Polistes apachus

Taxonomy and phylogenetics

P. apachus was originally named by Henri Louis Frédéric de Saussure in 1857. P. apachus can vary in haploid chromosome number (with either 22 or 25 chromosomes), and further investigation is necessary to determine whether this is evidence of two mophologically identical sibling cryptospecies. Changes continue to be made to the taxonomy and phylogeny, but detailed knowledge of the phylogeny remains relatively rudimentary at this point.

Description and identification

P. apachus shares the basic yellow and brown pattern with other species of social wasps in the genus Polistes. As a result, P. apachus is often misidentified. Specifically, P. apachus closely resembles P. exclamans. Though both species look very similar, P. apachus can usually be differentiated by wider yellow bands on its abdomen. The fact that P. apachus is the largest and most brightly-colored Polistes in the state of California also helps with differentiation. The length of P. apachus is about 20 mm. Its pronotum is bordered with a yellow stripe, and its mesonotum has two transverse yellow stripes. The anterior stripe is narrow and the posterior stripe is broader. The extent of color differentiation can vary amongst individuals. Either brown or yellow can predominate on certain individuals, while other individuals display an equal amount of yellow and brown. There is no recognizable difference in size or appearance between egg-laying queens and her workers.

Nests tend to be large, containing about 150 cells. Combs of the nest also tend to be large, reaching 15X20 cm. The nests are single-layered and circular or umbrella-shaped. The nests tend to be supported by longer pedicals than are found in other vespids.

Distribution and habitat

P. apachus is found in the United States, specifically in central valleys and southern California and Texas, as well as adjacent areas to the north, west and south. Evidence suggests that the species was introduced into California from Texas around 1920. Since then, P. apachus has been extending its range. P. apachus has not been able to extend further north than Southern Colorado and Kansas, suggesting that the species has spread as far north as it can spread.

P. apachus establishes itself in vines and orchards, but can also be found in more urban areas. It appears that P. apachus originated in habitats associated with mesquite and grassland more so than wooded areas.

Colony cycle

The queen generally initiates colonies in the spring. Nest construction signals nest initiation. One overwintering female generally begins nest construction. Sometimes, a group of cooperative foundresses can work together to initiate a nest. After nest initiation has begun, other fertile females can join the founding female(s). These cooperating females can help with nest construction and maintenance, but do not always remain in the nest permanently. Nest sites tend to be reused, and females often return to locations near the parental nest site. New nest sites can also be initiated. Ultimately, mature nests generally consist of 20–30 individuals.

Dominance hierarchy

Additional fertile females often join founding females, which results in the establishment of a dominance hierarchy within the nest. The queen maintains her role as the only egg-laying individual, while the other fertile females are relegated to worker status. They help in nest construction and maintenance. The dominant queen acts aggressively against females who attempt to lay eggs of their own by eating eggs laid by other females. This behavior can also be observed in the related species Polistes instabilis. If the dominant queen dies, however, one of the other fertile females can take over her duties to ensure the survival of the nest.

Genetic relatedness within colonies

Colonies of P. apachus almost always have one female who lays the eggs. Studies indicate that a colony is headed by one queen at a time, but that a single colony sees a succession of queens over the colony lifespan. As a result, the average degree of relatedness between workers and their female brood is less than .5. This suggests that Hamilton’s theory of kin selection does not provide an adequate explanation for eusociality in P. apachus. Though evidence does exist that eusociality is in some ways a result of kin selection, studies reject the evolution of eusociality based on the maintenance of a relatedness greater than .5.

Kin recognition

Nest layover decreases genetic relatedness within the nest. Because nest layover is common in P. apachus, kin recognition is important. Kin recognition occurs by the recognition of cues. Studies suggest that the ability to recognize certain cues may exist between sisters of greater genetic relatedness. Though evidence has not conclusively shown that this occurs in P. apachus, studies certainly suggest it as a possibility.

Predators and prey

P. apachus is considered a predatory wasp. Like other species of Polistes, the diet of P. apachus consists heavily of caterpillar meat. Two species that often prey on P. apachus are the robber flies Mallophora orcina and Proctacanthus hinei.

Parasites

Another wasp, Pachysomoides fulvus is a parasite to P. apachus and other paper wasps in the United States. P. fulvus lays eggs on the larvae of P. apachus. This especially affects new nests with only one foundress, as the queen must therefore leave the nest to find food. This leaves the nest especially vulnerable.

Pests

P. apachus has a variety of undesirable characteristics to humans. It has established itself in some areas of California as the main Polistes species in urban areas. Because it also nests in orchards and vineyards, this creates a problem for workers in orchards or vineyards who are often stung. Efforts of pest control of P. apachus have been attempted. Most commercially available aerosol sprays containing pyrehtrins are effective. In addition, dusting nests with 10% DDT have shown to be successful. On the other hand, poisons using beef liver and honey have proved unsuccessful. With that being said, P. apachus is generally considered beneficial to its habitat.

Stings

As outdoor activity has increased, so too has the nuisance of P. apachus. Its stings can lead to serious allergic reactions in humans. Recent studies have used venom specific detection to determine that P. apachus stings have led to anaphylaxis. Venom immunotherapy (VIT) can sometimes be used to treat allergies to insect stings, specifically in individuals who experience systematic reactions to insect stings. Though the safety of VIT with the honeybee has been questioned, VIT appears to safe for P. apachus venom.