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The Trypanosomatidae family includes the genera Trypanosoma and Leishmania, protozoan parasites displaying complex digenetic life cycles requiring a vertebrate host and an insect vector. Trypanosoma brucei gambiense, Trypanosorna cruzi, and Leishmania spp. are important human pathogens causing human African trypanosomiasis (HAT or sleeping sickness), Chagas' disease, and various clinical forms of Leishmaniasis, respectively. They are transmitted to humans by tsetse flies, triatomine bugs, or sandflies, and affect millions of people worldwide. In humans, extracellular African trypanosomes (T. brucei) evade the hosts' immune defenses, allowing their transmission to the next host, via the tsetse vector. By contrast, T. cruzi and Leishmania sp. have developed a complex intracellular lifestyle, also preventing several mechanisms to circumvent the host's immune response. This review seeks to set out the immune evasion strategies developed by the different trypanosomatids resulting from parasite-host interactions and will focus on: clinical and epidemiological importance of diseases; life cycles: parasites-hosts-vectors; innate immunity: key steps for trypanosomatids in invading hosts; deregulation of antigen-presenting cells; disruption of efficient specific immunity; and the immune responses used for parasite proliferation.

International audience; While the effects of deforestation and habitat fragmentation on parasite prevalence or richness are well investigated, host–parasite networks are still understudied despite their importance in understanding the mechanisms of these major disturbances. Because fragmentation may negatively impact species occupancy, abundance and co‐occurrence, we predict a link between spatiotemporal changes in habitat and the architecture of host–parasite networks. For this, we used an extensive data set on 16 rodent species and 29 helminth species from seven localities of South‐East Asia. We analysed the effects of rapid deforestation on connectance and modularity of helminth–parasite networks. We estimated both the degree of fragmentation and the rate of deforestation through the development of land uses and their changes through the last 20 to 30 years in order to take into account the dynamics of habitat fragmentation in our statistical analyses. We found that rapid fragmentation does not affect helminth species richness per se but impacts host–parasite interactions as the rodent–helminth network becomes less connected and more modular. Our results suggest that parasite sharing among host species may become more difficult to maintain with the increase of habitat disturbance.

International audience; We studied the effect of host gender and body mass on species richness of flea infracommunities in nine rodent host species from three biomes (temperate zone of central Europe, desert of the Middle East and the tropics of East Africa). Using season- and species-specific generalized linear mixed models and controlling for year-to-year variation, spatial clustering of rodent sampling and over-dispersion of the data, we found inconsistent associations between host characteristics and flea species richness. We found strong support for male-biased flea parasitism, especially during the reproductive period (higher species richness in male hosts than in females) in all considered European rodents (Apodemus agrarius, Myodes glareolus and Microtus arvalis) and in one rodent species from the Middle East (Dipodillus dasyurus). In contrast, two of three African rodent species (Lophuromys kilonzoi and Praomys delectorum) demonstrated a trend of female-biased flea species richness. Positive associations between body mass and the number of flea species were detected mainly in males (five of nine species: A. agrarius, M. glareolus, M. arvalis, D. dasyurus and Mastomys natalensis) and not in females (except for M. natalensis). The results of this study support earlier reports that gender-biased, in general, and male-biased, in particular, infestation by ectoparasites is not a universal rule. This suggests that mechanisms of parasite acquisition by an individual host are species-specific and have evolved independently in different rodent host-flea systems.

The diversity of ways in which parasites reduce the fitness of their hosts has been documented during the past decades, and clearly indicates that parasites can often be considered as direct agents of selection. In natural systems, however, the outcome of a host-parasite interaction might be strongly determined by other ecological factors. Parasites can be detrimental to host fitness in one environment, whereas they can be beneficial to it in another. From an evolutionary perspective, this phenomenon is of considerable importance for understanding the dynamics of coevolution among geographically structured populations evolving under different ecological pressures. Here, Frédéric Thomas and colleagues review several ecological situations in which parasitized individuals enjoy a selective advantage over unparasitized conspecifics. (Résumé d'auteur)

Oomyzus sokolowskii (Kurdjumov) is a gregarious larval-pupal parasitoid of the diamondback moth Plutella xylostella (L.). The objective of this study was to investigate the interactions between host and parasitoid by examining the effects of biotic factors such as gregariousness, host origin and stages, and female parasitoid age on the parasitism rate, developmental time, the number of offspring and the offspring sex ratio of O. sokolowskii under laboratory conditions. The percentage of parasitism and the number of parasitoids increased with the number of O. sokolowskii females. Oomyzus sokolowskii preferred fourth larval instars over other larval stages. The parasitism rate and the progeny production of O. sokolowskii decreased with parasitoid age; however, the developmental time and the sex ratio of the offspring were not significantly different. Our results confirm previous findings on larval preferences of O. sokolowskii. The study also confirmed the importance of geographical origin of the host on the performance of O. sokolowskii. (Resume d'auteur)

Eurytoma erythrinae Gates and Delvare, new species, is described and illustrated. This species was reared from fieldcollected galls on Erythrina spp. (Fabaceae) induced by Quadrastichus spp. (Hymenoptera: Eulophidae), in Tanzania, Ghana, and South Africa. It is compared with very similar African species, Eurytoma radicicola Risbec. Afrotropical species classified in Eurytoma are reviewed and twenty-seven new combinations are proposed: Aximopsis acaciacola (Hedqvist) comb. n., A. caryedocida (Rasplus) comb. n., A. lamtoensis (Rasplus) comb. n., A. mateui (Hedqvist) comb. n., A. mimosarum (Rasplus) comb. n., A. obocki (Risbec) comb. n., A. oryzivora (Delvare) comb. n., A. saharensis (Hedqvist) comb. n., A. senegalensis (Risbec) comb. n., A. tropicana (Risbec) comb. n., Bruchophagus conapionis (Rasplus) comb. n., Fronsoma ellenbergeri (Risbec) comb. n., Gibsonoma amborasahae (Risbec) comb. n., G. aphloiae (Risbec) comb. n., G. bararakae (Risbec) comb. n., G. eugeniae (Risbec) comb. n., G. mandrakae (Risbec) comb. n., G. pauliani (Risbec) comb. n., G. plectroniae (Risbec) comb. n., G. tavolae (Risbec) comb. n., Philolema arachnovora (Hesse) comb. n., P. arnoldi (Waterston) comb. n., P. bambeyi (Risbec) comb. n., P. braconidis (Ferrière) comb. n., and P. syleptae (Ferri_re) comb. n., Phylloxeroxenus cressoni (Howard) comb. n., and Sycophila plectroniae (Risbec) comb. n. Lectotypes are designated for ten species: Eurytoma perineti Risbec, E. radicicola Risbec, E. toddaliae Risbec, Gibsonoma amborasahae (Risbec), G. aphloiae (Risbec), G. eugeniae (Risbec), G. mandrakae (Risbec), G. pauliani (Risbec), G. tavolae (Risbec), and P. bambeyi (Risbec). We also provide a checklist of Afrotropical species that are or were classified in Eurytoma and tabulate the known host/associations of these species with references.

International audience; Parasite-mediated selection on major histocompatibility complex (MHC) genes has mainly been explored at the intraspecific level, although many molecular studies have revealed trans-species polymorphism. Interspecific patterns of MHC diversity might reveal factors responsible for the long-term evolution of MHC polymorphism. We hypothesize that host taxa harbouring high parasite diversity should exhibit high levels of MHC genetic diversity. We test this assumption using data on rodent species and their helminth parasites compiled from the literature. Controlling for similarity due to common descent, we present evidence indicating that high helminth species richness in rodent species is associated with increased MHC class II polymorphism. Our results are consistent with the idea that parasites sharing a long-term coevolutionary history with their hosts are the agents of selection explaining MHC polymorphism.

The nematodes specificities and their interactions with plants are reviewed, considering host plants quality and compatibility. The potentials of nematode resistance and diversity of antagonists and parasitism are discussed, in relation to host specificity and obligate multitrophic relationships. The ecology and management of nematode communities are also reviewed, focusing on soil health approaches and new paradigms for plant protection.

International audience; Patterns of ectoparasite species richness in mammals have been investigated in various terrestrial mammalian taxa such as primates, ungulates and carnivores. Several ecological or life traits of hosts are expected to explain much of the variability in species richness of parasites. In the present comparative analysis we investigate some determinants of parasite richness in bats, a large and understudied group of flying mammals, and their obligate blood-sucking ectoparasite, streblid bat flies (Diptera). We investigate the effects of host body size, geographical range, group size and roosting ecology on the species richness of bat flies in tropical areas of Venezuela and Peru, where both host and parasite diversities are high. We use the data from a major sampling effort on 138 bat species from nine families. We also investigate potential correlation between bat fly species richness and brain size (corrected for body size) in these tropical bats. We expect a relationship if there is a potential energetic trade-off between costly large brains and parasite-mediated impacts. We show that body size and roosting in cavities are positively correlated with bat fly species richness. No effects of bat range size and group size were observed. Our results also suggest an association between body mass-independent brain size and bat fly species richness.

Introduction: Parasites, diversity, and the ecosystem 1. Linking ecosystem and parasite ecology 2. Are there general laws in parasite community ecology? The emergence of spatial parasitology and epidemiology 3. Parasitism and the regulation of host populations 4. Food web patterns and the parasite's perspective 5. Ecosystems and parasitism: the spatial dimension 6. Parasitism and hostile environments 7. Parasitism and environmental disturbances 8. Parasitism, biodiversity, and conservation 9. Subverting hosts and diverting ecosystems: an evolutionary modelling perspective 10. Parasitism in man-made ecosystems Conclusion: Parasites, communities, and ecosystems: conclusions and perspectives References Index

Variations observed in parasite virulence and host resistance may be the outcome of coevolutionary processes. Recent theoretical developments have led to a 'geographic mosaic theory' of coevolution according to which there are some localities where reciprocal selection occurs (hot spots) and others where it is strongly reduced (cold spots). Studies of host-parasitoid systems back this up, revealing a geographical variation of traits subjected to antagonistic selection governed by variations in the strength of the ecological interactions. A more detailed analysis of the genetic basis of these geographic variations in a model system -- the interaction between Drosophila melanogaster and its specific parasitoid Leptopilina boulardi -- suggests that cold spots and hot spots are also driven by the amount of genetic variation available for the trait considered. Our approach, based on isolating reference strains, has been found to predict the result of sympatric interactions and it will be helpful in identifying the selective forces responsible for the coevolution. In this model, host resistance to a standardised reference strain is a weak predictor of the outcome of interactions in the field, and the main parameter accounting for the geographic variations is the number of host species available, with less parasitoid virulence towards D. melanogaster being found in areas displaying a more diversified host community.

Most of the evidence for a key role of parasites in structuring communities is based on the idea of a differential susceptibility of host species to infection and its consequences. Recent advances in community ecology suggest that life-history traits of free-living species can be an important determinant of their co-existence within communities. On the other hand, parasites have the potential to indirectly alter the life-history traits of their hosts, such as developmental time or dispersal. We discuss the idea that these indirect effects could influence the structure of free-living and parasites communities. We explore this idea in relation to related concepts including "parasitic arbitration" and engineering processes. (Résumé d'auteur)

Although the term endemism refers to restricted areas of taxa, this term is used in a different way in epidemiology and host-parasite relationship. An endemic disease refers to the maintenance of a disease over a long-term period in a limited geographic area (endemic area). In biogeographical studies, endemism refers to the organisms that are restricted to a given area. However, little is known about parasitism in endemic hosts. Here, we show how epidemiological models and the derivation of the basic transmission rate (R0) can help to understand the pattern of parasite species richness among endemic hosts. The main prediction arising from epidemiological models concerns the host density threshold, i.e. the minimum host density that allows a disease to spread into a population of susceptible hosts. When host density, or host range, increases we can predict a concomitant increase of parasite species richness, in the case of parasites transmitted directly or through predator-prey relationship. This prediction can be tested using comparative data. These predictions are successfully tested using several data sets on parasites of marine and freshwater fish. We will show that restricted areas and/or low density is correlated with a decrease in parasite species richness. The epidemiological theory is also helpful for predictions concerning parasite and disease introductions in endemic host faunas (or isolated hosts). We emphasize why and how this endemic fauna may be susceptible to introduce pathogens and parasites. (Résumé d'auteur)

In recent years, there has been a growing interest in understanding the ecological importance of ecosystem engineers. In this paper, we argue that parasites, through the phenotypic alterations they induce in their hosts, are likely to be involved in engineering processes for at least two reasons. First, when ecosystem engineers are themselves infected, phenotypic alterations induced by parasites can interfere with host traits involved in the engineering processes. Secondly, parasites themselves can be ecosystem engineers since the phenotypic alterations of hosts directly modify the habitat of all the species inhabiting free-living organisms. This new research area at the interface between ecology and parasitology should improve our understanding of the ecological consequences of phenotypic alterations induced by parasites in ecosystems. (Résumé d'auteur)

Des études en conditions contrôlées de serre ont permis de comparer la sensibilité de diverses cultures maraîchères (tomate, aubergine africaine [#Solanum aethiopicum$], gombo) et de cultures de rotation (arachide, mil, oignon, niébé) au nématode #Meloidogyne javanica$ et d'évaluer la production de #Pasteuria penetrans$, actinomycète parasitoïde de ces nématodes. La sensibilité à #M. javanica$ opposait le groupe des cultures sensibles (tomate, aubergine, gombo, niébé) au groupe des cultures non-sensibles (arachide, mil, oignon). La production de spores de #P. penetrans$, impossible sur les cutures non-sensibles, a été plus importante sur l'aubergine africaine que sur la tomate, alors que le gombo n'a permis aucune production. Les cultures ont eu aussi des effets rémanents sur une culture suivante : ainsi la production des spores de #P. penetrans$ sur tomate a été beaucoup plus importante après aubergine africaine ou gombo qu'après tomate. Des études au champ effectuées sur un site naturellement infesté en #M. javanica$ et en #P. penetrans$ ont permis de suivre l'évolution des populations totales de juvéniles de #M. javanica$ et des juvéniles infestés par #P. penetrans$, d'une part au cours d'une succession de trois cycles de cultures sensibles, d'autre part au cours d'une rotation de sept cycles de cultures sensibles et non-sensibles. Quelle que soit l'étude, l'évolution des effectifs de juvéniles infestés est assez synchrone de celle des effectifs totaux de juvéniles. Mais, alors qu'une culture continue de plantes sensibles a entraîné une diminution constante des effectifs de juvéniles totaux et infestés par #P. penetrans$, la rotation de cultures sensibles et non-sensibles a permis une augmentation périodique de ces effectifs. Cependant, l'étude de l'évolution des proportions de juvéniles infestés apporte des précisions sur les interactions entre les populations de #M. javanica$ et celles de #P. penetrans$... (D'après résumé d'auteur)

L'association entre le nématode #Schistonchus caprifici$, la guêpe pollinisatrice #Blastophaga psenes$ et le parasitoïde #Philotrypesis caricae$ a été étudiée en hiver, au printemps et en automne dans les inflorescences (sycones) du figuier (#Ficus carica$ var. #sylvestris$) dans le sud de l'Italie. C'est la première fois qu'est signalée l'association d'un #Schistonchus$ sp. avec une guêpe parasitoïde. Tous les stades biologiques de #S. caprifici$ ont été trouvés dans l'hémocoele des femelles ailées de #B. psenes$ et de #P. caricae$. Aucune association n'a été observée avec les mâles aptères des deux guêpes. Pour ces deux guêpes de la figue, le nombre de femelles ailées transportant des nématodes est plus élevé en juin qu'en mars. Cependant, le pourcentage de #P. caricae$ transportant #S. caprifici$ est de 50% (mars) et 20% (juin) moins élevé que pour #B. psenes$. Le nombre de nématodes transportés par chaque femelle ailée est de 1-3 et 1-23 pour #P. caricae$ et 1-14 et 1-116 pour #B. psenes$ en mars et juin, respectivement. Les mensurations de femelles associées aux insectes (provenant des deux guêpes) et, de celles phytoparasites, de #S. caprifici$ ne diffèrent pas. Les examens histopathologiques révèlent la présence des colonies de nématodes à l'intérieur et à l'extérieur des bouquets d'anthères et des filets. Le nématode provoque des nécroses de l'épiderme et du parenchyme cortical des filets et la formation dans les anthères de cellules épidermiques hypertrophiées, riches en cytoplasme à coloration foncée. (Résumé d'auteur)

Des données quantitatives et qualitatives concernant les plantes hôtes des bruches des palmiers sont fournies pour une région de l'Amazonie où l'on disposait jusqu'à présent de peu d'informations. Ces données permettent d'étendre la distribution géographique et le spectre alimentaire de plusieurs espèces. Le rôle de la structure du fruit dans sa sensibilité à l'infestation par les bruches, le rôle de la maturité du fruit dans la sélection du site de ponte sont discutés. L'importance des conditions mésologiques, en particulier en zone inondable, dans la dynamique des populations de bruches, est relevée. Un parasitoïde spécialiste de #Caryoborus serripes$, qui est un prédateur spécifique des noix d'#Astrocaryum$, est obtenu pour la première fois; un trichogramme parasite des oeufs de cette même bruche est également identifié. (Résumé d'auteur)

International audience

Le parasitisme naturel de Syllepte derogata (Fabricius, 1775) a été étudié pour la première fois au Togo de 1988 à 1990. Treize espèces de parasites et sept espèces d'hyperparasitesont été recensées. Les mêmes espèces sont rencontrées du nord au sud du pays. Les parasites màjeurs de larves sont les Braconidae Apanteles syleptae Ferrière et A. sagax Wilkinson, ceux de nymphes sont l'Ichneumonidae Xantbopirnpla pUllctata F. et des Chalcididae du genre Bracbyrneria. Parmi les hyperparasites, Nesolynx phaeosoma (Waterston) (Eulophidae) est l'espèce la mieux représentée. Les pourcentages de parasitisme des larves étaient respectivement de 3,4%, 12,5% et 7,1% en 1988, 1989 et 1990. Dans le cas des chrysalides récoltées au champ, ces valeurs étaient de 21,5% (1989) et 35,4% (1990), En 1989, 56,4% des cocons de A. syleptae et 77,0% des amas de cocons de A. sagax étaient parasités. En 1990, les valeurs observées étaient de 18,2% et 14,4%. L'action des hyperparasites limite celle, déjà modeste, des parasites de larves.

Nous essayons de montrer comment l'utilisation des principes de la modélisation évènementielle peuvent être utilisés pour une introduction pédagogique à l'utilisation de concepts statistiques en biologie. Nous traitons du cas de la circulation des microfilaires chez l'hôte vertébré, et de leur absorption par leurs vecteurs (moustiques) ; mais les résultats obtenus nous permettent, à notre avis, en considérant l'hôte comme le siège d'un flux parasitaire, de donner une approche globale des caractéristiques quantitatives du parasitisme. (Résumé d'auteur)

Le trichogramme #Uscana caryedoni$ Viggiani se développe aux dépens des oeufs de #Caryedon congense$ Decelle et de ceux de la bruche de l'arachide, #Caryedon serratus$ (Olivier), sur les fruits d'une légumineuse arbustive commune au Congo, #Piliostigma thonningii$ (Schum.). Dans la région de la Bouenza, dans le sud du pays, les taux de parasitisme dus à #U. caryedoni$ s'accroissent au cours de l'année, à mesure que mûrissent les gousses, pour atteindre en novembre près de 40 % (taux cumulé). La biologie du parasitoïde a été étudiée au laboratoire sur oeufs de #C. serratus$. A 30°C, la femelle pond en moyenne 66 oeufs et vit un peu plus de 5 jours. Le développement préimaginal s'effectue en 16 jours à 26° et 12 jours à 30°. L'effet de la densité de l'hôte sur divers paramètres biologiques du parasite a été étudié. Un essai réalisé dans les conditions du laboratoire a révélé chez #U. caryedoni$ de très faibles potentialités comme agent de limitation des populations de #C. serratus$ dans les stocks d'arachide. (Résumé d'auteur)

Etude de certains paramètres épidémiologiques de la Cercosporiose des agrumes (Cercospora angolensis) dans la zone écologique de Dschang au Cameroun. Ce travail constitue dans son ensemble une première approche des relations hôte-parasite. La poursuite de ces recherches devrait permettre à plus long terme une amélioration de la lutte contre cette maladie

Apres un rappel du cycle (heterogonique) de Heterogonema ovomasculis n. sp., ce nematode fait l'objet d'une description detaillee. Ses principales particularites resident dans la presence de quatre tres grosses cellules perioesophagiennes ("tetrade") et dans le developpement des gonades ou toutes les cellules evoluent simultanement ou presque (pas de zone germinative). Chez le mâle, - la gonade, unique chez la jeune larve, se divise en deux: la partie anterieure forme un testicule fonctionnel ; la partie posterieure est a l'origine d'une gonade femelle produisant un petit nombre de larves qui se developpent dans le corps meme du nematode. La femelle de la premiere generation, parthenogenetique et ovovivipare, ne possede pas de vulve. Chez la femelle de la deuxieme generation, sexuee et ovipare, la vulve ne sert qu'a l'accouplement. Les deux femelles liberent larves et œufs par eclatement. Ce parasite, a specificite etroite puisque associe essentiellement a une seule espece de Nitidulidae, provoque chez les insectes parasites au debut de la vie imaginale, une reduction de la fecondite ou meme une sterilite complete.

This note presents the results of a current study on the parasitism of the yellowfin Thunnus albacares in the Gulf of Guinea: a list of encountered crustaceans and helminths, remarks concerned with localisations, frequencies and intensities of the infestations is given. A hypothesis on the existence of three ecological stocks corresponding to three great fishing areas of the Gulf is suggested.