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

The relative contribution of visual and chemical components in the ori entation of Lasius niger and Iridomyrmex humilis (Argentine ant) worke rs during mass recruitment to newly discovered food sources is analyze d over short time intervals. While both species orient in response to the trail pheromone, a large number of L. niger foragers rapidly switc h to a more individual orientation, based on their memory of environme ntal cues. I. humilis workers, on the other hand, predominantly use co llective 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 behavio r 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 trip s performed by L. niger workers, while remaining constant for the Arge ntine ants. These results are interpreted with respect to the species' behavioral ecology.