[Effectiveness of three biological larvicides and of an insect growth regulator against Anopheles arabiensis in Senegal]. / Efficacité de trois larvicides d'origine biologique et d'un régulateur de croissance contre Anopheles arabiensis au Sénégal.

Urban malaria is a major public health problem in Africa. In Senegal, the environmental changes seem to favor the persistence of malaria transmission in Dakar suburbs by creating, throughout the year, potential breeding sites of malaria vectors. In such a situation and in a context of a growing threat of insecticide resistance in anopheline vectors, the larval control making use of products from biological origin or growth regulators could represent an additional tool to the current strategies developed against anophelines. In this study conducted in 2012, the efficiency and residual effect of three biological larvicides (VectoBac® WG, Vecto-Max® CG, and VectoBac® GR) and an insect growth regulator (MetaLarv™) were evaluated on Anopheles gambiae s.l. larvae in seminatural conditions (experimental station) and natural breeding sites in the suburbs of Dakar. The formulations were tested according to the manufacturer recommendations, namely 0.03 g/m2 for VectoBac® WG, 0.5 g/m2 for VectoBac® GR, 0.75 g/m2 for VectoMax® CG, and 0.5 g/m2 for MetaLarv™. In experimental station, the treatment with larvicides was effective over a period of 14 days with a mortality ranging between 92% and 100%. The insect growth regulator remained effective up to 55 days with a single emergence recorded in the 27th day after treatment. In natural conditions, a total effectiveness (100% mortality) of larvicides was obtained 48 hours after treatment, then a gradual recolonization of breeding sites was noted. However, the insect growth regulator has reduced adult emergence higher than 80% until the end of follow-up (J28). This study showed a good efficiency of the larvicides and of the growth regulator tested. These works provide current data on potential candidates for the implementation of larval control interventions in addition to that of chemical adulticide for control of urban malaria.

Assessment of trace metal contamination in mangrove ecosystems from Senegal, West Africa.

The inorganic contamination of sediment and harvested molluscs was investigated in the mangrove environment of Southern West Senegal. Trace metals were analysed in surface sediments, two bivalves (Arca senilis and Crassostera gasar) and three gastropods (Conus spp., Hexaplex duplex and Pugilina morio) collected from four stations: Dionewar, Niodor and Falia localised in the Saloum Delta, and Fadiouth from the Petite Côte. A geochemical normalisation approach by using aluminium allowed for discrimination of sediment contamination among sites. Indeed, Fadiouth appeared highly contaminated with Cd, Hg and Ni compared to the Saloum Delta. For all mangrove sites, trace metals exhibited significant higher concentrations (on a dry weight basis) in shellfish compared to sediments, excepted for Ni and Pb. The distribution pattern followed a similar global trend in molluscs regardless of the spatio-temporal variability, with the predominance of Zn (80% of total metals) followed by Cu and Cd. However, strong differences of metal bioavailability and bioaccumulation in biota were demonstrated, revealing the requirement of employing a suite of organism bioindicators to monitor metal contamination in mangrove ecosystems. From an ecotoxicological point of view, trace metal levels in sediments from the Petite Côte and the Sine-Saloum Estuary were below the effects range-low (ERL) threshold limit of the sediment quality guidelines for adverse biological effects (SQGs). On the opposite, some concerns about Cd contamination of edible shellfish from Southern West Senegal were highlighted, from both the safety point of view of local populations' health, and the chemical quality point of view of exported resources.

Impact of glaciations and geographic distance on the genetic structure of a tropical estuarine fish, Ethmalosa fimbriata (Clupeidae, S. Bowdich, 1825).

We assayed the mtDNA phylogeography [196 base pairs (bp) of the cytochrome b] and population structure (n = 680) in the estuarine fish, Ethmalosa fimbriata, from its whole distribution range: 14 locations along the West African coasts were sampled. Specifically, we considered Pleistocene glaciations as well as the hydrodynamics and climatic conditions of the estuarine environments in order to identify the main evolutionary forces that have shaped the genetic variation in mtDNA, i.e., the contemporary or the historical gene flow. There was an overall significant population differentiation among estuaries (Fst = 0.10). Although E. fimbriata showed a significant pattern of isolation by distance over the entire sampled range, this genetic structure did not mirror contemporary gene flow but the colonization sequence of the present distribution range. Finally, the mtDNA genetic structure traced the past historic dispersion that occurred at the end of the Pleistocene glaciations. The central part of the present distribution area was probably the species origin and due to difference in the historic migration rate northward and southward, isolation of a South group occurred first, 110,000-190,000 years ago, before the divergence of the North group 47,000-82,000 years ago.

Maturation of mosquito spermatozoa during their transit throughout the male and female reproductive systems.

The testes, seminal vesicles and spermathecae of 22 species of mosquitoes belonging to the genera Aedes, Anopheles, Culex, Mansonia and Toxorhynchites are investigated under the electron microscope. Modifications of the acrosome and sperm wall occur during the transit of the spermatozoon from the lower region of the testes to the spermathecae throughout the seminal vesicles. The origin and fate of the cell coat and the possible roles of somatic cell layers both in the testes and the seminal vesicles are discussed.

Spermatogenesis in mosquitoes (Diptera: Culicidae).

An ultrastructural study of spermatogenesis has been carried out on 18 species of mosquitoes of the Anophelinae, Culicinae and Toxorhynchitinae sub-families. In this spermatogenesis, which follows a classical way, primordial cells, primary and secondary spermatogonia, as well as primary and secondary spermatocysts are considered. We have identified 9 stages of development all along the spermiogenesis. This process ends up with the formation of a needle-like spermatozoon showing head and tail regions. After a treatment with tannic acid, the protofilaments of the axoneme of Culex tigripes are counted. For the first time we have carried out a complete study of spermatogenesis in mosquitoes.

Extracellular and intracellular rickettsia-like microorganisms in gonads of mosquitoes.

The mosquitoes Culex tigripes, C. decens and C. quinquefasciatus have been investigated by electron microscopy. An intracytoplasmic rickettsia-like microorganism is present in ovaries and testes of the three species. An extracellular form of a rickettsia-like microorganism is described in the testis of C. tigripes in which it sometimes appears in great number. The extra- and intracellular forms present ultrastructural differences. The possibility they represent two different morphotypes of the same microorganism or simply two different types is discussed. They both disappear after treatment with tetracycline. This is believed to be the first electron microscope description of extracellular rickettsia-like cells in mosquitoes.

Natural degenerating mitochondria in ovarian follicles of a cyprinodontidae fish, Epiplatys spilargyreus (teleost).

This study examines the evolution of mitochondria in the follicular cells during the development of the ovarian follicle in the teleostean fish Epiplatys spilargyreus. The mitochondria are few in number until the end of previtellogenesis; their matrix is dense, and their cristae are well developed. They proliferate during vitellogenesis and then are modified by deterioration of their matrix. Multilamellar structures are organized in the vacuolized mitochondria. During postvitellogenesis, these modifications become more advanced. The mitochondria degenerate, leaving vacuoles that contain heterogeneous structures, which will be released into the intercellular spaces. At the end of these mitochondrial transformations, the follicular cells degenerate. They release the elements which will participate in forming the secondary envelope.

Morphogenesis of the secondary envelope of the oocyte in a teleostean fish of the family Cyprinodontidae: Aphyosemion splendopleure.

The follicular epithelium of the oocyte in Aphyosemion splendopleure is made up of prismatic cells in which the density of the cytoplasm is variable. At the end of vitellogenesis the follicular cells show polarity. The rough endoplasmic reticulum is localized in the cytoplasm situated between the nucleus and the basal lamina. This reticulum splits up into vesicles limited by a membrane covered with ribosomes. At the beginning of postvitellogenesis the Golgi apparatus produces numerous secretion granules in the cytoplasmic region contiguous to the surface of the oocyte. These Golgi elements, together with amorphous material whose origin we have not been able to define, form the secondary envelope of the egg. This envelope is made up of two layers: an inner layer formed by an agglomeration with a membranous aspect and a superficial layer made up of tubular elements. The superficial layer forms an ornamentation clearly shown up by scanning electron microscopy.

Reinvestigation of spermatic flagella structure: the teleostean Cyprinodontidae.

The study of 7 genera and 15 species of teleostean fishes belonging to the family Cyprinodontidae shows a similar morphology of mobile spermatozoa and a wide diversity of structure of the spermatic flagellum. The flagellar membrane has one, two, or three lateral expansions depending on the species. Peripheral doublets of axonema show only the external arm, except for two species that completely lack them. Intratubular differentiations (ITD) are present in A or B tubules of peripheral doublets as in central tubules of some species, whereas others are totally devoid of them. The ITD can affect all doublets or preferentially doublets 1, 5, and 6. These variations may be due to neutral mutations.

Microtubules and macrotubules in fish meiosis.

During meiosis in the male of a cyprinodontid fish, Aphyosemion splendopleure, and during the organization of the spindle of division, the spindle is made of two types of tubules: microtubules (20-25 nm) and macrotubules (30-50 nm). The macrotubules are associated only with the polar region of the meiotic apparatus and are located outside the spindle of microtubules. At the end of meiosis, the spindle microtubules depolymerize whereas the macrotubules remain. One can find them throughout the entire process of spermiogenesis; later, they disappear only at the end of spermatid maturation. We have studied four populations from Cameroon, three of them with macrotubules.