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This investigation shows that olfactory learning can be involved with food identification. An experimentally induced food preference can be obtained by presenting a scented food to newly hatched workers of Lasius niger (L.) (Hymenoptera Formicidae). Ten colonies were followed from their foundation. From the emergence of the first workers, the colonies were fed with a flavoured (anise) sugar solution (0.5M sucrose) during 1 month. After 3 months of hibernation without food, the colonies were submitted lo a choice test. The preference for the scented food indicates the existence of a “pre-hibcrnal learning” process with long term effects. Older foundations which were exposed to the flavoured food after the 3 months hibernation period preferred the known food, but the preference was less strong than that shown by the first group. Finally, mature workers from adult colonies, submitted to the same treatment, did not respond to the olfactory cues and exhibited no food preference. These results suggest the exist...

Foragers of the ant Lasius nigerexploiting a 1 Msugar source were found to lay 43 %more trail marks than those exploiting a 0.05 or a 0.1 Msource. The trail laying per forager decreased during the course of individual recruitment episodes, and the mean lifetime of the trail pheromone was estimated to be 47 min. A mathematical function describing the probability that a forager chooses one of two paths in relation to the amount of trail pheromone on them closely fitted experimental data. These results were incorporated into a model describing the recruitment dynamics of L. niger.Simulations of this model showed that the observed modulation of trail laying with respect to food source quality is sufficient in itself to account for the systematic selection of the richer source seen in the experiments.

A series of laboratory experiments show how colonies of the ant Lasius niger systematically select the shorter of two paths of varying length and form between nest and foraging area, and do so with a large majority of foragers. Three different mechanisms were considered to contribute to this selection, and were evaluated by comparing mathematical models with experimental data. Bi-directional trail laying was shown to contribute much less than U-turns, where the proportion of ants that turned back depended on the path's geometry and length, and also on the trail strength. A strong modulation of the amount of pheromone deposited per ant as a function of the path's geometry was found. This modulation can also contribute to the selection of the shorter branch in the experiments where the rate of U-turns is initially the same. The selection of the path is shown to be a collective process whereby trail laying and following amplifies small initial differences in the traffic on each path caused by these three mechanisms. The foragers show no significant tendency to follow the path they used previously.

This paper presents a series of experiments where a group of mobile robots gather 81 randomly distributed objects and cluster them into one pile. Coordination of the agents’ movements is achieved through stigmergy. This principle, originally developed for the description of termite building behaviour, allows indirect communication between agents through sensing and modification of the local environment which determines the agents’ behaviour. The efficiency of the work was measured for groups of one to five robots working together. Group size is a critical factor. The mean time to accomplish the task decreases for one, two, and three robots respectively, then increases again for groups of four and five agents, due to an exponential increase in the number of interactions between robots which are time consuming and may eventually result in the destruction of existing clusters. We compare our results with those reported by Deneubourg et al. (1990) where similar clusters are observed in ant colonies, generated by the probabilistic behaviour of workers.

The relative contribution of visual and chemical components in the orientation of Lasius niger and Iridomyrmex humilis (Argentine ant) workers during mass recruitment to newly discovered food sources is analyzed over short time intervals. While both species orient in response to the trail pheromone, a large number of L. niger foragers rapidly switch to a more individual orientation, based on their memory of environmental cues. I. humilis workers, on the other hand, predominantly use collective chemical cues. The effect of the number of reinforcements on visual learning and its interference with chemical communication show that olfactory cues always prevail in the Argentine ant. In L. niger, the proportion of ants orienting to visual cues is independent of the trail concentration. Detailed observations of the trail-laying behavior of individually marked foragers show that nearly all the I. humilis workers initially lay a trail, whereas only half the L. niger foragers do so. This proportion decreases considerably with the number of trips performed by L. niger workers, while remaining constant for the Argentine ants. These results are interpreted with respect to the species' behavioral ecology. © 1993 Birkhäuser Verlag., SCOPUS: ar.j, info:eu-repo/semantics/published

SCOPUS: ar.j, info:eu-repo/semantics/published

Observing insect societies, we are deeply impressed by their capacity to build structures and solve problems, and it is not really surprising that popular litterature is full of anthropomorphic explanations stressing the capacities of individual ants. In such blueprints, however, a central unit manages the whole system, and to achieve this it must collect all the data needed. The algorithms to treat these data are necessarily complex and therefore highly specific. They can tolerate neither internal errors, inexact or incomplete information, nor changes in the problem which is assumed to be stable. The consequences of this type of organisation are such that each solution must be constantly monitored and overhauled to cope with unforseen events, leading to a spiral of mutually increasing complexity and fragility.

One of the most striking features of an ant colony’s behaviour is its capacity for the spatial organisation of foraging activity. The use of trail pheromone to guide fellow workers in the nest to a large food source or rich foraging zone has been extensively studied (e. g. Wilson 1971) and obviously contributes to foraging efficiency. We have recently, however, been able to show that trail laying and trail following behaviour are more than just a means of communicating a food source’s location. When more than one trail is present at a time, the interactions between foragers and the trails can lead to the collective selection of the shortest path or the best food source, despite the fact that individual foragers have no means of making such choices.

SCOPUS: ar.j, info:eu-repo/semantics/published

To the Editor.— In a recent article,1 Bloom discussed the problem of future reductions in infant mortality. He has proposed three ways of meeting this problem: by determining the efficacy, effectiveness, and cost of each intervention in medical care, by substituting less expensive interventions in place of more expensive care, and by separating social solutions from medical solutions for illness. We appreciate his proposals, but we find that such an approach rules out the following two steps: (1) It is necessary to have a better understanding of the current changing trends in neonatal and postneonatal mortality.