Search

International audience; The presence of competitors may affect the pay-off of individuals’ foraging strategies. They should therefore modify their resource exploitation decisions accordingly. In such a direct competition situation, theory predicts that individuals should stay longer on a resource patch than when foraging alone. However, models predicting patch residence time focus on intraspecific competition without agonistic interactions. Here, we investigate the patch use strategies of females of two parasitoid species, Eupelmus vuilleti and Dinarmus basalis, attacking the same host, Callosobruchus maculatus, knowing that D. basalis is more aggressive and can exclude E. vuilleti during pairwise contests for single hosts. Our results showed that time allocation and oviposition strategies differed in relation to the species and type of competition (i.e., presence/absence of competitor, simultaneous/sequential female introduction or resident/intruder female). Eupelmus vuilleti females tended to wait in the patch surroundings for D. basalis females’ departure to return and exploit hosts parasitized by the opponent (after destruction of her eggs). In contrast, D. basalis females tended to self-superparasitize and stay motionless near the hosts. After detecting an E. vuilleti female entering the patch, they attacked and chased her permanently from the patch. Females of both species spent less time in the patch when faced with a competitor than when alone. This study is the first to test the influence of direct interspecific competition and arrival order on patch exploitation strategies in parasitoid species, and highlights the necessity to include agonistic behaviors in theoretical models predicting optimal patch residence time in competitive situations.

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 eupelmid Eupelmus vuilleti CRW. and the pteromalid Dinarmus basalis Rond. are sympatric in West Africa. The reproduction of E. vuilleti and D. basalis females was analyzed in 10, 20, and 40 host patches when present alone or together. In 10- and 20-hosts patches, the presence of E. vuilleti affected the reproduction and offspring survival chances of D. basalis. In 40-hosts patch, only the offspring survival of D. basalis was affected by the presence of E. vuilleti. In contrast, the presence of D. basalis did not influence the reproduction of E. vuilleti and the survival chances of its offspring at all host densities tested. Multiparasitism did not occur at random. In a choice test, E. vuilleti showed a preference for hosts previously parasitized by D. basalis on healthy hosts. This attraction is mediated by chemical markers deposited by D. basalis females on the surface of the seed. At high host density, the likelihood of encountering a seed containing a host previously parasitized by D. basalis was lower for E. vuilleti, affecting moderately D. basalis reproductive success.

The parasitoid species, Dinarmus basalis, attacks bruchid beetle larvae concealed within hard seeds. Female wasps are able to discriminate the quality of their host but the position in the concealed host system where this discrimination takes place remains unclear. Under laboratory conditions, we investigated whether the cues were detectable: (1) at a medium or short distance from the seed, (2) on the seed, or (3) within the seed, at the point of contact with the host. In particular, we investigated whether internal or external markings are applied by the parasitoid and then recognized in a subsequent encounter or by a conspecific encountering the host. Detailed behavioral observations did not provide evidence of markings being applied onto the seed or used, but showed that host discrimination occurred on the basis of internal cues. The lack of evidence of external markings is unexpected and raises the question as to which circumstances in the parasitoid's ecology and life history could result in such a lack not causing a reduction of fitness.

Dinarmus basalis (Rond) and Epelmus vuilleti (Crw) are two Hymenopteran species, which are solitary ectoparasitoids of bruchid larvae. In the presence of seeds of Vigna unguiculata (Walp) containing hosts parasitized by E. vuilleti, a high percentage of D. basalis females avoided multiparasitism whatever the age of the eggs or the larvae present on the host. The least avoidance was observed when the hosts were parasitized by E. vuilleti 30 min beforehand. This avoidance behavior is adaptive and is related to the low survival chances of the D. basalis larvae when they are in interspecific competition with E. vuilleti larvae. The analysis of the behavior of D. basalis demonstrated that the avoidance of multiparasitism could be due to the perception of two signals; an external signal deposited on the surface of the seeds during the E. vuilleti oviposition phase and an internal signal due to the presence of the eggs and larvae at the surface of the hosts. E. vuilleti females did not avoid multiparasitism and multiparasitized the hosts bearing D. basalis eggs or larvae. The behavior of E. vuilleti females was not disturbed by the presence of its competitor. Under these conditions of interspecific competition, the survival chances of E. vuilleti larvae were very high whatever the age of its competitor D. basalis. The two species of parasitoids could move in a column containing healthy seeds of V. unguiculata and patches with seeds containing parasitized or unparasitized larvae. The distribution of D. basalis females introduced into these columns depended on the host quality. They avoided the patches containing the hosts parasitized E. vuilleti and were found in the patches with healthy hosts. The behavior of E. vuilleti females was very different; the distribution of the females and the parasitism and multiparasitism rates were not affected by the quality of the hosts present in the patches. The adaptive significance of the behaviors of these two species was analyzed in relation to the survival chances of their offspring.

Eupelmus vuilleti (Crw) is a solitary ectoparasitoid of several bruchid species which develop inside Leguminosae seeds. In this hymenopteran a preemergence learning process is responsible for a specific response of females toward the host and host-plant volatiles. This learning occurs after the imaginal molt, while the adult remains in the larval chamber of its host. The persistence of the response toward host and host-plant volatiles of females reared onBruchidius atrolineatus (Pic) larvae developing inVigna unguiculata (Walp) seed was investigated in this study. In the absence of any reinforcement, the response towardB. atrolineatus larvae persisted for 6 days after female emergence from the seeds, whereas the response towardV. unguiculata seed volatiles was maintained for 7 days. Our experiments showed that a later learning process also takes place inE. vuilleti. An ovipositional experience on a given plant-host complex enabled females to learn the stimuli from that complex. This learning occurred even if the complex experienced during oviposition differed from the one on which females were reared. After an ovipositional experience on a new plant-host complex, the response acquired through preemergence learning was maintained. These experiments demonstrate that theE. vuilleti females can memorize cues from several species during successive learning processes. The adaptive significance of these learning capacities, which confer an important behavioral plasticity to this generalist parasitoid, is discussed.