Chemical Releasers of Social Behavior—IV. The Hindgut as the Source of the Odor Trail Pheromone in the Neotropical Army Ant Genus Eciton1

Abstract

Among the legionary or army ants in the Dorylinae, foraging workers lay continuous exploratory trails during emigrations and raids. Especially during emigrations these odor trails become very concentrated since they are being reinforced by the innumerable individuals in the massive columns. The most highly developed of the Neotropical genera, Eciton , lays persistent trails which may be followed even if encountered weeks after the trail was originally generated (Schneirla and Brown 1950). Although rainfall does not rapidly destroy these old trails, they appear to last longer during dry seasons (Schneirla and Brown 1950). These facts indicate that the Eciton odor trail pheromone is a substance which is relatively photostable, thermostable, and water-insoluble, and which possesses a low vapor pressure. With the exception of a recent investigation on the primitive doryline genus, Neivamyrmex, in which artificial trails were successfully prepared from recta and midguts (Watkins 1964), nothing is known about the source of army ant trail pheromones. The present experiments were carried out to establish the glandular origin of the odor-trail pheromone of E. hamatum (F.). The ants were collected along the Ucayali River at Buenos Aires, 25 km south of Pucallpa, Peru.