Search

Using knowledge about plant–insect interactions in a crop protection perspective is a pre-requisite to promote the development of novel pest management strategies. Enhancing plant natural defenses has been described as a promising way to improve the management of pests. In cotton, plant topping (cutting off the top of the plant) for inducing such defenses has been proposed as a promising tool for integrated pest management. The main objective of this study was to explore the effect of cotton topping on the performance of the cotton aphid, Aphis gosypii, under greenhouse conditions. The effect of plant topping was evaluated on topped and on neighbor non-topped plants. Results showed that cotton topping disturbed A. gossypii aphids not only on the topped plant but also on neighbor non-topped plants. The population of aphids grew slower in the topped compared to the control treatment and lower abundances of aphids were found in the topped treatment up to a distance of 100 cm to the topped plant. When an individual nymph was confined in a clip-cage, the production of winged adults after 15 days of confinement was higher in the topped compared to the control treatment. This difference decreased as the distance to the topped plant increased. In conclusion, our study proves that cotton topping mediates plant-pest interactions on the focal and neighbor plants. We discuss how cotton topping is a promising technique that could be used as part of an integrated pest management program, particularly for smallholders in West Africa, for controlling aphid infestations.

The South American tomato pinworm, Tuta absoluta (Meyrick) (Lepidoptera: Gelechiidae), has invaded most Afro-Eurasian countries and is threatening worldwide tomato production. Various strategies have been developed and implemented to manage this pest. Here, we present a timely review on the up-to-date development and practical implementation of integrated pest management (IPM) programs for tomato crops across different world regions infested by T. absoluta. While insecticide resistance is a growing concern, biological control via releasing or conserving arthropod natural enemies and sex pheromone-based biotechnical control are the most successful management practices. Agronomic control-related research is an emerging area where the soil fertilization and/or irrigation, as well as breeding of resistant cultivars, has the potential to enhance IPM effectiveness. Grower survey responses in the native areas (i.e., South America), early-invaded areas (i.e., first report between 2006 and 2012) and newly invaded areas (i.e., first report after 2012) showed that the control programs evolved along with the areas and time since invasion. Growers in the early-invaded areas shifted more rapidly from chemical control to biological control compared to those from the native area. In all concerned regions, the pest control failure risk following chemical insecticide applications and the high cost associated with either biological or biotechnical control methods have been the greatest concerns for growers. The information gathered from the native and/or early-invaded areas may help achieve a more effective management in newly invaded areas. Lastly, researchers are expected to break the bottlenecks of some key issues that would enable lowering application cost of novel biorational alternative management options.

Competent arbovirus vectors are found in the culicid mosquito fauna of south-west Indian Ocean (SWIO) islands. In La Reunion, Aedes albopictus and Aedes aegypti mosquitoes are known vectors of dengue and chikungunya viruses. Culex quinquefasciatus is a potential vector of Rift Valley fever and West Nile viruses. To prepare a vector-control field trial against Ae. aegypti, this study aimed at identifying the best trapping strategy to catch adult Ae. aegypti, using BG-Sentinel traps (Biogents, Germany). It was implemented in two sites in southern La Reunion. Catches of Ae. albopictus and Cx. quinquefasciatus mosquitoes were also recorded. A Latin square design was used to estimate the detection probability and the apparent daily density—according to the BG-Sentinel trapping strategy: none, carbon dioxide (CO2), a commercial attractant—BG-Lure (Biogents, Germany), or both. The use of CO2 alone was associated with a higher detection probability for Ae. aegypti and Cx. quinquefasciatus mosquitoes, as well as a large increase in their apparent density. Traps with BG-Lure—alone or in combination with CO2, did not improve the detection probability of Ae. aegypti and Cx. quinquefasciatus mosquitoes. The same result was found for male Ae. albopictus. For females, baiting BG-Sentinel traps with CO2 or BG-Lure had no significant effect. The same apparent densities were found for Ae. aegypti and Ae. albopictus mosquitoes in both study sites—where Ae. aegypti mosquitoes were found at very low densities during previous surveys.

Sur la période 2016-2020, les agriculteurs des filières légumes-maraîchage, horticulture, arboriculture et cultures tropicales du réseau DEPHY FERME ont adopté des modèles décisionnels, des pratiques particulièrement remarquables, des trajectoires d'exploitations et ont produit des notes techniques. Cet ensemble de données dresse un panorama des pratiques alternatives mises en oeuvre dans le réseau pour diminuer l'usage des produits phytopharmaceutiques. C'est aussi une source d'information sur les coûts, les inconvénients et les bénéfices de ces pratiques aux yeux des agricultrices et des agriculteurs. Bien que des modifications profondes de systèmes soient rarement évoquées, certaines exploitations combinent de nombreuses pratiques, souvent en lien avec la gestion de l'enherbement et de la fertilité.

En une trentaine d'années, les moustiquaires imprégnées de pyrétrinoïdes se sont imposées en protection personnelle et en santé publique comme un moyen de prévention du paludisme. Un des acteurs de ces découvertes présente un panorama des moustiquaires imprégnées d'insecticide et apporte ici son témoignage, se fondant particulièrement sur les circonstances et les états d'esprit qui ont prévalu dans les années 1980, décennie cruciale pour ces avancées qui ont servi l'humanité. C'est en 1983 qu'a été réalisée la première expérimentation testant l'effet des moustiquaires imprégnées de pyréthrinoïdes et qui a mis en évidence l'impact de cette méthode sur la réduction de la transmission du Plasmodium. Cette découverte a été faite dans une station expérimentale de terrain au Burkina Faso montrant que chacun des nombreux paramètres entomologiques mesurés allait dans le sens d'une nette réduction du contact moustique-humain. Quelques années plus tard, toujours au Burkina Faso, il a été montré que les moustiquaires imprégnées, utilisées massivement dans un village, réduisaient la longévité et la capacité vectrice de la population de moustiques, à tel point que ces moustiquaires agissaient comme un moyen de lutte antivectorielle. Ces recherches ont toutes été effectuées par des chercheurs de l'Office de la recherche scientifique et technique outre-mer, devenu Institut de recherche pour le développement, dans le cadre du centre Muraz de l'Organisation de coordination et de coopération pour la lutte contre les grandes endémies, en bénéficiant de l'appui scientifique et financier de la Division de la biologie et de la lutte contre les vecteurs de l'Organisation mondiale de la santé.

International audience; The Sterile Insect Technique (SIT) is a promising technique to control mosquitoes, vectors of diseases, like dengue, chikungunya or Zika. However, its application in the field is not easy, and its success hinges upon several constraints, one of them being that the treated area must be sufficiently isolated to limit migration or re-invasion by mosquitoes from the outside. In this manuscript we study the impact of males and (fertile) females migration on SIT. We show that a critical release rate for sterile males exists for every migration level, in the context of continuous or periodic releases. In particular, when (fertile) females migration is sufficiently low, then SIT can be conducted successfully using either open-loop control or closed-loop control (or a combination of both methods) when regular measurements of the wild population are completed. Numerical simulations to illustrate our theoretical results are presented and discussed. Finally, we derive a threshold value for the females migration rate, when viruses are circulating, under which it is possible to lower the epidemiological risk in the treated area, according to the size of the human population.

Biological control can be an effective conservation strategy to manage invasive species when other conventional methods cannot be implemented. Estimating the benefits of biological control for the conservation of native biodiversity remains a challenging task. Following the introduction of a defoliating sawfly, Cibdela janthina, for biological control of invasive giant bramble, Rubus alceifolius, on Reunion Island (Mascarene Archipelago), we monitored the consequent change in R. alceifolius cover as well as species richness and cover of non-native species and native species within a set of patches along an altitudinal gradient in the National Park of Reunion Island. There was an increase in native species richness and cover together with a decrease in R. alceifolius cover, showing that biological control positively impacted the native plant communities. The effectiveness of C. janthina was influenced by the altitudinal range, the surface area of the patches and the location of each patch, i.e forest edge or forest matrix. We discuss the extent to which the use of biological control within an integrated approach can optimize benefits for biodiversity conservation in the short to medium term by selecting complementary and standardised protocols.

International audience; The expansion of mosquito species worldwide is creating a powerful network for the spread of arboviruses. In addition to the destruction of breeding sites (prevention) and mass trapping, methods based on the sterile insect technique (SIT), the autodissemination of pyriproxyfen (ADT), and a fusion of elements from both of these known as boosted SIT (BSIT), are being developed to meet the urgent need for effective vector control. However, the comparative potential of these methods has yet to be explored in different environments. This is needed to propose and integrate informed guidelines into sustainable mosquito management plans. We extended a weather-dependent model of Aedes albopictus population dynamics to assess the effectiveness of these different vector control methods, alone or in combination, in a tropical (Reunion island, southwest Indian Ocean) and a temperate (Montpellier area, southern France) climate. Our results confirm the potential efficiency of SIT in temperate climates when performed early in the year (mid-March for northern hemisphere). In such a climate, the timing of the vector control action was the key factor in its success. In tropical climates, the potential of the combination of methods becomes more relevant. BSIT and the combination of ADT with SIT were twice as effective compared to the use of SIT alone.

Suppression or eradication of insect pest populations by the release of sterile insects is often dependent on supplementary methods of pest reduction to levels where the target pest population can be overflooded with sterile insects. Population suppression activities often take place in advance of, or coincide with, the production and release of sterile insects. Supplementary methods to remove breeding opportunities, or management methods that prevent access of pests or vectors to the hosts, may reduce the population or prevent damage or disease transmission. Insecticides have been used widely in direct applications or applied as baits, in traps, or on specific sites where the pest makes contact or reproduces, although they are increasingly being replaced by biopesticides. As sterile insect release does not kill the pest, adult biting pests or fertile mated females of the pests will continue to attack hosts after the release of sterile insects. Thus supplementary pest suppression programmes and quarantine measures are essential to prevent damage or the spread of disease. Eradication or effective pest management requires that the entire population of the pest be treated, or that the programme apply immigration barriers. It also requires taking into account interactions among control methods; they can be additive, synergistic or antagonistic. When supplementary pest control activities directly benefit the human population in areas being treated, such as in mosquito or screwworm control programmes, these area-wide suppression activities are usually acceptable to the public, but when the public receives no direct benefit from supplementary control activities such as in crop pest programmes, social resistance may develop unless public information is managed properly.

National audience; Ralstonia solanacearum species complex (RSSC) is one of the most devastating bacterial plant pathogens causing bacterial wilt in a wide range of hosts including crops and wild plants. These soil-borne Gram-negative bacteria have a worldwide geographic distribution and significantly reduce crop yields especially in tropical regions such as the southwestern Indian Ocean. Due to the lack of efficient curative measures and the high persistence of RSSC, phage therapy represents a sustainable plant disease management strategy to be applied in agricultural settings. However, using phages as a biocontrol tool raises concerns about the potential of phage resistance evolution in plant pathogenic bacterial populations. To explore this question, we first evaluated the in vitro virulence of a local phage collection against the most prevalent strain of RSSC in Reunion Island. Then, we examined the temporal adaptation of the strain to these phages, and its consequences for bacterial fitness. Analysis of the virulence of the 10 phages tested showed that they were all able to effectively reduce bacterial growth. The emergence of bacterial resistance was reported after two or three days. Absence of clear lysis plaques were observed in evolved bacteria not only against the phage encountered but also against the entire phage collection, which included several phage species and genera. These results show high cross-resistance emergence, which resulted in a fitness cost for the bacteria, as measured by a reduction in growth rate and loss of swimming ability for 8 of 10 evolved bacteria exposed to the different phages. These results suggest that phylogenetically distant phages can be rapidly blocked in bacteria. Mechanistically different phages or complementary strategies may be needed to efficiently control phytopathogens. Conversely, fitness costs in bacteria point in the direction of a reduced virulence in planta. Further in vivo and genetic analysis will bring light to these questions.

Le moustique tigre, Aedes albopictus, représente une menace sanitaire par la transmission de maladies virales humaines. Malgré l'existence de moyens de lutte, le contrôle des populations d'Ae. albopictus reste un enjeu contraint par une connaissance fine de leur dynamique dans l'espace et le temps. Dans ce contexte, les modèles mathématiques sont des outils de choix pour tester et optimiser ces stratégies de contrôle. L'objectif de cette thèse était d'explorer les effets des méthodes de contrôle sur les populations d'Ae. albopictus en milieu tropical (La Réunion) et tempéré (Montpellier). L'étude s'est basée sur l'utilisation de modèle déterministe détaillant l'ensemble du cycle de vie du moustique, piloté par le climat et l'abondance de gîtes larvaires. Nous avons intégré au modèle les effets de différentes méthodes de lutte sur la dynamique des populations d'Ae. albopictus. Une attention particulière a été portée aux méthodes basées sur des lâchers de mâles stériles. L'analyse du modèle nous a permis de mieux comprendre et identifier les stratégies de lutte efficaces en terme de réduction et résilience des populations d'Ae. albopictus, afin de les optimiser en conséquence. Les stratégies de lutte intégrée ont pour objectif final de prévenir l'émergence d'épidémie. C'est pourquoi le modèle de dynamique des populations à La Réunion a été couplé avec un modèle épidémiologique. Des études supplémentaires devront être réalisées pour ajuster les prédictions du modèle avant de pouvoir étudier l'impact de stratégies de lutte intégrée sur la transmission de la dengue.

Dès 1917, dans l’article où il décrit ses premières observations et propose le nom de bactériophage, Félix d’Hérelle rapporte une première utilisation de ces virus pour traiter des infections bactériennes, donnant ainsi naissance à la phagothérapie. Le développement de cette application a montré qu’il était possible de mettre en place des traitements ciblant spécifiquement les bactéries, tels que ceux basés sur l’utilisation d’antibiotiques. Ces derniers, de par leur très grande efficacité et simplicité d’utilisation, ont provoqué le quasi-abandon de la phagothérapie. Aujourd’hui, un nombre croissant de bactéries pathogènes pour l’homme présente des phénotypes de résistance à plusieurs familles d’antibiotiques. Les infections causées par ces bactéries imposent l’utilisation de molécules au spectre d’activité toujours plus large et placent certains patients en situation d’impasse thérapeutique. Cet état de fait a relancé les recherches pour permettre le déploiement de la phagothérapie afin de traiter des patients mais aussi des animaux et des plantes. En fait, les domaines d’applications thérapeutiques des bactériophages s’élargissent au fur et à mesure que les agents antibactériens de nature chimique sont remis en cause, voire interdits. Cette revue revient sur les principes fondamentaux des applications thérapeutiques des bactériophages et expose les données récentes dans les domaines pour lesquels une exploitation commerciale est en cours ou sur le point d’émerger., In the 1917 article in which Félix d'Hérelle describes his first observations and proposes the name of bacteriophage, he also reports the first use of these viruses to treat bacterial infections, thus giving birth to phage therapy. Soon after antibiotics supplanted bacteriophages. Today, bacteria resistant to multiple antibiotics become a growing public health issue worldwide. This situation has revived research aiming at developing the antibacterial activity of bacteriophages to treat patients as well as diseases in animals and plants. In fact, the areas of applications of bacteriophages as antibacterial are widening as current solutions of chemical nature are questioned. This review summarizes the basic principles of therapeutic applications of bacteriophages and presents recent data in areas where commercial exploitation is occurring or about to emerge.

Three phages targeting Pseudomonas syringae GAW0113 have been isolated from organic waste samples: Pseudomonas phage Bertil, Misse and Strit. The phages have double-stranded DNA genomes ranging from 41342 to 41374 bp in size comprising 50 to 51 open reading frames. The three phages genomes are highly similar and genomic comparison analyses shows that they all belong to the Autographivirinae subfamily of the family Podoviridae. The phages are however only distantly related to other members of this family, and have limited gene synteny with type-phages of other genera within Autographivirinae, suggesting that the newly isolated phages could represent a new genus.

Au Mali, l’efficacité de la lutte chimique systématique (traitements calendaires) contre les ravageurs du cotonnier est régulièrement remise en cause. Des alternatives à cette lutte, comme la lutte étagée ciblée, l’intervention sur seuil et la culture biologique, visant toutes à réduire les quantités de pesticides utilisées, sont diffusées ; d’autres sont testées chez les producteurs, comme l’écimage du cotonnier. Cette étude analyse la perception de la technique de l’écimage du cotonnier par des producteurs. Elle a été conduite dans quatre villages de la zone cotonnière, à l’aide de focus groups d’hommes et de femmes et d’entretiens avec 40 producteurs ayant pratiqué ou non l’écimage. Les avantages de l’écimage identifiés par la majorité des producteurs interrogés sont : (i) une technique manuelle facile à mettre en œuvre, (ii) la diminution des risques de chute d’organes fructifères, (iii) la réduction de la hauteur des plants, s’étalant davantage (iv) une amélioration du rendement et (v) la réduction de la population des ravageurs et donc de l’utilisation des pesticides, ayant des effets positifs sur la santé humaine et l’environnement, et diminuant les coûts de production. Ses principales contraintes sont le besoin supplémentaire de main-d’œuvre et son coût par rapport à la culture de coton non écimé. Des partenariats avec les sociétés cotonnières et les organisations paysannes et la formation de leurs agents à l’écimage sont indispensables pour une adoption de cette technique à une plus large échelle.

International audience; African swine fever is a devastating disease that can result in death in almost all infected pigs. The continuing spread of African swine fever from Africa to Europe and recently to the high-pig production countries of China and others in Southeast Asia threatens global pork production and food security. The African swine fever virus is an unusual complex DNA virus and is not related to other viruses. This has presented challenges for vaccine development, and currently none is available. The virus is extremely well adapted to replicate in its hosts in the sylvatic cycle in East and South Africa. Its spread to other regions, with different wildlife hosts, climatic conditions, and pig production systems, has revealed unexpected epidemiological scenarios and different challenges for control. Here we review the epidemiology of African swine fever in these different scenarios and methods used for control. We also discuss progress toward vaccine development and research priorities to better understand this complex disease and improve control.

We analyze the alignment mechanisms involved in socio-technical transitions. The multi-level perspective has made the notion of alignment one of the pillars of its analytical framework, but its definition remains rather vague. Using a case study of the development of biological alternatives to agricultural pesticides in Brazil, we show that alignments are based on pairings between entities of the same nature, positioned in the niche and in the regime. The strength of these pairings relies on the coherence of the new sets formed. Several types of entities need to be matched to enable alignments. In this case study, we identify three types of paired entities: technologies, users and their interests, public and private organizations. Understanding these alignment mechanisms is an invitation to deepen the analysis of the relationships between incumbent and alternative technologies in sociotechnical transitions.

The invasive fruit fly Bactrocera dorsalis poses a major threat to the production and trade of mango in sub-Saharan Africa. Farmers devise different innovations to manage the pest in an attempt to minimize yield loss and production costs while maximizing revenues. Using survey data obtained from Embu County, Kenya, we analyzed farmers’ knowledge and perception as regards the invasive fruit fly, their innovations for the management of the pest, and the determinants of their adoption and dis-adoption decisions of recently developed and promoted integrated pest management (IPM) technologies for suppression of the pest. The results show that farmers consider fruit flies as a major threat to mango production (99%) and primarily depend on pesticides (90%) for the management of the pest. Some farmers (35%) however use indigenous methods to manage the pest. Though farmers possess good knowledge of different IPM strategies, uptake is relatively low. The regression estimates show that continued use of IPM is positively associated with the gender and education of the household head, size of a mango orchard, knowledge on mango pests, training, contact with an extension officer, and use of at least one non-pesticide practice for fruit fly management, while IPM dis-adoption was negatively correlated with the size of the mango orchard, practice score and use of indigenous innovations for fruit fly management. We recommend enhancing farmer′s knowledge through increased access to training programs and extension services for enhanced adoption of sustainable management practices for B. dorsalis.

La lutte contre l'onchocercose, ou cécité des rivières, une maladie parasitaire endémique, fut entreprise en Afrique de l'Ouest dans une perspective do développement durable. Tous les moyens technologiques disponibles ont de ce fait été mobilisés pour le contrôle du vecteur, une simulie, puis du parasite responsables de cette maladie, par le Programme de Lutte contre l’Onchocercose en Afrique de l'Ouest (OCP). La lutte antivectorielle consistant en épandages d’insecticides chimiques sur les sites de développement de la simulie dans les rivières, il est apparu indispensable d’assurer la sauvegarde de l’environnement aquatique qui fournit aux communautés riveraines eau et ressources biologiques. Les technologies les plus modernes ont été mises en œuvre dès leur mise au point, pour combattre la maladie, contribuant ainsi à la protection de ce milieu. Le programme de surveillance écologique des rivières traitées par des larvicides anti-simulies a été mis en place dès le lancement d’OCP. et assuré par des spécialistes de I' hydrobiologie des pays africains participants du Programme, sous la supervision d’un groupe international d’experts indépendants, le Groupe Écologique. OCP est incontestablement un succès aussi bien pour ce qui est du contrôle de la maladie que de la protection de l'environnement. Il est l'exemple unique au monde d’un programme de santé publique de longue durée qui depuis son origine a mis en œuvre tout ce qui était possible pour harmoniser les enjeux de l’amélioration de la santé et ceux de la protection de l’environnement. Il s'est achevé avec la satisfaction de laisser aux générations montantes un environnement non dégradé et des vallées libérées de l’onchocercose, qui permettront d’accroître la productivité agricole des pays africains. The control of onchocerciasis, or river blindness, an endemic parasitic disease, was implemented in West Africa in the perspective of sustainable development AH the available technological means to fight this disease, by way of the control of its blackfly vector, then its parasite, were therefore implemented by the Onchocerciasis Control Programme in West Africa (OCP). Vector control being achieved through applications of chemicals on its river breeding sites, it was necessary, at the same time, to fight for the preservation of the aquatic environment, which supplies the communities that live along the rivers with water and biological resources. This was the spirit in which the OCP was set up and implemented, and the most modem technologies were used as they become available to fight the disease, thus facilitating the preservation of the aquatic environment. This Programme has indisputably been a success as regards the control of the disease as also from the point of view of the preservation of the environment The aquatic monitoring programme of the rivers under treatment with anti-simulid larvicides was set up right from the very beginning, and performed by national experts of the Participating Countries of the Programme, under the aegis of a group of international independent experts, the Ecological Croup The Onchocerciasis Control Programme in West Africa is an unique example in the world of a long-term public health programme which has made every effort possible from its inception to adequately combine health and environment issues. It ended with the satisfaction of bequeathing to the coming generations a non degraded environment and valleys freed from onchocerciasis which would increase the agricultural productivity of the countries.

Since its inception in 1974, the Onchocerciasis Control Programme in West Africa (OCP) has implemented a strategy of onchocerciasis (river blindness) control which has been aimed at the long-term interruption of the transmission of the causative agent (the filarial worm Onchocerca volvulus), in all areas where there was a human reservoir of infection of the severe blinding form of the parasite. In operational terms, this has required the weekly application of insecticides (mainly by aircraft)...

Avant les années 1980, la seule méthode de lutte contre l’onchocercose était l’élimination des populations de simulies vectrices. Cette stratégie a été utilisée avec un succès considérable dans le cadre du Programme de Lutte contre l’Onchocercose en Afrique de l’ouest (OCP). La découverte de l’ivermectine, premier médicament efficace contre Onchocerca volvulus et pouvant être distribué à large échelle, suscite depuis 10 ans une nouvelle mobilisation internationale tant au niveau de la recherche fondamentale que de l’élaboration de nouvelles stratégies de lutte applicables en dehors de l’aire d’OCP. Cet article résume l’état des connaissances sur les aspects parasitologiques, cliniques, diagnostiques et épidémiologiques de l’onchocercose. Si le mode de développement des premiers stades parasitaires chez l’homme est encore très mal connu, des progrès importants ont été accomplis dans la connaissance de la dynamique de population d’Onchocerca volvulus. L’étude de la pathogénie des lésions dermatologiques et oculaires a fait l’objet de nombreux travaux. Des études épidémiologiques sont menées en vue d’apprécier l’importance des manifestations systémiques de l’onchocercose. De nouvelles méthodes diagnostiques, plus sensibles que la technique parasitologique classique, ont été mises au point. La répartition de l’onchocercose a été précisée grâce à l’utilisation systématique d’une méthode d’évaluation rapide des niveaux d’endémie. Les techniques de biologie moléculaire, utilisées en routine en Afrique de l’ouest, permettent de différencier les différentes espèces du genre Onchocerca ainsi que plusieurs souches d’Onchocerca volvulus, de pathogénicité différente. Enfin, de nouvelles méthodes de quantification des handicaps ont permis de préciser l’impact socio-économique des complications oculaires et cutanées de l’onchocercose. Before the 1980s, the only available method for control of onchocerciasis was elimination of blackfly vector populations. This strategy was used with considerable success in the Onchocerciasis Control Programme in West Africa (OCP). The discovery of ivermectin, the first effective drug suitable for mass treatment of onchocerciasis, has revived international interest not only in fundamental research but also in development of new strategies to control onchocerciasis in the countries outside the OCP area. This report gives an overview of current parasitological, clinical, epidemiological and diagnostic data about onchocerciasis. Although little is known about the early development of Onchocerca volvulus in the human host, significant insight has been gained into the population dynamics of the parasite. The pathogenesis of cutaneous and ocular manifestations in onchocerciasis is now better understood. Epidemiological studies are under way to evaluate the extent of systemic manifestations. Recently developed diagnostic methods are more sensitive than conventional parasitological techniques. A new method for rapid assessment of endemic level has provided a detailed picture of the distribution of onchocerciasis. Species-and strain-specific DNA probes have been developed for identification of parasites in West Africa. New methods for quantifying disability allow evaluation of the socio-economic impact of the cutaneous and ocular complications of onchocerciasis.

9.1 Introduction Human onchocerciasis, or river blindness, is a filarial disease caused by Onchocerca volvulus which, in West Africa, is transmitted by the adult female of the blackfly, Simulium damnosum s.l. (Zimmerman et al, 1992). It was common mainly along the fertile valleys of the watercourses and was not only a major public health problem but also an obstacle to the socioeconomic development of the infested areas. In 1974, the concern of the governments of seven of the most affected co...

Among the many larvicides tested for the control of Simulium damnosum s.l. larvae, the vector of human onchocerciasis in West Africa, pyraclofos proved to be 100% effective at 100 µg x L-1 for 10 min in river, with a cany of 20 km at 100m3 xsec-1. Tests were then performed both in laboratory and field conditions to evaluate its toxicity on the non-target aquatic fauna. In experimental short-term gutter tests, the detachment of the total benthic insects was 35% al 100 µg x L-1 for 10 min against 17% for temephos at the same dose and 59% for chlorphoxim at 50 µg x L-1 for 10 min. Centroptilum, Baetis and Pseudopannota bertrandi were the most affected organisms. The treatment of a river resulted in a considerable detachment of the same taxonomic groups, plus Orthocladiinae. On the other hand, investigations conducted in tanks showed that the 24-hr LC50 for Chrysichthys nigrodigitatus is 150 µg x L-1 and that for Pollimyrus isidori 170 µg x L-1, values which are not very different from the operational dose of the larvicide (100 µg xL-1 for 10 min.). Nevertheless, in a river, no fish mortality was recorded. Based on fish LC50 and drift of benthic insects, pyraclofos at 100 µg x L-1 was judged to be less toxic to aquatic fauna in the short term than permethrin and carbosulfan.

From 1976 through 1989, weekly aerial spraying operations against blackflies were carried out along the rivers of a wide savanna area of West Africa (~700,000 km2) where onchocerciasis was hyperendemic. The level of endemicity began to decrease significantly after 4 years of vector control and became very low in 1989. This situation has been maintained without any vector control activity or chemotherapy, and no incidence of any new cases has been detected. An ophthalmological study carried out in 2000 has confirmed these good results, showing only cicatricial ocular lesions in the examined population. These results led to the conclusion that 14 years of vector control may achieve long-term elimination of onchocerciasis, even in the absence of chemotherapy, provided that the treated areas are not subjected to any contamination by exogenous parasites carried in infected humans or flies.

Since vector control began in 1975, waves of Simulium sirbanum and S. damnosum s.str., the principal vectors of severe blinding onchocerciasis in the West African savannas, have reinvaded treated rivers inside the original boundaries of the Onchocerciasis Control Programme in West Africa. Larviciding of potential source breeding sites has shown that these ‘savanna’ species are capable of travelling and carrying Onchocerca infection for at least 500 km northeastwards with the monsoon winds in the early rainy season. Vector control has, therefore, been extended progressively westwards. In 1984 the Programme embarked on a major western extension into Guinea, Sierra Leone, western Mali, Senegal and Guinea-Bissau. The transmission resulting from the reinvasion of northern Côte d’Ivoire and Burkina Faso has been reduced by over 95%, but eastern Mali has proved more difficult to protect because of sources in both Guinea and Sierra Leone. Rivers in Sierra Leone were treated for the first time in 1989 and biting and transmission rates in Sierra Leone and Guinea fell by over 90%. Because of treatment problems in some complex rapids and mountainous areas, flies still reinvaded Mali, though biting rates were approximately 70% lower than those recorded before anti-reinvasion treatments started. It was concluded that transmission in eastern Mali has now been reduced to the levels required to control onchocerciasis.

Maladie largement répandue en Afrique intertropicale l’onchocercose est un fléau, tant social qu’économique, qui provoque, à son stade ultime, une cécité irréversible. Avant l’instauration des premières mesures de lutte anti-vectorielle, on estimait à près de trois millions le nombre d’onchocerquiens en Afrique occidentale. La maladie est transmise par un petit moucheron Diptère, Simulium damnosum, qui présente une phase larvaire et nymphale aquatique. Ce sont les gîtes larvaires de ce vecteur, biefs à courant rapide des rivières, que le Programme de Lutte contre l’Onchocercose en Afrique de l’Ouest (OCP : Onchocerciasis Control Programme) traite lors ses campagnes de lutte. Comme toute lutte insecticide OCP représente une menace importante pour l’environnement. C’est pourquoi le programme s’est doté d’un réseau de surveillance des écosystèmes aquatiques, couvrant l’ensemble de la zone exposée aux épandages d’insecticides. Au total, près de dix équipes de chercheurs ichtyologues et entomologistes, de nationalités diverses, ont durant vingt ans effectué une surveillance régulière de la faune aquatique susceptible d’être atteinte par les traitements larvicides. C’est la première fois au monde qu’une telle entreprise a été mise en place sur une si grande échelle d’espace et de temps. Sont exposées ici les conclusions du bilan écologique.À l’état naturel, les communautés d’invertébrés aquatiques de la zone sont essentiellement composées de “collecteurs moissonneurs” et de “collecteurs filtreurs”. Après 20 années d’épandages insecticides, la tendance générale montre que les populations de “collecteurs” sont toujours affectées par les traitements larvicides, mais que le stress est différent en fonction des insecticides employés. Après arrêt des traitements insecticides, il y a de façon générale un retour à une structure communautaire sensiblement identique à celle observée avant les premiers épandages.L’ensemble des paramètres étudiés, qu’ils concernent la richesse et la structure des communautés de poissons ou la biologie des espèces ne montrent pas d’effets décelables de vingt années d’épandages dans les rivières traitées. En revanche, les variations observées montrent que des facteurs d’origine naturelle (hydrologie, saisons…) ou anthropique (barrages), peuvent avoir une influence particulière sur les peuplements de poissons. Ces facteurs semblent avoir une pression d’autant plus importante qu’ils se produisent en synergie. Dans un souci d’économie, mais aussi d’un point de vue éthique, vis-à-vis de l’environnement, OCP limite ses épandages d’insecticides aux seuls gîtes productifs en larves de S. damnosum. De ce fait, par rapport aux milliers de kilomètres de rivières qui auraient pu théoriquement être traitées, beaucoup ne le furent que rarement, voire parfois jamais. Ainsi subsistent de vastes zones refuges qui peuvent servir de réservoir potentiel et permettent en cas d’arrêt des traitements une recolonisation des biefs par la faune.La conclusion générale rassurante du suivi de 20 années de surveillance écologique de la faune non-cible est qu’il n’y a jamais eu d’effets drastiques du fait des larvicides employés même lorsque les peuplements, notamment les invertébrés, ont subi des cycles de traitements longs et-ou d’assez forte toxicité. Il faut, à cet égard, tenir compte de l’attention particulière qui a été accordée, par les instances opérationnelles d’OCP, aux recommandations du Groupe Écologique, même si ce suivi scrupuleux a pu, parfois, limiter l’efficacité de la lutte proprement dite contre les simulies.

The great successes achieved by the Onchocerciasis Control Programme in West Africa (OCP) in the large-scale control of the blinding savanna form of onchocerciasis (river blindness) have allowed vast tracts of previously abandoned valleys to be resettled and developed. Among the many issues and problems that have to be addressed, to ensure the most effective long-term management of settlement and development in these onchocerciasis-controlled areas, is that which relates to the potential impa...

Le Bacillus thuringiensis var. israelensis est un insecticide entomopathogène qui agit par ingestion et provoque une lyse des tissus épithéliaux de l’intestin ainsi qu’une paralysie des pièces buccales. Le sérotype H-14 (de Barjac), présente une très forte spécificité d’action vis-à-vis des larves de moustiques ainsi que des simulies.Utilisé de manière expérimentale en Côte d’Ivoire dans le cadre d’essais de contrôle des populations larvaires de Simulium damnosum s.l., puis en campagne de lutte contre ces mêmes Diptères, il s’est avéré peu toxique pour la faune aquatique non-cible.Son épandage dans un milieu vierge entraîne une augmentation de l’intensité de dérive des invertébrés présents qui ne dépasse pas 4 à 5 fois sa valeur normale (contre 50 à 200 fois pour des insecticides organophosphorés comme le téméphos ou le chlorphoxim). L’action traumatisante induite par les traitements semble par contre plus longue qu’avec d’autres produits mais est sans conséquences pour le maintien des équilibres.Une action significative sur les Trichoptères Hydropsychidae, qui s’était traduite par une baisse sensible de leur densité après neuf semaines d’un traitement expérimental de saison sèche avec une formulation de B.t.i. H-14, n’a pas été retrouvée à la suite de traitements de campagne de plusieurs mois effectués sur de nombreuses rivières de Côte d’Ivoire, avec une autre formulation.En milieu stagnant, des concentrations très supérieures aux doses actives contre les larves de moustiques ont été lestées et se sont révélées très peu toxiques pour la faune non-cible.D’une manière générale, l’utilisation de B.t.i. H-14 comme moyen de lutte antivectorielle, avec application en milieu aquatique, ne semble pas devoir entraîner de risques écologiques, tout au moins à court et moyen terme. Bacillus thuringiensis var. israelensis is a spore forming bacterium with a pathogenic action caused by the production of a toxic protein. The ingestion by insects of the cristal produced by the spores lead to a paralysis of the mouthparts and a rapid destruction of the gut epithelium. The H-14 serotype isolated by de Barjac (1978) present a strong larvicide specificity against mosquitoes and also Simuliidae.Experimental use of the primary powder or formulations have been done in several rivers of the Ivory Coast, in order to estimate their toxicity against aquatic non-target organisms in the case of Simulium control applications.Some medium term experiments have also been studied as well as a dry season campaign of weekly treatments, covering the main rivers of that country.Applications of a formulation of B.t.i. H-14 on a virgin biotope produces an increase of the invertebrate drift intensity which rise about 4 to 5 times its normal value. Such an increase as to be considered as very low compared to the value which occures after organophosphorus insecticides treatments (respectively 50 to 200 times with temephos and chlophoxim for example…). However, the traumatisation induced on invertebrates by action of B.t.i. seems to be longer than in the case of application of other compounds, but is without any consequences lo the aquatic population balance.A significant decrease of density was found for Hydropsychidae after a 9 weeks experimental treatment of a small river with a B.t.i. formulation. The same phenomenon was not detected after the campaign of treatments with an other formulation, covering most of the Ivorian rivers.A B.t.i. H-14 Sandoz formulation experimented in stagnant biotopes in order to control mosquitoes larvae has been applied without any injury for the non target fauna, even at high dosages never used in a normal campaign.It can be concluded from the present results that B.t.i. H-14 have a nearly total short term innocuity against non target fauna associated lo Simulium damnosum s.l., or mosquitoes larvae. There is also no evidence of a deleterious action on invertebrate populations after a regular application at medium term.

The Simulium sanctipauli Vajime & Dunbar subcomplex of the West African S. damnosum Theobald complex is cytotaxonomically revised for the western part of the Onchocerciasis Control Programme area. The subcomplex is defined and a chromosomal key provided for the identification of the sibling species and forms recognized. Two sibling species are newly described, S. leonense Boakye, Post & Mosha (Sierra Leone) and S. konkourense Boakye, Post, Mosha & Quillévéré (Guinea and Sierra Leone). Detailed chromosomal data are provided as warranty for the conclusions about the specific or infraspecific status of the taxa recognized.

Repeated DNA sequences have been instrumental in the development of DNA probes for many different parasites. Isolation of such DNA probes has generally been accomplished by differential screening of genomic libraries with total genomic DNA preparations. In the current work, a rational design strategy is presented for the development of oligonucleotide probes based upon repeated sequence families. A repeated sequence family present in the genome of Onchocerca parasites, designated O-150, has been amplified from various samples of genomic DNA using PCR. DNA sequence analysis of the resulting PCR products demonstrated that the sequences may be arranged into clusters within which the individual sequences are identical or nearly identical. Differences among the cluster consensus sequences have been exploited to explain the specificities of previously isolated O-150 based probes and to develop two new oligonucleotide probes. One of these probes hybridizes specifically to Onchocerca volvulus O-150 PCR products, while the second hybridizes specifically to O-150 PCR products from the closely related bovine parasite O. ochengi. These oligonucleotide probes have been used to characterize Onchocerca infective larvae isolated from wild caught infected flies in West Africa. Because repeated sequence families are a common feature of most genomes, including those of parasites, this method should be applicable to the rational design of oligonucleotide probes for other parasitic infections.

It is concluded that, at least for the time being, organic loads and nutrients in the upper Léraba basin are only of relevance along limited stretches of the main Léraba rivers, where settlements are located close to the river banks and provide point sources of contamination, with localized effects on river water quality and thus on fish and aquatic invertebrates. Assuming that the input data for the SoilFug model were reasonably correct, it can be concluded that contamination of river water ...

Blackflies are reappearing in areas of West Africa where they used to be controlled with insecticides because they were vectors of the parasite Onchocerca volvulus. Even though they no longer transmit onchocerciasis in these areas they can hinder optimal land use through their biting behaviour. The authors discuss the problems associated with resuming the use of insecticides to control the blackfly and recommend that ground treatment be restricted to areas where it is likely to be effective on a continuing basis. In communities lacking technical and financial resources the only alternative consists of individual protection through the use of repellents or protective clothing.

Commencing in 1975, under the auspices of W.H.O., weekly applications of insecticides have been employed to control the blackfly which transmits human river blindness in West Africa. The results provided in this paper do not show, as a whole, any clear impact of OCP-applied pesticides on fish populations. The total catch, the number of species caught in each sample and coefficient of condition, appeared to fluctuate around a mean value, and no long-term drop was observed over the period investigated. The seasonal pattern is generally clear. In some cases longer term declines occur, generally being followed by a rise correlating with changing hydrological conditions.

A cloned sequence, pOvs134, was isolated from a genomic library prepared from Onchocerca volvulus of savanna origin in the plasmid pUC9. pOvs134 hybridizes to all the geographic isolates of O. volvulus tested from both the New and the Old World, but not to the species Onchocerca gibsoni, Onchocerca gutturosa, Onchocerca ochengi, Onchocerca cervicalis, the filarial parasites Brugia malayi. or Dirofilaria immitis, nor to human or simuliid DNA. As little as 250 pg of DNA can be detected on a dot blot hybridization. suggesting that pOvs134 is sensitive enough to detect a single third stage larva. DNA sequence analysis of the inserted DNA of pOvs134 revealed that it consisted of twelve examples of a 149-bp repeat. The sequence of this repeat is strikingly similar to that of two O. volvulus genomic clones previously described, one of which has been reported to be specific for forest form O. volvulus. and one of which hybridizes to genomic DNA of several species of Onchocerca. These results suggest that the 149-bp repeat sequence is highly repeated in the genome of O. volvulus, and that variants of this repeat with different specificities exist.

L’utilisation hebdomadaire d’insecticides pour lutter contre les Simulles modifie l’abondance des populations benthiques. Les variations ne sont ni de la même ampleur ni du même signe, selon l’insecticide (Abate, chlorphoxime, B.t.) et les taxons.Parmi les dizaines de rivières savanicoles traitées aux insecticides antisimulidiens, seules quelques unes font l’objet d’une surveillance de la faune non-cible. La problématique de ce travail est de savoir s’il est possible de généraliser à l’ensemble des rivières, les fluctuations d’abondance des populations observées sur une station de référence.Sur la station de référence, l’évolution de l’abondance des populations pour les trois insecticides étudiés est mesurée à l’aide du rapport : R/P = log APTi/log AVT, où log APTi est le logarithme de l’effectif moyen pour la période de traitement à l’insecticide i et où log AVT est le logarithme de l’effectif moyen avant traitement. Pour chaque taxon ainsi que pour la faune totale on obtient donc un rapport Abate, un rapport chlorphoxime et un rapport B.t.Les valeurs de ces rapports obtenus pour la station d’Entomokro, sont ensuite appliquées aux effectifs récoltés avant traitement sur trois autres stations. Les valeurs calculées sont comparées aux valeurs observées dans le cadre de la surveillance des rivières.Pour la faune totale, l’écart entre les valeurs calculées et les valeurs observées est très faible, r = 0,98.L’étude par taxon montre que la prédiction de ce modèle est excellente pour les Caenidae et les Hydropsychidae, bonne pour les Baetidae, les Chironomini, les Tricorythidae et les Orthocladiinae, médiocre pour les Tanypodinae et les Tanytarsini. The weekly utilization of insecticides sprayed by the Onchocerciasis Control Programme to control Simulium damnosum larvae modifies the abundance of the non target benthic populations. These insecticides (B.t., Abate and chlorphoxim) have neither the same toxicity nor the same selectivity for the principal taxa. In consequence, the long-term variations of the abundance of the populations are neither of the same importance nor of the same sign (some of them remain the same or decrease while others increase), according to the product and the taxa. In long term, these variations being mainly the consequence of direct toxicity but also take into account the duration of the life cycles as well as spatial and trophic competitions.In this study, only the saxicolous fauna is taken into account. It has been collected on rocks with the Surber sampler during the low water period (December to March).Among the ten savannah rivers treated with antiblackfly insecticides, only few are the object of a non-target fauna monitoring. The object of this work is to find out if it is possible to generalize to all the rivers, the variations in population abundance observed for an insecticide on a control station.In the reference station, the variation of population abundance for each of the insecticides is calculated by means of the ratio R/P = log APTI/log AVT, where log APTi is the logarithm of the average for the period treated with the i insecticide, and where log AVT is the logarithm of the average before treatment. For each taxa as well as for the total fauna, Abate, chlorphoxim and B.t. ratio were defined.The values of these ratio obtained for the Entomokro station on the Marahoué river in the Ivory Coast are then applied to the data collected before treatment on three rivers or stations (Amou-Oblo on the Amou river in Togo, Asubende on the Pru river in Togo and Danangoro on the Marahoué river in the ivory coast). The calculated values are then compared to the values collected after treatment in the river monitoring programme.In the reference station the ratio of the populations collected before and after treatment are sometimes greater, sometimes lower than unit (when the ratio is greater than unit, it means that there is an increase of the abundance of populations during the Processing period).The ratios are very close to the one for the B.t. which is the less toxic insecticide against the non target fauna, the greatest for the chlorphoxim which is the more toxic product and intermediate for Abate which has an intermediate toxicity. It appears that the more insecticides were estimated to be toxic in gutter tests, the more population abundance differ from the reference ones.For the total fauna, differences between the values calculated ans observed were very low (r = 0,98). For the taxa, the prediction of this model is excellent for Caenidae and Hydropsychidae, good for Baetidae, Chironomini, Tricorythidae and Orthocladiinae, but mediocre for Tanypodinae and Tanytarsini. The authors submit some hypotheses to explain the bad adequation of the model for these two taxa; hypotheses based on taxonomic problems and niche releasing.

Qu’est-ce que l’onchocercose ? Une maladie de santé publique d'importance socio-économique L'onchocercose est une filariose cutanée provoquée par le développement dans le corps humain du ver filarien Onchocerca volvulus (Duke, 1990). Ce parasite est transmis à l'homme par une simulie du genre Simulium. En Afrique de l’Ouest, il s’agit de simulies appartenant au complexe Simulium damnosum dont les stades larvaires se développent exclusivement dans les eaux courantes des rivières. C'est pourquo...

Des traitements aériens à l’ActellicR M20 (Pirimiphos methyl) en formulation microencapsulée ont été réalisés sur différentes rivières du Mali et de Côte d’Ivoire, en vue de ta destruction des larves de Simulium damnosum s.l., vecteur de l’Onchocercose.A la concentration de 0,2 mg/l/10 mn, aucune mortalité de poissons n’a été observée. Par contre, les évaluations de l’intensité de dérive témoignent d’une forte toxicité des traitements vis-à-vis des invertébrés benthiques. Cet effet est maximum environ deux heures après les épandages et atteint un niveau vingt fois supérieur à celui provoqué par l’utilisation du téméphos (AbaleR) dans les conditions normales de campagne.Baetidae, Tricorythidae et Chironomidae sont parmi les taxons les plus sensibles et un niveau global de décrochement pour l’ensemble des invertébrés de l’ordre de 60 % a été obtenu sur une période de 24 heures en utilisant la méthode des « gouttières in situ ».Un tel niveau d’impact sur la faune des invertébrés n’est pas sans risque pour l’environnement aquatique et l’utilisation de l’ActellicR M20 microencapsulé sur une grande échelle n’est pas recommandable, sous la forme de ta formulation testée. Aerial applications of ActellicR M20 (Pirimiphos methyl), in a micro-encapsulated formulation were tried as a larvicide against Simulium damnosum s.l. in different rivers in Mali and Ivory Coast. Al 0.2 mg/l/10 mn concentration, no fish mortality was observed. However, drift rate measurements indicate a strong effect on the invertebrate fauna, about two hours after application with a maximum level of 20 times in comparison to a normal temephos (AbaleR) treatment.Baetidae, Tricorythidae and Chironomidae are the most sensitive taxa and a total detachment of 60% have been recorded during a 24 hours period, using the in situ gutter technique.Such an impact on the invertebrale fauna is not without any risk for the aquatic environment and the use of Actellic R M20 micro-encapsuled on a large scale is not recommended, as far as the tested formulation is concerned.

Medium Scale Land Utilization Analyses, 1972, 1983 and 1993 From the maps presented in Figures 4.1, 4.2 and 4.3, it is to be noted that there have been appreciable extensions of settlement and of cultivation in the Land Settlement Analysis area (LUA) since 1972, and corresponding decreases in the savanna woodland. More detailed analytical information on these developments is presented below. The Situation in 1972 From the data presented in Figure 4.1, it is evident that in 1972, before onchoc...

As part of the WHO Onchocerciasis Control Programme in West Africa (OCP), the attack phase of operations in the Niger basin in Guinea began in 1989 with the simultaneous use of ivermectin and vector control. Larvicide applications coupled with annual large-scale ivermectin distribution have greatly reduced blackfly infectivity (by 78.8% for the number of infective larvae per 1000 parous flies). The combination of vector control and ivermectin has permitted excellent control of transmission. In the original OCP area, it took 6-8 years of vector control atone to obtain an equivalent decrease in blackfly infectivity. For the same number of flies caught, transmission was much higher in areas where ivermectin had not been distributed. The combined use of ivermectin and vector control has opened up new prospects for carrying out OCP operations with, notably, the possibility of reducing larviciding operations. Dans le cadre du Programme OMS de lutte contre l’onchocercose en Afrique de l’Ouest, la phase d’attaque des opérations dans le bassin du Niger en Guinée a démarré en 1989 avec l’utilisation simultanée de l’ivermectine et de la lutte antivectorielle. Parmi les seize points retenus pour cette étude, tous situés dans des foyers holoendémiques de savane, la moitié sont répartis dans le bassin du Haut Niger en Guinée et les autres dans l’aire initiale du Programme.Après trois à quatre années d’opérations avec une distribution annuelle d’ivermectine à grande échelle, on note en Guinée une forte réduction de l’infestation des simulies (78,8 % pour la proportion de mouches infestantes et 82,9 % pour le nombre de larves infestantes pour 1 000 femelles pares). La prévalence des microfilaires a peu diminué; en revanche, les charges microfilariennes des communautés qui mesurent l’intensité de l’infestation ont chuté de 60 à 80 % par rapport aux données de prétraitement. La combinaison de la lutte antivectorielle et de la distribution de masse de l’ivermectine a permis un excellent contrôle de la transmission. Par contre, dans l’aire initiale du programme, il a fallu 6 à 8 ans de lutte antivectorielle seule pour obtenir une réduction équivalente de l’infestation des simulies. A nombre égal de mouches capturées, la transmission est beaucoup plus forte dans les zones où l’ivermectine n’est pas distribuée, même après plusieurs armées de lutte antivectorielle efficace et ininterrompue.L’utilisation combinée de l’ivermectine et de la lutte antivectorielle ouvre des perspectives nouvelles dans la conduite des opérations avec notamment une possibilité d’allégement de la lutte antivectorielle.

Après avoir réalisé plusieurs séries d’expérimentations, en laboratoire et dans le milieu naturel, afin de tester l’impact de nouveaux insecticides sur la faune aquatique non cible, nous avons pu juger les avantages et les inconvénients liés à ces 2 techniques. Afin d’améliorer la représentativité des résultats obtenus, nous proposons une technique nouvelle d’expérimentation qui tout en gardant les avantages des méthodes classiques, en supprime les inconvénients. Cette méthode utilise un modèle réduit de cours d’eau, installé in situ et dont l’utilisation permet la mise en évidence de la sensibilité des différents organismes testés vis à vis du pesticide expérimenté.Un premier essai de l’appareil a donné des résultats qui confirment ceux obtenus par d’autres méthodes. Lethal effects of new pesticides on non-target organisms are often estimated on the basis of laboratory bioassays. The relevance of such experimental data to natural conditions is questionable. In other respects, field trials mode on a large scale, can have unexpected and noxious effects on the aquatic environment.Our purpose was to carry out a new in situ method having the same accuracy as laboratory tests. The environmental conditions of the treated area are simulated.The method is based on the utilization of one apparatus which has been specially designed and which represents a reduced model of a river bed. It is made of sheet-iron, and ils lower part is closed by removable drift-net.The pesticide formulation to be tested is kept in a storage tank, set up above the upper part of the apparatus and can flow regularly into the System. This device is anchored into shallow and running water beds. Different types of substrates (sand, gravels, stones, etc.), containing fauna, are transferred into the U-shaped part of the apparatus, and this one is kept open at both ends during 12 h for recovering. After this preparation phase, the lower part is closed with a drift-net and the pesticide solution is allowed to flow down, during a given time.Samples are taken successively, after 30 minutes, I, 2, 4, 8 and 24 h by removing the drift net collector. Finally, the substrates are taken off and the remaining fauna, not killed by the pesticide, is sorted by washing and sieving the sediment, after fixation into formalin. The total amount of experimented fauna is equal to the sum of killed fauna present in collectors plus living fauna which remains at the end of the bio-assay.The degree of susceptibility of experimented species can be derived from quantitative analysis of the different samples and curves depicting specific drift-rates versus time can be drawn. By that method sufficient numbers of organisms are tested and therefore, specific reactions related to different pesticides can be assessed statistically.

La présente étude porte sur la structure trophique des communautés de poissons subsistant dans quelques mares résiduelles du Baoulé (haut bassin du Sénégal) au Mali.Il est d’abord montré que les espèces limnivores et phytophages possèdent un intestin significativement plus long que les espèces des autres catégories trophiques, notamment les carnivores et les omnivores. Ce sont ces dernières espèces qui, d’un strict point de vue alimentaire, devraient s’adapter le mieux puisque peu spécialisées. On doit donc s’attendre à voir subsister dans ce type de biotopes des espèces généralistes ou opportunistes capables d’adapter leur régime aux ressources alimentaires disponibles.De fait, en ce qui concerne le régime alimentaire des espèces subsistant dans les mares résiduelles, il ressort assez clairement que les affinités de régime alimentaire pour différentes espèces sont plus fortes à l’intérieur d’un même prélèvement qu’entre mêmes espèces d’échantillons différents. Cela signifie que pour survivre dans des conditions extrêmes, les espèces adaptent, dans certaines limites, leur régime aux ressources dominantes disponibles. On peut ainsi montrer que face à une faible variabilité de nourriture, liée également à une moindre quantité, les espèces utilisent la ressource la plus abondante, et à l’inverse lorsque les proies deviennent nombreuses, les poissons s’alimentent à partir d’un nombre de taxons plus important. We have studied the trophic structure of the fish assemblage which remains in the residual ponds of the Baoulé river in Mali (upper Senegal basin).There is a correlation between the diet and the gut length relative to body length: the relative gut length of limnivorous and phytophagous species is significantly longer than that of other trophic groups such as carnivores or omnivores. In terms of diet, generalists (i.e. omnivores) or species which may exhibit some trophic flexibility could have a better adaptive advantage than others. Consequently, the more opportunistic species, with respect to the available resources, are the best adapted to survive in residual ponds.The study of the feeding habits of the fish species which remain in the residual ponds indicates that there is a higher degree of diet affinities between different species of the same sample than between the same species in different samples. Therefore to survive in severe environmental conditions, the species choose to adapt, within limits, their diet lo the dominant available resources. We demonstrated that, when the food is scarce, opportunistic fishes can feed upon the more abundant resource, and, conversely, when the food is abundant, individuals can feed upon a greater prey variety.

What is Onchocerciasis ? A public health disease of socio-economic importance Onchocerciasis is a dermal filariasis caused by the development in human of the filarial worm Onchocerca volvulus (Duke, 1990).The main clinical manifestations of the disease are skin lesions and visual impairment which may result in blindness. O. volvulus is necessarily transmitted to man by the bites of a blackfly vector of the genus Simulium in West Africa. This fly breeds exclusively in fast-flowing stretches of...

Des espèces du complexe S. damnosum ont pu, en zone de forêt et dans certaines conditions d’isolement, développer rapidement une sérieuse résistance au téméphos. Cette résistance semble se manifester davantage chez S. sanctipauli que chez S. soubrense. In Ivory Coast, on the lower Bandama River, in forest area, larvae of the Simulium damnosum complex have rapidly developed a serions resistance to temephos (abate (R)). The resistance ratio to the LC 99,9 level can reach 45. This resistance seems to be more apparent in S. sanctipauli. We have noted for this species a high frequency of a heterozygote inversion on the chromosome III L in resistant larvae. Treatments fait completely at dosage 4 to 8 times the normal operational dosage (0,05 mg/l during 10 mn). The resistance occurs on a very limited portion of the river, 65 km long and limited upstream by a dam and downstream by the absence of breeding sites in the final 90 km of the river. The resistant population is currently being controlled with chlorphoxim, an alternative insecticide.

Within the Onchocerciasis Control Programme about 50,000 km of west African rivers have been regularly sprayed with larvicides to control the vector of dermal filariasis caused by Onchocerca volvulus. Since the beginning of the programme invertebrates and fish data were collected to monitor adverse effects on non-target organisms. The regular series of biological and hydrological data collected in two Guinean rivers were analysed to evaluate the effects of rotational larviciding with particular attention to permethrin, as preliminary acute toxicology tests and semi-field experiments suggest it has stronger effects on non-target fauna in respect to other larvicides. Invertebrates ard fish variations in biomass and species richness are seasonal and flow-related and the results presented here do not support any evidence of specific effects of permethrin application on the biological targets monitored. Larvicide applications influence community structures, putting pressure on some taxonomic groups, causing. for example, the rarefacion of some taxa. In spite of the above results, the scarcity of some invertebrate systematic units does not resuit in a significant reduction of total invertebrate density because of the corresponding increase in other systematic units. In nature the studied aquatic communities would rarely be in equilibrium because of frequent natural stresses, such as drougst and spate events, the biologicai variations discussed are to be considered ecologically acceptable. © 2001 Elsevier Science Ltd. All rights reserved.

Twenty-two years after the launch of the Onchocerciasis Control Programme in West Africa (OCP), Jean-Marc Hougard and colleagues critically review the vector-control strategy adopted. They go on to identify the few hydrological basins where transmission of the infection remains difficult to control, to analyse the causes and to propose appropriate corrective measures on a case-by-case basis. Most of these measures, which are mainly based on ivermectin chemotherapy, will continue to be applied after the end of the OCP in 2002, under the control of the countries concerned.

Since the launching of the African Programme for Onchocerciasis Control (APOC) at the end of 1995, all 30 African countries affected by endemic onchocerciasis have been involved in a merciless fight against the disease. Already, onchocerciasis is no longer a public-health problem or an obstacle to socio-economic development in the 11 countries monitored by the Onchocerciasis Control Programme in West Africa (OCP; Molyneux, 1995). This should soon be the case in the 19 APOC countries (Dadzie, ...

Le contrôle des populations de Simulium damnosum dans le bassin des Voila est actuellement réalisé à l’aide d’épandages hebdomadaires d’un insecticide organophosphoré : l’Abate 200 CE. Malgré une sélectivité certaine de ce produit vis-à-vis du vecteur de l’Onchocercose, les groupes d’insectes non cibles des milieux aquatiques traités subissent un certain impact du produit utilisé, impact que nous avons cherché à mettre en évidence de manière expérimentale ou à l’aide d’observations suivies et régulières des milieux traités.Quelle que soit la concentration employée, l’épandage d’Abate dans un cours d’eau entraîne un décrochement des organismes en place qui induit une très forte augmentation des valeurs de l’indice de dérive. Cette augmentation suit toujours de très près le passage de la vague insecticide, témoignant d’une réaction extrêmement rapide de la faune d’Invertébrés. L’effet du toxique s’atténue ensuite rapidement et devient négligeable après 24 heures. Tous les groupes présentent une cinétique de décrochement de ce type avec cependant des variations en fonction de leur sensibilité intrinsèque. Parmi les plus sensibles, il faut signaler les Éphémèroptères Baetidae et Caenidae, les Trichoptères du genre Macronema et les Chironomides d’une manière générale. Il est très important de noter que les traitements isolés sur un milieu vierge sont le plus souvent très toxiques et peuvent entraîner, selon la concentration employée, une mortalité des Invertébrés de 50 % et plus. Par contre, quand les traitements sont répétés régulièrement, après une première série ayant des effets toxiques importants, les suivants n’induisent à chaque fois qu’un faible décrochement. Ce fait explique que, après maintenant deux années de traitements à l’Abate, la faune d’invertébrés des rivières ouest africaines soit toujours abondante. Population control of Simulium damnosum in the Voila basin is presently done by weekly sprays of Abate 200 CE, an organophosphorus insecticide. In spite of the relative selectivity of Abate against the larvae of blackflies, the non-target organisms living in the aquatic biota are affected by the toxicity of the product. By using experimental methods and also after regular observations carried out on treated and untreated rivers, we try to point out the toxicity rate of Abate against the aquatic invertebrate fauna.At all the concentrations tested in the rivers, Abate treatments induce detachment of invertebrates from their substrates, especially insect larvae, and an increase of the drift rate. This increase always appears very soon after the passage of the insecticide wave, giving evidence of a rapid response of the organisms to the Chemical. After this very sensitive effect, the drift rate decreases rapidly and rises to its normal level 24 hours later.The general detachment kinetic is similar for all the invertebrate groups but some differences occur in relation to the specificity of the animals concerned. Ephemeroptera: Baetidae and Caenidae, Chironomids in general and Trichoptera of the genus Macronema are some of the more sensitive taxa.It is very important to point out that isolated treatments done on virgin biotas often have a very drastic effect and could involve a mortalily of 50% and more at normal concentrations used for Simulium control. On the other hand, if treatments are regularly done in a river, after a first series of drastic effects, the following ones each time induce a relative small detachment of organisms. This is certainly the reason why the invertebrate fauna is always present in the treated rivers at a quite satisfactory level, even after two years of traitments.

The effect of aerial treatment of rivers with chlorphoxim, in connection with the ongoing Onchocerciasis Control Programme (OCP) in the Volta River Basin, on the brain acetylcholinesterase (AChE) activity of three fish species Tilapia galilaea, Tilapia zilli and Alestes nurse has been studied in the Ivory Coast. A cage experiment with Tilapia zilli, placed just below the breeding site of Simulium damnosum s.l. in the river Marahoué and aerially treated with chlorphoxim at a concentration of 0.05 mg litre-1 per 10 min of river discharge, showed a 16% reduction in the brain acetylcholinesterase activity of the caged Tilapia zilli after 2 h and about 20 % after 5 h of the river treatment. However, there was no reduction in the brain AChE activity of some Tilapia galilaea, Tilapia zilli and Alestes nurse randomly taken with a cast net from the rivers Bandama and N'zi, which had been similarly treated with chlorphoxim for about 10 months. It appears that during river treatment the fish avoid the impact of the larvicide by swimming downstream.

The side-effects of permethrin (20% EC) as a Simulium larvicide on aquatic invertebrates and fish was studied under operational vector control conditions to contribute to the evaluation of the product for its possible adoption by the Onchocerciasis Control Programme in West Africa. After 15 weekly applications of the formulation at 0.045 litre per m3 of water discharge, drift samples virtually contained no Ephemeroptera. Saxicolous fauna density and proportional diversity were also affected. However, both drift and saxicolous fauna recovered to almost pretreatment levels a month after treatment was terminated. Fish showed some evidence of stress but remained in the active treated zone to make trends of catches in the area comparable with those of the control station. The treatment did not resuit in fish mortalities, and the condition of fish before and after the experimental period was significantly unchanged. Thus, operational use of permethrin by the Programme would not be expected to have permanent adverse effects on the non-target fauna.

The Onchocerciasis Control Program of the World Health Organisation is carrying out an extensive screening program in a search for new larvicides to be used for control of Simulium damnosum s.l. Emphasis has been given to finding a pyrethroid and a carbamate to supplement the organophosphates currently in use. These Chemicals with differing modes of action, together with Bacillus thuringiensis H-14, are being used in an attempt to cope with the development and spread of resistance to the organophosphates temephos and chlorphoxim.