Worker size polymorphism and ethological role of sting associated glands in the harvester ant Messor barbarus

Though harvester ants are closely similar in ecology, species differ in the ir worker size polymorphism as well as in the glandular source of their tra il pheromones and defensive compounds. In the harvester ant Messor barbarus , we find that the recruitment trail pheromone is located in the Dufour gla nd while defence-alarm substances are produced in the poison gland. We also investigated how the glandular development and the ethological response to these abdominal glands are related to worker body size. For both glands, M . barbarus workers show monophasic and nonisometric growths with slopes of allometric regression lines lower than 1. The highest trail-following respo nse is elicited by the Dufour gland secretion from media workers, responsib le for most foraging activities in M. barbarus. Aggressive behaviour is mor e frequently observed in the presence of poison gland secretions from mediu m and large-sized workers. Differences between species and between worker s ize classes in the ethological role of sting associated glands are discusse d in relation to the foraging ecology and defensive characteristics of harv ester ants.