Parischnogaster jacobsoni

Parischnogaster jacobsoni is a species of social wasp within Parischnogaster, the largest and least known genus of Stenogastrinae. It is distinguished mainly by its tendency to construct ant guards on its nests. Natural selection has led this wasp to have a thick substance emitted from its abdominal glands that allows it to protect its nest from invasions. Parischnogaster as a genus has been relatively unstudied; P. jacobsoni is one of the few investigated species because it has sufficient durability to live near human populations and it has demonstrated unusual resilience to pollution. While P. jacobsoni is a more complex organism than other wasps in Parischnogaster, the genus overall is relatively primitive with respect to social wasps as a whole. The French entomologist Robert du Buysson described Parischnogaster jacobsoni in 1913. The species has no common name. Most common in Malaysia, stenogastrine wasps like P. jacobsoni wasps are generally found in South-East Asian rainforests. P. jacobsoni falls within the genus Parischnogaster, which is one subset of the hover wasps, or Stenogastrinae. Its relatively primitive traits are key to describing the evolution of social behavior in wasps. P. jacobsoni, like all Parischnogaster wasps, has a wide, short head, though the width of its head is smaller than other Parischnogaster wasps. The larvae also present with much smaller salivary glands than larvae belonging to Polistes and Vespula species, indicating that trophallaxis does not occur with P. jacobsoni wasp offspring. Parischnogaster females present with shiny black or dark brown coloration, whereas males have gastral terga striped with white to mark them out during aerial patrols. Males of the species can be identified as distinct from P. nigricans serrei, their closest cousin, because of a knife-like spine in the center of the clypeus. The nests of P. jacobsoni generally reach their maximum size at 48 cells, and can house up to 6 females and 6 males, as well as a total of 33 larvae in a brood. P. jacobsoni wasps always use plant matter to construct their nests. They are composed of one or two linear rows anchored on a slim support or scattered across a flat surface. According to the theory that conserving material by utilizing wall-sharing cells and constructing structures to protect the nest are evidence of evolved wasp characters, P. jacobsoni constructs nests that are perhaps the most primitive of all wasp nests. It has almost no wall-sharing whatsoever, with cells scattered across the underside of a leaf. The nest, similar to that of P. nigricans serrei, differs particularly because the alveolar walls are adjoined to the neighboring cells and because pupal cells, instead of being sealed, are simply narrowed. Like all Parischnogaster wasps, P. jacobsoni builds nests rather than living in open habitats. However, P. jacobsoni generally has been found to build nests mostly in open spaces and even on or near man-made structures. The species is scattered throughout Southeast Asian rainforests and is most commonly found in Malaysia. Like all Stenogastrinae, wasps of P. jacobsoni prefer to nest in very humid environments in the rainforest, near streams or waterfalls, or on the surfaces of caves. They also can live near human settlements, which may explain, at least in part, why this species of Parischnogaster is one of relatively few that has been discovered. The foundation of each nest is generally by a single female founder haplometrotically. It is possible, rarely, for two females to cohabit a colony at its founding, but this scenario does not represent the norm. There are a limited number of females per colony, suggesting that the females tend to abandon the colony once they achieve a certain level of ovarian development. Nevertheless, because satisfactory sites for nidification are rare, there is a large number of females without colonies that are looking for a good region on which to found a nest, or a nest that they could strategically usurp. As a result, the rare cases where there are two females at foundation are more likely to be a form of usurpation rather than cooperation. Researchers have yet to perform long-term studies on P. jacobsoni; like most hover wasps, P. jacobsoni has not undergone long-term observation so there is only limited information on their colony cycles. Similar Parischnogaster species, however, demonstrate a five-stage colony cycle, with a pre-emergence period divided into foundation and initial nest segments, and a post-emergence period divided into young colony, middle-age colony and mature colony segments. The behavior of female P. jacobsoni include various interactions with other wasps including begging, dominance hierarchies, pursuit, avoidance, and aggression. As a result, the behavior of the wasp is to a large extent social. Dominant individuals in P. jacobsoni nests, for example, will cow subordinate wasps into submission as they crawl through their nests. Subordinates, in turn, attempt to avoid the dominant; however, when avoidance is impossible, they halt completely, turn their head to the side and, after being inspected by the antennae of the dominant individual (often considered to be a form of solicitation), emit fluid that the dominant often sucks up. Subordinate wasps often will flee interactions with the dominant wasp. Potential egg laying (PEL) females are less likely than other females to leave the nest and are also more dominant. Otherwise, they behave similarly to other females. Dominance in females is usually correlated with the size of their ovaries. Interactions between nestmates are relatively rare when compared to other wasp species; as a result, only the first ranks of dominance hierarchies are actually established and the females with low ovarian development do not participate in dominance at all. Relative to the other species of Parischnogaster, P. jacobsoni seems to demonstrate a higher relative level of complexity because it has relatively larger colonies, defined social hierarchies, and labor division schemes. In all Stenogastrinae wasps, division of labor is determined by dominance hierarchies based on some defining physical characteristic of the wasps in question. Particularly for the P. jacobsoni wasp, the reproductive capacity of the females in a colony determines the structured division of labor observed in their nests. The alpha female with the largest ovaries will remain in the nest for most of her day, limiting herself to patrolling the nest and asserting her dominance over the other wasps or resting. The females with very low levels of ovarian development will generally avoid the nest altogether. Rarely, this division of labor is reversed and females with developed ovaries are subordinate to those with less reproductive potential. This type of system occurs when old alpha females are ousted by younger ones. In addition, after the emergence of the first daughter, the original foundress may become a primary forager for the colony.