Chemical communication among workers of leaf-cutting ants (Hymenoptera: formicidiae)

Jaffé, Klaus (1979) Chemical communication among workers of leaf-cutting ants (Hymenoptera: formicidiae). University of Southampton, Doctoral Thesis.

Abstract

The recruitment system of Atta cephalotes workers was studied in the laboratory. The number of ants recruited to a food source depends on the quality of the food and on the duration of starvation of the colony, and is related to the concentration of trail pheromone on the trail but not to the number of ants initially returning to the nest from the food source. There is a relationship between the concentration of pheromone on the trail and the attractiveness of the food. A component of the trail pheromone, methyl4-methylpyrrole-2-carboxylate was found to elicit similar recruitment behaviour to a natural trail. Individual workers of A. cephalotes appear to modulate the number of ants recruited for food retrieval by varying the quantity of pheromone secreted from the poison sac during trail-laying. A theoretical analysis of chemical mass recruitment in ants showed that the participation of an important proportion of scout ants in the recruitment process is essential. The optimum proportion depends mainly on the distance to the food. Orientational cues different from the trail pheromone increase the recruitment efficency. Attraction to the trail and orientation to the food source need to be maintained as separate events, either by using two behavioural thresholds towards the same pheromone or using different pheromones for each purpose. Thus, the pheromone concentration on the trail is maintained constant by scouts during recruitment, and is related to the quality of the food. Equilibration of recruitment is achieved by the ants by reacting to increasing ant densities on the food source and on the trail, with decreasing recruitment efforts. A. cephalotes and Acromvrmex octospinosus use various different cues for orientation when following an odour trail. Each cue has a different importance in orientation along a trail, in which there is a hierarchy for As cephalotes in which the most important cue is the presence of an odour trail,followed by visual navigation; gravity cues; maze learning with secondary visual cues; maze learning in the dark; and odour differences on the trails.Workers of A. cephalotes mark the area around their nest with a pheromone that has at least two components, one of which is colony-specific (probably the alarm pheromone from the mandibular gland). Another, which was isolated and tested for its activity, is genus- or species-specific. This pheromone is produced by the valves gland located near the sting and consists probably of a nonadecadiene. A. cephalotes recognises workers from other species and from other colonies of its own species as alien. Species-recognition appears to be based on volatile substances on the cuticle, probably from the mandibular glands. There is some evidence that colony-specific recognition rests on detection of colony differences in the composition of the cephalic alarm pheromone. These ants dispose of waste products from the nest in a way different from that in which they dispose of wastes of other origins. The process of dumping refuse seems to involve a different programme of behaviour from that used for collection of food, although no caste-specificity in this behaviour could be detected. Chemical signals are used to recognise the wastes originating from the nest.

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