MEMORY AND CHEMICAL COMMUNICATION IN THE ORIENTATION OF 2 MASS-RECRUITING ANT SPECIES

The relative contribution of visual and chemical components in the orientation of Lasius niger and Iridomyrmex humilis (Argentine ant) workers during mass recruitment to newly discovered food sources is analyzed over short time intervals. While both species orient in response to the trail pheromone, a large number of L. niger foragers rapidly switch to a more individual orientation, based on their memory of environmental cues. I. humilis workers, on the other hand, predominantly use collective chemical cues. The effect of the number of reinforcements on visual learning and its interference with chemical communication show that olfactory cues always prevail in the Argentine ant. In L. niger. the proportion of ants orienting to visual cues is independent of the trail concentration. Detailed observations of the trail-laying behavior of individually marked foragers show that nearly all the I. humilis workers initially lav a trail, whereas only half the L. niger foragers do so. This proportion decreases considerably with the number of trips performed by L. niger workers, while remaining constant for the Argentine ants. These results are interpreted with respect to the species' behavioral ecology.