Anne-Genevieve BAGNERES-1, M. Cristina LORENZI-2, Georges DUSTICIER-1,
Stefano TURILLAZZI-3 Jean-Luc CLEMENT-1 .
1- CNRS UPR so24-Lab. Neurobiologie-Communication Chimique 81 Chemin Joseph Aiguier,
13402 Marseille Cedex 20-France.
2-Dpto di Morfofisiol. Veterinaria, univ. di Torino, Viale Mattioli 2s, 10125 Turin-ltaly.
3-Dpto di Biol. Anim. e Genet., Univ. di Firenze, Via Romana 17, 50125
Florence- ltaly.
Social parasite must not only to enter a host nest, but also maintain the control throughout the colonial cycle. Polistes atrimandibularis (P.a.) is an obligatory social parasite of Polistes big/umis bimacu/atus (P.b.b.) (1). Although Pb.b. has a short colonial cycle (2), maintaining control over the host nest poses a particularly difficult problem for the P.a. queen which must live alone with the host queen for one month and later requires the cooperation of host workers for rearing her brood. To solve this problem the parasite uses a four- step strategy involving a progressive change in its chemical signature.
Before host nest invasion the chemical signatures of the two wasps are completely distinct with that of P.a. being characterized by unsaturated cuticular hydrocarbons (alkenes) and few saturated hydrocarbons (linear and methyl-alkanes), and that of P.b.b. being characterized only by saturated cuticular compounds. Within a few hours or days after entering the nest the parasite surpresses alkenes. Although the two signatures remain distinct during this step, the parasite rapidly gains dominance over host queen and takes control of the nest. In the second phase, which begins about one month afler invasion, the signatures of the parasite and host queen are indistinguishable. The most likely purpose of this mimicry is to ensure cooperation of the emerging host descendants which cannot discriminate between their own mother and the parasite queen. During the third step, which begins at the emergence of parasite brood, alkenes reappear and chemical differences between the hosts and parasites (queen and descendants) are intermediate resulting in a hybrid signature. It is probable that, after the nest has been secures, signature differences could become necessary to distinguish individual functions. In the last step which occurs about three months after invasion, there is reversion to the original signature by parasite queen which dies shortly after. Parasite descendants who retain the hybrid signature mate before hibernation. P. b. b. has a distinct cuticular signature which differs from one colony from another (3). It is also possible to distinguish a parasitized from a non- parasitized nest by hydrocarbons odor (4).
This model provides an example of a full range integration strategy and documents an unprecedended pheromonal tactic that can be compared to a real chemical mystification (5). In this model evolution has cast the cuticule as the key player in the host-parasite interaction.
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