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International audience; Contests for indivisible resources are often settled on the basis of the asymmetry that exists between contestants in their ownership status: Owners (i.e., individuals already possessing a resource) usually retain the resource when facing intruder competitors. This owner advantage is predicted to be more pronounced as the asymmetry in ownership status accentuates: when the residency period increases, the probability of owners keeping their resource should increase and contestant aggressiveness should be reduced. In the present study, we tested this prediction in a parasitoid wasp, Eupelmus vuilleti, where females fight for hosts, larvae of Callosobruchus maculatus, on which to lay their eggs. To do so, we experimentally varied the arrival times of 2 conspecific females on a host, generating different asymmetries in ownership status between them. We further explored the strategies adopted by intruder females according to the stage reached by the owners in their host exploitation sequence. When the residency period was short, both females fought and contests were won by the female valuing more greatly the host, rather than by the owner per se. The loser left the host vicinity and the winner exploited the host alone. In contrast, when the residency period was long (the owners were ready to parasitize the host), the intruders did not leave but instead waited for the departure of the resident female in order to superparasitize the host. This "waiting strategy" seems particularly adaptive in this species, in which females tend to prefer already parasitized hosts to healthy hosts. Key words: contest resolution, Eupelmus vuilleti, female egg load, ownership status, resource value. [

International audience; When 2 species exploit the same limiting resource, interspecific competition may lead to the exclusion of one of them. For the 2 species to coexist, resource exploitation strategies exhibited by both species must somehow counterbalance each other. Eupelmus vuilleti and Dinarmus basalis are 2 solitary parasitoid species exploiting the same hosts (larvae and pupae of Callosobruchus maculatus) in sub-Saharan Africa. They display different strategies when in indirect (exploitative) competition situations: D. basalis females tend to avoid multiparasitism, whereas E. vuilleti females tend to accept parasitized hosts. Therefore, E. vuilleti seems dominant and potentially able to exclude D. basalis. Thus, how can D. basalis persists when in sympatry with E. vuilleti? Here, we studied the strategies adopted by females of either species when in direct (interference) competition. We investigated the effect of certain factors affecting females' competitive abilities or the value that they place on the resource such as female size, female physiological state (egg load), the quality of the habitat previously encountered by females (rich or poor in hosts), and the ownership status. This study revealed that D. basalis females tended to outcompete E. vuilleti females when competing for a given host. They were more aggressive and won most contests, whereas E. vuilleti females only won contests when being an owner with a high egg load or when having experienced high host availability. Thus, both species seem to show counterbalancing strategies when in exploitative and interference competition, which could promote their coexistence in nature. Key words: female egg load, female size, interspecific competition, ownership status, previous habitat quality, sympatry. [Behav Ecol]