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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 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.

Background An often confounding facet of the dynamics of malaria vectors is the aquatic larval habitat availability and suitable conditions under which they can thrive. Here, we investigated the impact of environmental factors on the temporal and spatial distribution of larval habitats of Anopheles arabiensis in different locations on La Reunion Island. Methods A retrospective examination was made from archival data which provided the complete enumeration of An. arabiensis breeding habitats in three distinct geographic zones - extending North-east, West and South of the island over 14 years, from January 1996 to December 2009. Data on the occurrence and the number of active larval habitats at each of a total of 4376 adjacent ellipsoid grid cells (216,506 square meters each) were used (1) to provide the geographic extent of breeding site availability from year to year and (2) to analyze associations with prevailing environmental factors, habitat types, and locations. Results Anopheles arabiensis utilized a spectrum of man-made and natural aquatic habitats, most of which were concentrated primarily in the rock pools located in ravines and river fringes, and also in the large littoral marshes and within the irrigated agricultural zones. The numbers of breeding site per sampling grid differed significantly in different parts of the island. In contrast to an originally more widespread distribution across the island in the 1950s, detailed geographic analyses of the data obtained in the period extending from 1996-2009 showed an intriguing clustered distribution of active breeding sites in three discontinuous geographic zones, in which aquatic habitats availability fluctuates with the season and year. Seasonality in the prevalence of anopheles breeding sites suggests significant responsiveness to climatic factors. Conclusions The observed retreat of An. arabiensis distribution range to lower altitudinal zones (< 400 m) and the upward shift in the most remote littoral areas in the northeast and southwest regions suggest the possible influence of biogeographic factors, changes in land use and control operations. The results of this study would allow for a more rational implementation of control strategies across the island.

Background Trapping male mosquitoes in the field is essential for the development of area-wide vector control programs with a sterile insect technique (SIT) component. To determine the optimal temporal and spatial release strategy, an estimation of the wild population density and its temporal dynamics is essential. Among the traps available for such data collection, the BG-Sentinel trap developed by the Biogents company uses a combination of visual cues, convection currents and olfactory signals. Although in numerous cases, this trap has shown high efficiency in sampling Aedes albopictus, in some cases low capture rates of Ae. albopictus males were recorded for the BG-sentinel mosquito trap baited with synthetic attractants. Methods The effects of modifying the BG-sentinel trap (by adding one mouse, two or three live mice to the trap) on the efficiency of trapping Ae. albopictus males and females was tested. The experiment was carried out in three distinct areas on La Réunion that have been selected for pilot field testing of the release of sterile male Ae. albopictus mosquitoes. The effect of four types of attractant (including the generic BG-Lure, one mouse or two to three mice) in baited BGS traps was tested with a Latin square design in order to control for the variability of different sampling positions and dates. Results At the three studied sites, the number of Ae. albopictus adults caught and the proportion of males per trap consistently increased with the number of mice present in the trap. Conclusion The results from this study suggest that some new attractants derived from, or similar to, mouse odors could be developed and tested in combination with other existing attractive components, such as CO2 and heat, in order to provide a reliable estimation method for Ae. albopictus adult male abundance in the wild. Electronic supplementary material The online version of this article (doi:10.1186/s13071-016-1801-1) contains supplementary material, which is available to authorized users.