Polistes annularis

Polistes annularis (P. annularis) is a species of paper wasp which lives in North America. Its species name is Latin for "ringed" and it is known for its distinct red body color. It builds its nest under overhangs near bodies of water that minimize the amount of sunlight penetration.^[1] It clusters its nests together in large aggregations,^[2] and consumes nectar and other insects.^[3] Its principal predator is the ant, although birds are also known to prey on it.^[4] It is a primitively eusocial wasp, meaning that all individuals develop the capacity for reproduction, regardless of social caste.^[1] This primitive eusociality has been seen in bees as well, including the sweat bee, Lasioglossum zephyrum.^[5] As such, P. annularis demonstrates behavior typical of other polistine wasps, and has a dominance hierarchy, relatively small colony size, and a female-biased sex ratio. Unlike other wasps, P. annularis is relatively robust in winter conditions, and has also been observed to store honey in advance of hibernation. It is closely related to P. major, P. buysonni, and others in the subgenus Aphanilopterus, and slightly less related to the more common P. bellicosus, P. carolina, P. metricus, and P. fuscatus.^[6]

Description

While many other North American Polistes species show sexual dimorphism in coloration, P. annularis and P. erythrocephalus do not.^[7] This species differs from P. metricus in terms of the coloration of the antennae and thorax.^[7] There is geographical variation in coloration between northern and southern populations. In the north, the thorax of P. annularis has ferruginous (rust-red) markings on a predominantly black background, while in the south, the thorax is mostly ferruginous, with black markings.^[7] The legs also vary from black to ferruginous.^[7] In terms of size, the fore wings are 18.5–23.5 mm (0.73–0.93 in) long in females, and 17.5–19.5 mm (0.69–0.77 in) long in males.^[7] Both males and females are red-faced, which makes intersex determination less straightforward; however, it also makes it easier to recognize members of this species compared to other closely related species. Its initial metasomal segment is narrow, a feature that it has in common with P. bahamensis.

Identification

P. annularis is very similar in appearance to P. bahamensis. To distinguish P. annularis from P. bahamensis, one should notice that P. annularis has no yellow mark on its mesopleuron and usually also has no yellow apical tergum band. In addition, its mesosomal yellow markings show less development.^[8] Within the P. annularis species, reproductives and foundresses can be readily distinguished, as well. Reproductive females can be recognized visually because their wings are unworn, since they do not forage much (unlike the workers). In their abdominal cavities, large amounts of white-colored fat are stored beneath the intersegmental membrane.^[1] Foundresses can be discriminated from workers on the basis of their differential behaviors.^[2] Nests can be identified by their paper material and the way their cells are openly exposed to the external environment. P. annularis is also classified as a primitively eusocial wasp, which means that all individuals develop the capacity to reproduce over their lifetimes, whether or not they actually do so.^[1]

Mandibular gland and groove

The mandible is the insect organ for biting and crushing, analogous to the jaw in mammals. In the genus Polistes, the lateral mandibular groove is smaller in size than in other genera of social wasps. A common misconception is that the mandibular gland is the anatomical portion shaped like a sac. In actuality, the sac formation is the gland reservoir that feeds into the gland itself. The actual gland is pressed up against the sac surface. Gland cells are shaped like polygons. Like poisonous structures in formicine ants, gland cells are continuous with the gland reservoir, but no filaments extend from the gland or sac as they do in the ants. The sac is closest to mandible’s medial portion. A duct exits the sac. The duct opening is encircled by a sphincter muscle controlling the gland’s secretions. The duct is opened by sclerotized bars in conjunction with the hypopharynx. When the hypopharynx moves, pressure forms on the opening of the duct via the bars. When the bars dissipate this pressure, the duct closes.^[9]

Composition of nest pedicel, nest paper, and larval silk

The nest pedicel, which is the stalk by which the entire nest hangs from the horizontal face of the overhang, is made from a durable material composed of the wasps’ oral secretion. It has a nitrogen content of 11% and is mainly carbohydrates and proteins. Pedicel proteins are rich in glycine, proline, alanine, and serine. These amino acids are also found in the silks of other insects. Another minor component is N-acetylglucosamine, which is probably bound to the pedicel protein. Proline is a major component of structural proteins and likely contributes to the structural strength of the pedicel in holding up the rest of the nest. The pedicel suspends the nest high in the air and precludes many predators from getting close to the nest.^[10] However, birds often try to knock nests off the cliff, and colonies that hang low toward the ground can be attacked and eaten by raccoons.^[2] Cellulose makes up most of the nest paper. Larval silk is a protein with high amounts of serine and alanine. When larvae mature, silk is produced in their labial glands. Larvae spin cocoons that enclose themselves into their cell in the nest.^[10]

Surface lipids of wasps, nest, and nest pedicel

Members of P. annularis have cuticular hydrocarbons on the surface of their bodies that may serve as social recognition factors. These are composed of a complex mixture containing dimethylalkanes, n-alkanes, and monomethylalkanes. They are straight-chain and have methyl branches. The most common chemicals are 13,17- dimethylhentriacontane (18%) 3-methyl-nonacosane (13%), 3-methylheptacosane (11%), and n-heptacosane (8%). These serve to protect the wasps from dehydration. Their composition tends to be unique to each species of wasp. Hydrocarbons are present on the surface of workers, males, eggs, and larvae, as well as the surface of the nest and its pedicel. The lipids in the nest paper probably function in kin recognition among workers, while those in the pedicel likely deter predators. The free fatty acids of the pedicel induce the necrophoric response in ants, which causes them to avoid the pedicel rather than cross over it and prey on the nest’s inhabitants. In ants, the necrophoric response is defined as the behavior of recognizing dead colony members and carrying them to a refuse pile away from the nest. Adult males have the hydrocarbon compounds as the workers, but they are present in different amounts. In males, the most common component is 3-methylnonacosane (21%); in eggs, 3-methylnonacosane makes up 23% of lipids; in larvae 13- and 15-methylnonacosane are the most common (15%). Nest paper and pedicel have much larger hydrocarbon units, between 27 and 31 carbons in length. The pedicel also contains hexadecanoic acid and octadecanoic acid.^[4]

Model species for maternity assignment

P. annularis has been used as a model species to investigate the power of microsatellite markers in maternity assignment of social insects. Historically, maternity assignment has been problematic in social insects for several reasons: 1) Possible mothers are usually related so their offspring are highly genetically similar. 2) The real mothers may already have died, increasing the risk of assigning offspring to the wrong surviving mothers. 3) The father’s genome is inaccessible because males mate and pass away before their offspring are even born. Microsatellite markers have been demonstrated to nullify these problems in P. annularis. They are single-locus, codominant markers that vary dramatically for number of simple sequence repeats. They can be readily amplified using the polymerase chain reaction, and the samples of DNA can be minuscule. This allows scientists to access the genotypes of very young embryos and even sperm from spermathecae. Through the genotypes of stored sperm, alleles of dead fathers are recovered. They can then combine these data with the maternal genotype to improve the accuracy of the maternity assignment.^[11]

Taxonomy and phylogeny

The first description of P. annularis was published by Carl Linnaeus in his 1763 Centuria Insectorum, where he named the species Vespa annularis.^[12] It was moved to the genus Polistes by Johan Christian Fabricius in 1804, two years after Pierre André Latreille had erected the new genus.^[13]

P. annularis is classified as part of the kingdom Animalia, the phylum Arthropoda, the subphylum Hexapoda, the class Insecta, the order Hymenoptera, the suborder Aculeata, the superfamily Vespoidea, and the family Vespidae. Its subphylum Hexapoda indicates it has six feet; the order Hymenoptera includes ants, bees, wasps, and sawflies; the Aculeata include ants, bees, and stinging wasps in particular; the Vespoidea include yellow jackets, hornets, paper wasps, potter wasps, mason wasps, and pollen wasps. The genus name Polistes is most likely derived from the Greek polistes (πολιστης) which is translated as “founder of a city”. The species name annularis is the Latin word that means “ringed”. A common name for P. annularis is the red paper wasp, due to its distinctive red coloration.^[8]

P. annularis is placed within the subfamily Polistnae (paper wasps), which is the second-largest of the subfamilies within the Vespidae. The Polistinae contain two main behavioral groups: wasps which form nests with large number of workers, and those wasps which found nests with few workers and foundresses (the latter including P. annularis). This subfamily likely arose in the mid- to late Jurassic period, around 145 to 175 million years ago. P. annularis diverged from P. bellicosus between 10 and 80 million years ago.^[6] It is currently placed in the New World subgenus Aphanilopterus.^[14]

Distribution and habitat

P. annularis is found across the eastern United States from New York to Florida, and west to a line from South Dakota to Texas.^[7] This range is similar to that of P. exclamans.^[15]

P. annularis forms its nests on the branches of trees and shrubs, as well as in sheltered parts of some buildings.^[7] However, it is also known to group its nests in large colonies called aggregations. These tend to be built on the underside of overhangs (rocky cliffs, for example) in close proximity to bodies of water. Ideally, the overhanging structure should block exposure to sunlight for most of the day. In the natural environment, P. annularis prefers cliffs by riversides. A limiting factor to nest building is the presence of a suitable overhang that minimizes sun exposure.^[2] The nests differ markedly from those of other species in the genus Polistes. They are much larger, with around 500 cells, and are wide, rather than the slender, elongated nests seen in some other species.^[16] P. annularis lives in nests made of paper that have cells exposed to the external environment. The word “cells” is used to describe the room-like excavations or depressions built by the foundresses and workers that house the wasps, their larvae, and their food stores.^[1]

Colony cycle

Founding the nest

In the springtime, mated females called foundresses join together in groups to start a new nest.^[1] They emerge from cracks within the rocky cliff wall where they have spent the winter in hibernation, and return to their natal nests from the previous fall season. They initiate construction of wholly new paper nests,^[2] normally only a few meters away from the natal nest of the foundresses, and the group of foundresses usually consists of females from the same natal nest. Groups of foundresses are termed “associations”, which vary in size, but they can vary from one (a sole foundress) to as many as 22 foundresses cooperating together to found a new colony (nest), with five females on average. Each of the foundresses has spermathecae that are fully loaded with sperm, since they have just mated the previous winter. Their ovaries are full of mature oocytes. Of all the foundresses in an association, only one foundress assumes the role of queen.^[1] This occurs promptly once the nest has been initiated, and at this time the foundresses establish a dominance hierarchy among themselves. The most dominant foundress becomes the queen.^[2] She lays the vast majority of eggs in comparison with the other foundresses. In the meantime, the other foundresses serve as foragers and nest-builders. They manage the nourishment and physical defense of the brood of larvae that are developing in the nest, until the larvae pupate and finally emerge from their pupae as the first generation of workers. At that point, the co-foundresses have finished their work of foraging, and remain on the nest from then on.^[1]

Colony offspring

The first generation of offspring is composed mainly of female workers, but some males may be present. The appearance of males in the first brood varies from nest to nest. Only in subsequent generations (after the first generation of offspring) will some offspring develop as reproductives: females first, then males.^[1] Generally, several generations of female worker offspring emerge (hatch) from the nest over the course of the summer, and then reproductives start to be produced.^[2] Reproductives tend to emerge about one month before the nest is empty of developing brood. A few days after males emerge, they leave their natal nest. The probability of a given female developing as a worker or as a reproductive likely depends more on ambient conditions than on predetermined factors. Although the probability is very low, a worker herself can eventually mate and assume the role of queen in the event that all foundresses of the nest die or leave permanently. Between mid-July and mid-October, P. annularis nests arrest their brood production.^[1]

After brood-production

During the fall season, females prepare for winter by collecting nectar. This is stored in highly concentrated form in the cells of the nest. During the winter, P. annularis abandons its nest and resides in hibernacula, which are locations of shelter at which animals hibernate. On warmer days during the winter, females of P. annularis fly back to their nests to consume their stored nectar (which is now honey) and to interact with their nestmates. In early January, reproductive males and females commence mating at the hibernacula. In the following spring, foundresses are observed to retain association with their nestmates from the natal nest of the previous autumn.^[1]

Variations in the colony cycle

P. annularis has been found to exhibit slight variations in its colony cycle from year to year based on environmental conditions, in part due to the ability of females to switch castes. Typically, the largest and top-ranking female founds a nest and lays the largest percentage of eggs, while subordinates forage. After workers emerge from the eggs, many of the subordinate foundresses disappear; the nest usually loses its original queen before more eggs can be laid at the end of the season. A worker with fully developed ovaries takes over the nest and becomes a gyne. Earlier queen death corresponds to an earlier arrest in rearing brood, which may be due to a decrease in relatedness between the new queen and the nascent females, or due to internal conflict on the nest. Additionally, if resources decrease, such as during a drought, brood rearing ends sooner than in more prosperous years, and females choose to become gynes as opposed to workers. Many of these variations can be rationalized via relatedness.^[17]

Miscellaneous factoids

P. annularis queens have the tendency to outlive all of the subordinate cofoundresses of their associations. Over the course of the colony season, the number of mated workers with the ability to lay eggs increases, while queens’ dominance shows a trend of becoming stronger and more pronounced. In general, foundresses have greater inclusive fitness if they are associated with smaller colonies. Notably, lone foundresses (with no other foundresses in the association) tend to produce far more offspring than do the subordinate co-foundresses of other nests. The ability of a foundress to found a nest on her own is likely in correlation to the length of her wings (her body size), the mass of her dehydrated body, and the mass of her body fat. At nighttime and in the early morning, P. annularis’ entire female nest population is located on the nest.^[1] The moment that a foundress is established in the association of a new nest, she will from then on never leave that nest and join up with foundresses of a separate nest unless her proper nest is wrecked. In the event of a destroyed nest, a foundress may occasionally enter into the association of another nest’s foundresses who originally came from her same natal nest.^[2]

Behavior

Dominance hierarchy

P. annularis, a eusocial animal, demonstrates a dominance hierarchy, due to group competition over scarce resources.^[18] Within a colony, certain wasps will chew on or attack others to demonstrate power. Individuals that are ranked differently demonstrate different behaviors; higher ranked wasps have a propensity for “tailwagging” and “checking cells” as compared to lower ranked workers, similar to Polistes dominula.^[19][20] Workers have been observed to forage for caterpillars more often than queens. Queens, the highest ranked individual in a nest, will usually lay the highest percentage of eggs, though subordinates are sometimes allowed to lay eggs as well. Should a foreign organism attempt to land, a female on the nest will engage the arriving wasp with her antennae. This clash may last for several minutes and may escalate into grappling. Queens are more active on larger and newer nests. Many of these behaviors are the result of high reproductive competition between females.^[21] Despite the hierarchy and its dependence on queen size, larger queens do not necessarily inhibit egg laying by subordinates better than smaller queens. However, queens do develop far larger and more developed ovaries than their subordinates, and often have more mature eggs within.^[22]

Proportional variation

Much of P. annularis’s dominance hierarchy is dependent on dry weight, residue weight, wing length, and fat content. Females from different nests exhibit considerable variation in these factors, while females originating from the same nest are quite similar to each other in these factors. In some cases, the queen may be smaller than some of the worker wasps on the nest, weighing less and having a lower fat content, though this is atypical. Heavier wasps, as well as those with more fat content, typically have greater ovarian development; dry weight is typically more correlated with ovarian development than any other parameter.^[23] Ovarian development has been correlated with dominance hierarchy in other polistine wasps, Polistes gallicus and Polistes metricus.^[24]

Foundress grouping

Group nesting is especially prevalent and varied in P. annularis, with reports of foundresses per nest ranging from one to 28, with an arithmetic mean of 3.82 to 4.93, depending on the year. However, variation by year only explains 2% of the variance in the grouping size of foundresses. Only a small number of queens run a nest without a partner (about 5%), while about three-quarters of foundresses become subordinate to a queen on the nest. This species only become foundresses with other wasps if they were born in the same nest. Large aggregations of foundresses are seen when females reuse the nest in which they were born, either by reusing the cells themselves (uncommon) or by building a new nest on top of the old one.

Impact of association size on colony success

Where females reuse the natal nest, between seven and eight foundresses typically may be seen on the nest, a significantly greater number than those seen on new nests (4.34).^[25] Foundress number plays a major role in determining the success of a colony. Colonies are on average 60 to 65% successful at producing workers and reproductives, respectively. However, nests with one foundress are only 20% successful at surviving until workers emerge. Nests with four or more foundresses have an 80% chance of success. Strangely, the inclusive fitness of subordinate foundresses is lower than their fitness in the case where they established a nest alone; it remains unclear why such subordinates do not leave the nest to establish their own. They may be “making the best of a bad job”,^[26] though evidence to indicate this is scant.

Foundress eviction and mortality due to worker emergence

Multiple foundresses may create a nest; some studies have shown that four or five foundresses may inhabit a P. annularis nest.^[27] However, selective pressure tends to eliminate any additional foundresses once workers emerge. This is due to multiple factors. First, given the scarcity of space and resources, the foundresses compete with each other to raise the best offspring. In addition, workers can perform all the same functions as foundresses with minimal competition. Lastly, the relatedness between workers and their eggs versus those of the foundress - workers would be more related to their sisters than their own offspring. These factors may combine to result in the expulsion of the subordinate foundresses. Such behavior was first seen in another polistine wasp, P. gallicus.^[28] Subordinate foundress mortality has been found to significantly increase following worker emergence when compared to mortality rates prior to worker emergence. This pattern is also observed in P. exclamans and P. carolinus, but not P. bellicosus. In some of these species, including P. annularis, subordinates decrease foraging rate following worker emergence.

Effects of senescence and aggression

Unlike other polistine wasps, P. annularis tends to more severe consequences after worker emergence, despite this change in behavior. This puzzle is currently unsolved, though it may deal with senescence. Decreased foraging also accompanies decreased aggression. Comparing across polistine wasps, foundress eviction is generally independent of rate of usurpation; P. annularis has a usurpation rate around 9%. When all foundresses are evicted, colony failure rate is high; in nests where multiple foundresses are evicted, around 19% of nests fail, but when only one foundress was originally present, almost 80% of nests fail. When pupae appear, queens are less aggressive towards their subordinates, as compared to the times at which only larvae are present.^[27] Some other social insects, such as ants, evict queens,^[29] while others, such as termites, seem to permit multiple queens.^[30]

Queen determination, behavior, and succession

In the absence of a queen, dominance conflicts arise between foundresses on the nest. Wasps routinely attack each other over a several-week period, and certain wasps eventually remit, leaving room for a new queen. Subordinates may then be chased from the nest. During the competitions, cell construction has been observed to stop, as well as oviposition.^[31] The new queen will lay more eggs than her cofoundresses, and dominate them as explained above. In so doing, she causes the ovaries of other workers to decrease in size, to the point that they will be eliminated following the hatching of new workers. The queen lays eggs, while the other females are constrained to laying eggs solely at the beginning of the association of the group.^[32] The queen may lay up to 55% of eggs, while her direct subordinates, named beta subordinates, lay most of the remaining eggs. Should the queen disappear, the previous beta subordinate takes over as the new queen, leading to increased aggression, which may result from the competition to lay eggs. When a foundress succeeds as the new queen, no additional aggression is observed, but if a worker becomes queen, aggression rises, likely because the dominance hierarchy is not as well established on these nests. Often when the queen dies, the oldest foundress succeeds her, due to her size and dominance in the nest. Despite aggression after the removal of a queen, brood care does not decrease.^[33]

Sex ratios

Other species of Polistes exhibit a female-biased sex ratio due to the 3:1 relatedness between sisters, while still other members of the genus have a virtually unbiased sex ratio. Northern wasps tent to have biased ratios, while southern wasps are less biased, in large part because southern wasp sisters have lower relatedness. Since the relatedness between sisters in P. exclamans is 0.39, and since P. exclamans and P. annularis have similar geographic distributions, one may presume that the sex allocation patterns of P. annularis follow that of P. exclamans.^[34]

Members of the brood are highly related to the queen, but are less related to the subordinates and their mates, aligning more with a 1:1 sex ratio. As such, it is to the benefit of the wasp to be a reproductive queen as opposed to a worker, if feasible.^[35]

Honey caching

P. annularis was the first wasp which did not form large colonies to be observed storing honey in the autumn. The wasps store the honey over the winter to facilitate their survival in colder months and assist in the recognition of sisters, which will help construct new nests near their original one. The caching begins in early to midautumn, after which time the wasps retreat from the nest to hibernacula when the temperature drops below about 5 °C. They return to the nests when the weather permits, such as on warmer days. This behavior exposes P. annularis to attack from other insects of the same species, wasps of other species, such as those of the genus Vespula, and from mammals. However, Polistes species have evolved to hide their nests from most mammals or put them in areas as to make them inaccessible. Invading insects are attacked. Despite the fact that birds are common enemies of polistine wasps, none has been observed attacking nests for honey.^[36] The wasps may either gorge on the honey, or ration it, given that they are social insects. Additionally, wasps with nests containing honey are significantly more likely to survive the cold winter than those wasps whose nests do not contain honey.^[37]

Winter behavior and cold hardiness

Despite morphological similarities,^[38] queens and workers exhibit different behaviors over the winter. Queens overwinter, whereas workers do not. This difference in behavior may be s a direct consequence of the dominance hierarchy. Experimental treatment of wasps to cold conditions resulted in increased trehalose in both sexes, though females also increased levels of glucose and fructose, while males maintained or decreased these levels. Wasps at normal foraging temperature showed significantly lower carbohydrate levels than wasps treated at colder temperatures. In addition, exposing P. annularis to low temperatures over a two-week period caused many workers, but no foundresses and few males, to die. Foundresses appear to have greater glycogen storage capability than workers, helping them survive low temperatures. Males often have higher glucose, fructose, and trehalose levels higher than those of queens, indicating that mating may continue into autumn or winter. P. annularis cannot tolerate frost, though it has been shown to be able to survive at temperatures below the minimum temperature in the area in which it resides.^[39]

Pre-nesting aggregations

As new nests are established by P. annularis, many behavioral characteristics from the prior nest are taken to the new one. Notably, related siblings tend to aggregate together and go to the same nest. However, unlike in other Hymenoptera (eusocial insects), these wasps tend to act as independent agents; while the queen is at the top of the dominance hierarchy, the other wasps may lay eggs and forage for themselves as they see fit. As queens or foundresses evict other females, the aggregations begin to dissolve.^[40]

Nest construction and site selection

Characteristic design of a paper wasp nest

P. annularis females select a new nest site every year; they never use the same nest twice. The site is often within several meters of the previous one. Nests have been seen on cliffs and buildings, and less commonly in trees and on shrubs. Occasionally, wasps construct a new nest on the face of the old one, but they do not use the old one to store larvae. The old nest probably is not reused because it is often damaged, dirty, and parasitized in the late summer or winter. Other animals, such as moths, may use the empty nest during the winter.

Being a paper wasp, P. annularis gathers wood fibers to construct the new nest. The queen typically remains on the nest while subordinates search for wood. Fibers are often acquired by scraping the surface with the mandible, and mixing the resulting fibers with saliva to create a pulp. The pulp is added to the nest in a consistent manner.^[40]

Kin selection

Kin recognition and discrimination

When it comes to identifying how related a worker is to other workers, in P. annularis, this ability seems to be largely absent, or they are unable to make use of it to good effect. This comes at the cost of being able to especially aid closer relatives and thereby improve inclusive fitness. A super-sister relationship is one where sisters come from the same set of two parents (the same mother and father). Another way to consider this relationship is that they are full sisters instead of half sisters. Super sisters are related to each other genetically by three-fourths due to the specific sexual reproduction process among the Hymenoptera. Nonsuper-sisters have much lower relatedness by comparison. Therefore, preferentially helping one’s super-sisters is much better for inclusive fitness, but P. annularis seems not to follow this behavior when deciding which spring nest to join. The novel nests in springtime come from the same natal nests of the preceding fall, and generally the population of wasps in a new nest all have the common background of being from the same natal nest, but when two or more spring nests are derived from the same fall natal nest, workers may choose whichever nest they wish to join in the spring. Strangely, it seems, they do not show any preference for the nest whose members to which they are most genetically related.^[41]

Costs and benefits of colony aggregation

For several reasons, P. annularis tends to form nests in crowded clumps. The species prefers overhangs that minimize sunlight exposure and flooding, and are near a body of water. This constraint means only a few locations are suitable for nesting. Consequently, aggregations of multiple nests tend to form on the same overhang in a very crowded manner. One cost of this crowding is direct reproductive competition between colonies. This takes the form of a usurpation of the current colony queen by a female from another colony. A foreign female can arrive at the nest, fight the reigning queen to the death or until the current queen is banished or becomes a subordinate, and then takes over the role of reproducing the majority of offspring in the colony. No selfish herd advantage is seen for a colony to be in the center of the aggregation, whereby the center would be safer than the periphery from predators, whereas in Ropalidia plebeiana, another species that forms nest aggregations, the entire nest aggregation is protected more so from predators.^[42] However, the cost of reproductive competition is increased for colonies in the center of the aggregation relative to colonies closer to the edge. Also, no advantage exists for a new colony to be established in close proximity to its preceding natal colony. P. annularis seems to nest in aggregations only because viable nesting locations are greatly limited.^[2]

Altruism

As with many other species in the Hymenoptera, as well as other polistine wasps,^[43] P. annularis has been noted to engage in altruistic behavior. For example, despite the lack of drastic morphological differentiation between workers and foundresses, and the benefits procured by a worker becoming a foundress on a new nest, a worker may lay less than 10% as many eggs as her queen, independent of the number of females on the nest. This results in vastly decreased inclusive fitness for the worker and greatly increased inclusive fitness of the foundress, even if the sisters are related by a factor of 0.75, the maximum possible relatedness for outbred sisters. The workers acting in such a manner may create a direct cost upon which selection can act. However, evidence for this has been scant, and researchers are currently investigating why and how such levels of altruism are sustained in P. annularis.^[44]

Diet

Due to the dominance hierarchy, the queen leaves the nest as little as possible, and has the other wasps forage on her behalf. In small groups of wasps (two to three foundresses), the queen may be forced to forage. As workers emerge, they take over the role of foraging. P. annularis preys on moths, butterflies, flies, and other insects. Unlike other wasps in the genus, P. annularis generally takes its food from wooded areas, and not from fields. However, prey represents only 20% of food resources; the other 80% is liquid.^[45] P. annularis preys on caterpillars from a large number of lepidopteran families, including the Arctiidae, Saturniidae, Geometridae, Limacodidae, Lymantriidae, Notodontidae, Nymphalidae, Sphingidae, Erebidae, Noctuidae, Amphisbatidae, and Elachistidae.^[7] P. annularis tends to forage primarily in trees.

Predators, parasites, and defense

Ants, birds, and raccoons are predators of P. annularis.^[2] The principle predator is the ant.^[4] It is parasitized by Elasmus polistis and the moth Chalcoela iphitalis.^[2] P. annularis defends itself with venomous stingers. Antigen 5, which is present in their venom, is a major allergen.^[3] The nest pedicel contains lipids that provoke a necrophoric response from ants, protecting the nest from ant invasion.^[4]

See also

• Characteristics of common wasps and bees
• Vespula vulgaris (common wasp)

References