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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...

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.

Callosobruchus maculatus (F.) (Coleoptera : Bruchidae) is a tropical beetle that develops in the seeds of Vigna unguiculata. C. maculatus adults show an imaginal polymorphism with differences in morphological, behavioral and reproductive characteristics. Adults of the flight morph that emerge in cowpea storage systems were studied under natural climatic conditions. A large number of the flight morph females were in reproductive diapause and had a long imaginal life. These females did not synthesize vitellogenin, produced a specific diapause protein and possessed significant protein reserves. This suggests that the beetles survived in the tropical ecosystem for a long time and colonized the crops during the cowpea growing and flowering phases. Analysis of reproductive activity in females captured in the V. unguiculata crops indicates that they terminated their reproductive diapause and began to lay eggs as soon as the pods were formed. Few females of the flight morph were sexually active at the beginning of imaginal life. In this paper we discuss the adaptive significance of these two reproductive strategies in females of C. maculatus.

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.

The response to different host and plant species odours was investigated in Eupelmus vuilleti (Crw). This hymenopteran is a solitary ectoparasitoid of several species of bruchids developing inside Leguminosae seeds. The locomotor behaviour of females reared on Bruchidius atrolineatus (Pic) larvae developing in Vigna unguiculata (Walp) seeds was analysed using a tubular olfactometer. Females showed a specific sensitivity to the semiochemicals emanating from the host and the seed species on which they had developed. Odours from V. unguiculata seeds were attractive to the parasitoid and stimulated their locomotor activity. Odours from Vigna radiata (Wil) seeds had no effect on the locomotor behaviour. Odours from B. atrolineatus larvae were attractive to the females whereas odours from Callosobruchus maculatus (Fab), another bruchid species, had no effect. By isolating the females from the seed and the host at different developmental stages, we found that the specific sensitivity observed resulted from an early adult learning. This learning which occurs before the emergence from the seed while the imago is in the larval chamber of its host is dependent on contact with the seed and the host larval remains.

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.

Eupelmus vuilleti (CRW) is a solitary ectoparasitoid which, under our experimental conditions, developed at the expense of the larvae and pupae of Bruchidius atrolineatus (Pic) (Coleoptera, Bruchidae). The larvae of this beetle are found inside the seeds of cowpea, Vigna unguiculata (Walp). Using a tubular olfactometer, we determined the olfactory stimuli involved in the orientation of females of the hymenopterous species E. vuilleti towards one of its hosts; B. atrolineatus. Several odours were tested including those from host plants of B. atrolineatus, from non-host plants, from the host itself and from the waste products of the host. The odours of pods or dry seeds of V. unguiculata (host plant of the phytophagous insect) affected the locomotor behaviour of females of E. vuilleti. The odours from the plant in the vegetative stage had no effect. Kairomones from larvae, pupae or faeces of B. atrolineatus were attractive to the parasitoid females. Odours from adult male or female B. atrolineatus, as well as the sex pheromone emitted by females were not attractive to E. vuilleti females. This sex pheromone did however stimulate the locomotor activity of the parasitoid. The adaptive significance of these olfactory stimuli is discussed. Resume Reponse du parasitoide Eupelmus vuilleti aux odeurs de son hote phytophage et de la plante-hote dans un olfactometre Eupelmus vuilleti (CRW) est un ectoparasitoide solitaire qui se developpe dans nos conditions experimentales aux depens des larves et des nymphes de Bruchidius atrolineatus (Pic) (Coleoptere: Bruchidae). Les larves de ce Coleoptere se trouvent a l'interieur des graines d'une Legumineuse Vigna unguiculata (Walp). Grâce a un olfactometre tubulaire, nous avons determine les differents stimuli olfactifs intervenant dans l'orientation des femelles de cet hymenoptere, vers l'un de ses hotes; Bruchidius atrolineatus. Plusieurs odeurs emanant soit de plantes-hotes ou non-hotes de B. atrolineatus, soit de l'hote lui-meme ou resultant de son metabolisme ont ete testees. Les odeurs de gousses ou de graines seches de Vigna unguiculata Walp (plante-hote du phytophage) influencent le comportement locomoteur des femelles. Par contre, les odeurs de plantes au stade vegetatif n'ont pas d'effet. Les kairomones emanant de larves, nymphes ou feces de larves de B. atrolineatus exercent un effect attractif sur les femelles parasitoides. Les odeurs emanant d'adultes mâles ou femelles de B. atrolineatus ainsi que la pheromone sexuelle emise par les femelles ne sont pas attractives pour les femelles de E. vuilleti. Cette pheromone sexuelle, par contre, stimule l'activite locomotrice des parasitoides. La signification adaptative de ces differents stimuli olfactifs est discutee.

Dinarmus basalis Rond. (Hymenoptera : Pteromalidae) et Eupelmus vuilleti Craw. (Hymenoptera : Eupelmidae) sont les deux principales especes d’ectoparasitoides solitaires de larves et de nymphes de Bruchidae en Afrique de l’Ouest. Des etudes anterieures effectuees sur ces parasitoides ont montre que D. basalis et E. vuilleti entraient en competition interspecifique. E. vuilleti est competitivement superieur a D. basalis et l’elimine quand les deux especes se developpent a densite initiale egale. Nous avons montre, dans les conditions du climat subtropical de type guineen que l’issue de la competition pouvait dependre du nombre de femelles de D. basalis exploitant le patch par rapport a celui de E. vuilleti. Quand la proportion initiale des concurrents est en faveur de D. basalis (75 % de D. basalis et 25 % de E. vuilleti), la descendance est majoritairement constituee de D. basalis. Ces resultats permettent d’expliquer en partie l’abondance de D. basalis par rapport a E. vuilleti dans les greniers de la zone subtropicale de type guineen. Dinarmus basalis Rond. (Hymenoptera : Pteromalidae) and Eupelmus vuilleti Craw. (Hymenoptera : Eupelmidae) are the two main solitary ectoparasitoids of larvae and pupae of Bruchidae in West Africa. Former studies carried out on these species showed that D. basalis and E vuilleti entered interspecific competition. E vuilleti is competitively higher than D. basalis and eliminates it when the two species develop with equal initial density. We showed under subtropical climate conditions in guinean zone that the exitence of the competition could depend on the number offemales of D. basalis exploiting the patch compared to that of E vuilleti. When the initial proportion of the competitors is in favour of D. basalis (75 % of D. basalis and 25 % of E vuilleti), the descent mainly consists of D. basalis. These results permitted to explain the abundance of D. basalis compared to E. vuilleti in guinean zone.

Callosobruchus maculatus (F.) is a tropical insect (Coleoptera: Bruchidae) that develops in Vigna unguiculata (Walp) seeds. In this beetle, there are two distinct adult forms that differ in their morphology, physiology and behaviour, the flight form and the flightless form. The development of C. maculatus is analyzed in a traditional store in Niger. During the dry season, 6 to 7 generations of the flightless form develop in the store. When the atmospheric water content increases during the rainy season, adults of the flight form appear and escape from the store. Experimental studies have shown that the adult polymorphism is induced during post-embryonic development and depends on prevailing abiotic factors during this period. The proportion of flight from adults is high when larvae develop in moist seeds (14–15% of water content). Under dry conditions (6–7% of water content) only flightless adult forms emerge from the seeds. Temperatures during development also influence adult polymorphism. In thermoperiodic conditions with 12–13% seed water content, the proportion of flight from adults increases with increasing duration of the thermophase. However, at low temperatures, a high proportion of flightless adult forms emerge, regardless of seed water content. The adaptive importance of these two abiotic factors on polymorphism induction is examined in this study. Resume Importance de la temperature et de la teneur en eau des graines sur l'induction du polymorphisme imaginal chez Callosobruchus maculatus F. Coleoptere Bruchidae Callosobruchus maculatus (F.) est un Coleoptere Bruchidae tropical qui se developpe aux depens des graines de Vigna unguiculata. Les adultes presentent un polymorphisme; il y a en effet deux formes, la forme voiliere et la forme non voiliere, distinctes par des criteres morphologiques, physiologiques et comportementaux. L'evolution des populations de C. maculatus a ete suivie pendant toute la saison seche et le debut de la saison des pluies dans la region de Niamey au Niger (13° LN) a l'interieur d'un grenier traditionnel. Pendant toute la saison seche, 6 a 7 generations de C. maculatus de la forme non voiliere se succedent a l'interieur du grenier. Les adultes de la forme voiliere, tres actifs, apparaissent surtout au cours de la saison des pluies lorsque la teneur en eau de l'atmosphere et la teneur en eau des graines augmentent. Les etudes experimentales realisees au laboratoire montrent que le polymorphisme imaginal est induit au cours du developpement post-embryonnaire et depend des conditions climatiques dans lesquelles celui-ci a lieu. Le taux d'adultes de la forme voiliere est eleve lorsque les larves se developpent dans des graines a forte teneur en eau (14 ou 15%). Lorsque la teneur en eau des graines est faible (6 a 7%), il n'y a emergence que d'adultes de la forme non voiliere. Lorsque la teneur en eau des graines est comprise entre 12 et 13%, le taux d'adultes de la forme voiliere s'accroit et varie avec la duree de la thermophase. A basse temperature il y a toujours emergence d'adultes de la forme non voiliere, quelle que soit la teneur en eau des graines. L'influence de ces deux facteurs abiotiques sur l'induction du polymorphisme imaginal joue probablement un role important dans les mecanismes adaptatifs permettant le maintien de cette espece en zone tropicale.

Eupelmus vuilleti (Hymenoptera; Eupelmidae) is a solitary ectoparasitoid producing yolk-rich eggs. The female oviposits mainly on the fourth larval instar of Callosobruchus maculatus (Coleoptera; Bruchidae), which develop within pods and seeds of Vigna unguiculata (Fabacae). Parasitoid females are synovigenic, i.e., they are born with immature eggs and need to feed from the host to sustain egg production during their entire lifetime. However, eggs are rapidly resorbed in unfavourable conditions and an efficient stop-and-go mechanism controls oogenesis in such animals. In this study, the possible involvement of ecdysteroids in the regulation of parasitoid oogenesis is examined. In a first step, the identity and titre of ecdysteroids in reproductively active and inactive female parasitoids were investigated by high performance liquid chromatography followed by enzyme immuno-assay (EIA/HPLC). A larger secretion of ecdysone was found in female during their reproductive period compared with inactive females. In a second step, both the secretion of ecdysteroids into the medium of in vitro incubated ovaries and the ecdysteroid content of females reared with or without host were measured (EIA). The presence of the host, which represents both the oviposition site and the nutritional source, induced an active biosynthesis of ecdysone. This synthesis started at a slow rate after host introduction and reached a maximum after 48 h. When hosts were available, this synthesis was cyclic and continuous during the entire female lifetime. These results showed that host presence triggered ovarian synthesis of ecdysteroids, which are involved in a stop-and-go regulation of egg production linked to host availability.

Eupelmus vuilleti (Hymenoptera; Eupelmidae) is a host feeding ectoparasitoid of fourth-instar larvae or pupae of Callosobruchus maculatus (Coleoptera; Bruchidae) infecting Vigna unguiculata seed and pods (Fabacae). Parasitoid females are synovigenic, i.e. they are born with immature eggs and need to feed from the host in order to sustain egg production. In this study, the role of sterols obtained through host feeding in parasitoid oogenesis are examined. Quantitative and qualitative analyses of the sterol contents in each partner of the tritrophic interaction show that a parasitoid female's larval sterol contents is sufficient to produce only 30% of the total number of eggs laid throughout a female's life cycle. In a second step, by manipulating the composition of the sterols hemolymph in the host, it is shown that cholesterol obtained through adult nutrition plays a crucial role in the eggs viability but does not affect the egg production quantitatively. This result has important implications for understanding both the nutrient allocation strategy in this species and the impact of cholesterol in parasitoid reproduction.

Eupelmus vuilleti ( Crawford) is an ectoparasitoid of the seed-eating beetle Bruchidius atrolineatus (Pic), which is an important pest of stored cowpea, Vigna unguiculata Walp, seeds in West Africa. Herein, we investigated the dispersal abilities of females within columns of seeds to assess the potential of E. vuilleti as a biological control agent of bruchids in cowpea granaries. The influence of host presence together with the 2 abiotic factors light and gravity on parasitoid movement and parasitization efficiency were analyzed. E. vuilleti females were able to travel through large seed masses and parasitize hosts located at the end of the seed column opposed to their introduction zone. Parasitoid movement was stimulated by light. E. vuilleti females exhibited a negative geotropism. Females introduced at the bottom of the seed column dispersed more and parasitized more hosts than females introduced at the top. Host presence had some influence on the dispersal of the parasitoids within the seed column at a host density of 10 infested seeds for 16,000-18,000 uninfested seeds. This depended on female introduction zone because gravity was the major factor influencing dispersal. The possible applications of these results for biological control of bruchids in cowpea granaries are discussed.

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.

Bruchidius atrolineatus (Pic) (Bruchidae: Coleoptera) is a bruchid beetle infesting Vigna unguiculata (Walp). During the dry season, adults are in reproductive diapause. Studies of adult populations in a traditional store containing contaminated pods of V. unguiculata show that the reproductive diapause is induced during the first larval instars. The temperature decrease from November to January probably is the main climatic factor inducing this diapause. The percentage of diapausing adults depends on the duration of the larval development at low temperatures. Experiments in climatic boxes confirm these results. At 12 h 25 °T–12 h 20° C 11–13 LD, a high proportion of the adults emerging from the V. unguiculata seeds are in reproductive diapause and the duration of their growth is variable. L1 L2 L3 larvae probably are sensitive stages to the thermal variations and the processes allowing emergence of diapausing adults probably are induced during these larval instars. Resume Induction de la diapause reproductrice chez Bruchidius atrolineatus coleoptere bruchidae durant la saison seche en zone Sahelienne Bruchidius atrolineatus (Pic) est un Coleoptere Bruchidae se developpant en zone sahelienne aux depens d'une legumineuse Vigna unguiculata. Pendant la saison seche, les adultes sont en diapause reproductrice. Un suivi des populations d'adultes a ete realise dans un grenier traditionnel en ‘terre sechee’ contenant des gousses recoltees dans la nature et portant des œufs de B. atrolineatus. Il a permis de constater que la diapause reproductrice etait induite durant les premieres phases du developpement larvaire. La decroissance des temperatures de Novembre a Janvier avec des minima de 15 °C et des maxima de 25 °C est probablement le principal facteur permettant l'induction de cette diapause. L'introduction dans le grenier de gousses portant des œufs venant d'etre emis a differentes periodes de la saison seche montre que le pourcentage d'adultes diapausants depend de la duree du developpement larvaire aux temperatures ‘basses’. Des experiences realisees dans des etuves programmees confirment ces resultats. A 12 h 25 °T/12 h 20 °C 11–13 LD, un taux eleve d'adultes emergeant des graines est en diapause reproductrice et la duree de leur developpement post-embryonnaire est tres variable. En conditions plus chaudes 12 h 40 °C/12 h 25 °C 11–13 LD, le taux d'adultes diapausants est plus reduit et la duree du developpement plus courte. L'analyse de la croissance larvaire montre que les premiers stades larvaires sont probablement des stades sensibles aux variations thermiques. Les modifications physiologiques permettant l'emergence d'adultes diapausants ou sexuellement actifs seraient induites durant ces stades.

The development of populations of two species of bruchids, B. atrolineatus and C. maculatus, in traditional stores containing cowpea pods was analysed in the Niamey area of Niger. At the beginning of the storage period, the first generation of B. atrolineatus adults is sexually active, mates and oviposits on the pods. Later, as the population increases dramatically, there is a correspondingly higher percentage of adults exhibiting reproductive diapause. Experiments showed that the diapausing insects leave stores during the dry season. This factor subsequently induces a regression of population growth inside the stores at the end of the dry season. There was no development of the C. maculatus population in the present experiment, because of the low level of infestation in the field before harvest and the fact that climatic conditions were probably unfavourable for this species in the Niamey area. In stores, the rate of B. atrolineatus population increase is very high in a limited number of generations resulting in significant losses of cowpea seeds.