Nutrition induced direct fitness for workers in a primitively eusocial wasp

Eusocial insects are characterised by a reproductive caste differentiation such that egg-laying is restricted to a small number of queens. The majority of the colony members function as non-reproducing workers and gain indirect fitness by rearing the offspring of the reproductives. In primitively eusocial species, some workers can also get direct fitness by sneaking in some eggs in the presence of the queens, replacing the queens and becoming new queens, or initiating new nests. Here we aimed to understand the factors that permit some workers to gain direct fitness and alter the number of workers doing so, using the primitively eusocial wasp Ropalidia marginata. We transplanted 12 naturally occurring colonies into large laboratory cages where there was adequate space for the workers to leave their natal nests and initiate new colonies. We compared six control colonies that we provided with ad libitum food placed near the nest to six test colonies in which we hand-fed the wasps in addition to the ad libitum food. Wasps in test colonies consumed more food, showed more aggression, replaced their queens, and initiated new nests significantly more often than those in control colonies. When considering all 12 colonies, the rates of queen replacement and nest foundation were significantly positively correlated with food consumption rates. The additional nutrition gained by hand-fed wasps appears to help workers in test colonies to develop their ovaries and lay eggs, implying that they are nutritionally castrated in control colonies.

Identification and ecology of wasps (apocrita: hymenoptera) of Dhaka city

During the study period a total 351 wasp was collected from three different areas of Dhaka city viz Curzon Hall, Ramna Park and Sher-e-Bangla Agricultural University from October 2017 to May 2019. Among them 14 species belonging to four families- Ampulicidae, Sphecidae, Vespidae and Scoliidae were identified. The species were Ampulex compressa, Chalybion bengalense, Scolia sp., Laeviscolia frontalis, Delta esuriens, Rhynchium quinquecintum, Antodynerus flavescens, Parapolybiavaria sp., Ropalidia marginata, Polistes olivaceus, Polistes watti, Polistes stigma, Vespa tropica, and Vespa affinis. Standard taxonomic keys and sharp perception of outside morphology like head, wing venation, antennal sort, physical coloration etc. of the wasps were examined to identify them. Maximum of the distinguished species were beneath the family vespidae (72%). In the present study, it was observed that the maximum number of wasps were collected in May (29.63%). The richness of wasp species was more plenteousin Curzon Hall area (47.58%) than the Sher-e-Bangla Agricultural University area (40.17%) and was less abundant in Ramna park (12.25%). The main reason for finding more richness of wasp species in Curzon Hall area was the presence of various types of hedging plants than other two areas as the wasps were found to prefer hedging plants for foraging. It was also observed that Polistes olivaceus (21.93%) was the most abundant and Chalybion bengalense was (0.85%) the least abundant species in the study areas. Bangladesh J. Zool. 48(1): 37-44, 2020

A place for everything and everything in its place: spatial organization of individuals on nests of the primitively eusocial wasp Ropalidia marginata

Non-random space use is common among animals across taxa and habitats. Social insects often use space non-randomly, outside as well as inside their nests. While such non-random space use outside the nest may improve foraging efficiency, inside the nest, it is often associated with the efficient division of labour. Non-random space use by adults on their nests has been hypothesized to result from dyadic dominance interactions, non-random distribution of tasks, differential activity levels, workers avoiding their queens or prophylactic avoidance of disease spread. These hypotheses are generally derived from species in which the tasks of the workers are themselves non-randomly distributed on the nest. Here, we study the primitively eusocial wasp Ropalidia marginata , in which tasks are not distributed non-randomly, and show that 62.4% ± 16.2% of the adults nevertheless use space on their nest non-randomly. In this species, we find that non-random space use may help optimizing nutritional exchange between individuals while prophylactically minimizing disease spread among nest-mates. We did not find evidence for the roles of dominance interactions, activity levels or location of larvae in non-random space use. Spatial organization appears to be a mechanism of minimizing the costs and maximizing the benefits of social life.

Ontogeny of familiarity with foraging landscape and foraging abilities in the tropical social waspRopalidia marginata

ABSTRACTPossessing spatial familiarity with their foraging landscape may enable animals to reduce foraging effort without compromising on foraging benefits. For animals inhabiting feature-rich landscapes, spatial familiarity can increase with increasing age/experience. To check whether this holds for individually foraging tropical social waspRopalidia marginata, we recorded the number and duration of all foraging trips, the identity of the materials brought to the nest (building material, water or food) and the directions of outbound and inbound flights (respective to their nests) of known-age foragers from three natural colonies, each for three consecutive days. The average trip duration and time spent daily in foraging increased rapidly until about first four weeks of their life, during which they rarely brought food to their nest, although many of them brought building material and water. Thereafter, their average as well as per day duration of foraging trip started decreasing gradually. Nevertheless, their foraging efficiency and success for food kept on increasing monotonically with age. These results suggest that older wasps were more efficient in foraging despite spending less time doing so. With increasing age, wasps developed individual preferences for the direction of their outbound flights, increased directionality of their inbound trips as well as the angular difference between their outbound and subsequent inbound flights, indicating development of spatial memory. We conclude that wasps acquire familiarity with their foraging landscape in their initial foraging phase and gradually develop robust memory for rewarding sites and routes to those sites, which enables them to increase their foraging capabilities.SUMMARY STATEMENTContrary to insects inhabiting less-featured landscapes, tropical social wasps invest weeks to get familiar with foraging landscapes during their early foraging lives. This eventually enables them to increase foraging gain with reduced effort.