Western yellowjacket

Appearance

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 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.

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."Western Yellowjacket." Plantwise Technical Factsheet. Web.. Nests are usually found 10–15 cm below ground or in other dark cavities, such as rodent burrows.

Distribution

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."Vespula Pensylvanica: Western Yellowjacket." Encyclopedia of Life. Web..

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.

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."Vespula Pensylvanica: Western Yellowjacket." Encyclopedia of Life. Web..

Reproduction

Though colonies of "V. pensylvanica" are generally monogynous and annual, polygyny and overwintering has been observed in non-native regions, specifically in Hawaii. The relaxation of the climate and climate-related constraints are believed to have contributed to the emergence of polygyny, and polygyny is a prerequisite for successful overwintering. Generally, climate is a constraining factor in the reproductive behavior of "V. pensylvanica". When temperatures drop, food availability decreases and colony decline occurs. In Hawaii, however, this does not occur.

Two genetic mechanisms have been proposed to explain polygyny in Hawaiian colonies. Hamilton’s kin selection theory provides an explanation for the divergence between polygyny and monogyny. Generally, monogyny should prevail unless polygynous benefits outweigh the costs of shared reproduction. If females are unrelated, the costs would usually outweigh the benefits, and monogyny would result. Using kin selection theory, two possible explanations exist as to why polygyny arises. First, daughter queens remaining in the natal nest possibly create kin associations that provide a mechanism allowing the benefits of polygyny to outweigh the costs. Another genetic mechanism explaining why polygyny arises is due to the bottleneck effect. Because a small number of founders gave rise to the population of "V. pensylvanica" in Hawaii, the entire population in Hawaii thus has an average degree of relatedness higher than presumed among the North American population. In both cases, genetic relatedness and kin selection could explain why polygyny has emerged in non-native regions.

Food

The diet of the "V. pensylvanica" is very broad. Food is obtained through both predation and scavenging. Adult workers are opportunistic predators and often return to areas of abundant prey to forage. The main foods obtained are high-protein foods such as small insects, caterpillars, and spiders. In addition, "V. pensylvanica" occasionally scavenges on dead animals, including dead honeybees. In Hawaii, the diet spans a total of 14 taxonomic orders, including both invertebrates and vertebrates. The most common taxa are small and inconspicuous, such as barklice or planthoppers. "V. pensylvanica" also preys on "D. silvestris" and other "Drosophila" flies native to Hawaii, disrupting the local ecosystem.

Defense

The western yellowjacket is often a pest to humans. As outdoor human activity has increased, so, too, has the presence of "V. pensylvanica". Concentrated garbage has become an alternative food supply, and colonies have emerged in and around areas of human impact, such as recreational parks and resorts. Though they tend not to sting unless a violent struggle occurs, they nonetheless violently protect their nests and can sting repeatedly. As a result, increased efforts into pest control have occurred. Because the chance of colony disturbance and resulting stings is great, the species is recommended to be controlled during outbreaks. The recommended treatment of stings is antihistamine ointments and tablets to reduce reactions. Those who are highly sensitive or allergic to stings should speak to a physician about alternatives such as emergency kits with premeasured doses of epinephrine or desensitization procedures.

Cultural

Periodic population outbreaks every three to five years have created problems within fruit orchards. The tendency of "V. pensylvanica" to cluster in areas of human impact has created problems for pickers in fruit orchards who are frequently stung. The costs to the grower to control the outbreaks can be extremely high. "V. pensylvanica" is often immune to efforts to control other pests, which often results in high costs to growers who have to use additional methods to control "V. pensylvanica.