Belonogaster petiolata is a species of primitively eusocial wasp that dwells in southern Africa, in temperate or subhumid climate zones. This wasp species has a strong presence in South Africa and has also been seen in northern Johannesburg. Many colonies can be found in caves. The Sterkfontein Caves in South Africa, for example, contain large populations of B. petiolata.Keeping, Malcolm G. "Social Behavior and Brood Decline in Reproductive-phase Colonies Of Belonogaster Petiolata (Degeer) (Hymenoptera: Vespidae)." Journal of Insect Behavior 10.2 (1997): 265-78. Web. 20 Sept. 2014.
This species primarily eats small insects, especially caterpillars, which are considered its "solid food", while nectar is its liquid food. It also requires water for survival.Keeping, Malcolm G. "Social Organization and Division of Labour in Colonies of the Polistine Wasp, Belonogaster Petiolata." Behavioral Ecology and Sociobiology 31.3 (1992): n. pag. Web. 20 Sept. 2014.
Taxonomy and phylogeny Belonogaster petiolata belongs to the genus Belonogaster, of the subfamily Polistinae, and is closely related to B. juncea and B. grisea. Belonogaster wasps are part of the family Vespidae and the order Hymenoptera."Animal Diversity Web." ADW: Belonogaster Petiolata: CLASSIFICATION. N.p., n.d. Web. 20 Sept. 2014. Species in this family display a full range of social organization, from completely solitary to highly eusocial life cycles. Many of B. petiolata characteristics are very similar to those of B. grisea. In both species, the production of smaller, unmated worker offspring reaches a maximum before the production of larger queens who leave the nest and mate.Keeping, M.g. "Morpho-physiological Variability and Differentiation of Reproductive Roles among Foundresses of the Primitively Eusocial Wasp, Belonogaster Petiolata (Degeer) (Hymenoptera, Vespidae)."Insectes Sociaux 47.2 (2000): 147–54. Web. 20 Sept. 2014.
Description and identification These wasps have a thorax (upper midsection area) and a longer striped gaster with a sting on the end. The peduncle is the first gastral segment. The legs are attached to the thorax. The queen B. petiolata has a large gaster and a smaller head, while the worker wasps have relatively large heads and smaller gasters. Also, queens, males and other members of the reproductive caste have larger fat reserves than the workers, allowing them to survive the winters.Keeping, M.g. "Reproductive and Worker Castes in the Primitively Eusocial Wasp Belonogaster Petiolata (DeGeer) (Hymenoptera: Vespidae): Evidence for Pre-imaginal Differentiation." Journal of Insect Physiology 48.9 (2002): 867–79. Web. 20 Sept. 2014.
B. petiolata construct paper nests out of pulp that often hang in caves or under shelter. The wasps often get pulp from old cells or from larvae just before maturation. Before the larvae mature, the wasps chew the cells at the base to help the offspring emerge. This cell debris is used to build nests. The nest has combs in which the queen often dwells. Later on, however, the queen may move to the top of the nest to rest.
Distribution and habitat B. petiolata can be found in southern Africa and they have a large presence in the country of South Africa. They prefer warm temperate or moist subhumid climates, with mean daily temperatures varying between a maximum of and minimum of in January and a maximum of and minimum of in June. This species primarily resides in sheltered caves. They build nests hanging from cave walls. This species is abundant in southern Africa, and it is not a threatened species.
Colony cycle The annual nesting cycle of B. petiolata is similar to other Polistines that dwell in similar temperate climates. Colonies which are started by a single queen are usually only primitively eusocial and smaller in size, while colonies started by groups of queens are more eusocial and house more individuals. The annual nesting cycle in B. petiolata typically begins in August, where nests are created by overwintered foundress females. In a colony, there is a pre-emergence period. This occurs before the emergence of the first offspring, which are the worker wasps. Next, there is a post-emergence period, which is the whole duration of the colony cycle following the appearance of offspring wasps. There is also a pre-matrifilial phase, which is the first part of the post-emergence period when subordinate foundresses are still present in nests and interact with workers. Following this period is the matrifilial phase which follows the disappearance of all subordinates. Now, colonies consist only of the queen and her workers. Lastly, there is a reproductive phase where reproductive offspring (gynes and males) are born. Typically, gynes begin emerging from nests in early February, so any female collected in colonies up to the end of January of each season will most likely be workers. Nesting is annual with single, overwintered foundresses initiating new nests in spring. The overwintering period is about 4.5 months. Later, in roughly half of the cases, one or more additional females come to form multiple foundress colonies and join these initial foundresses. Foundress associations of up to 16 foundresses can be formed. A dominance hierarchy then forms with the dominant female becoming the queen and the others becoming subordinates. The queen helps build and initiate the nest at first, during the pre and post emergence periods, but then becomes lethargic. She stops foraging for pulp and ceases her aid in the nest construction. At the end of the season, the female queen leaves the nest for the winter and returns the following year to create a new colony.
Mortality and decline of a colony Several factors appear to contribute to brood decline and the end of the colony cycle in B. petiolata. These include: cessation of the supply of solid food to colonies and larvae during the reproductive phase, a decrease in the worker/larva ratio during the latter phase due to the slow loss of workers, increasing the number of gynes and males, and an adult priority over food reception from foragers. The brood gets aborted to feed hungry adults. Eventually, the brood declines and the adults leave the nest. Usually, some cell demolition is done by the queen in post emergence colonies.
Behavior
Dominance hierarchy The workers carry out nearly all the basic work, like creating and fixing damage to the nest, getting food, and feeding the larvae. The queen's primary job is to lay eggs. When there is an active queen, workers often have undeveloped ovaries. However, when the queen is removed, 11% of workers develop mature ovaries. This is reproductive suppression under the power of the queen. If there are any eggs found that are not laid by the queen, she eats them (oophagy). Most of these eggs were likely laid by subordinates. Queens often get to rest in the central areas of the nest close to the growing larvae while subordinates and workers often position themselves in the outer areas of the nest.
Dominant interactions and communication The queen creates a dominance hierarchy by initiating dominant interactions. These include biting, hooking, and soliciting. In hooking, females grasp subordinates and hang from them in a hook like formation while receiving regurgitate. The queen often displays these behaviors to assert her dominant status to the other wasps. In soliciting, the dominant female approaches the other female with her antennae outstretched and antennates her head, especially her mouthparts. The other females respond by ignoring the soliciting, remaining immobile in a submissive way until the other wasp leaves, or by soliciting back. Sometimes the queens initially exhibit dominance behaviors, but then move to the top of the nest and become more inactive towards the end of the colony cycle. Other times, the queens are always dominant throughout the whole cycle. Females usually direct their dominance behaviors at the females directly below them in the dominance hierarchy. The queens are the most aggressive females in the nest, so receive fewer threats.
Oophagy and oviposition behaviors Sometimes, a queen or another female will eat eggs laid in her own colony. The majority of the time she eats the eggs of her subordinates, however, a female may occasionally eat her own eggs. Queens also undertake egg inspections to see if the eggs in the nest are their own or if they were laid by a subordinate. The majority of oophagies are committed by the queen (87.5%). Oviposition is the laying of eggs. Queens lay 83.3% of the eggs in pre-emergence colonies, which is a significantly higher rate of oviposition than that of subordinates. Workers were never observed eating or laying eggs.
Trophallaxis The larval saliva of B. petiolata contains many amino acids and nutrients that are useful for adult wasps. Females who are looking to lay eggs solicit larvae in order to receive some salivary fluid so they can gain some nutrients before laying the eggs. To do this, females undergo trophallaxis with the larvae. The larvae are first fed masticated food by the females wasps and then in return, the larvae produce salivary fluid. Usually, the wasps prompt the larvae to produce this salivary secretion by antennating a larva's head and vibrating its body. The larva then extends its head and produces a drop of clear saliva. Adults wasps prefer to solicit older larvae for trophallaxis, likely because they expect to receive more saliva from older larvae than from younger larvae. Sometimes, body vibrations of soliciting adults become synchronized and this seems to excite the larva in a positive way.
Kin selection
Caste system There is a caste system within the B. petiolata colonies. There are physiological and morphological differences between worker castes and reproductive castes. Foundresses and gynes (reproductive caste) are generally larger than workers. When workers are first born their body size is much smaller than gynes and foundresses, but later in the colony cycle, their size grows more similar to gynes. Foundresses and gynes have larger ovaries and more fat content than workers do. Workers have broad heads, while the reproductive caste wasps have broader thoraces and gasters. Typically, foundresses are larger than their subordinates. Also, about 98% of queens (foundresses) and 95% of gynes are found to be inseminated, while workers are not. They have immature ovaries that do not function in the presence of an active queen. When there is no active queen, about 11% of workers develop mature ovaries. Active queens are the primary egg layers in colonies and possess well-developed ovaries. Differentiation of castes sometimes occurs early during larval development, or it can happen during the later adult stage due to differing social communications and adult nutrition. A wasp's ability to survive winter, and its number of fat reserves, has been used to distinguish gynes from workers. Fat content is an indicator of caste.
The removal of the queen The dominance of the queen over the colony keeps the subordinant nature of worker wasps intact. When a queen dies, however, an older alpha worker, that was likely present when the colony was younger, often takes up the dominant position. The loss of a queen is also associated with the development of ovaries in 11% of worker wasps and in many alpha workers. During the pre-matrifilial stage, in colonies of B. petiolata, removal of the queen led to her replacement by the second most dominant foundress, who is known as a beta-foundress, instead of a worker.
Reproduction
Copulation