Polistes exclamans, the Guinea paper wasp, is a social wasp and is part of the family Vespidae of the order Hymenoptera. It has been found in Ontario, Canada and the eastern United States from Illinois down south to Florida and west to Nebraska and California. It is also found in Mexico from Chihuahua to Jalisco, Hidalgo. P. exclamans has shown variability in its range including an absence of the species in eastern Missouri from the 1920’s to 1940’s, a presence in the 1960’s to 1980’s, and an apparent absence again of the species in these same sites in eastern Missouri since 1989. This suggests that their range has either expanded northward and contracted southward or that they have large, long-term cycles of abundance. 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.
Taxonomy and phylogeny Polistes exclamans is part of subfamily Polistinae within the hymenopteran family Vespidae. Polistinae (paper wasps) is the second largest of six vespid subfamilies, containing around 950 species, and is composed entirely of social wasps. It is made up of four tribes; P. exclamans is part of tribe Polistini. Genus Polistes is currently split into four subgenera that are distributed across the world; P. exclamans is a part of the New World subgenus Aphanilopterus and is most closely related to P. annularis, P. buysonni, P. canadensis, P. lanio, P. cavapyta, P. simillimus, P. crinitus, P. versicolor, and P. instabilis.
Description and identification
There are two forms of Polistes exclamans in the United States: typical and variable. The typical form is found in the south-eastern United States and inhabits the following states: North Carolina, South Carolina, Georgia, Alabama, Florida, Texas, Louisiana, Oklahoma, Arkansas, Kansas, Colorado, and Arizona. Although this form's color can vary, it almost always has some yellow coloring. Both the propodeum and the mesonotum are marked with yellow. The propodeum normally has four yellow stripes, whereas the mesonotum has yellow lines. It also may have yellow markings on its head.McIlveen & Hamman. "Paper Wasp". Texas A&M Agrilife. Retrieved 6 December 2012. The wings, however, are not yellow in color or yellow tinged like some other wasps but are infuscate and purple in color. The typical form often can be confused with Polistes fuscatus, Polistes crinitus, or Polistes minor. The variable form is red-brown in coloring. The middle of the flagellum, the base of the abdominal segments, and the outer side of the mid and hind tibiae are infuscate or black colored, as are the wings. Instead of yellow markings, the variable form has pale ivory-white markings that are dispersed throughout the body. P. exclamans have antennae banded with red, black and yellow, while most paper wasps only have one antennae color. In females, the fore wing length can range from and in males the fore wings can range from . The extent of ferruginous (rust-colored) markings is variable.
Although no distinguishing structural features have been found to separate the workers and queens, the male is easily identified by its bulging eyes, subquadrate clypeus, and slender antennae. P. exclamans males are also more variable in external morphology compared to females. This is possible given the male's hemizygosity (females are homozygous).
Distribution and habitat Polistes exclamans is distributed throughout the United States in the following areas and states: New Jersey down to Florida, Florida to Texas, and west to Nebraska, Colorado, Arizona, and California. It has also been found in Mexico and the Bahamas, as well as Ontario, Canada.
As a vespid wasp, P. exclamans nests are typically made up of paper with a single layer of cells with open combs. Although nest size varies, the upper limit is around 500 cells. Although many vespid wasp nests have an outer envelope of paper, P. exclamans nests do not. As indicated by Strassmann and Orgren, “Nests are approximately circular, and have a single off-center pedicel [basal part] usually located towards the top of the nest. Cells near the pedicle are the oldest.” P. exclamans are particularly able to colonize new sites, as foundresses often disperse into new territories. P. exclamans have often been found to have nests located near man-made structures and tend to more readily build nests in and near these man-made structures. Out of six wasp species, P. exclamans was the only one that occupied artificial nesting sites. It prefers well-lit, open sites.
Polistes nests can be built from wood fiber which are collected from posts and plant stems. The fiber is formed into a paper-like comb with hexagonal cells. The nests are orientated downward and are held up by one filament. P. exclamans have also been observed occupying artificial nests put out by researchers and consisting of bundles of straws.
Colony cycle The colony cycle of Polistes exclamans is longer than that of northern wasp species, shorter than that of tropical wasp species, and as such is in “some respects intermediate between” the two. Their cycle occurs between March and September. The first brood of workers emerges between May and July. It takes about nine to fourteen days for eggs to develop, though eggs in smaller nests and that are laid later in the season take much longer to develop, about thirteen to eighteen days for larvae to develop, about thirteen days for pupae to develop, and about a total of six to eight weeks for an egg to develop into an adult. Reproductive wasps emerge later in August or September.
Queen
Queen characteristics
Polistes exclamans lives in a hierarchical society with one queen that lays the eggs. However, all of the females have the same morphology and they all have the physiological capability of taking over the egg laying if necessary (e.g., due to queen death or queen migration). Since the queen has the same morphology as the rest of the workers in the colony, this raises the question as to how the queen role is assigned and what makes her special. Studies have found that queens and males have higher levels of glucose, fructose and trehalose than workers, leading to higher cryoprotectant levels. P. exclamans use these sugars as cryoprotectant, which work by increasing the solute concentration in cells. This results in a greater survivability in colder weather. It was found that queens have a 76% survival rate in weather compared to 17% survival of the workers over a 15-day test period. The queens also have a 0.5mm layer of fat surrounding their bodies. This allows them to live longer into the winter and possibly extend their mating season. The queens seem to be the only ones capable of diapause.
Queen development and determination
While there aren't many external morphological differences between queens and workers, there are some internal traits that can be signals of a wasp's social status. It has also been found that caste determination is irreversibly determined by temperature during the immature stages of development. In one experiment, some wasps emerging in June were kept in long day chambers, or chambers set at 26 °C with 16 hours of light and 8 hours of darkness. These individuals had larger and more active ovaries as compared to those who were incubated in short day chambers, which are set at 22 °C with 14 hours of light and 10 hours of darkness. It is thought that this phenomenon may occur because of a juvenile hormone secretion that determines the castes and a suppression of the workers’ ovaries by environmental or hormonal factors.
Gerontocracy Given that Polistes exclamans nests are often destroyed or suffer through the death of the queen (most often through natural circumstances), it is necessary and adaptive for there to be a specific system for the replacement of the queen. The current system in place can best “be described as gerontocracy.” Furthermore, it is also closely related to the dominance system within the colony as well. In the dominance hierarchy, older individuals are higher in rank, whereas younger individuals serve in the lower ranks. These older female workers are generally more aggressive and forage more frequently. In reflection of this dominance ranking and the behavior of the female workers, it is seen that when a queen is no longer present in the colony, the next eldest worker becomes the new queen. This may be due to the genetics of the next eldest queen, as the replacement queen affects the overall relatedness of the females in the brood, thereby allowing the future brood to be more related to the adult workers rearing them.
The queen's role
P. exclamans tend to have smaller nests than other wasps, with typically fewer than one hundred individuals in a given nest. Because of the size of the nest, the queen tends to be the most active individual in the nest. This is because the queen has to monitor and directly control the activities of the nest. In addition to her reproductive role, the queen must also act as the pacemaker of the nest and synchronize the worker activity. However, these last two points have recently been disputed and the workers may be self organized. It has also been observed that the queen will act aggressively towards individuals that are the least active.
Development and reproduction
Sex determination system
P. exclamans are haplodiploid insects, as are other Polistes species including Polistes metricus, Polistes dominula, and Polistes annularis. This means they have haploid males that produce identical haploid sperm, and diploid females that produce haploid eggs through meiosis. This has consequences for genetic relatedness within colonies, since sisters receive identical sperm if they share a father, and the normal half identical contribution from the mother. This results in sex-biased conflicts between the queen and the workers with respect to the sex ratio, with workers preferring a more female biased sex ratio, and queens preferring equal investment in queens and males.
Sexual investment In Polistes exclamans, equal sex ratio is obtained when only 46.3% of investment is devoted to females as female wasps are 1.16 times larger than male wasps. In a study done by Strassmann, it was found that sexual investment is female biased, especially during years of high predation and when nests are generally less successful. It has been seen that in Polistes exclamans, females are produced before males. This female investment bias may result from the ability of females to become either a worker or a reproductive (this is more adaptive for the nest as it gives the nest increased flexibility compared to that of males and may be important for overall nest success) or because females provide the colony with greater nest defense. Even when the original queen is no longer present, the sexual investment is still biased towards females, which is not expected given the genetic implications of a new queen.
Early males