The European paper wasp (Polistes dominula) is one of the most common and well-known species of social wasps in the genus Polistes. Its diet is more diverse than those of most Polistes species—many genera of insects versus mainly caterpillars in other Polistes—giving it superior survivability compared to other wasp species during a shortage of resources.
The dominant females are the principal egg layers, while the subordinate females ("auxiliaries") or workers primarily forage and do not lay eggs. This hierarchy is not permanent, though; when the queen is removed from the nest, the second-most dominant female takes over the role of the previous queen. Dominance in females is determined by the severity of the scatteredness in the coloration of the clypeus (face), whereas dominance in males is shown by the variation of spots of their abdomens. P. dominula is common and cosmopolitan due to their exceptional survival features such as productive colony cycle, short development time, and higher ability to endure predator attacks.
These wasps have a lek-based mating system. Unlike most social insects, 35% of P. dominula wasps in a colony are unrelated. It is considered an invasive species in Canada and the United States.
Taxonomy The European paper wasp was originally described in 1791 by Johann Ludwig Christ as Vespa dominula. The specific epithet dominula is a noun meaning "little mistress", and following the International Code of Zoological Nomenclature, species epithets which are nouns do not change when a species is placed in a different genus. Authors who were unaware that dominula was a noun have misspelled the species name as "dominulus" for decades. P. dominula is often referred to as the European paper wasp because of its native distribution and its nests, which are constructed from paper and saliva. It is also frequently referred to in older literature as Polistes gallicus, a separate species with which it was often confused.
Description and identification
Little variation occurs among individuals of P. dominula; the wing lengths of males range from , while those of females range from . Its body is colored entirely yellow and black, similar to that of Vespula germanica, one of the most common and defensive wasps in its native range. The female mandible is black and sometimes has a yellow spot. Females have a black subantennal mark that rarely has a pair of small, yellow spots. The female vertex sometimes has a pair of small, yellow spots behind the hind ocelli. Mesoscutum with paired yellow comma-shaped spots, rarely minute or absent. Apical half of antenna uniformly orange-yellow dorsally and ventrally. In females, sternite VI is usually completely or at least in the apical part yellow. In males, clypeus not or slightly depressed medially and lateral ridges absent dorsally or slightly developed, its apical margin is triangular; typically, apical antennal segment comparatively stout and dorsally about 1.5 times as long as wide basally.
Variations amongst individuals Although the wasps do not display much conspicuous variation that enables one to tell them apart with the naked eye, definite features are unique to each individual. For example, the abdominal spots on males of P. dominula vary in sizes, locations, and patterns. They act as sexually selective signals and also are associated with social hierarchy within the colonies. Males with smaller, regular patterns of spots are more aggressive and dominant over those with larger, irregular patterns. Similarly, females' appearance varies between individuals and is associated with their social rank. The larger and the more scattered the clypeus marks on the foundress, the higher the probability that she is dominant over other females.
Distribution
The native range of P. dominula covers much of southern Europe and North Africa, and temperate parts of Asia as far east as China. It has also been introduced to New Zealand, Australia, South Africa, and North and South America. Since the mid-1980s, the population of P. dominula has expanded to rather cooler regions, especially towards northern Europe. Global warming is speculated to have raised temperatures of certain areas, allowing P. dominula to expand to originally cooler regions.
The first North American occurrence of P. dominula was reported in Massachusetts in the late 1970s, and by 1995, this species had been documented throughout the northeastern USA. Since then, the species have been observed as far west as Colorado as early as 2013. Although detailed mechanisms of the species' dispersal are still unknown, some number of individuals, including the foundresses, may have hidden inside transportable items such as shipping crates, trailers, boats, or other human-made structures used during international trading between countries.
Habitat P. dominula generally lives in temperate, terrestrial habitats such as chaparral, forest, and grassland biomes. They also have the propensity to colonize nearby human civilizations because man-made structures can act as great shelters and also are located close to the resources such as food.
Spread within North America
Behavioral adaptations of P. dominula have allowed it to expand outside its native range and invade the United States and Canada. While most Polistes species in the United States feed only on caterpillars, P. dominula eats many different types of insects. It also nests in areas with better protection, so is able to avoid predation that has affected many other Polistes species. Much of North America has a very similar ecology and habitat to that of Europe, and this has allowed a faster and more successful colonization. P. dominula was also compared to and found to be more productive than Polistes fuscatus, which is indigenous to the United States and Canada. P. dominula produces workers about a week earlier and forages earlier in the day than P. fuscatus. It is a concern for cherry and grape growers in British Columbia, as it injures the fruit by biting off the skin. It also spreads yeast and fungi that harm fruit and can be a nuisance to workers and pickers at harvest.
Displacement of native species Before 1995, P. fuscatus was the only species of Polistes in Michigan. In the spring of 1995, one single founder colony of P. dominula was discovered nesting in the Polistes nestbox at the Oakland University Preserve in Rochester, Michigan. In 2002, about one-third of the P. dominula colonies at the preserve were removed because of the concern about losing the resident population of P. fuscatus. Although the removal of P. dominula population did slow down their expansion, in 2005, 62% of the colonies at the Preserve were P. dominula. A number of researchers concluded that P. dominula was likely replacing P. fuscatus through indirect or exploitative competition, which was consistent with their finding that P. dominula was significantly more productive than P. fuscatus.
In Colorado, however, P. dominula has not been observed displacing native species. Polistes species native to Colorado strongly prefer environments far from human settlement, while P. dominula frequently settles directly on and around buildings.
Genetic variations Introduced populations of P. dominula contain relatively high levels of genetic diversity and these variations are most likely due to different dispersal events. Through genetic observations of diverse regional P. dominula populations, an allelic richness and distribution of private alleles was shown in the introduced population, as well as the oldest population (Massachusetts) had the lowest level of genetic variation. Various dispersion mechanisms existed amongst the P. dominula species and its origin might not be confined to a single regional area. Furthermore, the genetics of Southern Californian population differed from those of both Eastern and Northern California, suggesting the source of the Southern Californian population may be from either an unsampled area with the introduced range or from a different geographic area from within the native range.
Behaviors influenced by genetic diversity
Colony founding Typically, a Polistes colony is founded by a single or a small group of females that have just emerged from hibernation during the winter. They generally prefer warmer climates and initiate construction of new nests. However, a different approach has been observed during the spring colony-founding phase of P. dominula in some areas of North America, where a large group of more than 80 wasps aggregated to reuse and expand an old nest. Such an unusual nesting method is thought to contribute to the extremely extensive spread of the P. dominula species in novel areas where it might otherwise be difficult for newcomer individuals to find conspecifics.
Life cycle
Overwintering founding queens, or foundresses, spend about a month in the spring constructing a nest and provisioning offspring, the first of which become daughter workers in the growing colony. One or more foundresses begin the colonies in the spring. If multiple foundresses are present, the one that lays the most eggs will be the dominant queen. The remaining foundresses will be subordinate and do work to help the colony.
Males are produced later, and when they start to appear, a few daughters may mate and leave their nest to become foundresses the next season. The switch from production of workers to production of future foundresses (gynes) is not utterly abrupt, as has been considered the case for other species of Polistes. Males are often distinguished from female wasps by their curled antennae and lack of a stinger.
The colony disperses in the late summer, with only males and future foundresses produced instead of workers, and individuals frequently clustering in groups (called a hibernaculum) to overwinter. Hibernation does not usually take place on former nest sites.
Social hierarchies established within the colony can also influence individual P. dominulas longevity. Queens live longer than the males or the workers because the workers protect the queens from predators. The queen starts laying eggs in late March or early April, immediately after the "founding phase" of the newly built nest. Then, the colony disperses in the late summer, with only males and future foundresses produced instead of workers. Although individuals frequently cluster in groups (to overwinter), neither most nonreproductive males nor nonreproductive females survive the winter because their lifespans are shorter than a year (around 11 months) and they best survive during warm temperatures. Queens may survive the winter by hibernating.
Survival advantages Many regions have been reported which were originally home for P. fuscatus have slowly altered to that of P. dominula. A few possible factors contribute to the prevalence of P. dominula over P. fuscatus, specifically in settling into a territory. Some of the factors include productive colony cycle, short developmental time, aposematic coloration, a generalist diet, and the ability to colonize new environments.
Colony cycle P. dominula colonies are established by females that have left their natal combs to mate and find new settlements. These "foundresses" use three major strategies to establish new colonies, including building a nest by herself, finding "associate foundresses" to build the nest together, and sitting and waiting for the original foundress to leave the nest and then displace her. Once the foundresses have settled, the "founding phase" is over and is followed by the "worker phase", where the first generation of offspring are produced and grow as workers.