Polistes pacificus

P. pacificus is part of a monophyletic clade that makes up the membership of Richards’ (1973, 1978) subgenera Epicnemius.^[5] P. pacificus is most closely related to its sister species, P. cinerascens. Although previous studies found Epicnemius to be paraphyletic, the most recent and complete study done by Picket et al. reveals that it is likely monophyletic. The species included in this clade are P. cinerascens, P. pacificus, P. geminatus geminatus, P. occipitalis, P. testaceicolor.^[5]

P. pacificus was originally discovered in 1804 by the famous Danish entomologist, Johan Christian Fabricius (1745–1808). However, because P. pacificus has wide color variation depending on its geographic region, over time it has been mistaken for several new species and given new names. These names included P. flavipictus Ducke, 1918 P. liliaceusculus de Saussure, 1854, P. liliaciosus de Saussure, 1855, P. modestus Smith, 1862, P. trinitatis Bequard, 1937. These names are relatively obsolete, but may appear in erroneous or outdated literature.^[6]

P. pacificus has varied coloration patterns with markings that can be black, ferruginous and yellow. It is darker and less brightly colored than most other Polistes species, and it is morphologically very similar to P. boharti. In fact, the two species are classified as the same under Richard's key.^[4] However, there are some distinguishing characteristics between the two: Firstly, the digitus structure of the genitalia of P. pacificus males has many dark, stout, distally curved or hooked setae. Secondly, female P. pacificus will have a genal ridge that is usually weak below, and rarely reaches below the level of the lower one-fifth to one-fourth of the eye; on the rare occasions that it extends below this level, it will most likely not reach the base of the mandible and will be very weak. Additionally, in P. pacificus, the lobate humeral angle is not defined, and the lower lateral extension of the pronotal ridge will not be depressed.^[4]

A specimen of P. pacificus may also be identified by the following morphological criteria:^[5]

• Male antennae are hooked
• Clypeus is pointed (see diagram)
• Male eyes touch the clypeus (see diagram)
• There is much pigmentation on the head
• Claws are symmetrical
• There are two teeth, nearly equal in size, that are present in the mandible
• Setae on the underside of the thoracic segment are minute or short, while setae on the underside of the abdominal segment are long and hairy.

P. pacificus builds nests that are relatively small and made of paper. These nests are most likely to be found in areas of low second-growth vegetation,^[3] and are often sheltered by large leaves.^[7] The nests, which hang from a plant supported by one or more pedicels, are made up of a single comb of hexagonal cells and do not have an envelope.^[3] Polistes produce the water-resistant paper used to make nests by gathering wood fiber and other plant matter and combining it with saliva.^[8]

P. pacificus can be found from the southern United States to Uruguay and Argentina. P. pacificus can be found in Southern parts of Texas, various areas of Mexico, Guatemala, Honduras, Nicaragua, Costa Rica, Panama, Colombia, Ecuador, Peru, Venezuela, Trinidad, Guyana, Suriname, French Guiana, parts of Brazil, Paraguay, Bolivia, and Uruguay.^[9]

P. pacificus builds its nest on plants, using large leaves of the host plants as shelter. While some reports have been made that suggest that social paper wasps build nests where arboreal ants are also present, P. pacificus is only rarely associated with arboreal ants and frequently chooses nesting sites on plants that are unattractive to ants.^[7] Some of the most common plants for P. pacificus to build nests on are Clusia grandiflora and Vismia sessilifolia, but they have also been known to build nests that connect to long, thin thorns under the leaves on juvenile Astrocaryum sciophylum palm trees.^[7]

P. pacificus is one of several social paper wasp species that migrate seasonally depending on the times of the wet and dry seasons. In areas with less pronounced dry seasons, P. pacificus is more likely to brood continuously. However, when P. pacificus live in regions with a defined dry season, the dry season is the non-nesting phase of the colony cycle.^[10] During this period, wasps leave the low elevation habitats in which they normally nest and reproduce during the rainy season, and move to cooler areas at higher elevation. The aggregating wasps are sometimes found to be in small groups of individuals from different nests.^[10] Due to the fact that dry season aggregates of P. pacificus have been found in evergreen old growth forests, a place distinct from where they nest, it has been suggested that this behavior is evidence of altitudinal migration.^[10] The benefits to this type of seasonal migration could be that wasps in these cooler high elevation conditions have lower metabolic needs and costs.^[10] This behavior is similar to migrating behavior observed in temperate zone Polistes wasps during winter. Mating can occur either at leks away from nests or at newly founded nests, often late in the nesting season, but before the seasonal dormancy. Generally the inseminated females will pass the dormant season hibernating in a group of other females in a type of shelter, and at this time males most likely die off.^[10]

The Polistes have high nutritional demands because they nurse their broods.^[11] P. pacificus is an animal of prey, but it is also a flower-visiting wasp that gets carbohydrates from flower nectar.^[12] When P. pacificus is in the larval state, the majority of its diet comes from animal protein. In addition to the caterpillars which Polistes mostly preys on, the P. pacificus also visits flowers, thus picking up carbohydrates.^[12] Carbohydrates collected through flower nectar are a complement of its diet and thought to help maintain its own energy metabolism.^[13]

P. pacificus has at least several known predators: arboreal ants and vertebrates, including humans. The larvae of the P. pacificus is what predators eat, as it is localized within the nest and immobile. The larvae makes a very valuable food source because it is rich in amino acids and fats.^[3][14]

P. pacificus nest site selection and structure have evolved under selective pressures of weather and predation.^[14] In order to keep predators out, P. pacificus nests are built in specific places in which they are less susceptible to attack by arboreal ants or vertebrates.^[14] The placement of the nest not only aims to reduce predation, but also to provide protection from extreme weather.^[14] Nests are most often built on the underside of large leaves, which protect against weather and limit predator's views of the nest from above. The most preferable large leaves have spines along the central vein, which act as a pedicel and protect the nests from ant attacks.^[14] In the neotropics, P. pacificus nests are most closely associated with a specific plant, the Clusia grandiflora, which is most likely an adaptation due to the selective pressure of ant predation as Clusia is not an attractive host for arboreal ant nests.^[7]