Population genetic structure of the malaria vector Anopheles nili in sub-Saharan Africa

<p>Abstract</p> <p>Background</p> <p><it>Anopheles nili </it>is a widespread efficient vector of human malaria parasites in the humid savannas and forested areas of sub-Saharan Africa. Understanding <it>An. nili </it>population structure and gene flow patterns could be useful for the development of locally-adapted vector control measures.</p> <p>Methods</p> <p>Polymorphism at eleven recently developed microsatelitte markers, and sequence variation in four genes within the 28s rDNA subunit (ITS2 and D3) and mtDNA (COII and ND4) were assessed to explore the level of genetic variability and differentiation among nine populations of <it>An. nili </it>from Senegal, Ivory Coast, Burkina Faso, Nigeria, Cameroon and the Democratic Republic of Congo (DRC).</p> <p>Results</p> <p>All microsatellite loci successfully amplified in all populations, showing high and very similar levels of genetic diversity in populations from West Africa and Cameroon (mean Rs = 8.10-8.88, mean He = 0.805-0.849) and much lower diversity in the Kenge population from DRC (mean Rs = 5.43, mean He = 0.594). Bayesian clustering analysis of microsatellite allelic frequencies revealed two main genetic clusters in the dataset. The first one included only the Kenge population and the second grouped together all other populations. High Fst estimates based on microsatellites (Fst > 0.118, P < 0.001) were observed in all comparisons between Kenge and all other populations. By contrast, low Fst estimates (Fst < 0.022, P < 0.05) were observed between populations within the second cluster. The correlation between genetic and geographic distances was weak and possibly obscured by demographic instability. Sequence variation in mtDNA genes matched these results, whereas low polymorphism in rDNA genes prevented detection of any population substructure at this geographical scale.</p> <p>Conclusion</p> <p>Overall, high genetic homogeneity of the <it>An. nili </it>gene pool was found across its distribution range in West and Central Africa, although demographic events probably resulted in a higher level of genetic isolation in the marginal population of Kenge (DRC). The role of the equatorial forest block as a barrier to gene flow and the implication of such findings for vector control are discussed.</p

The dominant Anopheles vectors of human malaria in Africa, Europe and the Middle East: occurrence data, distribution maps and bionomic précis

<p>Abstract</p> <p>Background</p> <p>This is the second in a series of three articles documenting the geographical distribution of 41 dominant vector species (DVS) of human malaria. The first paper addressed the DVS of the Americas and the third will consider those of the Asian Pacific Region. Here, the DVS of Africa, Europe and the Middle East are discussed. The continent of Africa experiences the bulk of the global malaria burden due in part to the presence of the <it>An. gambiae </it>complex. <it>Anopheles gambiae </it>is one of four DVS within the <it>An. gambiae </it>complex, the others being <it>An. arabiensis </it>and the coastal <it>An. merus </it>and <it>An. melas</it>. There are a further three, highly anthropophilic DVS in Africa, <it>An. funestus</it>, <it>An. moucheti </it>and <it>An. nili</it>. Conversely, across Europe and the Middle East, malaria transmission is low and frequently absent, despite the presence of six DVS. To help control malaria in Africa and the Middle East, or to identify the risk of its re-emergence in Europe, the contemporary distribution and bionomics of the relevant DVS are needed.</p> <p>Results</p> <p>A contemporary database of occurrence data, compiled from the formal literature and other relevant resources, resulted in the collation of information for seven DVS from 44 countries in Africa containing 4234 geo-referenced, independent sites. In Europe and the Middle East, six DVS were identified from 2784 geo-referenced sites across 49 countries. These occurrence data were combined with expert opinion ranges and a suite of environmental and climatic variables of relevance to anopheline ecology to produce predictive distribution maps using the Boosted Regression Tree (BRT) method.</p> <p>Conclusions</p> <p>The predicted geographic extent for the following DVS (or species/suspected species complex*) is provided for Africa: <it>Anopheles </it>(<it>Cellia</it>) <it>arabiensis</it>, <it>An. </it>(<it>Cel.</it>) <it>funestus*</it>, <it>An. </it>(<it>Cel.</it>) <it>gambiae</it>, <it>An. </it>(<it>Cel.</it>) <it>melas</it>, <it>An. </it>(<it>Cel.</it>) <it>merus</it>, <it>An. </it>(<it>Cel.</it>) <it>moucheti </it>and <it>An. </it>(<it>Cel.</it>) <it>nili*</it>, and in the European and Middle Eastern Region: <it>An. </it>(<it>Anopheles</it>) <it>atroparvus</it>, <it>An. </it>(<it>Ano.</it>) <it>labranchiae</it>, <it>An. </it>(<it>Ano.</it>) <it>messeae</it>, <it>An. </it>(<it>Ano.</it>) <it>sacharovi</it>, <it>An. </it>(<it>Cel.</it>) <it>sergentii </it>and <it>An. </it>(<it>Cel.</it>) <it>superpictus*</it>. These maps are presented alongside a bionomics summary for each species relevant to its control.</p

Influence de la hauteur des cacaoyers et des facteurs climatiques sur la densité des populations de miridae (Hétéroptères) à Duékoué, Ouest de la Côte d\'Ivoire

En Côte d\'Ivoire, la culture du cacaoyer a toujours constitué la principale source de revenus des paysans. Ainsi, il était nécessaire de mener dans les nouvelles régions cacaoyères des études pour protéger les cacaoyers contre les Miridae, principaux déprédateurs du cacaoyer. Deux espèces de Miridae ont été observées à Duékoué. Il s\'agit de Sahbergella singularis (Hétéroptères, Miridae) espèce majoritaire (99,3 % des miridae) et de Distantiella théobroma (Hétéroptères, Miridae). Dans cette localité comme dans le Sud du Pays, une forte pullulation des Miridae a été observée entre la saison des pluies et la saison sèche. L\'étude de l\'impact des facteurs climatiques sur la densité des Miridae a révélé que la température et les précipitations n\'ont eu aucun effet direct sur les Miridae. Par contre, une corrélation négative significative entre, d\'une part, la hauteur des cacaoyers, le déficit hydrique et, d\'autre part, la densité des Miridae a été observée. Ainsi, en dessous de la valeur de - 284 mm de déficit hydrique cumulé seuil (DHCS), il n\'est pas opportun d\'effectuer des traitements phytosanitaires dans une plantationIn Ivory coast, cocoa plantation is the main source of income for farmers. Therefore it\'s an important to conduct studies in the new cocoa areas to protect cocoa plants from Miridae attacks, which are the main parasites of cocoa. Two Miridae species were observed in Duékoué. Sahbergella singularis (Hétéroptères, Miridae) were the most prominent, (about 99,3 %) and Distantiella theobroma (Hétéroptères, Miridae). In this area, as well as in the South of the country an important Miridae population was observed between the dry and the rainy seasons. The study of climatic impact on Miridae population density showed that temperature and precipitation had no direct effect. However, Miridae population were influenced by cocoa height and water deficit. Under - 284 mm of cumulated water deficits (DHCS) there was no need to treat cocoa plantations. Keywords: Déficit hydrique, hauteur du cacaoyers, Miridae, Côte d\'Ivoire.Agronomie Africaine Vol. 17 (3) 2005: pp. 179-18