Vespa Mandarinia as an Invasive Species: Overview

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Table of Contents

Introduction
Brief Systematic Information
Biological Description of the Species
Ecological Characteristics
Threats
Asian Giant Hornet Invasion
Hypotheses of Invasion
Conclusion and Forecast
References

Introduction

The natural living environment is characterized by high biological diversity, which predetermines the relationship between populations and species. It is wrong to believe that the natural evolutionary mechanisms, which led to the formation of a new species, were aimed at creating absolutely friendly conditions in which different taxons could coexist freely. On the contrary, among a large number of representatives of flora and fauna, it is possible to find organisms that purposefully cause damage to other animals or plants: both for food and to meet the ethological needs. Thus, the most dangerous species are invasive species, which is defined as artificially introduced species into an isolated area, embedded in trophic chains and threatening the local biological diversity. The Asian giant hornet, Vespa mandarinia, which is the subject of this study, is described as one of the most prominent examples of invasive animals destroying populations of honeybees in East Asia and recently discovered for the first time on the North American continent. The purpose of this term paper is to discuss the current state of knowledge about the invasiveness of V. mandarinia and the consequences it may have.

Brief Systematic Information

The common name for the species: Asian giant hornet, or murder hornet, or Japanese giant hornet.
Scientific name:Vespa mandarinia or V. mandarinia.

Biological Description of the Species

External Anatomy

It is known that Vespa mandarinia is a member of the hornet species belonging to the wasp group: thus, all the features traditionally prescribed for wasps are characteristic of the species under study. In particular, V. mandarinia has a narrow waist, a rigid pair of oppositely spaced side wings, the yellow and black color of the segmented torso, and straight antennae, as shown in Figure 1 (“Asian giant hornet,” n.d.). Moreover, as any wasp, V. mandarinia is characterized by a thin and sharp sting that penetrates the surface layers of the victim and kills the animal. Although the Asian hornet is very similar to an average wasp, it would be wrong to assume that this animal has no distinctive qualities. On the contrary, it is the unique features that form the body of V. mandarinia that determine the increased research interest and justify the environmental position of the hornet as a killer.

Figure 1. Appearance of the Asian giant hornet

It would be fair to note that V. mandarinia is justifiably considered the largest hornet of all currently described ones. The external anatomy of the insect attracts attention in several aspects at once. First of all, the hornet’s head is comparatively more extensive than the heads of other wasps. This increase is due to two reasons: the broader distance between the two complex eyes and the development of the masticatory muscles that form the structure of the cheek — this is how the insect copes with the enemy (“Common name: Asian giant,” n.d.). Another characteristic feature of the animal is a combination of complex facet eyes and three photosensitive ocelli, located in the interocular region of the face, as illustrated in Figure 2. Due to the unique peculiarities of the structure of simple eyes — broken focus location and geometric configuration — they do not allow the owner to distinguish between individual objects (Warrant, 2019). In other words, it means that the simple hornet’s eyes have a low visual perception, and with their help, a bee can only distinguish the degree of change in light intensity. Thus, simple eyes increase the overall light sensitivity of complex eyes.

Figure 2. Face structure of the hornet

The presence of an elongated sting, usually numerically larger than 0.3 inches, is the prerogative of wasp females. Without detailing the environmental aspects of V. mandarinia‘s social life here, it is only necessary to note that the use of the sting as a murder weapon is justified by evolutionary mechanisms (“Common name: Asian giant,” n.d.). In crisis situations, a female hunter must be able to withstand the threat, and consequently, she uses the sting to inject a nerve toxin into the victim (Gill et al., 2020). Undoubtedly, males also protect their nest and queen, but they cannot have a sting due to reproductive features of this organ formation.

Reproductive and Life Cycles

The life cycle of V. mandarinia is a closed ring process with a tendency of annual recurrence. More specifically, Asian hornet females who survive the winter anabiosis, stimulated by the rising temperatures of spring days, tend to create a social nest where wasps will live for the next year (“Asian hornet,” n.d.). The nest usually consists of a bark of branches, which the royal female crushes with its powerful jaws. Then, wood particles are wetted with the secret of salivary glands, resulting in the composition taking roughly ground paper, forming a nest of the necessary shape. Having found shelter, the female postpones the first batch of larvae. Although initially, the role of the hunter lies only on the queen, it is worthwhile for the cubs to grow up a little, and all the care for the management of the birth nest goes to them. This means that the only mission of the main female hornet will be to continue the birth while other females and males are doing the rest functions. Mating with males occurs in early autumn: as soon as the Asian hornet gives its seed to the main female, it dies. Soon, the fertilized female gives off offspring that will have to wait for winter to wake up and build a new nest.

Ecological Characteristics

Habitat and Prevalence

The traditional habitat of the Asian hornet is the subtropical climate zones, rich in woody vegetation. In combination with groves, forests, and parks isolated from urban settlements, V. mandarinia‘s nests can be located in wooden houses, apiaries, or in urban natural spaces (Gill et al., 2020). The common name of this species justifies its history of origin: the hornet grew from Asia and migrated to the nearby states of India, Afghanistan, eastern China, and the Indonesian archipelago. Meanwhile, more relevant data allow establishing that the habitat of V. mandarinia were also European settlements, namely France, Spain, and Belgium (“Asian hornet,” n.d.). Soon, the Asian hornet also reached the North American continent, laying the foundation for a change in the ecological levels of these natural communities (Wilson et al., 2020). The nature of the insect’s settlement underscores the urgent need to carefully study the ecological, genetic, and geographical features of the hornet in order to eliminate the undesirable effects of the invasion.

Feeding

The food ration of insects is quite diverse and directly depends on the age of the wasp. In the initial personality stages, V. mandarinia is prone to predation through the consumption of killed flies, butterflies, locusts, and, most importantly, honeybees. Closer to adulthood, individuals become more restrained in its diet and mainly use fruits and sugar-containing vegetables. However, this does not mean that the adult wasp will not attack the bees if it meets the hive. If it happens, a hornet marks the bee’s nest with a smelling pheromonic fluid, which allows it to return to the find together with other hornets (McClenaghan et al., 2019). During an attack, giant insects dismember the bodies of its victims, ripping heads from the trunk with powerful jaws (Ugajin et al., 2012). Once the adults have been slaughtered, the hornets take away the larvae and honey that will serve as food for them.

Figure 3. The Asian giant hornet eats the honeybee with its powerful jaws

Explanation of Evolutionary Patterns

The first point to discuss when describing Asian giant hornets is its dimensional characteristics. It seems strange that hornets born in Asia have such a severe superiority over its competitors. In fact, there are at least two biologically evidenced factors that have contributed to this growth. First, the explanation can be based on Allen’s environmental model, which affirms the relationship between the size of protruding body elements and ambient temperature (Fan et al., 2019). According to this rule, the larger the individual sizes of the body (wings, head, tail, limbs), the higher the ambient temperature: this approach can improve thermal regulation through increased evaporation area. Given that the homeland of the Asian hornet is a subtropical zone, this factor has good reasons for trust (“Asian hornet,” n.d.). At the same time, large body sizes can only be caused by evolutionary mechanisms. In particular, such sizes are a vivid example of evolutionary struggle and the ability of species to adapt to adverse environmental conditions. In the rich diversity of the animal world, which is typical for subtropical countries, large and poisonous insects are much more likely to find its food and not fall prey to natural enemies itself than its smaller and harmless related species. Thus, the apparent advantage of the Asian giant hornet, its size, can be due to either one of two factors or a combination of both.

Threats

For Honeybees

Insect mining is an integral part of the Asian hornet’s existence. The most significant damage that the hornet does to the natural community is expressed in the attack on honeybees. Thus, if a hive is found, a wasp marks the nest walls with pheromone, showing the other hornets the discovery. A group of several insects attacks a flock of bees, beheading them and eating its insides (Ugajin et al., 2012). However, some species of bees were able to develop protective mechanisms. Over thousands of years, Japanese bees, Apis cerana japonica, have learned to resist Asian giant hornets. Having smelled its pheromones, they immediately begin to reshape: about a thousand bees gather in a hive near the entrance, and a hundred more fly outside and look for approaching scouts. When they find the enemy, they lure it in and pounce on all sides. The hornet is surrounded by several bees, each of which begins to vibrate. It is known that such actions lead to a local temperature increase: McClenaghan et al. (2019) reported that when bees vibrate, the temperature reaches 46 degrees Celsius, which is a sufficient minimum for the hornet to die due to overheating. It is interesting to note the fact that the approach to protection strategies is differentiated: there is a correlation with the age of the population. The interaction of Asian hornets and honeybees is, apparently, a relatively new phenomenon that has not yet had time to form resistance genes in the gene pool of bees. This means that while Japanese honeybees may cause overheating through vibrations, European populations are not familiar with such strategies (McClenaghan et al., 2019). That is why they cannot destroy predators one by one and, therefore, become easy prey. In fact, this creates a problem of invasiveness: endemic species are not stable in the migrant’s influence, and the ecosystem is damaged. Thus, a colony of Asian hornets settled near the apiary, where there are several thousand individuals, which can cause very significant damage to the beekeeping industry.

For Human

It would be erroneous to assume that V. mandarinia poses a danger only to its immediate neighbors in trophic chains. In fact, there are two reasons why the Asian hornet can be dangerous to humans. First of all, insect damage concerns the economic damage that the human community will suffer from hornet invasion. According to Holland (2013), the loss of bees involved in the production of honey, wax, and other by-products will take the U.S. budget $15.0 billion. Coupled with a potential financial crisis, this means that the workers involved in this sector of agricultural production will remain unemployed, and the existing apiaries will be closed. At the same time, the toxin emitted by the hornet glands is extremely toxic and, at certain doses, poses a severe danger to humans. Although adult wasps use sting only in rare cases when the threat is very significant, improper human behavior near the nest can cause death (Main, 2020). The poison is known to contain several toxins, the most dangerous of which is mandaratoxin, the substance with a pronounced nerve action (Hirano & Tanikawa, 2020; Liu et al., 2016). Toxic components have a destructive effect on internal organs tissues, which is accompanied by severe pain and degradation of mucous membranes.

For Other Species

However, honey bees and humans do not limit the range of Asian hornet victims. It is about countless fruits, flowers, and other insects such as flies, caterpillars, spiders, and bumblebees, which become food resources for omnivorous V. mandarinia. Thus, hornet infestation becomes a threat to the existence of the entire equilibrium ecosystem because (i) the insect directly affects any of the sacrificial species, and (ii) it changes the natural food and energy chains.

Asian Giant Hornet Invasion

As long as the existence of Asian giant hornets in East Asia was not surprising, their expansion into areas of other states was a matter of concern. In light of the threats described above to local flora, fauna, and human communities, zoologists around the world are seeking to track hornet’s migratory flows and prevent it from settling in time. However, it is worth mentioning that the preventive guides developed today became possible only due to negative experiences in South Korea, France, Spain, and other European cities. Before discussing possible ways of invasion, it is necessary to discuss in detail two traces of insects of this species outside Asia.

The first victim of this expansion was South Korea, where the Asian hornet arrived in 2003. Studies conducted by specialists from Korea National University and other universities have shown that the hornet is now present throughout the country, causing significant damage to beekeeping and the environment (Choi et al., 2012). For instance, in the 15 years since the arrival of the Asian hornet, the populations of two of Korea’s most abundant native bumblebees have declined by 20% and 10%. Moreover, according to the authors, Asian hornet populations continue to move at a speed of up to 20 km a year northwards.

The first mention of Asian hornets in France dates back to 2004, when, according to some specialists, a female in a natural biological pause, was delivered to a European country from the Chinese province of Jiangsu along with commercial assets for sale (“Asian hornets claim another victim in France,” 2018). The wasp was able not only to settle in France but also to become one of the main threats to agricultural and economic development. It can be assumed that the spread of Asian hornets has contributed to deepening the systemic crisis experienced by beekeeping in France in recent years. Subsequently, bees settled in Spain, Portugal, Belgium, Italy, and the UK.

It is fair to note that the cases described above, although officially documented in European countries, actually refer to a slightly different biological species. Reports received from different labs of the world until 2019 were an erroneous identification of wasps as V. mandarinia, while they were related species: V. orientalis and V. velutina (Osterloff, 2020). Nevertheless, the first official fact of finding V. mandarinia outside Asia was described in August 2019, when the dead bodies of three Asian hornets were found in Canada (Wilson et al., 2020). A month later, their nest was found and destroyed, but probably there were others. In November 2019, another giant hornet was seen on the other side of the strait, and in early December, they were seen in the American state of Washington, which borders Canada. Thus, the Asian hornet snuck into the United States.

Hypotheses of Invasion

The Asian hornet infestation into new countries and the inclusion of the insect in sustainable ecological chains are unlikely to stop in the near future, and therefore, the study of migrations routes is key to the development of preventive measures. There are at least three different versions of how V. mandarinia could spread to new lands. First of all, one should take into account the migratory characteristics of the insect: it is rather fast-flying (“Asian hornet,” n.d.). Thus, it is assumed that the insects may have intended to end up on the North American continent. However, in this case, the migratory population would have to cross the Pacific Ocean, which is hardly possible for a swarm of wasps. Then, the truest hypothesis, the second one, refers to the trade routes linking the export-import relations of Asian countries and Canada (Kaufman, 2020). It is assumed that the royal female may have crossed the ocean on a ship with containers, and this seems to have happened in the fall when the female mates and enters the phase of anabiosis.

It is logical to assume that the Asian hornet female entered the territory of North America, began to develop local lands, and soon gave birth to offspring. In such a case, if to follow the chain of cause-and-effect relations, the subsequent generations of V. mandarinia should be phylogenetically connected with those who remained on the territory of Canada. Nevertheless, the genome analysis of microflora, by 16sRNA, for two species from different American locations, carried out in 2019, showed that they are not near related, and have parallel maternal lines (Suenami et al., 2019; Chen et al., 2016). Simply put, it results that Asian hornets from different populations could have been transported to the continent independently several times.

Fascinating in origin is the third version of the Asian hornet invasion due to culinary techniques based on the juice of these insects. In the Japanese bar Suzumebachi, which literally translates as the Asian giant hornet, the practice of drinking alcoholic beverages infusion on dead wasps is common (Kotzer, 2017). This liqueur is very popular in an Asian country and has apparently been exported to American lands. It may be assumed that, together with the “poisonous” liqueur, the sleeping hornet larvae were brought to the United States and Canada, which became active later.

Conclusion and Forecast

The Asian giant hornet represents a group of wasps with incredible size, strong jaws, and high speed of flight. Initially appeared in Asian countries, this species began to migrate to other lands, penetrating local ecosystems. Such an invasion could hardly bring positive results, and in the decades since the first media publications about single cases of individuals in unusual ranges, hornet populations have become a serious threat to countries. Hornet populations have the potential to cause a severe economic crisis, as they tend to destroy entire apiaries. In addition, the very existence of Asian hornets in unconventional habitats poses a threat to the survival of other species.

It is difficult to say in which country new hornet infestation cases will be detected, but the study by displacement allows predicting scenarios. About a year has passed since V. mandarinia was found in the U.S., and during this time, the hornets may have taken a stable position in the ecosystems. Alaniz et al. (2020) reported that the development of hornet populations would cause severe financial losses for America. For this reason, the country’s authorities seek to take preventive measures, including by informing the population. For instance, the state of Washington has already released an online form asking citizens to report cases of such hornets being discovered (“Hornet watch report form,” 2020). Therefore, it is difficult to underestimate the scale of the problem, and in the future, it is likely that humanity will observe ecosystem structural changes caused by V. mandarinia invasion.

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