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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]

For a facultative kleptoparasite, the decision to allocate time and energy to search for a prey or for a kleptoparasite opportunity could be influenced by its prior experience. In this study, we investigated the influence of experience on the proportion of the facultative kleptoparasitoid Eupelmus vuilleti females choosing an unparasitized host or a host parasitized by Dinarmus basalis. When exploiting hosts previously parasitized by D. basalis, a large proportion of E. vuilleti females reused the hole drilled by the D. basalis female, which led to a reduction in the time needed to reach the host. When submitted to successive choice tests between an unparasitized host and a host parasitized by D. basalis in a natural host-plant system, the proportion of E. vuilleti females which choose the parasitized host increased with the female experience. The same experiment carried out with an artificial host-plant system allowing an easy access to the host did not show a variation of the females’ choice with experience. A reward—here a faster access to the host through the hole drilled by the D. basalis female—seems necessary to mediate the associative learning expressed by the preferential choice of the parasitized host.

The solitary larval parasitoid Dinarmus basalis Rondani is a promising biological control of Callosobruchus maculatus F, a major insect pest of stored cowpeas in West Africa. Farmers traditionally introduce Hyptis suaveolens L. Poit. leaves in their granaries for protection of cowpea seeds against bruchid damage. However, effects of botanical treatment using this plant on host location behavior and reproduction of D. basalis remain unknown. Olfactometer studies showed that sublethal doses of volatiles emitted by the crushed leaves and the essential oils were repellent for naive females D. basalis, which had previously developed in the absence of H. suaveolens volatiles. These females were able to move in a three-dimensional device and to avoid the host patches associated with H. suaveolens volatiles. Their reproductive activity was consequently reduced in such patches. Females, which had been exposed to sublethal doses of H. suaveolens volatiles during their postembryonic development, were no lon...

International audience; Dinarmus basalis Rondani (Hymenoptera: Pteromalidae), an ectoparasitoid of Bruchid pest of stored cowpeas, is a potential biological control agent. We investigated whether grain protectants from Hyptis spicigera and H. suaveolens (Lamiaceae) disturb parasitism and post embryonic growth of the parasitoid. When cowpeas containing bruchid larvae were treated before being placed in the presence of D. basalis females, the rate of parasitism decreased on average up to 24 and 47% respectively in the presence of leaves dry powder and essential oils from both plant species. The estimated larval mortality was higher on treated (9.5 to 28.6%) than on non treated parasitized hosts (2.8%), depending on the plant species and the plant extract tested. Additional larval mortality was higher for essential oil, and for H. suaveolens..An in-depth analysis of the pre-imaginal development in capsules adapted for this purpose showed that without treatment, mortality was recorded only for eggs and the two first larval stages. In the presence of treatment, mortality not only significantly increased on eggs but also spanned over all other pre-imaginal stages. Pre-imaginal development was also significantly extended in the presence of treatment, depending on the type of extract and dose used. In conclusion, both plant species exert acute toxicity on D. basalis larvae and also act as growth inhibitors. These results provide additional information that enable to move towards a harmonious use of allelochemical compounds from plants while protecting biocontrol agentsfrom their adverse effects.

Bruchidius atrolineatus (Pic) is a tropical beetle (Coleoptera Bruchidae) that develops during the larval and pupal stages in the seeds of a legume Vigna unguiculata (Walp). Two species of Hymenoptera, Dinarmus basalis (Rond) and Eupelmus vuilleti (Craw), solitary ectoparasitoids of the larvae and pupae of B. atrolineatus, were introduced successively in the presence of their hosts, varying the interval between the two introductions. When D. basalis females were introduced 24 h, 3 days or 7 days after E. vuilleti, multiparasitism was low. The females had low fecundity, and their eggs were not distributed randomly over the different available hosts. When E. vuilleti females were introduced second, they oviposited on the different hosts availabe and did not avoid multiparasitism. The presence of hosts already parasitised by D. basalis increased the reproduction of E. vuilleti, and the fecundity of the females was higher than in control batches with E. vuilleti alone. E. vuilleti seems capable of detecting the ovipositor shafts drilled by the D. basalis females, and by introducing its own ovipositors killing the D. basalis eggs or larvae. When interspecific competition was occurring the number of E. vuilleti adults emerging from the seeds was no different from that observed in control batches with E. vuilleti alone, and there were always fewer D. basalis adults than in control batches (D. basalis alone). This interspecific competition reduces the influence of the two parasitoids in the biological control of bruchid populations.