Influence du sol sur l'infestation de Meloidogyne javanica (Treub, 1885) Chitwood, 1949 (Nematoda) par l'actinomycète parasitoïde Pasteuria penetrans (Thorne, 1940 ) Sayre & Starr, 1985

Des études menées dans un champ naturellement infesté par #Meloidogyne javanica et #Pasteuria penetrans ont montré par des analyses multivariées (ACP, Classification Hiéarchique Ascendante, AFD, Analyse de Correspondance) que les facteurs telluriques abiotiques influencent la distribution parcellaire des populations des deux organismes et que le niveau d'infestation des juvéniles de #M. javanica n'est pas seulement soumis au phénomène de densité-dépendance. En effet, certains facteurs telluriques notamment l'irrigtion, la texture, la structure du sol (particulièrement la porosité et la capacité de rétention en eau), et la fraction ionique sont corrélés au taux d'infestation et d'encombrement des juvéniles de #M. javanica ainsi qu'à la densité des populations de #P. penetrans$dans le sol. En fait, une irrigation intense diminue le taux d'infestation et d'encombrement des juvéniles de M. javanica$ par les spores de #P. prenetrans. En outre, une étude en serre a révélé qu'une forte irrigation provoque un transport vertical important des spores réduisant ainsi le stock de #P. penetrans dans les couches arables (horizon A). Elle provoque aussi une modification de la structure du sol consécutive au lessivage de la fraction fine (surtout au niveau rhizosphérique). Alors qu'une augmentation de la teneur en d'argile améliore la porosité des sols (en particulier sableux), une concentration en argile trop élevée inhiberait l'attachement des spores sur la cuticule des juvéniles. Les particules d'argile se fixeraient sur la paroi de la spore empêchant son adhésion sur les juvéniles laquelle adhésion serait de nature électrostatique ou hydrophobique. Par ailleurs, l'hétérogénéité structurale du sol est un facteur déterminant dans le contrôle des populations de #M. javanica$. En effet, l'interconnectivité des pores semble être une condition primordiale pour un contact entre les deux organismes... (D'après résumé d'auteur

Larval habitat segregation between the molecular forms of the African Malaria mosquito, Anopheles gambiae in a rice field area of Burkina Faso, West Africa

In West Africa, lineage splitting between the M and S molecular forms of the major Afro-tropical malaria mosquito, Anopheles gambiae (Diptera: Culicidae), is thought to be driven by ecological divergence, occurring mainly at the larval stage. Here, we present evidence for habitat segregation between the two molecular forms in and around irrigated rice fields located within the humid savannahs of western Burkina Faso. Longitudinal sampling of adult mosquitoes emerging from a range of breeding sites distributed along a transect extending from the heart of the rice field area into the surrounding savannah was conducted from June to November 2009. Analysis revealed that the two molecular forms and their sibling species Anopheles arabiensis are not randomly distributed in the area. A major ecological gradient was extracted in relation to the perimeter of the rice fields. The M form was associated with larger breeding sites mostly consisting of rice paddies, whereas the S form and An. arabiensis were found to depend upon temporary, rain-filled breeding sites. These results support hypotheses about larval habitat segregation and confirm the suggestion that the forms have different larval habitat requirements. Segregation appears to be clearly linked to anthropogenic permanent habitats and the community structure they support. (Résumé d'auteur

Evidence for divergent selection between the molecular forms of Anopheles gambiae: role of predation

The molecular forms of Anopheles gambiae are undergoing speciation. They are characterized by a strong assortative mating and they display partial habitat segregation. The M form is mostly found in flooded/irrigated areas whereas the S form dominates in the surrounding areas, but the ecological factors that shape this habitat segregation are not known. Resource competition has been demonstrated between species undergoing divergent selection, but resource competition is not the only factor that can lead to divergence. In a field experiment using transplantation of first instar larvae, we evaluated the role of larval predators in mediating habitat segregation between the forms. We found a significant difference in the ability of the molecular forms to exploit the different larval sites conditioned on the presence of predators. In absence of predation, the molecular forms outcompeted each other in their respective natural habitats however, the developmental success of the M form was significantly higher than that of the S form in both habitats under predator pressure. Our results provide the first empirical evidence for specific adaptive differences between the molecular forms and stress the role of larval predation as one of the mechanisms contributing to their divergence.https://doi.org/10.1186/1471-2148-8-

Personal protection of long lasting insecticide-treated nets in areas of Anopheles gambiae s.s. resistance to pyrethroids

BACKGROUND: The development of mosquito nets pre-treated with insecticide, Long Lasting Impregnated Nets (LLINs) that last the life span of the net, is a solution to the difficulty of the re-impregnation of conventional nets. Even if they showed a good efficacy in control conditions, their efficacy in the field, particularly in areas with resistance of Anopheles gambiae to pyrethroids, is not well documented. This study compares wide (Olyset(®)) and small (Permanet(®)) mesh LLINs in field conditions, using entomological parameters. METHODS: The two LLINs were tested in a rice-growing area of south-western Burkina Faso (West Africa) with year around high density of the main malaria vector An. gambiae s.s. In the study village (VK6), there is a mixed population of two molecular forms of An. gambiae, the S-form which dominates during the rainy season and the M-form which dominates the rest of the year. The two LLINs Olyset(® )and Permanet(® )were distributed in the village and 20 matched houses were selected for comparison with four houses without treated nets. RESULTS: Mosquito entrance rate was ten fold higher in control houses than in houses with LLINs and there was no difference between the two net types. Among mosquitoes found in the houses, 36 % were dead in LLIN houses compared to 0% in control houses. Blood feeding rate was 80 % in control houses compared to 43 % in LLIN houses. The type of net did not significantly impact any of these parameters. No mosquitoes were found inside Permanet(®), whereas dead or dying mosquitoes were collected inside the Olyset(®). More than 60% of mosquitoes found on top or inside the nets had had blood meals from cattle, as shown by ELISA analysis. CONCLUSION: The percentage of blood-fed mosquitoes in a bed net study does not necessarily determine net success. The efficacy of the two types of LLINs was comparable, during a period when the S-form of An. gambiae was carrying the kdr gene. Significantly higher numbers of mosquitoes were collected in control houses compared to intervention houses, indicating that the LLINs provided an additional deterrent effect, which enhanced their expected prevention capacity

Diversity in anopheline larval habitats and adult composition during the dry and wet seasons in Ouagadougou (Burkina Faso)

Background: Several cases of malaria are frequently recorded during the dry period in Ouagadougou town (Burkina Faso). This has led to the design of a series of studies focusing on both parasitological and entomological investigations intended to provide relevant health data on the risk of local malaria transmission according to the way of urbanisation. Methods: A cross-sectional entomological survey was carried out in various districts of Ouagadougou in April and October 2006. Adult malaria vectors were collected using CDC traps and indoor insecticide spraying performed in four houses during four consecutive days/nights. Intensive larval sampling was also done in available water ponds throughout the study sites. Results: In April, the anopheline breeding sites consisted only of semi-permanent or permanent swamps located mainly in the two peripheral districts. Despite the presence of anopheline larvae in these breeding sites, less than five Anopheles gambiae s.l. adults were caught by CDC traps and indoor insecticide spraying. In October, additionally to the permanent breeding sites reported in April, some rainfall swamps were also found positive to anophelines. The number of adults' mosquitoes was higher than that collected in April (2 vs 159 in October). Out of 115 larvae of An. gambiae s.l. analysed by PCR in April, 59.1% (68/115) were identified as Anopheles arabiensis, 39.1% (45/115) as An. gambiae M while the S form represented less than 2%. Overall 120 larvae and 86 females were identified by PCR in October as An. gambiae M form (51%) and An. arabiensis (42.2%). The S form represented only 6.8%. The global sporozoite rate recorded was high (6.8%) and did not differ between the districts except in the central district where no positive mosquito was detected. Conclusion: Although only few adults' mosquitoes were actively caught during the driest month, malaria vectors persisted all year long that increases the risk of urban malaria transmission. The distribution of breeding sites and especially the occurrence of malaria vectors were more abundant in the periphery, which is more like that of a rural settlement. The evolution of malaria prevalence and the factors sustaining the risk of transmission in Ouagadougou as well in many African cities during the dry season are discussed

Beer Consumption Increases Human Attractiveness to Malaria Mosquitoes

Background: Malaria and alcohol consumption both represent major public health problems. Alcohol consumption is rising in developing countries and, as efforts to manage malaria are expanded, understanding the links between malaria and alcohol consumption becomes crucial. Our aim was to ascertain the effect of beer consumption on human attractiveness to malaria mosquitoes in semi field conditions in Burkina Faso. Methodology/Principal Findings: We used a Y tube-olfactometer designed to take advantage of the whole body odour (breath and skin emanations) as a stimulus to gauge human attractiveness to Anopheles gambiae (the primary African malaria vector) before and after volunteers consumed either beer (n = 25 volunteers and a total of 2500 mosquitoes tested) or water (n = 18 volunteers and a total of 1800 mosquitoes). Water consumption had no effect on human attractiveness to An. gambiae mosquitoes, but beer consumption increased volunteer attractiveness. Body odours of volunteers who consumed beer increased mosquito activation (proportion of mosquitoes engaging in take-off and up-wind flight) and orientation (proportion of mosquitoes flying towards volunteers' odours). The level of exhaled carbon dioxide and body temperature had no effect on human attractiveness to mosquitoes. Despite individual volunteer variation, beer consumption consistently increased attractiveness to mosquitoes. Conclusions/Significance: These results suggest that beer consumption is a risk factor for malaria and needs to be integrated into public health policies for the design of control measures

Native entomopathogenic Metarhizium spp. from Burkina Faso and their virulence against the malaria vector Anopheles coluzzii and non-target insects

Genetically enhanced Metarhizium pingshaense are being developed for malaria vector control in Burkina Faso. However, not much is known about the local prevalence and pathogenicity of this fungus, so we prospected mosquitoes and plant roots (a common habitat for Metarhizium spp.) for entomopathogenic fungi. Our investigations showed that Metarhizium spp. represented between 29–74% of fungi isolated from plant root rhizospheres in diverse collection sites. At low spore dosages (1 × 106 conidia/ml), two mosquito-derived M. pingshaense isolates (Met_S26 and Met_S10) showed greater virulence against Anopheles coluzzii (LT80 of ~7 days) than isolates tested in previous studies (LT80 of ~10 days). In addition, the local isolates did not cause disease in non-target insects (honeybees and cockroaches). Our work provides promising findings for isolating local Metarhizium strains for application in mosquito biological control and for future transgenic biocontrol strategies in Burkina Faso.https://doi.org/10.1186/s13071-018-2796-