Recruitment and food-retrieving behavior in Novomessor (Formicidae, Hymenoptera) - II. Vibration signals

1. In this article, we report the communicative effect of stridulation signals in Novomessor cockerelli and N. albisetosus during foraging 2. The structure of the stridulatory organ and the main characteristics of airborne and substrate-borne stridulation signals are described. 3. The stridulation signals are not perceived by the ants over any appreciable distance. However, workers that contact an object transmitting stridulatory vibrations stay at this probe significantly longer than at a nonvibrating control probe. 4. An information transfer analysis was performed by comparing the probabilities of occurrence of different behavioral acts in workers both before and after contacting either a 'stridulatory' test probe or a 'silent' control probe. Stridulation did not affect the behavior of food carriers; diggers that carried debris from the nest were slightly but significantly influenced; but a remarkable change did occur in the probabilities of behavioral acts by scout ants. 5. Stridulation alone does not release a specific behavioral response but rather enhances more or less a change to different behavioral activities in workers. 6. In a series of field experiments, it was shown that a prey object too large to be retrieved by one ant stimulates the finder ant to stridulate. It was further demonstrated that the vibrational signals received by a second ant that also contacted a prey enhance the release of chemical short-range recruitment signals by this ant. In our experiments, the facilitating effect of stridulation on chemical recruitment led to a time advance of 1-2 min in both the recruitment of workers and in the retrieval of large prey objects by groups of foragers. It has been demonstrated that the rapid group retrieval of large prey objects enables Novomessor workers to successfully compete with mass-recruiting ant species such as Solenopsis and Iridomyrmex. 7. Significantly more digging is only released at a 'stridulatory' test probe if the probe is offered very close to a nest entrance. 8. Stridulation in ants seems to be a mechanism for modulating the state of readiness of receivers to react to other stimuli (modulatory communication). The stridulation signal adjusts the distribution of the worker force to a given situation and to group needs in a graded fashion, but does not by itself release specific behavioral reactions. This phenomenon is compared with similar functions in other communication systems of complex animal societies.