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Chemical Ecology: The Chemistry of Biotic Interaction
Aphaenogaster conducted by D. Morgan and his collaborators and subsequent behavioral tests of the identified compounds revealed that the main recruitment pheromone of A. cockerelli is (R)-(+)-l-phenylethanol, and that of A. albisetosus is 4-methyl-3-heptanone (41). But A. cockerelli poison gland secretions also contain 4-methyl-3-heptanone and 4-methyl-3-heptanol; A. cockerelli workers do not, however, respond to these latter secretions with trail-following behavior. On the other hand, A. albisetosus respond to the 4-methyl-3-heptanone in the A. cockerelli secretions but not to the phenylethanol. Incidentally, the latter substance was not previously known to be an ant pheromone and is very unusual for poison gland contents. Thus, although we find cross-specific responses in A. albisetosus, this species reacts to a different component in the A. cockerelli trail than do A. cockerelli workers themselves.
In addition to pheromone blends in a single exocrine gland, multicomponent signals can derive from multisource systems. In such systems various compounds are released from multiple glandular sources. The substances may serve the same essential functions, but often the roles are different. In the harvester ant Pogonomyrmex badius, for example, the recruitment pheromone is voided from the poison gland, whereas the long-lasting homing pheromones originate at least in part in the Dufour's gland (13). Further investigations of this multisource system in the genus Pogonomyrmex have revealed that the recruitment signal is, as far as we know, invariant among several sympatric Pogonomyrmex species, whereas the Dufour's gland secretions contain species-specific mixtures of hydrocarbons (14, 15). Field and laboratory investigations suggest that in the partitioning of foraging areas among sympatric species of Pogonomyrmex both the short-lived anonymous recruitment signals and the more persistent species-specific Dufour's gland secretions are involved. The latter appear to mark the trunk routes, which also bear colony-specific markers, the origins of which are not yet known. A similar situation has been observed in ants of the genus Myrmica, which produce relatively anonymous recruitment signals originating in the poison gland and species-specific mixtures of hydrocarbons in the Dufour's glands that are used as home range markers (10, 11).
Many ponerine ant species conduct predatory raids on termites and other arthropods, and generally these are organized by powerful trail pheromones which are often composed of secretions from several glands. In group-raiding Leptogenys species one component originates from the poison gland, but a second orientation pheromone, (3R,4S)-4-methyl-3-heptanol, derives from the pygidial gland (16, 17). We recently discovered an identical situation in Megaponera foetens (18). In both cases the poison gland secretions have a stronger orientation effect, while the pygidial gland secretions serve as the major recruitment signal. In several