Abiotic and biotic factors associated with the presence of Anopheles arabiensis immatures and their abundance in naturally occurring and man-made aquatic habitats

Gouagna Louis, Rakotondranary Manpionona, Boyer Sebastien, Lempérière Guy, Dehecq Jean-Sébastien, Fontenille, Didier Fontenille

Description

Anopheles arabiensis (Diptera: Culicidae ) is a potential malaria vector commonly present at low altitudes in remote areas in Reunion Island. Little attention has been paid to the environmental conditions driving larval development and abundance patterns in potential habitats. Two field surveys were designed to determine whether factors that discriminate between aquatic habitats with and without An. arabiensis larvae also drive larval abundance, comparatively in man-made and naturally occurring habitats. Methods In an initial preliminary survey, a representative sample of aquatic habitats that would be amenable to an intensive long-term study were selected and divided into positive and negative sites based on the presence or absence of Anopheles arabiensis larvae. Subsequently, a second survey was prompted to gain a better understanding of biotic and abiotic drivers of larval abundance, comparatively in man-made and naturally occurring habitats in the two studied locations. In both surveys, weekly sampling was performed to record mosquito species composition and larval density within individual habitats, as well as in situ biological characteristics and physico-chemical properties. Results Whilst virtually any stagnant water body could be a potential breeding ground for An. arabiensis , habitats occupied by their immatures had different structural and biological characteristics when compared to those where larvae were absent. Larval occurrence seemed to be influenced by flow velocity, macrofauna diversity and predation pressure. Interestingly, the relative abundance of larvae in man-made habitats (average: 0.55 larvae per dip, 95%CI [0.3–0.7]) was significantly lower than that recorded in naturally occurring ones (0.74, 95%CI [0.5–0.8]). Such differences may be accounted for in part by varying pressures that could be linked to a specific habitat. Conclusions If the larval ecology of An. arabiensis is in general very complex and factors affecting breeding site productivity sometimes not easy to highlight, our results, however, highlight lower populations of An. arabiensis immatures compared to those reported in comparable studies conducted in the African continent. Overall, this low larval abundance, resulting from both abiotic and biotic factors, suggests that vector control measures targeting larval habitats are likely to be successful in Reunion, but these could be better implemented by taking environmental variability into account.

Informations

• Publié par: biomed
• Publié le: 01 janvier 2012
• Nombre de lectures: 7
• Langue: English
• Poids de l'ouvrage: 1 Mo

Extrait

Gouagnaet al. Parasites & Vectors2012,5:96 http://www.parasitesandvectors.com/content/5/1/96

R E S E A R C HOpen Access Abiotic and biotic factors associated with the presence ofAnopheles arabiensisimmatures and their abundance in naturally occurring and manmade aquatic habitats 1,2* 22 2 Louis Clément Gouagna, Manpionona Rakotondranary , Sebastien Boyer , Guy Lempérière , 3 1 JeanSébastien Dehecqand Didier Fontenille

Abstract Background:Anopheles arabiensis(Diptera:Culicidae) is a potential malaria vector commonly present at low altitudes in remote areas in Reunion Island. Little attention has been paid to the environmental conditions driving larval development and abundance patterns in potential habitats. Two field surveys were designed to determine whether factors that discriminate between aquatic habitats with and withoutAn. arabiensislarvae also drive larval abundance, comparatively in manmade and naturally occurring habitats. Methods:In an initial preliminary survey, a representative sample of aquatic habitats that would be amenable to an intensive longterm study were selected and divided into positive and negative sites based on the presence or absence ofAnopheles arabiensislarvae. Subsequently, a second survey was prompted to gain a better understanding of biotic and abiotic drivers of larval abundance, comparatively in manmade and naturally occurring habitats in the two studied locations. In both surveys, weekly sampling was performed to record mosquito species composition and larval density within individual habitats, as well asin situbiological characteristics and physicochemical properties. Results:Whilst virtually any stagnant water body could be a potential breeding ground forAn. arabiensis, habitats occupied by their immatures had different structural and biological characteristics when compared to those where larvae were absent. Larval occurrence seemed to be influenced by flow velocity, macrofauna diversity and predation pressure. Interestingly, the relative abundance of larvae in manmade habitats (average: 0.55 larvae per dip, 95%CI [0.3–0.7]) was significantly lower than that recorded in naturally occurring ones (0.74, 95%CI [0.5–0.8]). Such differences may be accounted for in part by varying pressures that could be linked to a specific habitat. Conclusions:If the larval ecology ofAn. arabiensisis in general very complex and factors affecting breeding site productivity sometimes not easy to highlight, our results, however, highlight lower populations ofAn. arabiensis immatures compared to those reported in comparable studies conducted in the African continent. Overall, this low larval abundance, resulting from both abiotic and biotic factors, suggests that vector control measures targeting larval habitats are likely to be successful in Reunion, but these could be better implemented by taking environmental variability into account.

* Correspondence: louis[e-mail] 1 Institut de Recherche pour le Développement (IRD), UM1CNRS 5290IRD 224: Maladies Infectieuses et Vecteurs–Ecologie Génétique, Evolution et Contrôle (MIVEGEC), Montpellier, France 2 Centre de Recherche et de Veille sur les maladies Emergentes dans l’Océan Indien (CRVOI) Sainte Clotilde, Reunion Island, France Full list of author information is available at the end of the article

© 2012 Gouagna et al.; licensee BioMed Central Ltd. This is an Open Access article distributed under the terms of the Creative Commons Attribution License (http://creativecommons.org/licenses/by/2.0), which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited.