Polistes snelleni
Polistes snelleni, the Japanese paper wasp, is a common social wasp species in central and northern Japan. P. snelleni is also found in northern China, Korea, and the Russian Far East. Due to the different climates in these regions, P. snelleni is able to adapt to different temperatures and climatic conditions. P. snelleni is typically found in hilly or submontane areas, so they are classified in the semi-highland category.
Taxonomy and phylogeny
P. snelleni is in the genus Polistes, with the subgenus Polistella, a paraphyletic subgenus. P. snelleni is most closely related to Polistes stigma bernadii. It is also closely related to Polistes japonicus. P. snelleni has been studied alongside Polistes chinensis, and Polistes biglumis for comparison in worker-worker conflict, which are two other paper wasps.Description and identification
P. snelleni are black and yellow wasps. The queens are the biggest of the species, and the workers, young queens, and males follow. Workers typically have worn wings that distinguish them from young queens. The weight of new reproductive females is 102 mg. Workers can be identified by white-creamy body fat. Workers that have developed ovaries are workers, but not reproductive females.The nests created by P. snelleni are made vertically. They typically consist of a single comb. The comb is fan-shaped and the pedicel is attached to the basal cell. This set up allows new cells to be added distally. The founding queen uses twigs or the surface of rock overhangs as horizontal supports for the nest. The nest petioles are perpendicular to these supports. These wasps occupy a vertical zone of 200–400 meters.
Distribution and habitat
P. snelleni are typically found in Japan, and sometimes in China or Korea. They prefer grassy or bushy places in temperate areas. Their nests are typically found on south facing slopes in areas filled with small trees and short weeds. These nests are hung from small trees, oftentimes larch trees, and usually hang at about 20–60 cm above the ground. They also nest in roadsides and rocky cliffs, in the spaces under overhangs. The temperature in these sites rises in the daytime because the rocks absorb heat from the sun.Colony cycle
In northern Japan near Sapporo, nests are covered with snow until early April. About 2 weeks later, the single founding queen arrives to start the nest, falling under the category of haplometrotic foundation. The first worker in the nest emerges in early July, and all emerge within a couple of days. The workers are produced by eggs that were laid at the beginning of the nest formation. The incubation period is about 60 days for a worker. P. snelleni only has 5-15 workers in a single nest, proving to be one of the smallest in Japan. Males in P. snelleni emerge after workers, during a period of 1–2 weeks, in cells that are separated from those that produce workers. There are about 10-20 males in an average nest, which is only a bit more than the number of workers. Young queens also come about during this time, in late July, in northern Japan. In central Japan, the young queens come about a month later in the middle of August. Reproductive females mate during the nesting season. These young queens are particularly aggressive. It sometimes happens that there are dwarf queens that arise in the nest, that look vaguely like workers. These emerge in late August when only a few workers remain in the nest and the food supplies have dwindled. These dwarf queens have a low chance of mating because most of the males have died. Eggs and larvae disappear in middle and later August respectively.Construction of nest
The rate of construction of the nest begins as relatively high and then drops with the hatching of larvae. However during this time, the founding queen only constructs about one third of the total cells, and half of the cocoon spinning. The queen uses pulp for construction, collected from outside the nest or by taking it from workers who have collected it. This is a forcibly action by the founding queen, as the workers resist this. Later, the rate of construction picks up again, in conjunction with the maturation of larvae and cocoon spinning by the founding queen. The rate then increases consistently until the sign of the first workers arrival. During this time, prior to the first workers arrival, the queen successfully constructs more cells, leading to a total construction of about 70% of the nests total cells. The superindividual stage, where workers and the queen coexist harmoniously to meet the needs of the nest, lasts only about a week. Once the workers are born, the third peak in cell construction occurs, and about 15% of the cells are produced by workers who have had a few days to rest before working.Egg laying
The queen lays less than 1.5 eggs per day on average. She lays eggs parallel to the construction of the cells. She may lay two eggs in the same cell, even if there are open cells—in this case, only one egg develops. However, no more than 20% of the cells are empty at a time. However, a queen does not reuse cells once an egg has occupied them.Behavior
Division of labor
The P.snelleni queens rise at sunrise and stop their activities at sunset. The queens begin their activities only when their body temperature is high enough from receiving sunbeams. This may not occur right at sunrise, but in the later months when the temperature is higher, the queen can start her activities earlier. The behaviors of P. snelleni males and females are quite distinct. Males rest in the nest and beg the workers for food, occasionally visiting flowers. Females on the other hand have different behaviors. Females rarely leave the brood, only sometimes to bring water drops to ventilate the nest on hot days. Food regurgitation is observed among females.Water transport
P. snelleni exists in temperate locations, where cold and hot weather conditions can arise. When the temperature becomes hot, as it often does in Japan during the summer months when the P. snelleni nests are in existence, the paper wasps need to take measures to cool down the nest. Water transport to the nest occurs after the appearance of larvae, and once it starts, it occurs about 10-15 times in succession. Water drops are carried by the wasps and put on the concave nest roof. This aids in cooling the nest. When there is shade over the nest, the wasps move the water and throw it away.Interaction with other species
Diet
The founding queen of a nest goes through the process of first hunting, then the disposition of prey, transport, another disposition, and then finally giving food to the larvae. The larvae are fed with animal diet. The queen finds the prey in a single flight from the nest that lasts usually 10–30 minutes. The queen sucks fluid from a pellet on the nest or nearby, and feeds it to the young larvae. The feeding is done by an antenna inserted in a cell where the larvae are. There is solid residual left from the pellet which the queen eats or throws out. When there are different ages of larvae present, the pellet is given to older larvae first and then the queen gives the leftover fluid to all the larvae, both young and old.Parasitoidism
P. snelleni is a host wasp for the parasitoid Elasmus japonicus, a smaller species of wasp. Adults of E. japonicus sit on leaves and twigs near the nests of P. snelleni, and fly around the nests. When P. snelleni notice that E. japonicus is near the nest, they flutter their wings and dart on the comb. Sometimes, P. snelleni bite and kill E. japonicus. P. snelleni recognize parasitized cells in their nests and host the remnants of the parasite there. It is beneficial for P. snelleni to kill the parasitoid larvae because adult E. japonicus could reparasitize the nest.Worker queen conflict
Orphan colonies
Orphan colonies are colonies that are maintained by workers after the queen is gone from the nest. Orphaned workers have the ability to mate and produce female offspring, but they only begin to oviposit after the queen has disappeared. This is unique to P. snelleni. Orphaned workers can act essentially as replacement queens, because they can inhibit mating in other workers and founding queens. It has been said that P. snelleni goes by the mode of serial polygyny, however this was disproven because by the time new reproductive females are ready to reproduce, the season is ending. So, only a few queen replacements can occur. There are usually 1-2 laying workers that are elderly in these orphan colonies. The dominant laying workers in a nest have a monopoly over ovipositions by selectively egg-eating.Conflict over egg laying
Since the founding queens of P. snelleni are likely to disappear, it is necessary that these orphaned workers have the ability to reproduce females for future generations to exist. There is social tension over reproduction between queens and workers because of this, where queens monopolize egg production while they are in the nest.Queens of P. snelleni produce males before females, which is called protandrous production. This is driven by sexual selection for the optimum sex ratio, and so there is a higher fitness for all. Because of protandrous production, orphaned workers are selected to produce female offspring, since they are reproducing so late in the season. They mate in order to make diploid female offspring.