title: Response thresholds to recruitment signals and the regulation of foraging intensity in the ant Myrmica sabuleti (Hymenoptera, Formicidae).
abstract: The optimal foraging theory predicts that colonies of social insects must be able to adjust the intensity of their foraging behaviour as a function of the quality of the food discovered. Here, the mechanisms allowing the regulation of recruitment as a function of food concentration in the ant Myrmica sabuleti were analyzed. Although the total number of foragers engaged in food collection during recruitments increased with increasing concentration of sucrose solutions (0.1 vs. 1 M), neither the proportion of recruiting scouts nor the invitation behaviour performed by the scouts in the nest can explain this relationship. Foragers trail more when coming back from a 1 M than from a 0.1 M sucrose solution. However, this alone cannot explain the collective patterns observed since the mean numbers of workers leaving the nest after the entry of a scout coming back from either 0.1 or 1 M sources were not significantly different. We suggest that a spatial distribution of the foragers in the nest as a function of their motivational state could be part of the regulation process. The ants located near the nest entrance would respond to both low and high trail pheromone signals, but those located deeper in the nest would respond only to high level signals, resulting in higher recruitment rate towards richer sources.
authors.affiliation: Laboratoire de Biologie Animale et Cellulaire-CP 160/12, Université Libre de Bruxelles, 50 Avenue F.D. Roosevelt, 1050 Brussels, Belgium.
authors.forename: J C
authors.initials: JC
authors.lastname: de Biseau
authors.forename: J M
authors.initials: JM
authors.lastname: Pasteels