Recruitment in starved nests: the role of direct and indirect interactions between scouts and nestmates in the ant Lasius niger

Abstract

In social insects, the foraging activity usually increases with the length of food deprivation. In Lasius niger, a mass-recruiting ant species, the foraging adjustment to the level of food deprivation is regulated by the scout that fed at the food source and by the response of the nestmates to signals performed by the scout inside the nest. In this study, we look at the role of these direct interactions (antennations or trophallaxes) and indirect interactions (pheromonal emission) and how they are influenced by the level of food deprivation. At the beginning of recruitment, the relative number of nestmates leaving the nest to forage increases with the level of deprivation. The nestmates’ propensity to exit the nest is not influenced by a previous trophallactic and/or antennal contact with a scout. Our results strongly suggest that the exit of nestmates is triggered by a chemical signal emitted by a scout. Deprivation lowers the response threshold of nestmates to this chemical signal resulting in a more important exit from the nest. Surprisingly, 27% of starved nestmates that receive food from the scout relay the information by depositing a chemical signal before having discovered and drunk the food source. Both phenomena boost the recruitment process. Though successful foragers returning to the nest have a significant role in the recruitment to the food source, we observed that the response of the nestmates inside the nest also greatly influence regulation of the foraging activity.