Asian giant hornet

Asian giant hornet
Adults engaging in trophallaxis
Conservation status
Least Concern  (IUCN 3.1)
Scientific classification
Kingdom:	Animalia
Phylum:	Arthropoda
Class:	Insecta
Order:	Hymenoptera
Family:	Vespidae
Genus:	Vespa
Species:	V. mandarinia
Binomial name
Vespa mandarinia Smith, 1792

The Asian giant hornet (Vespa mandarinia), including the subspecies Japanese giant hornet (Vespa mandarinia japonica),^[1] colloquially known as the yak-killer hornet,^[2] is the world's largest hornet, native to temperate and tropical Eastern Asia. They prefer to live in low mountains and forests while almost completely avoiding plains and high altitude climates. V. mandarinia creates nests by digging, co-opting pre-existing tunnels dug by rodents, or occupying spaces near rotted pine roots.^[3] It feeds primarily on larger insects and honey from honey bee colonies.^[4] Some dimensions of this hornet are a body length of 50 mm (2 in), a wingspan of about 76 mm (3 in), and stinger of 6 mm (0.24 in) which injects a large amount of potent venom.^[5] Vespa mandarinia is the only social wasp that recruits members of its hive to potential food sources through food recruitment signals.^[6]

Taxonomy and phylogeny

Vespa

Vespa mandarinia is a species of wasp that falls under the order Hymenoptera. Its genus Vespa is composed of hornets. The genus is defined by a nearly circular (when viewed from the front) or dorsoventrally depressed head. The upper half of their mid-cranial sulcus is developed and may appear above the clypeus. A patch of the palate is sclerotized and extends towards the lateral side. Due to this development, it is rare to find a weak and fragmented palate amongst this genus. A median patch is occasionally present in species within the genus. The mandible is short and apically tridentate. Unlike Vespula, the first tooth does not distinctively project. The density of denticles on the maxilla vary. The collar process is thick, complex, and branched. Outside of this, the atrial wall has many intricacies and visible spines.^[3]

Subclassification of organisms within the genus based on adult features is difficult due to the anatomical similarity amongst species and the fact that behavioral similarity is not associated with phylogeny (in the case of this genus). The subdivision of the genus is considered highly artificial and does not hold much value. For example, Vespa mandarinia, Vespa tropica, Vespa dybowskii, and Vespa basalis are considered to be distinguished based solely on their behavioral properties.^[3]

Vespa tropica

Along with 7 other species, V. mandarinia is a part of the V. tropica group, defined by the single notch located on the apical margin of the seventh gastral sternum of the male. The new V. tropica species group comprises V. mandarinia and V. soror. The triangular shape of the apical margin of the clypeus of the female defines the species. Furthermore, the vertex of either species is enlarged and the shape of the apex of the aedeagus is distinct.^[7]

Description

Depending on their classification, V. mandarinia can range anywhere from 3.5 to 5.5 cm on average. Regardless of gender, the hornet’s head is a light shade of orange and its antennae are brown with a yellow-orange base. Its eyes and ocelli are dark brown to black. V. mandarinia is distinguished from other hornets by its pronounced clypeus and large genae. Its orange mandible contains a black tooth that it uses for digging.^[8]

The thorax is dark brown, with two grey wings varying in span from 3.5 to 7.6 cm. Its forelegs are brighter than the mid and hind legs. The base of the forelegs is darker than the rest.

The abdomen alternates between bands of dark-brown or black and a yellow-orange hue (consistent with its head color). The sixth segment is yellow. Its stinger is up to 6 mm long and contains a venomous poison that, at a high enough dosage, can kill a human.^[8]

Queens and workers

The only difference between queens and workers is that queens are considerably larger. Queens will exceed 4 cm while workers are between 3.5 and 3.9 cm in length. The reproductive anatomy is consistent between the two but workers do not reproduce.^[8]

Drones

Drones (males) are similar to females but lack a stinger. This is a consistent feature among Hymenoptera.^[8]

Geographic distribution

The Asian giant hornet

The Asian giant hornet

It can be found in the Primorsky Krai region of Russia, Korea (where it is called 장수말벌; "Commander wasp"), China, Taiwan (where it is called 虎頭蜂; "tiger head bee"), Indochina, Thailand, Nepal, India, Vietnam and Sri Lanka, but is most common in rural areas of Japan, where it is called giant sparrow bee (大雀蜂 or オオスズメバチ).

Nesting

V. mandarinia nest in low mountains and forests. As a particularly dominant species, there are no efforts directed towards conserving V. mandarinia or its habitats, as they are common and oftentimes undisturbed. Unlike other species of Vespa, V. mandarinia almost exclusively inhabit subterranean nests. In a study of 31 nests, 25 were found around rotten pine roots. Additionally, rodents, snakes, or other burrowing animals previously made some of the tunnels. The depth of these nests was between 6 and 60 cm. The entrance at the ground surface varies in length from 2 to 60 cm either horizontally, inclined or vertically. The queens that found the nest prefer narrow cavities.^[9]

Nests of Vespa typically lack a developed envelope. During the initial stages of development, the envelope is in an inverted bowl-shape. As the nest develops, one to three rough sheets of combs are created. Oftentimes, single primordial combs are created simultaneously and then fused into a single comb.^[9]

A system of one main pillar and secondary pillars connect the cones. Nests will have approximately 4 to 7 combs. The top comb is abandoned after summer and left to rot. The largest comb is at the middle to bottom portion of the nest. The largest combs created by Vespa measured 49.5 cm by 45.5 cm with 1,192 cells (no obstacles, circular) and 61.0 cm by 48.0 cm (elliptical; wrapped around root system).^[9]

Colony cycle

The nesting cycle of V. mandarinia is fairly consistent with that of other eusocial insects. There are six phases to each cycle:^[9]

Pre-nesting period

There are two different types of queens that enter hibernation following a cycle: Inseminated queens and uninseminated queens. They will first appear in early to mid-April and begin feeding on the sap of Quercus trees. Although this timing is consistent among Vespa, V. mandarinia dominate the order, receiving preference for premium sap sources. Among the V. mandarinia queens there is a dominance hierarchy. Top ranked queens will begin feeding while the other queens form a circle around her. Once the top queen finishes, the second highest ranking queen will feed on the sap. This process will repeat itself until the last queen feeds at a poor hour.^[9]

Solitary, cooperative and polyethic period

Inseminated queens will start to search for nesting sites in late April. The uninseminated queens will not search for nests since their ovaries never fully develop. They will continue to feed but then disappear in early July.

An inseminated queen will begin to create relatively small cells in which she raises around 40 small workers. It’s not until early July that workers begin to work outside of the hive. Queens participate in activities outside the hive until mid July where they stay inside the nest and allow workers to do extradinal activities. Early August marks a fully developed nest, containing 3 combs holding 500 cells and 100 workers. After mid September, no more eggs are laid and the focus shifts to caring for larvae. The queens will die sometime between the 19th and 31 October.^[9]

Dissolution and hibernating period

Males and new queens will take on their responsibilities in mid-September and mid-October, respectively. During this time, their body color becomes intense and the weight of the queen increases by approximately 20%. New males leave the nest in early October while the queens leave in early November. Once the males or queen leaves the nest, they do not return. In V. mandarinia, males will wait outside the nest entrance until the queen emerges. Once the queen emerges, they will attack her mid air, bring her to the ground, and copulate from 8 to 45 seconds. After this episode, the males will return to the entrance for a second chance while the queen leaves. Interestingly, many queens will attempt to fight off the males and leave unfertilized. After this episode, queens are found in moist, subterranean habitats.

When sexed individuals emerge, workers will shift their focus from protein and animal foods to carbohydrates. The last sexed individuals to emerge will die of starvation.^[9]

Sting

The stinger of the Asian giant hornet is about 6 mm (¼ in) in length,^[5] and injects an especially potent venom that contains, like many bee and wasp venoms, a cytolytic peptide (specifically, a mastoparan) that can damage tissue by stimulating phospholipase action,^[9] in addition to its own phospholipase.^[9]Masato Ono, an entomologist at Tamagawa University near Tokyo, described the sensation as feeling "like a hot nail being driven into my leg".^[5]

An allergic human stung by the giant hornet may die from an allergic reaction to the venom.

The venom contains a neurotoxin called mandaratoxin (MDTX),^[9] a single-chain polypeptide with a molecular weight of approximately 20 kD,^[9] which can be lethal even to people who are not allergic if the dose is sufficient. However if the victim is allergic to the sting this means an almost certain death

Each year in Japan, the human death toll caused by Asian giant hornet stings is around 30 to 40.^[9][10]

Advice in China is that people stung more than 10 times need medical help, and need emergency treatment for more than 30 stings. The stings can cause renal failure.^[11] Stings by Asian giant hornets killed forty-one people and injured more than 1,600 people in Shaanxi province, China in 2013.^[12]

Effects of venom on humans

Fatalities from envenomation are primarily related to anaphylactic shock or cardiac arrest. There are, however, multiple cases where patients will die as a result of multiple organ failure. Most of these cases were related to a relatively large number of stings. Furthermore, those who died of multiple organ failure exhibited signs of skin hemorrhaging and necrosis although presentation of hemorrhaging and necrosis is rare. There are two possible reasons for skin hemorrhaging and necrosis. One possibility is that the toxicity of the venom for that particular set of stings was particularly potent. The other condition would suggest an individual’s inability to effectively neutralize the venom. In either case, these stings lead to multiple organ injury. While not everyone presented with lesions or necrosis, there was a strong correlation between the number of stings and the severity of injury. Those who died, on average, were stung 59 times (with a standard deviation of 12) while those who survived suffered 28 stings (with a standard deviation of 4).^[13]

Parasites

Xenos moutoni is a common parasite among Vespa. In a study of parasites among species of Vespa, 4.3% of Vespa mandarinia females were parasitized. Males were not stylopized (parasitized by stylopidae) in any case. It was noted that the width of the stylopidae’s head and the host’s head are positively correlated. The major consequence of being parasitized is the inability to reproduce for the following year. Stylopized queens will follow the same fate as uninseminated queens. They will not search for an area to create a new colony and will feed on sap until early-July at which point they will disappear. In other species of Vespa, males also have a chance of being stylopized. The consequences between the two sexes are similar, as neither sex is able to reproduce.^[14]

Communication and perception

V. mandarinia use both visual and chemical cues as a means of navigating themselves and others to their desired location. Scent marking was discussed as a way for hornets to direct other members of the colony to a food source. It was observed that even with antennae damage, V. mandarinia was able to navigate itself. It wasn't until vision impairment was induced that they were unable to find their destination. This implies that while chemical signalling is important, visual cues play an equally important role in guiding individuals. Other interesting behaviors include the formation of a “royal court,” consisting of workers who lick and bite the queen thereby ingesting her pheromones.

These pheromones could directly communicate between the queen and her court or indirectly between her court and other workers due to the ingested pheromones. This is merely speculation as no direct evidence has been collected to suggest the latter. V. mandarinia communicate acoustically as well. When larvae are hungry, they will scrape their mandibles against the walls of the cell. Furthermore, adult hornets will click their mandibles as a warning to other creatures that encroach upon their territory.^[15][16]

Scent marking

V. mandarinia is the only species of social wasp known to apply a scent in order to direct its colony to a food source. The wasp secretes the chemical from the sixth sternal gland, also known as the van der Vecht‟s gland. This behavior is observed during autumnal raids after the hornets begin hunting in groups instead of individually. The ability of to apply scents may have arisen from the fact that the wasp relies heavily on honeybee colonies as its main food source. A single wasp is unable to take on an entire colony of bees. This arises from the fact that species such as Apis cerana have a well-organized defense mechanism. Honeybees will swarm one wasp and flutter their wings in order to heat up the wasp and raise carbon dioxide levels to a lethal level. For this reason, organized attacks are much more effective and will easily devastate a colony of up to tens of thousands of honeybees.^[17]

Interspecies dominance

In an experiment observing 4 different species of Vespa, including Vespa ducalis, Vespa crabro, Vespa analis, and Vespa mandarinia, it was found that Vespa mandarinia was the dominant species. Multiple parameters were set to determine this. The first set parameter observed interaction-mediated departures. Interaction-mediated departures are defined as scenarios where one species would leave its position due to the arrival of a more dominant individual. The proportion of interaction-mediated departures was the lowest for V. mandarinia. Another measured parameter was attempted patch entry. Over the observed period of time, conspecifics (interactions with the same species) resulted in refused entry far more than heterospecifics (interactions with different species). Lastly, fights between these hornets, Rhomborrhina japonica, Neopegoschkevitschii, and Lethe sicelis were observed and once more V. mandarinia was the most dominant species. In 57 separate fights, 1 loss was observed to Neopegoschkevitschii, giving V. mandarinia a win rate of 98.3%. Based on interaction-mediated departures, attempted patch entry and interspecific fights, it was determined that V. mandarinia is the most dominant species.^[18]

Predation

The Asian giant hornet is intensely predatory; it hunts medium- to large-sized insects, such as bees, other hornet species, and mantises.

An Asian giant hornet feeding on a mantis.

The hornets often attack hives to obtain the honey bee larvae as food for their own larvae. A single scout, sometimes two or three, will cautiously approach the hive, producing pheromones to lead its nest-mates to the hive. The hornets can devastate a colony of honey bees: a single hornet can kill as many as 40 honey bees per minute thanks to its large mandibles which can quickly strike and decapitate a bee. The honeybee stings are ineffective because the hornets are five times the size and too heavily armoured. It takes only a few hornets (under 50) a few hours to exterminate a colony of tens of thousands of bees. The hornets can fly up to 100 kilometres (60 mi) in a single day, at speeds of up to 40 km/h (25 mph)^[19]

Hornet larvae, but not adults, can digest solid protein; the adult hornets chew their prey into a paste that they feed to their larvae. Larvae of predatory social vespids generally (not just Vespa) secrete a clear liquid, vespa amino acid mixture, whose exact amino acid composition varies considerably from species to species, which they produce to feed the adults on demand.^[20]

Native honey bees

A defensive ball of Japanese honey bees (Apis cerana japonica) in which two hornets (Vespa simillima xanthoptera) are engulfed, incapacitated, heated, and eventually killed. This sort of defence is also used against the giant hornet.

Beekeepers in Japan attempted to introduce European honey bees (Apis mellifera) for the sake of their high productivity. European honeybees have no innate defense against the hornets, which can rapidly destroy their colonies.^[1] Although a handful of Asian giant hornets can easily defeat the uncoordinated defenses of a honey bee colony, the Japanese honey bee (Apis cerana japonica) has an effective strategy. When a hornet scout locates and approaches a Japanese honey bee hive, she emits specific pheromonal hunting signals. When the Japanese honey bees detect these pheromones, a hundred or so gather near the entrance of the nest and set up a trap, keeping the entrance open. This permits the hornet to enter the hive. As the hornet enters, a mob of hundreds of honey bees surrounds it in a ball, completely covering it and preventing it from reacting effectively. The bees violently vibrate their flight muscles in much the same way as they do to heat the hive in cold conditions. This raises the temperature in the ball to the critical temperature of 46 °C (115 °F). In addition, the exertions of the honey bees raise the level of carbon dioxide (CO₂) in the ball. At that concentration of CO₂, the honey bees can tolerate up to 50 °C (122 °F), but the hornet cannot survive the combination of a temperature of 46 °C (115 °F) and high carbon dioxide level.^[21][22] Some bees do die along with the intruder, much as happens when they attack other intruders with their stings, but by killing the hornet scout they prevent it from summoning reinforcements that would wipe out the entire colony.^[23]

Detailed research suggests that this account of the behaviour of the bees and a few species of hornets is incomplete and that the bees and the predators are developing strategies to avoid expensive and mutually unprofitable conflict. Instead, when bees detect scouting hornets they transmit an "I see you" signal that commonly warns off the predator.^[24]

Control of hornets in apiculture

6 different methods are used to control hornets in Japan. Though these methods decrease damage done by V. mandarinia, controlling them entirely is extremely difficult.

Beating

Hornets are crushed with wooden sticks with a flat head. What makes this tactic particularly efficient is if the hornet is in the hunting and slaughter phase, during which it will not counterattack. This makes it an extremely easy target. The biggest expenditure in this method is time as the process is extremely inefficient.^[9]

Nest removal

Applying poisons or fires at night is an effective way of exterminating a colony. The most difficult part about this tactic is finding the subterranean nests. The most common method of discovering nests is giving a piece of frog or fish meat attached to a cotton ball to a wasp and follow it back to its nest. With V. mandarinia, this is particularly difficult considering its common home flight radius of 1–2 km. Records have shown V. mandarinia traveling up to 8 km away from the nest.^[9]

Bait traps

Bait traps are placed in apiaries. The system consists of multiple compartments that direct the hornet into a one-sided hole which is difficult to return through once it is in the cul-de-sac compartment, an area located at the top of the box which bees can escape out of through a mesh opening but wasps cannot due to their large size. Baits used to attract the hornets include a diluted mellet jelly solution, crude sugar solution with a mixture of intoxicants, vinegar or fruit essence.^[9]

Mass poisoning

Hornets at the apiary will be captured and fed a sugar solution, dead bee or hornet that has been poisoned with diluted lead arsenate, malathon or other poison. It is then expected that the toxin will spread through trophallaxis. It should be noted that this method is good in principle but has not been tested extensively.^[9]

Trapping at hive entrances

The trap is attached to the front of beehives. The effectiveness of the trap is determined by its ability to capture hornets while allowing bees to escape easily. The process is as follows: The wasp will enter the trap and encounter resistance from bees or will catch one. The hornet will then try to fly back through the entrance and hit the front of the trap. The hornet will then fly upwards to escape and enter the capture chamber, which is where the hornets are left to die. There are many problems with the traps that make it inefficient. Some hornets find a way to escape the trap through the front. Others will wait at the top or front for bees to exit.^[9]

Protective screens

As explained in the trapping section, if met by resistance, hornets will lose the urge to attack and instead retreat. Different measures of resistance include weeds, wire or fishing nets or limiting the passage size so only bees can make it through. Experienced hornets will catch on and eventually stay on these traps, awaiting the arrival of bees. The best method of controlling hornets is to combine these protective screens with traps. ^[9]

Use of VAAM as a nutritional supplement

Vespa Amino Acid Mixture (often abbreviated VAAM) is a nutritional supplement consisting of larval saliva that is sold with the intent of improving endurance during exercise. Several companies in Asia and Europe have begun to manufacture dietary supplements and energy drinks which contain synthetic versions of secretions of the larvae of Vespa mandarinia, which the adult hornets usually consume. The manufacturers of these products make claims that consuming the larval hornet secretions (marketed as "hornet juice") will enhance human endurance because of the effect it has on adult hornets' performance. During laboratory testing on mice, increased lipolysis (metabolism of fat) was observed in rat adipocytes (fat cells) alongside improved swimming endurance, decreased lactate, and increased glucose concentration in the blood stream. While testing on mice has produced optimistic outcomes, trial tests on humans were inconclusive. 10 trained cyclists were given either an 80 mL serving of VAAM or a sports drink placebo. Variables that were tested included the time to complete the 20k, peak power, average power, max heart rate and average heart rate. Participants who consumed VAAM had significantly lower max heart rates but there were no other statistically significant changes. While this particular study produced inconclusive results, studies on longer endurance exercises may produce different results.^[9]

References

External links

Wikimedia Commons has media related to Vespa mandarinia.

Wikispecies has information related to: Vespa mandarinia

• The Asian Giant Hornet
• Yellowjackets and hornets
• Heat Tolerance as a Weapon
• Video footage at National Geographic