Agelaia multipicta

Agelaia multipicta is a swarm-founding, highly eusocial wasp that lives in Mexico, Argentina, Trinidad and southern Brazil.^[1] It nests in natural cavities such as hollow trees and aggressively defends the nest from ants, who are brood predators.^[2] The workers and queens are morphologically distinguished by ovarian development as well as external features such as a larger petiole and gaster in the queen.^[3] Like other carrion-eating (necrophagous) wasp species, A. multipicta plays a scavenging role in the ecosystem.

Taxonomy and phylogeny

A. multipicta is an insect of the order Hymenoptera, winged insects, and the family Vespidae, containing all species of eusocial wasps and many solitary wasps. The subfamily Polistinae, to which A. multipicta belongs, contains eusocial wasps as well as all the social wasps in the Neotropics. Four tribes are embedded within the subfamily, Polistini, Mischocyttarini, Ropalidinni and finally Epiponini, to which A. multipicta belongs. Agelaia multipicta was identified by the Irish entomologist Alexander Henry Haliday in 1836.^[4]

Description

James Carpenter's taxonomic key describes characteristic features of this species such as that the "hind-wing with jugal lobe normal, not reduced," and that the head has an occipital carina present.^[5] Additionally, in A. multipicta Carpenter notes the "pronotum without sinuous carina" and the "body without pale maculations, cuticle partly to entirely bluish metallic or yellowish with some bluish highlights; head in lateral view with tempera as wide or wider than eye at ocular sinus"^[5]

The species is not monomorphic because workers are significantly smaller than the queens.^[2] Caste differentiation arises from distinct biological functions; for the observer, caste differentiation presents significant differences in morphology. Most morphological differences between queens and workers are externally visible, but the ovarian development is also significantly different between the two castes. It is highly reduced in the non-reproductive workers. Queens have a larger petiole with more hairs and the queen's gaster is bigger. Worker's have a middle tibia and the space between their antennal insertions is brown, but in queen these areas are yellow.^[3]

Distribution

A. multipicta is found in Mexico, Argentina, Trinidad and Southern Brazil.^[1][2] Usually, their nests are observed in forest and rural habitats.^[4] This may be related to the tendency of A. multipicta to use natural cavities as nest building sites. These sites may be less prevalent in urban areas.

A. multipicta is the most abundant wasp species in Matão, in the state of São Paulo, Brazil, a well-preserved area which has little variety of wasp species. The area is surrounded by citrus crops. In a study regarding forest fragmentation there were no strong tendency in A. multipicta habitation regarding habitat type, this is probably due to their generalist nature.^[6]

Colony cycle

Wasps in the Epiponini tribe use an exposed, single-comb nest, attached with a broad pedicel to its substrate.^[7] A. multipicta's nests are exposed in a sense that they are not surrounded by an envelope. However, the nest usually occurs in spaces that are naturally enclosed, such as hollow trees and cavities in the ground. These natural structures may be filling the protective role usually fulfilled by an envelope. The combs can be irregular, not always parallel, and the cells in some findings are 3.0 mm wide and 9.0 mm deep. The variety of nest architecture and location observed in A. multipicta is thought to reflect their adaptability to the variations in cavity-like spaces present in the natural environment.^[2]

Behavior

Behavior of A. multipicta trends towards being physical as opposed to chemically influenced. When multiple wasps of A. multipicta encountered each other on a food source there were displays of aggression in some but not all cases, possibly indicating the difference between nestmates and non-nestmates.^[8] A. multipicta also uses aggressive behaviors to combat ants on their nests, with bursts of wing buzzing or throwing ants off the nest with their mandibles. Other wasps, usually non swarm-founding species, do not combat ants in this way and instead uses chemical repellents.^[7] Also there is no observed use of chemical markers or any communication between wasps that foraged on carrion and any nest-mates ^[8]

Feeding

Foragers from different colonies have been observed at the same feeding site, suggesting that colony foraging territories overlap. Scramble competition seems to be the main foraging strategy used by this species.^[8]A. multipicta is a major egg predator of the harvestman Acutisoma proximum, despite the maternal guarding attempts by this species.^[9] These wasps feed on vertebrate carrion itself as well as the larval flies growing on it. This makes A. multipicta both a predator and a necrophage, but the wasps favor fresh carcasses with more meat as opposed to more decomposed carcasses with more flies, suggesting that predation may not be their primary mode of obtaining food resources.^[4]

Lack of recruitment

It is thought that Polistinae wasps are unable to recruit nest mates to carrion and that there is no communication about food resources in the nest. This idea was supported in an experiment with A. multipicta in Brazil where foragers were marked upon arriving at an experimental carrion site. The number of incoming individuals were counted respective to time as well as the amount of returning wasps. There was no notable increase of new wasps coming to carrion over time. This included instances after marked wasps departed the carrion, left in the direction of the nest, and then returned to the carrion. This suggests that there is not a lack of opportunity to communicate to nest-mates, but perhaps a lack of ability. This supported the conclusion that there is no nest-mate recruitment for carrion occupation.^[8]

Possible reasons

There are several reasons why food recruitment might not be present in this species. One possibility is that carrion is relatively rare as a food source for A. multipicta and it was not advantageous enough to drive the development of food sharing communication. Another possibility is that groups could not actually conjure enough force to effectively dominate against other colony groups, the increased competition would waste energy. This could be dependent on a currently unknown critical colony size at which the costs of recruitment outweigh the benefits. Although meat is a rich larval food source, if it is not possible to store it at the nest it is less useful to recruit. If other storable food sources, such as nectar, were collected and stored, this argument may be supported. Any argument for the reason of this absent behavior requires more experimentation.^[8]

Queen relatedness

Queens of A. multipicta have been determined to be highly related, a condition called oligogyny. Although it has not been directly studied for this species, a similar case of high queen relatedness in a multi-queen swarming species, Polybia emaciata, supports the cyclical oligogyny hypothesis. This hypothesis entails that the number of queens declines as colonies age, making the future queens more related to each other. Cyclical oligogyny may be influencing the relatedness of A. multipicta queens, but this requires species specific scientific investigation.^[10]

Defense against ants

Ants can act as a predator of wasp broods. Swarm founding wasps evolved a different defense against ants from the chemical repellent used by species with independent founders. Swarm founders, like A. multipicta, rely on the vigilance of workers on the surface of the nest to prevent ants from reaching the brood. A. multipicta responds to ants by immediately removing them from the nest by directing blasts of air at the ants with wing buzzing. If this does not knock the ant off of the nest, the wasps then grab the ant in their mandible and toss it off. Although it seems like this species relies on active defense, A. multipicta still retains a 6th sternal gland, which secretes the ant repellent chemical. It has not been studied whether that chemical function is retained in this species, there is thus far no evidence for its use.^[7]

Predation

Despite their ability to sting, wasp nests in the Neotropics are attacked by a variety of species including birds, bats, and capuchin monkeys. In Brazil, Galbula ruficauda is an avian predator that has been witnessed attacking A. multipicta when isolated from the nest, as when foraging. It is however thought to be relatively uncommon for animals to prey on solitary wasps.^[11]

Roles in decomposition

A. multipicta and other wasps play an important role in the decomposition process, making holes and abrasions in carrion that allow other species access to further eat away the dead. However, by preying on fly larvae present on carrion, they are depleting other populations that are contributing to decomposition. Nevertheless, because of the demonstrated preference of this species for fresh carrion, which has less flies and fly larvae and more meat, the role of A. multipicta likely leads to greater decomposition overall.^[4]

References