Ropalidia fasciata

Ropalidia fasciata belongs to one of the largest wasp taxa. Roughly 180 other species belong to the genus Ropalidia.[2] In discussion, R. fasciata is often grouped with and compared to Ropalidia marginata.[4] R. fasciata was classified by Johan Christian Fabricius in 1804.[1]

R. fasciata appears with a red-brown body with yellow stripes, and some black and yellow markings. The species are variable in color pattern, displaying the black markings to various degrees.[2] Queen-like and worker-like individuals are not morphologically distinguishable, but instead are differentiated based on behavior.[4]

R. fasciata is distributed consistently throughout grasslands within its range, mainly inhabiting fields that are invaded by the sugarcane Miscanthus sinensis. The wasps prefer to build nests under the leaves of this plant.[5]

Colonies are founded in the spring, most often by associations of multiple females. Females that hatched early the year before are referred to as 'foundresses', as they can choose to go on to found a new colony. R. fasciata has an annual, relatively long colony cycle that begins in April and continues into November or December. The first group to emerge from the nest in the spring are females who quickly adopt forager or fighter roles in the colony. Potential foundresses and males emerge later in the summer. Males are commonly found in both established and newly founded nests, a quality specific to tropical eusocial wasps. Unlike many species of temperate wasps, females do not attack these individuals.[6] Foundress survival rate from April until September can be as low as 1.4%, indicating that most foundresses die before the end of the season. However, nest densities are quite stable from year to year due to the species' flexible reproductive habits and persistence in nest maintenance and rebuilding. The qualities of R. fasciata's colony cycle are very similar to that of other primitively eusocial wasps.[7]

A complication in the typical explanation of eusocial insects exists for R. fasciata. Since multiple females remain reproductive in a group, the colony must function less like a cooperative organism and a higher degree of reproductive competition is expected. Intercolony relatedness is expected to be reduced in these wasps.[3]

Ropalidia fasciata and related species construct nests by collecting fibers from dead vegetation, mixing them with saliva, and using this mixture to construct vertical cells. The resulting material has a paper-like structure, hence their common name, the paper wasp.[9] R. fasciata often builds additional satellite nests as alternatives to the nest where the colony resides. That way if the main nest is destroyed, damaged, or threatened, at least some of the group can move to another nest. Occasionally, groups may relocate to a new nest without obvious cause. The immature wasps in the colony are moved to the new location by adults. Both foundresses and their progeny will help reconstruct a nest. R. fasciata foundresses do not disperse far from their natal nests, and foundresses of the same nest are often sisters.[5] In this species, it has been shown that if many females collaborate to found a nest, it will grow faster and have a higher survival rate than one with fewer foundresses.[4]

Individuals in a colony habitually share food with one another. One wasp will transfer nectar or water by mouth to another wasp by regurgitation. This behavior takes place between individuals who have not received any food recently, and the touching of mouthparts will occur even when there is no food to be transferred. Liquid food sharing between individuals typically reinforces the dominance hierarchy in similar species of wasp, but in R. fasciata this behavior appears to be a simple nutrition sharing technique or even a greeting, unrelated to dominance.[4]

R. fasciata nests are often predated upon by various species of ants, which attack immature R. fasciata individuals and can have a severe impact on nest survival. An ichneumonid parasite Arthula formosana commonly parasitizes R. fasciata nests. The frequency of parasitism has been shown to increase during the summer months.[7]