Aiiiinnl hchaviour is probahilistic. This is exemplified by the comnninicalioii bchîU'iour of nuls diiriiig fooil-searcfiing. Expérimental évidence deinonsiratcs lliat speeies difïer in the accuracy of tlicir rccruitmenl. W e show hcrc. with the hclp of a vcry simple mathematical model, that the randomncss of behaviour can have an adaptative advantage for ants. The model demonstraies that the degree of randomness eould be optimally "luned" to pnrticulnr ecological conditions, siich as food quantity and distribution. Society is to try to eliminate external fluctuations. One way is to damp the external fluctuations with hoineostatic mechanisms: the colony tries to

Abstract:The mineral, total amino acid, and sterol compositions of pollen collected by Apis mellifera L. were compared with the pollen of a plant consumed by Bombus terrestris (L.): Arbutus unedo L. This plant provides the predominant food resource for the main autumn generation of B. terrestris in southern France. Honey bees also forage on this plant, although only for nectar. The mineral composition of 30 pollen samples collected by honey bees is close to the presently known requirements of A. mellifera, except for Cu and Mn, which are substantially lower. The total amino acid mean composition of a set of 54 pollen samples fits the basic requirements of honey bees except for valine, isoleucine, and methionine, which are present in lower concentrations in all the samples. For pollen of A. unedo, the amino acid balance is not very different from that of the survey. The main sterolic component in pollen of A. unedo, β-sitosterol, is known to have antifeedant effects on A. mellifera. Honey bees cannot dealkylate C 29 sterols like β-sitosterol or 85-avenasterol to obtain C 27 cholesterol and ecdysteroids. Because these phytosterols as well as cholesterol are nearly absent from pollen of A. unedo, the metabolic capabilities of Apis seem unadapted to this plant. On the contrary, pollen of A. unedo is freely consumed by B. terrestris, which develops huge autumn populations solely on this food. These data indicate that the sterolic metabolisms of B. terrestris and A. mellifera differ, allowing separation in foraging activity.

-The bumblebee Bombus sylvestris is an obligate social inquiline of B. pratorum and nestinvading females are known to integrate themselves into host colonies, usually without any aggression. We investigated whether cuticular compounds could be involved in discrimination processes in common bumblebees, and whether they play a role in the social integration of inquilines in host nests. We tested nestmate recognition in B. terrestris workers, and analysed cuticular chemical profiles of hairs taken from allocolonial individuals. Bumblebees belonging to the same colony shared a common odour. Then, we investigated how B. sylvestris females integrated into colonies of natural and non-natural hosts, B. pratorum and B. terrestris, respectively. Inquiline females apparently succeeded in entering a host colony by expressing non-aggressive behaviours and had no chemical signature; subsequently, acquisition of a chemical signature similar to the host colony might facilitate their integration into the host nest.Bombus sylvestris / inquilinism / discrimination process / chemical signature / non-aggressive strategy

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