Xenos vesparum

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Xenos vesparum
Xenos vesparum.jpg
Male Xenos vesparum in its winged insect stage
Scientific classification
Xenos vesparum

Rossi, 1793

Xenos vesparum is a parasitic insect species of the order Strepsiptera that are endoparasites of paper wasps in the genus Polistes (most commonly Polistes dominula) that was first described in 1793. [1] Like other members of this family, X. vesparum displays a peculiar lifestyle, and demonstrates extensive sexual dimorphism.



Males and female of this species show remarkable sexual dimorphism according to their mating system. Both develop inside the abdomen, where males pupate and emerge, while females permanently reside inside.


Adult males are free-living, flying insects, whose extremely short (<5 hours) adult lives are solely dedicated to finding a mate, which they are thought to locate by scent. [2] After locating a mate (who is protruding from the host wasp's abdomen), the male lands on the wasp's abdomen, holding on with its legs and wings, while avoiding the brushing of the wasp's hindlegs, which could potentially dislodge it. The male then inseminates the female by either spreading sperm around the female's genital opening, where it eventually reaches the haemocoel (body cavity), or by directly penetrating the female's cuticle (hypodermic insemination), injecting the sperm directly into the haemocoel. [3] The male then dies several minutes after mating. Their small size coupled with their extremely short lifespan has made male X. vesparum very difficult to study.

Males also develop very unusual eyes compared to other insects. The eyes consist of a very small number of ommatidia (around 65, but each eye can vary by 10-15), while most insect eyes have thousands per eye which are closely packed together. [2] The ommatidia are irregularly distributed across the eye and are well separated by cuticle. The function of these eyes is unknown, because mate finding, which is their only purpose as adults, seems to be done by scent and the structure of the eyes indicate that they are modified larval eyes. [2] Interestingly, they are externally quite similar to the eyes of phacopid trilobites. [4]

The forewings of these insects are modified into small, club-like organs called pseudohalteres. [5] These are to help the insect maintain equilibrium in flight, and function similarly to halteres found in Dipterans.[ citation needed ]

female Xenos vesparum - female.png


Female X. vesparum are markedly different from their male counterparts. They display a high degree of neoteny, and are permanent endoparasites of their hosts. They reside in the wasp's body cavity and never develop mouthparts, legs, eyes or wings, and their only form of genitalia is the ventral opening where males can inseminate them, as well as being the point of larval escape. [1] Females can often survive overwinter inside hibernating female wasps, which will emerge the following spring with underdeveloped ovaries, and will only be able to serve as vessels to spread the parasite's larvae as they are now effectively castrated. [6]

Life cycle

The first life stage of this species are, alongside adult males, the only free living stages of these insects' lives. Called "triungulins", these larvae exit the mother's genital opening via the ability to detect light, and are deposited either in a feeding/mating area for the wasps, or directly into the nest, depending on where the mother's host wasp was when releasing the larvae. [7] In the case of the former, they then must locate a foraging wasp using chemical cues, and then grasp on to it and be carried back to the nest. Once back in the nest, the triungulins seek out an appropriate host, which are immature wasps at various stages of development. This process is known to be nonrandom, because preference for infecting females has been recorded. [1] The penetration of the host's abdomen is done without creating a wound, instead the larva enters the wasp's abdomen via mechanical separation of the host's cuticle. This step is essential in delaying or avoiding the initial immune response that would come with creation of a wound. The triungulin then moults into its second stage without ecdysis, a feature only seen in strepsipterans. [1]

Polistes sp. parasitized by three Xenos vesparum parasites Xenos vesparum in Polistes dominulaXenos vesparum.jpg
Polistes sp. parasitized by three Xenos vesparum parasites

The second and third larval stages grow extensively, but slowly, possibly to avoid ill effects to the host, whose survival is paramount to the parasite's survival. [8] During these life stages, X. vesparum are able to passively and actively avoid the host's immune system. The exact mechanism for this is unknown, but it is possible that the parasite's surface has chemical properties that allow it to remain concealed from the host immune system, and the ability to moult without ecdysis is likely a method to retain this protection and is a preadaptation for its endoparasitic lifestyle. [1]

The fourth and final life cycle stage is the development to the free living male or neotenic female form, followed by their whole or partial emergence respectively. The male pupates and develops into the final free living form, and his pupae extrudes from the wasp's abdomen, providing an emergence route for the adult male. [8] Conversely, the female develops into the final neotenic form and extrudes from the host abdomen far enough for the genital opening to be reached by a mate, as well as far enough to allow larvae to escape. In both cases, this extrusion of the female parasite or male pupa from the host abdomen is referred to as "stylopization", referring to the family of these insects. [8]

Effects on host

Host manipulation

Polistes sp. parasitized by Xenos vesparum Polistes sp with Xenos vesparum.jpg
Polistes sp. parasitized by Xenos vesparum

Female worker wasps infected with X. vesparum appear to have their behaviour modified because they act as if they are future queens and cease working, abandoning the nest before the uninfected future foundresses and males do, and form aggregations outside of the nest. When the uninfected future queens leave the nest to go to these mating grounds, it provides an area where uninfected and infected wasps mix, and this is often where release of infective larvae occurs. [9] Because the parasite does not modify male wasp behaviour, it is a "dead end" for female X. vesparum as the male wasps do not join in these large aggregations and provide little opportunity for the parasite to receive a mate. Additionally, the male wasp dies before winter, eliminating the chance of the larvae spreading in hibernating aggregations. [10] However, if infected with a male parasite, the male wasp is not a "dead end" because the free living male parasite can emerge and fly to a suitable mate within the mating aggregations. This may explain the recorded preference X. vesparum larvae have for infecting female wasps. [1]

A trend noted in paper wasps infected by this parasite is that they appear to exhibit a strong preference to congregating on campsis radican (trumpet creeper) bushes. This indicates a likely case of coevolution between parasite and host because the wasps are manipulated to prefer trumpet creeper bushes which provide shelter and excellent nutrition for the wasp, increasing its chance of survival, and by extension, increasing the parasite's chances as well. [11] In addition, the preference towards a specific plant type allows a greater chance of the parasite spreading because many foraging wasps are congregated in one spot, providing a vector for released infective larvae to reach the nest and infect young wasps.

Host castration

Parasitized female wasps feature undeveloped ovaries as well as lowered levels of juvenile hormones and they abandon the colony without performing any of their caste's duties, meaning the host is castrated and reproductively "dead", leading some to describe X. vesparum a parasitoid as it applies to female wasps. [10] The effects on the male wasp's reproductive health is less understood. It appears that, at least for light to moderate parasite loads, the reproductive health of parasitized male wasps is virtually unaffected, while the effects of highly parasitized individuals (>4 parasites) is unknown. [12]

Related Research Articles

Strepsiptera Order of insects

The Strepsiptera are an order of insects with nine extant families that include about 600 described species. They are endoparasites in other insects, such as bees, wasps, leafhoppers, silverfish, and cockroaches. Females of most species never emerge from the host after entering its body, finally dying inside it. The early-stage larvae do emerge because they must find an unoccupied living host, and the short-lived males must emerge to seek a receptive female in her host. They are believed to be most closely related to beetles, from which they diverged 300–350 million years ago, but do not appear in the fossil record until the Mid-Cretaceous around 100 million years ago.

<i>Polistes</i> Genus of insects

Wasps of the cosmopolitan genus Polistes are the most familiar of the polistine wasps, and are the most common type of paper wasp in North America. Walter Ebeling coined the vernacular name "umbrella wasps" for this genus in 1975 to distinguish it from other types of paper wasp, in reference to the form of their nests. It is also the single largest genus within the family Vespidae, with over 300 recognized species and subspecies. Their innate preferences for nest-building sites leads them to commonly build nests on human habitation, where they can be very unwelcome; although generally not aggressive, they can be provoked into defending their nests. All species are predatory, and they may consume large numbers of caterpillars, in which respect they are generally considered beneficial. The European paper wasp, Polistes dominula, was introduced into the US about 1981 and has quickly spread throughout most of the country, in most cases replacing native species within a few years. This species is very commonly mistaken for a yellow jacket, as it is black, strongly marked with yellow, and quite different from the native North American species of Polistes. The cuckoo wasp, Polistes sulcifer, is an obligate social parasite, whose only host is P. dominula. Polistes annularis, whose species name is Latin for "ringed", is also known for its distinctive red body color. Polistes metricus adults malaxate their insect prey by chewing them into a pulp, sucking out and ingesting the body fluids, then feeding the rest of the morsel to their larvae. The most widely distributed South American wasp species, Polistes versicolor, is particularly common in the southeastern Brazilian states. This social wasp is commonly referred to as the yellow paper wasp due to the distinct yellow bands found on its thorax and abdomen. Polistes wasps can be identified by their characteristic flight; their long legs dangle below their bodies, which are also more slender than a yellow jacket.


A planidium is a specialized form of insect larva seen in the first-instar of a few families of insects that have parasitoidal ways of life. They are usually flattened, highly sclerotized (hardened), and quite mobile. The function of the planidial stage is to find a host on which the later larval instars may feed, generally until the insect pupates.

European paper wasp Species of wasp

The European paper wasp is one of the most common and well-known species of social wasps in the genus Polistes. Its diet is more diverse than that of most Polistes species—many genera of insects versus mainly caterpillars in other Polistes—giving it superior survival ability compared to other wasp species during a shortage of resources.

<i>Polistes gallicus</i> Species of wasp

Polistes gallicus is a species of paper wasp found in various parts of Europe, excluding England, Denmark, and Scandinavia, from warmer climates to cooler regions north of the Alps. Nests of these social insects are created in these various conditions. The Polistes species use an oral secretion to construct their nests, which consist of a combination of saliva and chewed plant fibers. This structural mixture physically protects the nest from various harsh elements and from weathering over time.

Wasp Members of the order Hymenoptera which are not ants nor bees

A wasp is any insect of the narrow-waisted suborder Apocrita of the order Hymenoptera which is neither a bee nor an ant; this excludes the broad-waisted sawflies (Symphyta), which look somewhat like wasps, but are in a separate suborder. The wasps do not constitute a clade, a complete natural group with a single ancestor, as bees and ants are deeply nested within the wasps, having evolved from wasp ancestors. Wasps that are members of the clade Aculeata can sting their prey.

<i>Xenos</i> (insect) Genus of insects

Xenos is a genus of insects belonging to the family Stylopidae. The word derives from the Greek word for strange. A species of the genus is Xenos vesparum, first described by Pietro Rossi in 1793. The females are permanent entomophagous endoparasites of Polistes paper wasps. They dwell their whole lives in the abdomens of wasps.

<i>Polistes metricus</i> Species of wasp

Polistes metricus is a wasp native to North America. In the United States, it ranges throughout the southern Midwest, the South, and as far northeast as New York, but has recently been spotted in southwest Ontario. A single female specimen has also been reported from Dryden, Maine. Polistes metricus is dark colored, with yellow tarsi and black tibia. Nests of Polistes metricus can be found attached to the sides of buildings, trees, and shrubbery.

<i>Polistes exclamans</i> Species of wasp

Polistes exclamans, the Guinea paper wasp, is a social wasp and is part of the family Vespidae of the order Hymenoptera. It is found throughout the United States, Mexico, the Bahamas, Jamaica and parts of Canada. Due to solitary nest founding by queens, P. exclamans has extended its range in the past few decades and now covers the eastern half of the United States, as well as part of the north. This expansion is typically attributed to changing global climate and temperatures. P. exclamans has three specific castes, including males, workers, and queens, but the dominance hierarchy is further distinguished by age. The older the wasp is, the higher it is in ranking within the colony. In most P. exclamans nests, there is one queen who lays all the eggs in the colony. The physiological similarities between the worker and queen castes have led to experiments attempting to distinguish the characteristics of these two castes and how they are determined, though males have easily identifiable physiological characteristics. Since P. exclamans live in relatively small, open combed nests, they are often subject to predators and parasites, such as Chalcoela iphitalis, Elasmus polistis, and birds. P. exclamans have defense and recognition strategies that help protect against these predators and parasites.

<i>Polistes carnifex</i> Species of wasp

Polistes carnifex, commonly known as the executioner wasp, is a neotropical vespid wasp in the cosmopolitan genus Polistes, known for its extremely painful and potent sting.

<i>Polistes nimpha</i> Species of wasp

Polistes nimpha is a eusocial paper wasp found all over Europe, with particular sightings in Turkey, Finland, Estonia, and Latvia. It is also found in northern Africa, Pakistan, Iran, India, Kazakhstan, Mongolia, and China. The climate in these areas is relatively cold and snowy in the winter, while summers are usually hot and dry, with steppe vegetation. Polistes nimpha colonies are relatively small and easily manipulated.

Polistes atrimandibularis is one of three obligate social parasites among the Polistes wasps found in Europe. Of the three social paper wasp parasites, it is the smallest. It parasitizes multiple species such as P. dominula, P. nimpha, P. associus, P. gallicus, and P. biglumis. Females of P. atrimandibularis are unable to build a nest or produce workers, and therefore rely entirely on the host colony.

<i>Polistes semenowi</i> Species of wasp

Polistes semenowi is a kleptoparasitic paper wasp that is found in several regions of high altitude in Europe. As one of only three obligate parasites in the genus Polistes, it uses the nests of other paper wasps to rear its young. To evade detection by the host nest, P. semenowi employs mimicry by adjusting its cuticular hydrocarbons to match those of the host. Once the host nest has been infiltrated, the parasitic female physically attacks the host queen to subdue her and become the colony's new queen. P. semenowi displays several morphological adaptations for parasitism such as increased mandible size and an enlarged Van der Vecht's organ. This species is unusual because it does not have the ability to produce workers and is only able to produce individuals who have the capacity to reproduce..

<i>Polistes biglumis</i> Species of wasp

Polistes biglumis is a species of social wasp within Polistes, the most common genus of paper wasp. It is distinguished mainly by its tendency to reside in montane climates in meadows or alpine areas. Selection pressure from the wasp's environment has led to several idiosyncrasies of its behavior and life cycle with respect to its relative species in the genus Polistes. It alone among paper wasps is often polyandrous. In addition, it has a truncated nesting season that gives rise to unique competitive dynamics among females of the species. P. biglumis wasps utilize an odor based recognition system that is the basis for all wasp to wasp interaction of the species. The wasp's life cycle is highly intertwined with that of Polistes atrimandibularis, an obligate social parasite wasp that frequently invades the combs of P. biglumis wasps.

Polistes sulcifer is a species of paper wasp in the genus Polistes that is found in Italy and Croatia. It is one of only three known Polistes obligate social parasites, sometimes referred to as "cuckoo paper wasps", and its host is the congeneric species Polistes dominula. As an obligate social parasite, this species has lost the ability to build nests, and relies on the host workers to raise its brood. P. sulcifer females use brute force, followed by chemical mimicry in order to successfully usurp a host nest and take over as the queen.

<i>Ropalidia romandi</i> Species of wasp

Ropalidia romandi, also known as the yellow brown paper wasp or the yellow paper wasp. is a species of paper wasp found in Northern and Eastern Australia. R. romandi is a swarm-founding wasp, and manages perennial nests. Its nests are known as 'paper bag nests' and have different architectural structures, depending on the substrates from which they are built. The specific name honors Gustave, baron de Romand, a prominent French political figure and amateur entomologist.

<i>Polistes dorsalis</i> Species of wasp

Polistes dorsalis is a species of social wasps that can be found throughout various parts of North America. It is classified under the Vespidae within the genus of Polistes. Male Polistes dorsalis wasps can be distinguished from other Polistes species by their distinctly prominent median tubercle of sternum 7. Both sexes can also be recognized due to their v- shaped yellow markings on their head. They are distributed widely across North America and can be found in sheltered nests, typically closer to the ground. These wasps live in a dominance hierarchy in which the queen's role differs from that of ordinary workers. When threatened, these wasps can deliver moderately painful stings. Their venom might also be of human interest for their antimicrobial uses.

Polistes erythrocephalus is a species of paper wasp in the subfamily Polistinae of family Vespidae found in Central and South America. P. erythrocephalus is a eusocial wasp, meaning that it possesses both reproductive and non-reproductive castes. The cooperation between the two castes to raise young demonstrates the altruistic nature of these wasps. P. erythrocephalus exhibits a four-stage colony cycle, as do many other Polistes wasps. This species generally feeds on larvae, occasionally their own, and is preyed upon by species such as army ants.

<i>Melittobia australica</i> Species of wasp

Melittobia australica is a species of chalcid wasp from the family Eulophidae which is a gregarious ecto-parasitoid of acuealate Hymenoptera.

<i>Caenocholax fenyesi</i> Species of insect

Caenocholax fenyesi is a species of twisted-winged parasitic insects in the order Strepsiptera and family Myrmecolacidae. It has a sporadic distribution throughout North America, Central America, and South America. Chaenochlax brasiliensis is the only other named species in the genus.


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