The responses of workers of the leaf-cutting ant Atta sexdens rubrophilosa to their alarm pheromone

The composition of the alarm pheromone of the polymorphic workers of the leaf-cutting ant Atta sexdens rubropilosa varies with the size of the work. This study examined the responses of different sizes of workers to two main components of the alarm pheromones, citral and 4-methyl-3-heptanone.In the laboratory, the threshold concentrations of citral and 4-methyl-3-heptanone needed to elicit attraction, arrestment and biting in minim and mead workers were measured and dispersion dynamics of these chemicals predicted. In all cases, except biting elicited by citral, there was no difference between the thresholds of minims and medias. Whole pheromone, from both large and small workers also attracted all sizes of worker and elicited aggressive biting behaviour. Tests of increasing concentrations of citral and 4-methyl-3-heptanone showed that low concentrations of both compounds attracted more workers than higher concentrations.Field experiments showed that the response to alarm pheromone varied with positional context. At mound entrances workers retreated and at foraging sites little alarm response was seen. However on the trails, both close to and far from the nest entrance, a strong alarm response was elicited with minims in particular responding in large numbers close to the nest entrance. Laboratory experiments also showed that more workers responded to alarm pheromone when they activity collecting leaves than when they were not.Sensilla on the antennae of workers, queens and male ants were studied using the scanning electron microscope. Eight morphological types were identified and their numbers and distributions were compared between workers, queens and males. Both antennal area and total number of sensilla were found to increase with the size of worker.