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.     

Building activity and longevity of queenless groups of the Oriental hornet,Vespa orientalis

The effect of group size on behavioral parameters of the Oriental hornet,Vespa orientalis, was assessed experimentally under laboratory conditions. Hornet groups of various sizes (ranging from 1 to 100 individuals per group) comprised of young individuals (0–24 hr of age) devoid of a queen were placed in artificial breeding boxes (ABBs). The following three quantitative parameters were evaluated: the amount and rate of building as a function of the number of hornets in the group, the rate of oviposition as, related to group size and the longevity of hornets as a function of their group size. The probability for the occurrence of these events was similarly considered and additional behavioral parameters were only assessed qualitatively. Results of this investigation revealed a relation between the three mentioned quantitative behavioral parameters and the number of hornets per group. The number of hornets per group was positively related to the extent of building, the number of cells built by a group is , but negatively related to the rate of building. As for the delay of building, a non-monotone relation was found. The relation between number of hornets per group and the oviposition delay was found to be non-monotone; the number of hornets per group and their longevity were found to be inversely related. Discrepanices were recorded on the very small (1–2 individuals) or very large (100 individuals) hornet groups.     

Differences in heat sensitivity between Japanese honeybees and hornets under high carbon dioxide and humidity conditions inside bee balls

Upon capture in a bee ball (i.e., a dense cluster of Japanese honeybees forms in response to a predatory attack), an Asian giant hornet causes a rapid increase in temperature, carbon dioxide (CO?), and humidity. Within five min after capture, the temperature reaches 46°C, and the CO? concentration reaches 4%. Relative humidity gradually rises to 90% or above in 3 to 4 min. The hornet dies within 10 min of its capture in the bee ball. To investigate the effect of temperature, CO?, and humidity on hornet mortality, we determined the lethal temperature of hornets exposed for 10 min to different humidity and CO?/O? (oxygen) levels. In expiratory air (3.7% CO?), the lethal temperature was ≥ 2° lower than that in normal air. The four hornet species used in this experiment died at 44-46°C under these conditions. Hornet death at low temperatures results from an increase in CO? level in bee balls. Japanese honeybees generate heat by intense respiration, as an overwintering strategy, which produces a high CO? and humidity environment and maintains a tighter bee ball. European honeybees are usually killed in the habitat of hornets. In contrast, Japanese honeybees kill hornets without sacrificing themselves by using heat and respiration by-products and forming tight bee balls.     

Both olfactory and visual cues promote the hornet Vespa velutina to locate its honeybee prey Apis cerana

Predators use olfactory, visual and sometimes acoustic cues from the preys to assess food information. However, it is not known if the aggressive hornets (Vespa spp.) use olfactory, visual, or both types of information to find and recognize prey. In the present study, we trained hornet workers (Vespa velutina) to a feeding area. Once the hornets began consistently foraging at this feeding area, we determined whether they located prey (bees, Apis cerana) via olfactory or visual cues. We did this by testing whether hornets were attracted to a dummy bait (bee dummy bait or non-bee dummy bait) treated with extracts of honeybee cuticular hydrocarbons. We then tested whether hornets could distinguish between bee dummy bait and cotton ball dummy bait, both treated with bee odors. Hornets preferred the dummy treated with bee odors, and bee dummies (with bee images) were more attractive to the hornet than the cotton ball dummies with only bee odors. These results clearly indicate that a combination of olfactory and visual cues helps the hornet to locate its prey.     

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.     

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.     

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.     

A keystone-like grain in hornet comb cells: its nature and physical properties

In the roof of cells built by the Oriental hornet, Vespa orientalis (Vespinae, Hymenoptera), there is one or more grains differing in their composition and shape from the surrounding structures. These grains have a diameter of 100-200 microm and protrude slightly from the roof inward. They contain primarily a large percentage of Ti but also Fe and occasionally Si. The mineral makeup in the grains is still uncertain, but it seems that the minerals belong to the group called perovskite. These grains in the hornet's comb may originate from the soil around the nest, that is, comprised of ceramic matter, but it is also possible that they are secreted from a gland within the frons plate of the hornet because the fungus-like secretion in this gland contains elements similar to those in the roof of the comb cells. We conjecture that the grain in question serves as a reference point for the hornets that build the cell walls in the direction of gravity. The cement whereby the building hornets conjoin the various building materials, whether organic (cellulose and the like) or inorganic (sand grains or tiny stones), is a saliva that is secreted from their oral gland, which upon release hardens into a polymeric glue. The ceramic grain embedded within this polymeric matrix is endowed with different physical properties and can therefore respond differently to the tension or pressure of the surrounding walls.     

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.     

Temperature-dependent electrical resistivity of the hornet cuticle: Changes induced by colchicine and purine in the diet

Various cuticular areas of the Oriental hornet (Vespa orientalis) were measured for their electrical resistivity within the range of 3–40°C. It was found that: (1) the electrical resistivity is temperature dependent; (2) there are no significant differences in this respect between hornets collected in different regions; (3) there are no differences in the electrical resisitivity between the yellow and brown areas of the cuticle in control hornets; (4) there are however, significant changes in resistance between the yellow and brown strips of hornets fed on purine; (5) hornets fed on colchicine reach a minimum resistance at a higher temperature than do the control hornets; and (6) hornets fed on purine reach a minimum resistance at a lower temperature. It is suggested that the cuticular changes in resistivity at different temperatures reflect the hornets' mechanism of detecting and adjusting to changes in the ambient temperature.     

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.     

European honeybee defense against Japanese yellow hornet using heat generation by bee‐balling behavior

The Japanese honeybee, Apis cerana japonica Radoszkowski, uses unique generation of heat by bee‐balling to defend against, overheat and kill predacious Japanese hornets. We have now observed the European honeybee, Apis mellifera Linnaeus, using similar bee‐balling behavior and heat generation against the Japanese yellow hornet, Vespa simillima xanthoptera Cameron. We monitored temperatures in the center of the bee‐ball and inside thoracic muscles of the captured hornet and found that the thoracic internal temperature (45.8 ± 2.32°C) was higher than that of the bee‐ball (44.0 ± 0.96°C). Although the thoracic temperature of captured hornets rose to the upper lethal level, defending European bees also showed some stinging attempts against the hornet, unlike the sympatric Japanese honeybee, which never stings during bee‐balling. The European honeybee bee‐balling behavior consists of three phases: (i) heating; (ii) heat‐retaining; and (iii) break up. Our results suggest that European honeybees kill hornets by raising the body temperature of hornets rapidly without stinging. The tactics of bee‐balling against hornets are complex and may be performed by extended division of labor.     

Relationship between the age of Vespa velutina workers and their defensive behaviour established from colonies maintained in the laboratory

As the structural bases of insect societies are essential to colony survival, nests must be protected from predation. Nest defence behaviours are among the most important roles assigned to worker members. However, in hornet societies, temporal polyethism (age-dependent division of labour among workers) is assumed to be weak. Few studies have investigated this phenomenon, probably because hornet nests are aggressively defended and dangerous to approach. In the present study, we propose a method for rearing nests of Vespa velutina, a species newly introduced into Europe. This method enables the handling of hornets, and thus the design of experiments. By marking all newly emerged hornets, we recorded aggressiveness in workers of different ages from three captive colonies. We observed that nest defence behaviour in V. velutina depends on the age of the workers. Nest defence appears to be mediated by the queen, probably through pheromones that promote nest organization. We also identified a previously unreported but important behaviour in V. velutina that workers are aggressive towards male hornets. This behaviour might be a strategy to avoid inbreeding. Collectively, our results provide new research perspectives for the management of social hymenopteran predators.     

Frequencies of the sounds produced by the oriental hornet, Vespa orientalis

Three distinct categories of sounds have been detected in the Oriental hornet colony: (a) hunger signals produced by the larvae, (b) tapping sounds produced by workers facing the queen, and (c) awakening taps produced by workers at a different rhythm than (b) (Ishayet al., 1974). These sounds have been analysed by means of a real time analyser. The possible correlation between the main frequencies of the various noises produced by the hornets and the absorption values of the hornet comb is discussed.     

The structure and antimicrobial potential of wasp and hornet (Vespidae) mastoparans: A review

Wasp venom is a complex mixture of biologically active components, including high molecular weight proteins, small peptides, bioactive amines, and amino acids. Peptides comprise up to 70% of dried venom. In social wasp venoms, three of the major peptide types are mastoparans, which cause mast cell degranulation, chemotactic peptides, which promote chemotaxis of polymorphonucleated leukocytes, and kinin‐related peptides, which are known to produce pain and increase vascular permeability. Among these, the bioactive tridecapeptide mastoparan is the most common and may even have antimicrobial activity. Herein we summarize the results of studies on vespid mastoparans, focusing on hornets (Vespa spp.) identified following a systematic literature search for mastoparans of hornets in the genus Vespa, the most active mastoparan research taxon. The common features of hornet mastoparans are C‐terminal amidation, amphipathic helical structure, and multiple functions such as mast cell degranulation and hemolysis, as well as membrane permeabilization. Most interestingly, all tested hornet mastoparans have strong antimicrobial activities, suggesting that they can provide useful insights into and opportunities for development of novel antibacterial peptides.     

Attack or retreat: contrasted defensive tactics used by Cyprian honeybee colonies under attack from hornets

This study describes the tactics used by Cyprian honeybees (Apis mellifera cypria) to defend their colonies against hornet (Vespa orientalis orientalis) attacks. We use simulated hornet attacks and a combination of video recordings and image analysis to reveal, for the first time, contrasted intra-subspecies defensive tactics that operate at the colony level during predation. In some colonies, when attacked, the numbers of guards at the hive entrance increases rapidly to attack, engulf, and kill invading hornets. In other colonies, guards avoid conflicts with hornets by retreating gradually and by forming a defensive line of honeybees at the hive entrance. Retreater colonies have propolis walls at the hive entrances with small apertures that are too narrow to allow the hornet to access the hive and that therefore reinforces entrance protection. On the contrary, attacker colonies have propolis walls with large openings through which the hornet can pass; these bees block the hornet's access by intensively guarding the hive entrance. We experimentally destroy propolis walls to test whether colonies consistently rebuild walls with the same intrinsic characteristics and we also monitor the survival rate of each anti-predator tactic after massive natural predation by hornets.     

Honey Bee Inhibitory Signaling Is Tuned to Threat Severity and Can Act as a Colony Alarm Signal

Alarm communication is a key adaptation that helps social groups resist predation and rally defenses. In Asia, the world’s largest hornet, Vespa mandarinia, and the smaller hornet, Vespa velutina, prey upon foragers and nests of the Asian honey bee, Apis cerana. We attacked foragers and colony nest entrances with these predators and provide the first evidence, in social insects, of an alarm signal that encodes graded danger and attack context. We show that, like Apis mellifera, A. cerana possesses a vibrational “stop signal,” which can be triggered by predator attacks upon foragers and inhibits waggle dancing. Large hornet attacks were more dangerous and resulted in higher bee mortality. Per attack at the colony level, large hornets elicited more stop signals than small hornets. Unexpectedly, stop signals elicited by large hornets (SS _{large hornet}) had a significantly higher vibrational fundamental frequency than those elicited by small hornets (SS _{small hornet}) and were more effective at inhibiting waggle dancing. Stop signals resulting from attacks upon the nest entrance (SS _nest) were produced by foragers and guards and were significantly longer in pulse duration than stop signals elicited by attacks upon foragers (SS _forager). Unlike SS _forager, SS _nest were targeted at dancing and non-dancing foragers and had the common effect, tuned to hornet threat level, of inhibiting bee departures from the safe interior of the nest. Meanwhile, nest defenders were triggered by the bee alarm pheromone and live hornet presence to heat-ball the hornet. In A. cerana, sophisticated recruitment communication that encodes food location, the waggle dance, is therefore matched with an inhibitory/alarm signal that encodes information about the context of danger and its threat level.     

Honey Bees Modulate Their Olfactory Learning in the Presence of Hornet Predators and Alarm Component

In Southeast Asia the native honey bee species Apis cerana is often attacked by hornets (Vespa velutina), mainly in the period from April to November. During the co-evolution of these two species honey bees have developed several strategies to defend themselves such as learning the odors of hornets and releasing alarm components to inform other mates. However, so far little is known about whether and how honey bees modulate their olfactory learning in the presence of the hornet predator and alarm components of honey bee itself. In the present study, we test for associative olfactory learning of A. cerana in the presence of predator odors, the alarm pheromone component isopentyl acetate (IPA), or a floral odor (hexanal) as a control. The results show that bees can detect live hornet odors, that there is almost no association between the innately aversive hornet odor and the appetitive stimulus sucrose, and that IPA is less well associated with an appetitive stimulus when compared with a floral odor. In order to imitate natural conditions, e.g. when bees are foraging on flowers and a predator shows up, or alarm pheromone is released by a captured mate, we tested combinations of the hornet odor and floral odor, or IPA and floral odor. Both of these combinations led to reduced learning scores. This study aims to contribute to a better understanding of the prey-predator system between A. cerana and V. velutina.     

Comb bulding by the oriental hornet (Vespa orientalis)

Oriental hornet young queens and workers have been induced to build combs in observation boxes. Both workers and queens displayed bulding activity over a period of 2 to 6 weeks, which is approximately the time range necessary for the development of one generation (from egg to pupa or maximally from egg to imago). Building activity and the comb architecture have been found to be influenced by such factors as: size of group, age of hornets, amputation of wings, tarsi and tips of antennae and light, and by feeding with mannose and barbiturates. Cell size is influenced by various drugs.