (i.e., x 1/10 - x 1/100). The brown and yellow cuticles are each about 20 microm thick, but owing to the yellow pigment inserted in pockets of the yellow cuticle the total thickness of the latter is about 45 microm. The morphology of the yellow granules that contain the yellow pigment is shown and discussed. Below 20 degrees C and above 40 degrees C the specific heat (Cp) readings for both types of cuticle coincide, their values lying between approximately 1.55 and 1.60 J kg(-1), but in the temperature range 20-40 degrees C, the specific heat of the yellow strips displays a sharply non-monotonic behaviour, attaining a value of Cp = 1.8 J / Kg at 30 degrees, which contrasts with the relatively smooth curve shown by the brown strips. This anomaly (hump) does not occur following preheating of the samples to 70 degrees C. The shape of the repeated (annealed) 'yellow' curve is basically the same as that of the brown curve. The pockets of yellow pigment and their thermal contribution can be evaluated quantitatively by integration and correspond to an enthalpy of H = 3.5 J g(-1). The difference between the two types of hornet cuticle and the significance of this difference is discussed.

In most poorly controlled glyburide-treated type 2 diabetic patients drug withdrawal causes further increase in glycemia not accompanied by changes in insulin secretion

To find out whether the secondary failure of glyburide in type 2 diabetes is complete or partial, we studied 38 patients, age (M +/- SD) 69 +/- 9 years, suffering from diabetes from 13.5 +/- 8.4 years and treated with glyburide for 5-13 years, with poor glycemic control (glycohemoglobin 10.6 +/- 2.6%). Serum glucose, insulin and C-peptide were assayed before and 1 h and 2 h after a simulated meal load (355 Cal), after which the drug was replaced with placebo for 4 weeks, and the test repeated. After glyburide withdrawal, fasting glycemia increased from 10.3 +/- 3.3 to 15.1 +/- 4.4 mmol/L (p < 0.001), but in 3/38 patients, it even decreased and in five others the changes were less than +/- 2 mmol/L. These changes negatively but only weakly correlated with initial glycemia: r = 0.4123, p < 0.010. The mean post-meal glycemia at 1 h and 2 h increased respectively by 3.3 and 5.9 mmol/L (both p < 0.001). Neither the levels of glycemia nor its changes after the glyburide withdrawal correlated with the levels of, or changes in, insulin or C-peptide. We conclude that in most but not all type-2 diabetic patients, poorly controlled with glyburide, the drug still retains some limited therapeutic effectiveness, and therefore its withdrawal causes further deterioration of control with the almost equal increases in fasting and post-meal levels of glycemia. These changes are not accompanied by decrease in insulin secretion.

Duration of hornet sleep induced by ether anesthesia is curtailed by exposure to sun or UV irradiation

Irradiation of hornets anesthetized by diethyl ether curtails their sleep duration from the ordinary 20-30 min to a mere 2-3 min. This effect on sleep is dependent on the intensity of the sun irradiation or, when exposed to monochromatic UV at 366 nm, on the duration of the irradiation. Of the various hornet cuticular areas of the body, the yellow cuticular areas of the abdominal segments are the most sensitive to the treatment. We assume that the cuticles of both live and dead hornets act as a converter of light to electric energy.