Individual flexibility and choice of foraging strategy in Polyrhachis laboriosa F. Smith (Hymenoptera, Formicidae)

We report in this study that the tree-dwelling African ant Polyrhachis labo riosa (Formicinae) uses different foraging strategies according to the size of the available food sources. We demonstrate that a recruitment behaviour can be induced with a 125 mu 1 alimentary reward and that foraging remains solitary when rewards are smaller. Small rewards do not elicit trail-layin g behaviour, and exploration behaviour is considerable. With large permanen t food sources, scouts use group recruitment and there is less exploration around the reward. The choice of the foraging strategy is determined by the first forager, which modifies its behaviour according to the volume of the food supply. Independently of the size of the reward, the forager shows ma ny exploratory displays during the first visit to the source, and contrary to most ants, it never lays a trail during its first return to the nest. Vi sual cues remain mainly used for individual orientation; information collec ted during the first trips are then transmitted to nestmates thanks to temp orary trail laying behaviour.