Biogeography of the two major arbovirus mosquito vectors, Aedes aegypti and Aedes albopictus (Diptera, Culicidae), in Madagascar

Background: In the past ten years, the Indian Ocean region has been the theatre of severe epidemics of chikungunya and dengue. These outbreaks coincided with a high increase in populations of Aedes albopictus that outcompete its sister taxon Aedes aegypti in most islands sampled. The objective of this work was to update the entomological survey of the two Aedes species in the island of Madagascar which has to face these arboviroses. Methods: The sampling of Aedes mosquitoes was conducted during two years, from October 2007 to October 2009, in fifteen localities from eight regions of contrasting climates. Captured adults were identified immediately whereas immature stages were bred until adult stage for determination. Phylogenetic analysis was performed using two mtDNA genes, COI and ND5 and trees were constructed by the maximum likelihood (ML) method with the gene time reversible (GTR) model. Experimental infections with the chikungunya virus strain 06.21 at a titer of 107.5 pfu/mL were performed to evaluate the vector competence of field-collected mosquitoes. Disseminated infection rates were measured fourteen days after infection by immunofluorescence assay performed on head squashes. Results: The species Aedes aegypti was detected in only six sites in native forests and natural reserves. In contrast, the species Aedes albopictus was found in 13 out of the 15 sites sampled. Breeding sites were mostly found inman-made environments such as discarded containers, used tires, abandoned buckets, coconuts, and bamboo cuts. Linear regression models showed that the abundance of Ae. albopictus was significantly influenced by the sampling region (F = 62.00, p < 2.2 × 10-16) and period (F = 36.22, p = 2.548 × 10-13), that are associated with ecological and climate variations. Phylogenetic analysis of the invasive Ae. albopictus distinguished haplotypes from South Asia and South America from those of Madagascar, but the markers used were not discriminant enough to discern Malagasy populations. The experimental oral infection method showed that six Ae. albopictus populations exhibited high dissemination infection rates for chikungunya virus ranging from 98 to 100%. Conclusion: In Madagascar, Ae. albopictus has extended its geographical distribution whereas, Ae. aegypti has become rare, contrasting with what was previously observed. Changes are predominantly driven by human activities and the rainfall regime that provide suitable breeding sites for the highly anthropophilic mosquito Ae. albopictus. Moreover, these populations were found to be highly susceptible to chikungunya virus. In the light of this study, Ae. albopictus may have been involved in the recent outbreaks of chikungunya and dengue epidemics in Madagascar, and consequently, control measures should be promoted to limit its current expansion.Rôle des moustiques Culicidae, de leurs communautés microbiennes et des réservoirs vertébrés, dans la transmission des arbovirus à Madagasca

Nouvelle répartition géographique des espèces Aedes albopictus et Aedes aegypti (Diptères, Culicidae, Aedinae) à Madagascar

Depuis 2006, Madagascar et les îles avoisinantes de l’Océan Indien ont été victimes d’épidémies sévères de dengue et de chikungunya. Les moustiques Aedes albopictus et Aedes aegypti, vecteurs majeurs de ces arboviroses, sont présents à Madagascar et en particulier dans les régions d’émergence épidémique. En vue d’actualiser les données entomologiques, des campagnes de capture d’adultes et de récoltes de larves ont été menées dans 8 régions sélectionnées selon différents niveaux d’anthropisation. Nos résultats ont démontré des changements importants dans la répartition de ces deux espèces vectrices à Madagascar.Rôle des moustiques Culicidae, de leurs communautés microbiennes et des réservoirs vertébrés, dans la transmission des arbovirus à Madagasca

Soil-vegetation patterns in secondary slash and burn successions in Central Menabe, Madagascar

Slash and burn agriculture is a traditional and predominant land use practice in Madagascar and its relevance in the context of forest preservation is significant. At the end of a cycle of culture, the fields become mostly weed covered and the soil fertility starts to drop. As a consequence, these fields are abandoned (they are called “monka”) and the farmers, in the best case, re-use old surfaces where the vegetation has recovered to some extent. Nevertheless, some of the farmers continue to extend part of their cultures into the natural forest. In order to decrease deforestation, the paper focuses on the potential for agricultural re-use of monkas. To do so, we present the soil–vegetation pattern along a slash and burn successional gradient from newly cultivated surfaces to surfaces abandoned for 40 years. Vegetation relevés were carried out on 61 plots sampled on yellow and red soils, and soil variables such as loss of ignition, pH, total carbon content and total nitrogen content were measured. Results show that: (1) by the 10th year of abandonment woody species are increasing, and after 21–30 years herbaceous plants become less dominant, (2) the species richness increases with age of abandonment, but flattens out by 40 years, (3) by 20 years of fallow, the loss of ignition, total carbon and total nitrogen show similar values or even higher values than in cultivated surfaces, (4) the yellow soils are related to higher pH more than the red soils and are preferred for cultivation, but the higher pH of yellow soils is not associated with higher species richness. Given these results, we conclude that fields older than 20 years have recovered sufficient fertility to be re-used as agricultural land. This re-use would decrease impacts on natural forests. But beyond the nutrient perspective, critical problems remain, including the growing demand for arable land and the need for cultivation to control invasive weeds