Vespula pensylvanica, the western yellowjacket (western yellowjacket), is a Nearctic species of wasp in the genus Vespula.Akre, Roger D., Albert Greene, John F. MacDonald, Peter J. Landolt, and Harry G. Davis. Agricultural Handbook Number 552. United States Department of Agriculture, 1981. Print. It is native to regions of North America, largely in areas with northern temperate climates. Its reproductive behavior is constrained by cold weather, which successfully reduces the number of western yellowjackets in cold months. However, in the absence of cold weather, this wasp's population can explode. The western yellowjacket has become particularly invasive in the Hawaiian Islands, resulting in their label as a major pest.Invasive Species in the Pacific: A Technical Review and Draft Regional Strategy. Samoa: South Pacific Regional Environment Programme, 2000. Print.Wilson, E. E., L. M. Mullen, and D. A. Holway. "Life History Plasticity Magnifies the Ecological Effects of a Social Wasp Invasion." Proceedings of the National Academy of Sciences 106.31 (2009): 12809-2813. Web.
Taxonomy and phylogeny V. pensylvanica was originally named by de Saussure in 1857; it falls into the subgenus Paravespula, within Vespula. Paravespula consists of 11 species, which have been divided into four groups on the basis of morphological differences. V. pensylvanica falls into the same group as V. germanica.Archer, Michael E. "Taxonomy, Distribution, and Nesting Biology of The Species of The Genus Paravesupla or The Vespula Vulgaris Species Group (Hymenoptera: Vespidae)." Entomologist's Monthly Magazine June 2007: 5-29. Web. With the exception of Allovespula, the subgenera recognized within Vespula are natural groups. The separation of Rugovespula and Paravespula appears to be monophyletic; however, this is not well established.Carpenter, James M. "Phylogenetic Relationships and Classification of the Vespinae (Hymenoptera: Vespidae)." Systematic Entomology 12.4 (1987): 413-31. Web.
Description and identification The western yellowjacket shares the basic yellow and black pattern with other species of social wasps in the genus Vespula. As a result, it is often misidentified. Specifically, it closely resembles V. germanica. Though both species have a similar diamond-shaped black mark on the first tergum, V. pensylvanica can usually be differentiated by the continuous yellow ring (often referred to as an eye-loop) present around each eye. The eye-loop is not always present, however. Though few females lack this distinguishing characteristic, males often do not have the eye-loop. In such cases, V. pensylvanica can be identified by a spotted mark on the frons below the antenna, a slender aedeagus, and a denser apical region of tergum 7. The fore wing length ranges from 8.5–10.5 mm for workers, 12.5–14.5 mm for females, and 12.5–14.0 mm for males.Buck, Matthias, Stephen Marshall, and David Cheung. "Identification Atlas of the Vespidae (Hymenoptera, Aculeata) of the Northeastern Nearctic Region."Canadian Journal of Arthropod Identification (2008). Web.
Western yellowjackets build large nests made of wood fibers, enclosed in a hexagonal paper envelope with a small 10– to 30-cm entrance tunnel at the bottom.Landolt, Peter J., and Arthur L. Antonelli. Yellowjackets and Paper Wasps. Washington State U, 2003. Print. Nests are usually found 10–15 cm below ground or in other dark cavities, such as rodent burrows or old logs.
Distribution and habitat The western yellowjacket is native across the western half of North America, in temperate zone climates. Its range overlaps with that of V. atropilosa. Individuals have been identified in the Canadian and Transition Zones in western North America. It has been found in all states west of the Rocky Mountains, from Mexico through western Canada. It is also found in Hawaii on the islands of Kauai, Oahu, Maui, and Hawaii. V. pensylvanica can be found in open forest, prairies, urban zones, gardens, parkland, meadows, and houses.
Colony cycle Colonies are initiated by the queen. After emerging from the diapause when winter ends, the fertilized queen searches for a nest site. When it is located, a small nest is formed. The queen continues to forage for construction materials and food until four to seven workers have emerged. At this point, the queen focuses solely on laying eggs and the nest continues to expand. Between August and September, males and queens are produced, which then leave the nest and mate. The nest begins to decline around this time. The males eventually die, and the inseminated queen begins diapause. The inseminated queen is the only member of the colony to survive winter.Akre, R. D., and H. C. Reed. "A Polygynous Colony of Vespula Pensylvanica (Saussure) (Hymenoptera, Vespidae)." Entomological News 92.1 (1981): 27-31. Web. Longevity of the workers varies with colony activity and development, with the lifespan of the earliest-born workers averaging 22 days and the latest-born workers averaging 40 days.Akre, R. D., W. B. Garnett, J. F. MacDonald, A. Greene, and P. Landolt. "Behavior and Colony Development of Vespula Pensylvanica and V. Atropilosa (Hymenoptera: Vespidae)." Journal of the Kansas Entomological Society 49.1 (1976): 63-84. Web.
Typically, colonies are monogynous and annual. In these colonies, attempts of other queens to enter result in fierce fighting between the intruder and the residing queen and/or workers. Perennial colonies, though, have been reported, containing numerous queens. Most perennial colonies have larger nests and more individuals.
Behavior
Dominance hierarchy As the size of a colony increases to the point where at least 30 workers are foraging at the same time, competition develops between workers. Often, one worker will attack the prey of another worker, resulting in neither worker bringing back prey. Older workers are more successful in attacking. They may also maul to exhibit dominance over nest mates; mauling entails one individual chewing another individual that remains motionless throughout. Generally, this occurs between two workers, with the aggressive worker beginning the mauling process when a returning forager enters or is near the entrance of the nest. At any given time, certain individuals repeatedly express mauling tendencies and recipients remain constant. Over time, the recipients become the maulers as they approach old age. As the colonies decline, mauling becomes less frequent.
Division of labor Division of labor within the nests of V. pensylvanica is not sharply defined and is seemingly age-dependent. Within four days of emergence, workers begin foraging for fiber, nectar, water, and prey; larval feeding; construction of envelope and cells; nest sanitation; guarding and colony defense; thermal regulation; and “mauling” or aggressive behavior. Workers that emerge from the nest after the first 20–30 workers since its development express more variable behavior. Queens exhibit the same range of behavior with the exception of mauling; however, after four to seven workers emerge in mid-June, workers take over foraging. The queen does not leave the nest again after this point. The queen is responsible for ovipositing. Behavior becomes less variable as the colony begins to decline, when growth of the nest ceases. Larvae are not fed during colony decline, and most workers forage only for honey during this time.
Foraging
The western yellowjacket foraging behavior is similar to other Vespula species. Yellowjackets forage for insects and dead animals for meat and plant nectar for carbohydrates. The captured prey is typically taken to a more vertical surface and malaxated by chewing off legs and wings. In larger insects, the head is typically removed first. Foraging for prey requires visual cues, but odors can be used when scavenging for protein. Hunting for prey and dead animals occurs individually because yellowjacket workers are unable to communicate the location of food to other workers in the colony. All workers forage for honey, water, and fiber. In Hawaii, yellowjackets rob honey bee colonies through two major types of raids. Sometimes, yellowjackets enter and leave in a slow but steady traffic faced by opposition from honey bee workers. In the more common raid, yellowjackets enter individually and experience no apparent opposition. V. pensylvanica utilize their mandibles to scrape weathered wood and dried herbaceous stems to obtain resources rich in fiber. Most yellowjackets forage relatively close to the nest. The foraging distance ranges between 540 and 1800 feet. The average foraging distance is within 1,100 feet of the nest. In addition to visual and olfactory cues, learning also plays a role in foraging. They rarely return to a constant location for protein and shift foraging patterns when necessary.Akre, Roger D., W. B. Hill, J. F. MacDonald, and W. B. Garnett. "Foraging Distances of Vespula Pensylvanica Workers (Hymenoptera: Vespidae)." Journal of the Kansas Entomological Society 48.1 (1975): 12-16.
Mating behavior Mating behavior of V. pensylvanica has been observed to be very similar to mating behavior of V. germanica. Pairing occurs midday and receptive queens remain stationary throughout. Mating occurs between one male and one female, with the female generally upright on her legs and the male attached solely by genitalia. Other males in the nest do not interfere with the mating, but often antennate the pairs during the mating process. Sometimes, queens may be unreceptive and will exhibit this by twisting away from the males and biting. Unreceptive behavior from females, however, does not always prevent mating from occurring. Vespula queens often mate more than once with the same or different males. Mating involves only one male.MacDonald, J. F., R. D. Akre, and W. B. Hill. "Comparative Biology and Behavior of Vespula Atropilosa and V. Pensylvanica (Hymenoptera Vespidae)."Washington State University, College of Agriculture Research Center. 4272nd ser. (1974). Web.
Brood/parental care In early development, the queen lays eggs and takes care of larvae. Before the emergence of workers, the queen is responsible for feeding the brood. To feed developing larvae, the queen captures prey by incapacitation, trims it to an appropriate size for carrying, and brings it back to the nest to further malaxate the item. Males do not contribute to parental care. In fact, many males solicit liquids from developing larvae. Workers forage for food, capture and malaxate prey, defend territories, and monitor the distribution of resources among larvae. The larvae twitch back and forth in their nests to attract the attention of the workers and queens. When approached by adults, larvae reach back to expose their heads. If this reaction takes too long, workers give the food to another larva.
Nest sanitation also serves an important role in parental care. The western yellowjacket keeps its nest relatively clean compared to other social wasps. Most waste is removed, including paper waste, remains of prey, and dead larvae. In addition, a pre-defecation head dance occurs in both workers and the queen, and this fecal material is then removed. Workers also have been found to remove healthy larvae from their cells. Two or more workers together pull otherwise healthy larva from the cell and frequently cut it up and feed it to other larvae. This tendency increases during colony decline.
Thermoregulation