Vespa borealis, Vespa arborea, Vespa biloba, Vespa infernalis, Vespa tripunctata
Vespula austriaca is an obligate parasitic wasp, parasitizing the nests of other species in the genus Vespula. Its common host species include V. acadica in the United States and V. rufa in Europe, Japan, and East Siberia. It is sometimes called the cuckoo yellowjacket wasp due to its inquiline lifestyle. V. austriaca wasps pollinate orchids. They differ from other parasitic wasps in their intensely aggressive behavior during invasion and occupation of the host colony. Several morphological adaptations such as bigger body parts and more curved sting shafts are observed in these wasps to aid their aggressive parasitic behavior. Once they occupy a host's nest, V. austriaca are known to engage in mauling and chasing of host workers and forced trophallaxis. Larvae will feed on spiders and other insects. Female wasps will also force host workers to feed and take care of their brood[how?].
- 1 Taxonomy and phylogeny
- 2 Description and identification
- 3 Distribution and habitat
- 4 Colony cycle
- 5 Parasitic behavior
- 6 Invasion
- 7 Post-invasion: parasite and host worker interactions
- 8 Diet
- 9 Characteristics of the venom
- 10 Human importance
- 11 Reproduction
- 12 References
Taxonomy and phylogeny
Vespula austriaca is a member of the family Vespidae. The genera Vespula and Dolichovespula are thought to be closely related and are considered sister groups. Their similarities include absences of strong seta on third segment of labial palpuls, smaller scutal lamella, and a characteristic twisted pedicel in embryo nests. Furthermore, Vespula vulgaris is similar to V. austriaca and is considered a sister species. Parasitism of V. austriaca is an autapomorphy.
More recently the Nearctic population has been proposed as a separate species due to sculptural differences in the quenns between the Nearctic and Palearctic populations. The name Vespa infernalis which was coined by de Saussure in 1854 has been put forward as the scientific name for the Nearctic species.
Description and identification
This wasp is an obligate social parasite. As a result, it possess special morphological adaptations to take over host colonies. These adaptations include larger body parts such as a larger head width than its host Vespula acadica. V. austriaca also has a wider interocular (space between the centers of rotation of the eyeballs) distance, longer mesonotum, longer forewing (anterior wings), longer gastrula tergum, and an overall larger front femur. Because of its parasitic lifestyle, V. austriaca has a large stinger with very curved sting shafts; this curving allows the parasitic wasp to puncture through the intersegmental membranes of host colony workers who are defending their nests.
The male abdomen is longer with thick lateral black bands while the female abdomen is wider with fewer lateral black bands and black dots. V. austriaca wasps have a characteristic black and yellow coloring throughout their bodies. Irregular margins and narrow yellow marks on the scape are often used to identify Vespula austriaca.
Distribution and habitat
Vespula austriaca is found in the Holarctic region, including Japan. Its distribution extends to the Boreal region of North America. The species is not considered rare and is stable throughout its range. These wasps are seen throughout all the provinces and territories of Canada and in certain states in the United States. (Alaska, New Jersey, Michigan, Wisconsin, North Dakota, New Mexico, Arizona, and California). They are also found in Palearctic region including Europe to Kamchatka, Japan and northwest China, Turkey, northern Pakistan and northern India. In Europe,V. austriaca is most common in Ireland and Scotland. Surprisingly, its distribution does not completely match that of its hosts.
As an obligate parasite, these wasps do not build their nests. As a result, the queens will hibernate longer than their host queens. This ensures that the nests will be ready when they leave their hibernation spots.
This wasp is known as a labor parasite. Their lifestyle depends on invading and usurping other colonies. First, females kill the queens of the host colony and force the host workers to care of their offspring. As an obligate parasite, Vespula austriaca wasps lack a worker caste and the ability to build their own nest. After killing the host queen, the female V. austriaca tends to be aggressive towards the host workers who rear her brood. As a result, the inquiline wasp will hibernate and only emerge at a certain time when it knows its host is active. These wasps have very short seasons with flight periods from June to mid July and August to mid September.
Vespula austriaca parasitizes European hosts Vespula rufa and Vespula acadica. Near the dorsal edge of V. austriaca, there is a fourth marginal tooth whereas the host, V. acadica does not. When researchers dissected individuals of V. austriaca, they found that they had larger, sturdier mature muscle bundles in abdominal sterna and tergum than the muscles in a queen of V. acadica. As a result, it was more difficult to dissect V. austriaca.
A significant morphological adaptation mentioned before of V. austriaca is that they have a wider head. This suggests larger mandibular muscles. These muscles along with the snout mandibles are key in usurping a host’s colony. It equips the wasp with an advantageous offensive weapon.
Another adaptation of V. austriaca is that they have stout legs making them stronger and robust like. This adaptation is helpful during initial stages of colony invasion because V. austriaca wasps are subject to scratching and tearing by host workers.
Sharp clypeal (plate in front of insect head) teeth is another characteristic of this species that enables their parasitic lifestyle. Vespula austriaca takes advantage of hosts such as Vespula rufa from East Siberia, Europe, and Honshû Japan. Nests of V. acadica were found to be smaller than normal due to the parasitism of V. austriaca.
Queen-reared worker stage
When a female V. austriaca wasp invades a host’s nest such as Vespula acadica during the queen-reared worker stage, the usurpation can be divided into two phases. The first phase is preusurpation. During this phase, interactions between the intruder and the host queen could be relatively calm and civil or aggressive. The queen may ignore the intruder and refrain from firing an attack first. Likewise, the workers exhibit a similar behavior like their queen. But if the intruder attacks first by mauling or attempting to sting a worker, interactions between the queen and intruder become intense. The parasite, if successful, will use its stinger to paralyze the head, thorax, and legs of the host queen. This stage is considered the most vulnerable and hence, the most popular time to invade. It is susceptible to invasion because both the queen and workers are less defensive.
Post-emergence colony stage
During this stage, the colony is larger. In one experiment, a Vespula austriaca female wasp was allowed to invade a Vespula atropilosa colony. Different from the queen reared worker stage, the workers in this stage were much more defensive; more aggression was observed in the form of stinging, mauling and chasing. Additionally, the parasite displays more aggression than the host’s queen. During a fight between the parasite and the queen, the parasite will do anything to harm or gain a better position by using her mandibles and stinger. Injuries to the queen include but are not limited to broken antennae and injured fore and hind-leg. Surprisingly, the host queen retracted from using her mandibles whereas the workers were quick to use theirs in defense.
Post-invasion: parasite and host worker interactions
Once the invasion of a host nest is successful, V. austriaca will take over the nest, inspecting and patrolling the cells. Interestingly, the host workers will avoid the parasite and the colony, ignoring any colony duties. In response, the parasite will maul and chase the workers. While there is tension, a Vespula austriaca parasite does not sting the workers and does not engage in egg eating (oophagy) once it has successfully invaded. A suggested strategy may be to kill older workers of the host colony first and leave the younger workers behind to take care of the brood. During this period, a female will assert her dominance over the younger workers.
This obvious display of dominance by the parasite over the host workers is more common during early colony occupations and absent later on. The parasite displays mauling behavior: it grabs the workers with its legs and chews on their dorsums. Furthermore, the parasite also displays mauling behavior after trophallaxis, which it initiates by soliciting and chasing a worker." Unfortunately, the worker will remain defenseless during mauling. Many would agree that coexistence is not possible because Vespula austriaca wasps are very hostile and aggressive in invading and killing or driving away the host queen. Vespula austriaca wasps are also very selfish. They rarely forage, build cells, feed larvae, defend the colony, and thermo regulate. The workers participate in fanning during hot temperatures or warming postures during low temperatures. Furthermore, even when a nest is dislocated, the parasite will remain inside the nest rather than help the workers defend it.
Suppression of reproduction of host workers
Several signs indicate that the inquiline Vespula austriaca wasps participate heavily in repressing the reproduction of host workers. The most obvious one is that there are no worker ovipositions in nests of Vespula acadica parasitized by Vespula austriaca wasps. Secondly, if workers were ovipositing then there would be higher levels of aggression between workers. However mauling was reduced between workers. As mentioned before, frequent aggressive and assertive behaviors in parasites aid in asserting reproductive monopoly. Another indication is that parasites are observed to patrol cells frequently, hence defending oviposition sites. Lastly, during gastral dragging (dragging of abdomen across comb), substances that prevent oogenesis in workers are said to be released from the Dufour’s gland of the parasite.
While other wasp queens depend on secretions from larvae for food, Vespula austriaca parasites obtain their nourishment in the liquid form through solicitations and trophallaxis of host workers. They rarely solicit larvae for nourishment. The parasites will often use force to obtain what they need. During forced feeding, the parasite will grab the host worker using its forelegs to reel in the worker. More forceful behavior includes pushing the host worker against a comb of the nest. While some parasitic behavior (i.e. maulings) only occurs during early post-invasion stages, forced trophallaxis behavior occurs throughout. Towards the later stages, the intensity of forced feeding declined, leading to host workers escaping forced encounters. Usually forced trophallaxis encounters were short lasting from 1–5 seconds. But some encounters lasted for as long as 43 seconds. Lastly, the larve of Vespsula austriaca obtain nutrients from insects and spiders.
Characteristics of the venom
Due to the parasitic lifestyle of Vespula austriaca wasps, the sting is a vital apparatus. It consists of the shaft, aculeu, Dufour’s gland, and the venom glands. The Dufour’s gland and venom reservoirs are the biggest among Vespula austriaca females. In an experiment where the oily venom extracted from V. austriaca wasps was injected into Vespula pensylvanica workers, the lethality (LD50) value was between 20 and 30 mg/kg. V. pensylvanica queens had a higher tolerance to V. austriaca venom than the workers did (LD50=81 mg/kg). On average, it took 18.6 μg of venom to kill about half of the queens and 2–3 μg of venom to kill half the workers. The venom has the ability to paralyze and impair activities such as flying. Material obtained from the Dufour’s gland was also injected into V. pensylvanica wasps; no significant effects were observed, indicating the gland does not contain a poison. Generally, in order to kill a host worker, a V. austriaca wasp has to use about a third of its venom supply. More venom is needed to kill a queen. Surprisingly, V. austriaca venom is as lethal as the venom from Vespula atropilosa and V. pensylvanica.
These wasps are not considered a pest. But one of its hosts, Vespula rufa is a pest because it frequently enters buildings. Considered a nuisance, one Vespula austriaca wasp was found in a shipping container. In 2002, a new wasp controlling pesticide was invented to kill Vespula austriaca wasps early before they have a chance to sting someone. The main ingredients of this pesticide include pyrethroid compounds and saturated hydrocarbon. Previous repellents were too weak to target a large number of wasps.
In preusurpation V. austriaca individuals, Dufour’s gland contains clear oil material. It is part of the reproductive organs along with the ovaries and a poison gland. Distinctly enough, in new fall parasites, the Dufour’s gland was empty and flat and in older parasites, the gland had a little oil but flatten as well. Hypertrophy of the Dufour’s gland is known to occur but more evidence is needed. During and after the mauling period, female Vespula austriaca wasps will oviposit. This time period is brief. The females insert eggs in new cell combs. Workers act no differently during period of oviposition. However, one instance of a worker interrupting the oviposition of the parasite was recorded, which led to mauling of the worker by the parasite and the egg falling out of the designated cell. Eggs laid by Vespula austriaca females are not only found in cells but also found on the cell wall, exterior of the comb, between two cells, or along the caps. As mentioned before, the Vespula austriaca species do not produce any workers. Instead the queens lay eggs that eventually produce more queens and male adults. Normally in wasps, males move in swarms during mating season. A male Vespula austriaca male was seen hovering over a fig tree in Ireland.
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