Dolichovespula norwegica

Norwegian wasp
Female
Scientific classification
Kingdom:	Animalia
Phylum:	Arthropoda
Class:	Insecta
Order:	Hymenoptera
Suborder:	Apocrita
Family:	Vespidae
Genus:	Dolichovespula
Species:	D. norwegica
Binomial name
Dolichovespula norwegica (Fabricius, 1781)

The Norwegian wasp (Dolichovespula norwegica) is a species of eusocial wasp. It is common in Scotland and can also be found in areas in Britain and Ireland. Often known for being a tree wasp, it nests in low branches and bushes and feeds on insects. It also obtains nectar from blueberry and snowberry flowers.^[1] Although Dolichovespula norwegica were rarely considered as pests in the past, a few cases of pest problems relating to D. norwegica have been reported multiple times.^[2] The species is not endangered.^[3]

Taxonomy and phylogeny

The Norwegian Wasp is under the Vespidae family and the Dolichovespula genus. Based on recent studies on mitochondria genes, Dolichovespula and Vespula are monophyletic, meaning they descended from common ancestral group. Two species groups, maculata and norwegica form the Dolichovespula clade. While the maculata has physical attributes such as pronotal striae, emarginate apex of the seventh metasomal sternum in males, and aedeagal medial lobes, the D. norwegica females have long oculo-malar space and lateroanterior clypeal angles with less prominent semicircular projections.^[4]

In the past, Dolichovespula norwegica and Dolichovespula albida, the Arctic yellowjacket from northern North America, were considered to be the same species but studies in 2011 of the male genitalia show that they are not conspecific. Often, the male genitalia are used to characterize the Nearctic and Palearctic forms of Dolichovespula norwegica.^[5]

Description and Identification

Dolichovespula norwegica has eye-catching black and yellow color patterns throughout its body. Starting from the face, it has a long malar space and is separated by a black bar that runs vertically. The sides of the thorax contain small black hairs that project outwards and the rear has distinct yellow spots. One can often see red coloring on the front of the abdomen.^[6] Dolichovespula is derived from the Greek word, dolichos, which means long. Its genus name matches with physical characteristics.^[7] The average length of an individual of this species is 11– 18 mm long.^[1] Compared to the dolichovespula maculata species, whose adults range from 2–3 cm. Queens are generally around 1.7 cm and workers are smaller, around 1.3 cm ^[8]

Nests

Most nests of these species have a loose, coarse woven texture which suggests that D. norwegica are terrestrial. One such nest was found, spherical in size, approximately 10.5 cm long, 10.5 cm at its widest point and 15 cm off the ground. This nest was fastened from the top of a willow branch and was further stabilized by a side branch attachment. The nest consisted of eleven envelope layers with a few extra layers on the edge of the top comb. The texture of each layer is rough with some holes from weaving.

There a few contenders for fiber sources. Some fibers were fine and grey, while some were coarse and straw-colored. Occasionally there were black and rust colored fibers as well. Most common source of nests is weathered wood. On the outer layer of the nest, leaves of broad plants were observed as well.

The observed nest had a total of three combs and 357 cells. From close observations, the worker cells in comb one was an average of 5.17 mm while the reproductive cells in combs two and three had an average of 6.33 mm. It has been reported that some nests of D. norwegica in Europe have a maximum of 1,400 cells.^[9]

Overall, nests of D. norwegica wasps are commonly found on tree branches, bushes, walls of houses, and even cavities in the ground. It appears that these wasp species prefer to build their nests in rural areas.^[8]

Distribution and Habitat

Members of D. norwegica typically construct their nests on tree branches or bushes, often selecting areas that are closed rather than exposed such as moors. Despite its common name, Norwegian Wasp, D. norwegica is also found throughout England, Ireland and commonly in Scotland.^[1]

Since nests are of a coarse, woven texture with a few holes, they are detracted from thermoregulation. Furthermore, nests are also less durable, therefore must be built in protected areas.^[9]

Colony Cycle

Around late summer, the queens and males leave their home colonies. At this point, the queens will become fertilized and will pass the winter season by finding an overwintering site. Before spring arrives, D. norwegica males will die. Upon arrival of spring season (around mid April or early May), the queens will emerge and feed with the goal of finding a new nest.

First the queen will start building her nest and rear workers in the first cells (average diameter of 4.5 mm). The workers then will replace the queen in the nest and assume brood rearing activities. Later cells where queens and males are reared at on average 5.5 mm in diameter. By June, there are about 50 workers and by the end of July, there are about 300 workers. After this period, however, the number of workers decline pretty rapidly. The largest number of workers in colony ever reported was 363 while other colonies had around 150 workers. A mean colony produced 1471 wasps (measure from 14 colonies with large cells) and out of that total, 43% were queens and 57% were male.

The colony cycle of D. norwegica is short because these species have a tendency to start in the spring. Their life-history strategy is known as Summer Advantage Strategy (SAS), which is distinctive of the Dolichovespula species. Such a strategy is implemented and used to take advantage of the short, yet favorable conditions of the summer season. Most colonies will die out after mid August and a few will go till early September. The average number of days a colony exists is 95–115 days.^[10]

Behavior

Mating Behavior

Mating amongst wasps commonly occurs during warm season. There is a tendency for males to occupy a dense area on trees and shrubs and perform nuptial flights. They swarm in groups. D. norwegica males and a few workers have been found with on a rocky summit in Scotland in groups.^[7]

Kin Selection

Generally in wasps, queen mating frequency and sperm use both influence paternity. Paternity is important for influencing colony kin structure and reproductive tendencies of the colony. In Dolichovespula norwegica colonies, it has been shown that male paternity is low contrary to their sister genus, Vespula. This leads to worker queen conflict over male production. Out of five species of the Dolichovespula genus studied, D. norwegica has the second lowest value for effective paternity (1.08). Worker- worker relatedness is high among Dolichovespula norwegica with an r-value of 0.71.^[11]

Genetic Relatedness within Colonies

Since the effective mating frequency of D. norwegica queens is low, worker- worker relatedness is higher than worker-queen relatedness. Genetically speaking, this means that each worker is more related to other workers’ sons that the queen’s sons, creating worker queen conflict over reproduction.

In one colony of D. norwegica, two matrilines were found, suggesting that the nest was once taken over by another queen. This is intriguing because it is the first case in Dolichovespula.^[11]

Worker Queen Conflict

There are several examples of worker queen conflict among members of D. norwegica. Few workers were detected to have full ovary activation and were producing males. Ovary activation is most likely due to the absence of the queen. Workers may kill off their queens so that they can reproduce: there was no queens found on collection of 12 out of 14 D. norwegica nests. Queens are often recognizable due to their heavily, worn wings. Matricide is common after workers are reared and queens have laid their eggs in annual colonies with low paternity.

Despite possibilities of matricide and ovary activations, workers produce very few males. Worker policing over eggs is also seen where workers will choose to keep queen-laid eggs and remove worker-laid eggs. It is also unlikely for workers to reproduce because it is too costly; when workers reproduce, it can reduce colony productivity and/or obstruct reproduction of females in the colony. Furthermore, even though very few workers have active ovaries, the majority of workers did not.^[11]

Worker Policing

Three general forms of egg policing are found to conclusively contribute to reproduction ratios of D. norwegica. All three forms targeting worker-laid eggs over queen-laid eggs. Two forms that are probably most influential of policing are worker policing and selfish policing. Despite being more related to other workers’ sons, worker-laid eggs were consumed by other workers. Approximately two thirds of those workers were reproductive workers. Occasionally these workers replaced the egg with one of their own (in 31% of the cases were due to selfish policing). Workers never removed their own eggs and if a non-reproductive worker removed a worker-laid egg, then the queen would replace it with her own egg.

Furthermore, an important part of worker policing among D. norwegica is specialization. Evidence for specialization in policing was found when observed number of policy workers was lower than the estimate true number of policing workers. It was approximated that an average of 14 workers specialized in policing (~a fourth of the total work force).^[12]

Queen Policing

The last form is queen policing of eggs. It was estimated that about 32% of policing over worker-laid eggs was done by the queen (roughly one-third). There are two cases where queen-laid eggs were eaten: one if a reproductive worker eats the egg then, it will replace it with its own egg and if a non-reproductive worker eats the egg, then the queen always lays the replacement. These situations were less common and only occurred 8% of the time. Queen policing is popular in colonies that are small and of low paternity. Relatively smaller colonies are better because the queen can monitor and control her workers.^[12]

Interaction with other species

Diet

Larvae of D. norwegica commonly feed on flies, other insects and spiders that are brought to them and chewed up by the adult wasps in paste form. The adult individuals will feed on nectar from Angelica sylvestris, Heracleum spondylium and chamerion angsutifolium.^[13] They generally prefer a sweeter taste. Larvae of D. norwegica have a single tooth that is used to feed on the paste.^[7] Once it feeds, the larvae will expel a sweet liquid, which the adult wasp consumes. D. norwegica also enjoys flowers of umbelifers such as the wild parsnip ^[14]

Parasites

Dolichovespula adulterina is a known social parasite of Dolichovespula saxonica.^[2] However, it has been shown that Dolichovespula adulterina also uses D. norwegica as another host. One suggestion for this inquiline interaction between D. adulterina and D. norwegica is that D. adulterina has been found to cohabitate with D. norwegica. The two species were found to occupy the same space in Northern Norway, where there was no D. saxonica to be found nearby.

Furthermore, in a few nests of D. norwegica, there were D. norwegica workers with a queen from D. adulterina. Other accounts report as many as 46 queens and 24 males of D. adulterina in a nest of D. norwegica. Another case observed two unemerged males of D. norwegica and one unemerged male of D. adulterina from the nest.^[15]

There have also been cases of D. norwegica displaying parasitic behavior on D. sylvestris. Moreover, D. norwegica shows aggression towards individuals of Dolichovespula sylvestris. Evidence of damaged legs and wings of D. sylvestris were found.^[16]

Human Importance

Previously, wasps of D. norwegica were rarely considered to be pests. The built their nest far from human activity and rarely visited buildings, picnics and fruits. However, if their nests were built on a hedge, low eaves or close to humans, it was best to remove the nests. Although they are less aggressive than other wasps in the Vespula'genus, individuals of D. norwegica will aim to protect their nest with their stingers.^[2]

However more recently, more cases of pest problems relating to D. norwegica have been reported. A carbohydrate-baited trap placed closely to a nest captured more wasps of Vespula vulgaris species than D. norwegica.^[17]

References