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.     

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.     

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.     

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.     

Exoskeletal thinning in Cephalotes atratus ants (Hymenoptera: Formicidae) parasitized by Myrmeconema neotropicum (Nematoda: Tetradonematidae)

Some parasites modify the color of their arthropod hosts, presumably to facilitate transmission to a new host. Mechanisms for such changes often are unknown, but altered exoskeletal color in adult insects typically occurs via structural modifications or redistribution of pigments. Here, we examine the cuticle structure of workers of the Neotropical canopy ant Cephalotes atratus infected with the nematode Myrmeconema neotropicum. We hypothesized that the conspicuous red color of the gaster (the globular posterior body region) of infected ants results from structural changes, specifically localized exoskeletal thinning. We used scanning electron microscopy to quantify the thickness of gaster cuticle in healthy and infected ants. For comparison, we also measured the cuticle thickness of the head of each ant, which is black in both infected and healthy individuals. The gaster cuticle was 23% thinner in infected ants (average ±SE: 14.8 ± 1.02 μm) versus healthy ants (19.2 ± 0.65 μm) after correcting for body size. In contrast, the thickness of the head exoskeleton was similar among groups. We conclude that parasite-induced thinning of the exoskeleton is associated with the red color of the gaster. Other mechanisms, including translocation or leaching of melanin (by the ant or the parasite, respectively) may operate in concert with thinning to effect the color change, and would be an appropriate extension of this research.     

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.     

Ant body posture: gaster curling increases ant speed

1. Body postures adopted by an animal can serve behavioural functions, homeostasis, or energy balance. 2. We investigated the function of holding the gaster curled forward under the thorax in acacia ants, Pseudomyrmex spinicola Emery, by testing whether ants adopted this posture for defence, thermoregulation, or for efficient locomotion. 3. For the defence hypothesis, we expected an increase in the proportion of ants with curled gasters after a visual threat, a vibrational disturbance of a branch, or the release of nestmate's alarm pheromones. Our data did not support these predictions. 4. For the thermoregulation hypothesis, we found a positive correlation between temperature and proportion of curled‐gaster ants. However, we did not find a reduction in the proportion of curled‐gaster ants after shading them, as predicted by this hypothesis. 5. Our data supported the locomotion hypothesis: curled‐gaster ants walked 1 cm s^?1 faster than ants with the gaster held straight. Straight‐gaster ants walked with the thorax closer to the surface, a posture that likely shifts the centre of gravity closer to the surface in a manner similar to gaster curling. 6. Studying the role of the body posture in acacia ants and other insects will provide a better understanding of the kinematics of walking in challenging angles with respect to gravity.     

Electrical properties of hornet silk: temperature dependence

Hornet silk is a polymer of amino acids. One of the known properties of polymers is their electrical activity. The present study describes the results of electrical measurements carried out vertically on the silk cap of pupae of the Oriental hornet Vespa orientalis (Hymenoptera, Vespinae). The measurements undertaken were the temperature-dependent electric current, voltage and resistance, all measured within the range of biological temperatures, as well as the capacitance. The temperature-dependent spontaneous current attained values up to 327 nano Amperes (nA) while the maximal voltage reached 347 millivolt (mV). The electrical resistance was low and steady (1-20 mu omega) at temperatures ranging between 19-32 degrees C, but at lower or higher temperature it increased fairly sharply by about three orders of magnitude. The electrical capacitance, computed according to the discharge curve (decay curve) amounted to 0.4 microFarad (microF). The paper also discusses the role of the pupal silk as producer of a 'clean room' while the cuticle is being laid down by the pupae after undergoing metamorphosis, as well as the significance of the measured electrical parameters vis-à-vis the developing pupae.     

Electrical properties of the cuticle,silk caps and comb of Oriental hornet Vespa orientalis (Hymenoptera : Vespidae)

Electrical and physical phenomena have been recorded and measured in the cuticle, silk caps and comb of the Oriental hornet Vespa orientalis (Hymenoptera : Vespdnae). Cuticle of active or narcotized live hornets as well as dead ones, produce, at optimal temperature for Vespinae biological activity, voltages of several hundred mV, currents of up to several hundred nA and the appropriate electric power. The cuticle has a large electrical capacitance, relative to its volume and contains non-linear and active electrical elements. A theoretical model was proposed to explain the capacitance phenomenon. An additional phenomenon observed is the production of electric energy under the influence of light and heat. Some electrical phenomena, especially the photoconductivity were measured also in 3 ant species.Measurements of the electrical capacitance of silk caps revealed that it is dependent on: (a) age of the pupa; immediately on pupation, the values are highest and diminish with maturation; (b) caste; capacitance for the queen pupae is 20–50 mF; and which is higher than for worker pupae, where it ranges between about 5–7 mF; and (c) location of the measuring electrodes; in the case of external-internal measurements, the values obtained were greater by 2 orders of magnitude than those obtained with both electrodes placed on the same side of the silk cap. In all cases, it was found that the capacitant values are high when compared with the size of the caps and the available commercial capacitors of the same size.The hornet comb may be regarded as comprised of an array of 3-dimensional capacitors linked in parallel, thereby forming a large dry battery having one negative pole — the pedicel — which grounds the comb, and one positive pole — the silk domes of the comb cells. The possibility that the electric energy stored in the comb cell walls may have a thermoregulatory function, serving both the brood and the adult nest population was discussed. We assumed that this mechanism is common for the combs of all social as well as many solitary wasps.     

Thermal properties of hornet colonies: thermography of individual hornets and their nests and the role of the pupal silk in thermoregulation.

The present study focused on temperature assessments within a hornet nest. The measurements encompassed adult hornets, brood combs and the various stages of brood, and involved a thermographic method. Body parts of adult hornets were found to vary in their temperature, with the thorax eliciting the highest temperature and the abdomen the lowest. Similarly, there were thermal variances between larvae at instars 4-5, light-colored pupae and dark pupae. The measurements were made at day and night (when the entire population was present in the nest) on nests containing thousands of individuals at various ages. Most of the pupae measured during October were hornet drones. The usual air temperature between the (subterranean) combs was 28.7 degrees C, while the outside (ground level) temperature was 23.5 degrees C. The paper discusses the creation of heat by hornets, the thermoregulation throughout night and day, both by the hornets proper as well as by their products (comb and silk). Also discussed is the intra-nest conversion of one form of energy to another, as heat to electric current or vice versa.     

Electrical properties of the oriental hornet (Vespa orientalis) cuticle

Consistent electrical and physical phenomena in the cuticle of the Oriental hornet have been recorded and measured. Active or narcotized, live hornets as well as dead ones produce, at optimal temperature for vespine biological activity, voltages of several hundred mV, currents of up to several tenths of nA, and the appropriate power. The electric resistance of the hornet cuticle and hornet silk cocoon point to their being organic semiconductors. Both of these have a large electric capacitance relative to their volume. A theoretical model is proposed to explain the capacitance phenomenon. Other phenomena observed are the production of electric energy under the influence of light and heat and also change in the various other electric properties of hornet cuticle under the influence of solar irradiation. The distribution of daily hornet activities seems to be correlated with the hours of maximal irradiation. All the afore mentioned phenomena point to the fact that there is recourse to electric energy in the daily routine of hornets and that this electric energy seems to be derived from solar energy. The conversion of the latter into the former takes place in the body of the hornet which thereby functions in the manner of a solar cell. The presence of a cuticular exoskeleton containing chitin, characterizes very many species of Invertebrates (Arthropoda). We assume that the phenomena similar to those described in this paper take place also in many other species. We hope that part of our findings will be utilizable in future developments in the fields of semiconductors and the use of solar energy.     

The properties of the lining membrane of the insect tracheal system

In the surface layer of the lining cuticle of the tracheae of adult Calliphora there is no sign of any waterproofing layer of cuticulin (sclerotin + lipid) as seen in the surface of the general body cuticle. In a few insects: Calliphora adult thorax, Rhodnius adult tracheae serving the ovary, Periplaneta abdominal tracheae, it has been possible to introduce silver hydroxide solution into the lumen of tracheae in the living insect. In each case the silver hydroxide reacted at room temperature with the argentaffin structures in the cuticle, as happens in the soft surface cuticle of Rhodnius larva before moulting or after gentle abrasion. In the thorax of Calliphora the taenidia of the tracheae are stiffened by argentaffin cuticulin. but immediately upon entering the cleft in the flight muscle the taenidia disappear and are replaced by simple folds, so that no stiff taenidia enter the muscle and there is no argentffin material deeper in the flight muscle system.     

Regional and functional differentiation in the fat body of pharaoh's ant queens, Monomorium pharaonis (L.)

The insect fat body is generally described as a uniform tissue with multiple functions, but we have found evidence of cell differentiation in the Monomorium fat body. We show that the fat body of a mature egg-laying pharaoh's ant queen is a result of a preceding remodeling of cell material comprising at least 11 different fat cell types, located at specific positions in the head, alitrunk (thorax) and gaster (abdomen). The cell types are classified based on their position, histochemistry, ultrastructure, and immunoreactivity for vitellogenin/vitellin. Some of these cells are primordial cells present at emergence, others invade the histolysing flight muscle tissue, and still others disappear during the maturation process. Only one type, the subepidermal fat cell of the gaster, is active in vitellogenin synthesis and is the only cell type in close association with oenocytes. Although only this type produces vitellogenin, our material indicates that most fat cell types are essential to support egg production. In some queens vitellogenin was found to form crystals in ventral vitellogenin-producing fat cells. This indicates an imbalance between vitellogenin production in the fat cells and uptake in the oocytes, which is probably related to a cyclic regulation of egg production.     

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.     

Thermoregulation of water collecting honey bees (Apis mellifera)

Honey bees (Apis mellifera carnica, Apidae, Hymenoptera) visited a pond in order to collect water. During their stays at the pond the body surface temperature of water foragers was measured using contactless thermography. Irrespective of the ambient temperature (T(A)) which ranged from 13.6 to 27.2 degrees C, the water carriers reached thoracic temperatures of 36-38.8 degrees C (mean values of the measuring periods). The maximum thoracic value of an individual bee was 44.5 degrees C. At higher T(A) (20.9-27.2 degrees C) head and abdomen were only about 3 degrees C and 2 degrees C on the average higher than the surroundings, respectively. In the lower range of T(A) (13.6-16.6 degrees C), however, the bees warmed their heads up to 29.2 degrees C (13 degrees C above T(A)) and the abdomen up to 23.3 degrees C (7.1 degrees C above T(A); mean values of the measuring periods).The head and abdomen were even provided independently of one another with heat from the thorax. At a higher T(A) only little heat came from the heated thorax into the abdomen, at a cooler T(A) (13.6-16.6 degrees C) more heat reached the abdomen. In all probability, at a higher T(A) only a small amount of haemolymph was pumped from the thorax into the abdomen; the most warm blood probably circulated in the head-thorax area. The average duration of stays at the pond decreased linearly from 110 to 42 s with rising T(A). Head and thorax showed great fluctuations of temperature. For example, the head was heated by 4.6 degrees C within 25 s, the thorax by 6.1 degrees C within 30 s.Foragers drinking sucrose solution are known to increase their thoracic temperature with rising concentration of the sucrose solution. The water foragers had thoracic temperatures similar to that of bees feeding on 0.5 molar sucrose solution. It is hypothesized that the foraging motivation of both groups was similar and therefore they regulated their thoraces at the same temperature level.     

Thermoelectric (seebeck) effect of the cuticle of social wasps

The thermoelectric (Seebeck) coefficient ($\text{S =}\text{ΔV}\text{ΔT}$) in various cuticular areas of the Oriental hornet (Vespa orientalis) fluctuates from 0·3 to 2·4 mV deg^?1 within a temperature range of 27–36°C and when the temperature difference between the two measuring electrodes (ΔT) is 0·6–8·0°C. The values measured on the brown-colored cuticle suggest an n-type conduction, while those measured on the yellow-colored cuticle point to a p-type conduction. It is suggested hornets use this phenomenon for temperature detection.     

Finite difference calculations of current densities in a homogeneous model of a man exposed to extremely low frequency electric fields

This paper presents three-dimensional finite difference calculations of induced current densities in a grounded, homogeneous, realistically human-shaped phantom. Comparison is made with published experimental values of current density at 60 Hz, measured in conducting saline manikins with their arms down by the side. The congruence between calculation and experiment gives confidence in the applicability of the numerical method and phantom shape to other configurations. The effect of raising both arms above the head is to reduce the current densities in the head and neck by approximately 50% and to increase those from the thorax downwards by 20-30%. A sensitivity analysis was performed on the shape and dimensions of the phantom, from a 45-kg, 1.5-m-tall person to a 140-kg, 1.9-m-tall person. When the phantom is grounded through both feet the current densities range from 50 to 90 microAm-2 in the head (all values for a 60-Hz, 1-kVm-1, vertical applied field), 70 to 140 microAm-2 in the thorax, 150 to 440 microAm-2 at the crotch, and 500 to 2,230 microAm-2 in the ankle. When grounded through only one foot the current densities at the crotch range from 400 to 1,000 microAm-2 and from 1,000 to 4,400 microAm-2 in the ankle of the grounded leg. Scale transformations of the short-circuit current with phantom height, weight, and surface area are confirmed.     

Frictional surfaces of the elytra-to-body arresting mechanism in tenebrionid beetles (Coleoptera : Tenebrionidae) : design of co-opted fields of microtrichia and cuticle ultrastructure

In beetles, the system responsible for an attachment of forewings (elytra) to the thorax consists of interlocking fields of microtrichia (MT) located between thorax and body and between left and right elytra. The present study provides comparative data about microtrichia design on the thorax and elytra in three species of tenebrionid beetles (Tribolium castaneum, Tenebrio molitor, Zophobas rugipes) (Coleoptera : Tenebrionidae), which are different in their size. The length, width, density and directionality of microtrichia in 13 MT fields (4 on the thorax, 1 on the abdomen, 7 on the elytra, and 1 on the costal vein of the hindwing) were quantified. (1) Parameters studied are dependent on the dimension of an insect. The length of the microtrichia of most fields compared increases with an increase in body size. The MT width in the majority of fields increases with an increase in the elytra length. The MT density decreases with an increase in the elytra length. (2) Both width and length of microtrichia increase with an increase in the distance between single MT. The density of outgrowths increases with an increase in their length and width. (3) The fields oriented along the same spatial axis constitute functional groups responsible for a particular direction. Co-opted fields can be oriented in the same or opposite directions. (4) The design of MT correlates in co-opted surfaces. There are 3 field groups, which were stated as functionally corresponding to one another : the medial, anterio-lateral, and posterio-lateral. The lengths and widths of microtrichia from fields of these functional groups were quite similar in corresponding fields. Length-to-width ratios of MT in elytral fields were usually weakly correlated with those of thoracic fields. The distances between microtrichia on the elytra surface directly depended on those of the thorax. Distance-to-width ratio of MT of one surface slightly increased with an increase in this parameter on the co-opted surface. The MT densities on co-opted fields were usually quite different. (5) The ultrastructure of the cuticle suggests differences in the material properties of the cuticle between MT fields. The thoracic fields usually consist of elastic cuticle, whereas elytral fields are much harder. Usually, a MT field of elastic cuticle corresponds to the field composed of hard cuticles. The study also provides information about the ultrastructure of epidermal cells and about the design of pore channels, which are presumably responsible for production and transport of an adhesive secretion into the area of contact between lateral fields. Sensory organs monitoring contact between co-opted binding sites were also studied. The results of this study may aid in understanding the morphological basis of cuticular microsculptures acting as frictional devices.     

The Morphometry of Solenopsis Fire Ants

Size-related changes of body shape were explored in 15 polymorphic species of Solenopsis fire ants by analyzing body weight along with linear measurements of 24 body parts. Log regression slopes were used to detect changes of shape with increasing size. Within species, the largest workers weighed from about 5 to 30-fold as much as the smallest. The range of within-species body lengths varied from 1.6 mm to 4 mm. As worker size increased, the gaster tended to make up a larger proportion of body length, usually at the cost of the petiole, and rarely at the cost of head length or mesosoma length. In most, the relative volume of the gaster increased and that of the head and mesosoma decreased. Most also showed an increasingly “humped” mesosoma. For all species, head shape changed from barrel-shaped to heart-shaped as worker size increased. Antennae became relatively shorter as the relative size of the club decreased. Shape changes of the legs were more variable. S. geminata was exceptional in the extreme nature of its head shape change, and was the only species in which relative head volume increased and gaster volume decreased with increasing body size. With the exception of S. geminata, the allometric rules governing shape are remarkably similar across species, suggesting a genus-level developmental scheme that is not easily modified by evolution. It also suggests that the evolution of shape is highly constrained by these conserved growth rules, and that it acts primarily (perhaps only) through allometric growth. The results are discussed in light of the growth of imaginal discs in a resource-limited body (the pupa). The substantial variation of allometries within species and across localities is also discussed in relation to using allometric patterns to identify species or to construct phylogenies.