The foraging system ofPheidole militicida (Hymenoptera: Formicidae)

Abstract

1 -Foragers of the harvester antPheidole militicida travel along well defined trunk trails to their foraging grounds. These trails can be subdivided into three major sections: trunk, branches and twigs (fig. 2). 2 -Trunk and branches can last several days or even weeks, whereas the design of the outermost twig section changes daily. 3 -The persistence of a trunk route depends on the amount of seeds available in the foraging area to which it leads. When an area has been greatly depleted of its suitable seed supplies, the trunk route is abandoned and a new one, leading to a different area, is established. 4 -Trail pheromones, originating from the poison gland of workers, play a major role in regulating the activity along the foraging routes. They contain not only a recruitment signal but also an orientation cue, which is responsible at least in part for the remarkable precision of orientation by workers during their foraging excursions. 5 -The trail pheromones are highly species-specific in those sympatricPheidole species that employ a trunk trail foraging system (P. militicida, P. tucsonica, P. rugulosa). 6 -Although the so-called soldier caste ofP. militicida follows natural as well as artificial trails drawn with worker poison gland secretions, their own poison gland substance does not contain a trail pheromone. 7 -It was demonstrated that the foraging pathways ofP. militicida are marked by very enduring chemical cues, which might be distinct from the poison gland trail pheromone. 8 -Not only chemical cues but also visual guidelines seem to play a role in the directional maintenance of the trunk route. The remarkable route fidelity of foragers ofP. militicida seems to depend in part on specific landmarks. 9 -The well defined, chemically marked trunk trails enableP. militicida to conduct extensive foraging excursions during the night, when almost no visual orientation seems possible. 10 -The trunk route foraging system ofP. militicida is compared with that ofPogonomyrmex rugosus andP. barbatus and with the column foraging ofveromessor.