Spatial organization of collective food distribution in a paper wasp society

Abstract

In social insect colonies, food transferred through space and time via nestmates carries both nutrition and information. We study the mechanism of spatio-temporal coordination (or the lack thereof) between multiple wasps for them to optimally solve the problem of feeding randomly placed larvae in a social insect colony. We followed each morsel of food brought into semi-natural colonies of the tropical paper wasp Ropalidia marginata, in each of 36 feeding bouts until the food was exhausted. We found that most acts of feeding larvae are performed by wasps that unload food from foragers, but unloading itself is highly skewed among individuals. We also found that larvae closer to the nest center were fed more frequently than those at the periphery, irrespective of their developmental stage. This differential feeding may have fitness consequences as it is known that well-fed larvae become voracious feeders as adults and have a higher likelihood to become reproductives. Using the analogies of the travelling salesman problem and the Hamiltonian path problem, we showed that individuals which disburse food to more larvae within a feeding bout adopted paths that were considerably shorter than expected by chance while the distinction between adopted and random routes was not as pronounced when the number of larvae fed in a bout was fewer. There was no spatial segregation between wasps feeding larvae in parallel, possibly building redundancy and avoiding larval starvation across bouts. Understanding the spatial organization of food transfer may be a key to understanding how insect societies achieve efficient social organization and division of labor. SignificanceThe limited studies on within-nest spatial organization of food distribution have been performed on ants and not primitively eusocial insects like wasps that contain randomly placed yet trackable larvae within the colony. We address the gap in a holistic understanding of spatial organization of food distribution through our study in the social wasp Ropalidia marginata. Through the lens of task partitioning, colony-level larval landscape, and spatial strategies adopted at individual and collective scales, our study presents one of the most detailed account of behavioral and spatio-temporal data mapping sources and sinks of food in a colony chronologically. We found that feeding routes adopted by wasps while feeding randomly placed larvae within a colony may not be a result of random walk but instead the degrees of route optimization based on the food load available to distribute within each feeding bout. We suggest paper wasp colonies to be ideal model systems for spatial studies owing to their observable colony sizes and randomly placed brood. Understanding the mechanism of colony-level problem solving by individuals with limited local information has widespread real-life applications besides a better understanding of social organization in colonies of social insects.