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.     

Native Prey and Invasive Predator Patterns of Foraging Activity: The Case of the Yellow-Legged Hornet Predation at European Honeybee Hives

Contrary to native predators, which have co-evolved with their prey, alien predators often benefit from native prey naïveté. Vespa velutina, a honeybee predator originating from Eastern China, was introduced into France just before 2004. The present study, based on video recordings of two beehives at an early stage of the invasion process, intends to analyse the alien hornet hunting behaviour on the native prey, Apis mellifera, and to understand the interaction between the activity of the predator and the prey during the day and the season. Chasing hornets spent most of their time hovering facing the hive, to catch flying honeybees returning to the hive. The predation pressure increased during the season confirming previous study based on predator trapping. The number of honeybee captures showed a maximum peak for an intermediate number of V. velutina, unrelated to honeybee activity, suggesting the occurrence of competition between hornets. The number of honeybees caught increased during midday hours while the number of hornets did not vary, suggesting an increase in their efficacy. These results suggest that the impact of V. velutina on honeybees is limited by its own biology and behaviour and did not match the pattern of activity of its prey. Also, it could have been advantageous during the invasion, limiting resource depletion and thus favouring colonisation. This lack of synchronization may also be beneficial for honeybee colonies by giving them an opportunity to increase their activity when the hornets are less effective.     

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.     

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.     

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.     

Digging activity by the oriental hornet (Vespa orientalis; Hymenoptera,Vespinae) is correlated with solar radiation

Observations were made on the activities of workers of the Oriental hornetVespa orientalis, during flight to and from the nest, on fully active days in months of maximal colony activities. Two types of flight out of the nest were recorded: flight for removal of dug-up soil and flight for foraging of buiding materials and food from the field. The flights of digger workers occur and peak around 1200, (with even slopes down to zero on both sides of the peak). The flight activity curve is gaussian and in accordance with the intensity of solar irradiation. Flight activities of foraging workers are limited in the morning hours but subsequently increase, the curve resembling that of the air temperature at 2m above the soil surface. The flight rhythm of digger hornets in the presence of 2 adjacent outles and the rhythm of activity of digger hornets of 2 abutting nests were also investigated. The results indicate a strong competition among the diggers for flight opportunity during periods of highest insolation intensity. Due to the correlation between the flight of digger hornets and the intensity of sun radiation, it is assumed that hornets do make use of solar energy for flight purposes.     

The effects of micro-gravity on hornet's nest building and activity

Principal scientific objectives: 1.) Comb building by hornet workers in micro-G: randomness of orientation, structural integrity, delay or rapidity of construction, all as a function of developmental state of the hornet. 2.) Dark-light effects on building hornets--will light provide building cues? 3.) Effect of domicile geometry on building practices--will the hornets build in spherical, domed or cube-shaped containers? 4.) Semiconductive properties of hornet cuticle and comb--will these be different than in the controls? Will the yellow granules developed in space be physico-chemically different from control granules? 5.) Post flight experiments--Will the hornets returned from space--build and oviposit as usual? Will the laid eggs embryonate? Will the comb be orientated as usual? How about other parameters of orientation (geotaxis) and social behavior (thigmotaxis)? Will there be any changes in the dominant gut microflora of returned hornets?     

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.     

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.     

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.     

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.     

Rearing techniques for hornets with emphasis on Vespa velutina (Hymenoptera: Vespidae): A review

Of the 34 vespid species recorded worldwide as invasive aliens, particular attention is currently being given to the yellow-legged hornet Vespa velutina that has invaded Europe, Japan, and Korea. The hornet is a voracious predator of bees and a serious threat to bee colonies and bee pollination. Control measures are needed, but their development has been challenging as biological and ecological studies are limited by the short field season and the cryptic nesting behavior of these hornets. A Vespa rearing process can generate the large numbers of workers, gynes, and males that are essential for studying chemical ecology and life history and for experimental testing of various hypotheses. We present a synthesis of suitable methods and techniques for year-round Vespa hornet rearing. Particular reference is given to Chinese know-how and experience with Vespa rearing for medicinal and culinary motivations. We also draw on observations with reared insects that have a similar life history as Vespa hornets, namely Bombus bumblebees and Vespula yellowjackets. Key challenges to optimizing Vespa hornet rearing are identified and discussed.     

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.     

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.     

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.     

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.     

Testing muzzle and ploy devices to reduce predation of bees by Asian hornets

Since its accidental introduction in 2004, the Asian yellow-legged hornet (Vespa velutina) has quickly spread in France. V. velutina specializes in the emblematic honeybee, Apis mellifera which are unable to protect their colonies efficiently against this fierce new predator. Here, we investigated whether two defence devices, a ploy and a muzzle, can protect bee colonies. Our results showed that neither device was able to reduce the number of hornets present in front of the hive or their predation efficiency (i.e. the number of captured bees). However, we found more flying bees and a smaller bee carpet in the presence of a muzzle, evidence that this very cheap method of protection can reduce the hornets’ impact on the activity of the bee colony and thus probably enabling its survival. We also showed that the number of agonistic interactions among V. velutina individuals increased with the number of hornets but without influencing the predation rate in our experimental conditions. The threat to honey bees is now well described, but the Asian yellow-legged hornet very likely has an impact on another insect species that has been the subject of far fewer studies: The native European hornet (Vespa cabro). Monitoring of several apiaries suggests that high densities of both V. velutina and V. crabro are exclusive and that the two species are engaged in an exploitative competition interaction. We are thus already in a position to underline the need for combined protection, as well as for further studies to better understand the ecology of V. velutina, to reduce the damage they cause.     

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.