Search

Originating from African forests, Zika virus (ZIKV) has now emerged worldwide in urbanized areas, mainly transmitted by Aedes aegypti mosquitoes. Although Aedes albopictus can transmit ZIKV experimentally and was suspected to be a ZIKV vector in Central Africa, the potential of this species to sustain virus transmission was yet to be uncovered until the end of 2019, when several autochthonous transmissions of the virus vectored by Ae. albopictus occurred in France. Aside from these few locally acquired ZIKV infections, most territories colonized by Ae. albopictus have been spared so far. The risk level of ZIKV emergence in these areas remains however an open question. To assess Ae. albopictus’ vector potential for ZIKV and identify key virus outbreak predictors, we built a complete framework using the complementary combination of (i) dose-dependent experimental Ae. albopictus exposure to ZIKV followed by time-dependent assessment of infection and systemic infection rates, (ii) modeling of intra-human ZIKV viremia dynamics, and (iii) in silico epidemiological simulations using an Agent-Based Model. The highest risk of transmission occurred during the pre-symptomatic stage of the disease, at the peak of viremia. At this dose, mosquito infection probability was estimated to be 20%, and 21 days were required to reach the median systemic infection rates. Mosquito population origin, either temperate or tropical, had no impact on infection rates or intra-host virus dynamic. Despite these unfavorable characteristics for transmission, Ae. albopictus was still able to trigger and yield large outbreaks in a simulated environment in the presence of sufficiently high mosquito biting rates. Our results reveal a low but existing epidemic potential of Ae. albopictus for ZIKV, that might explain the absence of large scale ZIKV epidemics so far in territories occupied only by Ae. albopictus. They nevertheless support active surveillance and eradication programs in these territories to maintain the risk of emergence to a low level., Author summary Zika virus (ZIKV) has emerged worldwide and triggered large outbreaks in human populations. While the yellow fever mosquito Aedes aegypti is considered the primary vector of ZIKV, the Asian tiger mosquito Aedes albopictus has been shown experimentally to transmit the virus and has been involved in a few autochthonous transmission in France in 2019. Here, we provide a comprehensive study on the ability of Ae. albopictus mosquitoes to transmit ZIKV by considering the within-host dynamics of ZIKV infection in humans and its impact on both mosquito infection probability and time to mosquito infectiousness. These empirical data were then leveraged by in silico simulations to embed them into their epidemiological context. Our study reveals a low but existing epidemic potential of Ae. albopictus for ZIKV, whatever their tropical or temperate origins. We identified mosquito density as a predictor for ZIKV outbreak occurrence when vectored by Ae. albopictus. Our findings help to explain the absence of large scale ZIKV epidemics in territories occupied by Ae. albopictus but call for active surveillance and eradication programs to maintain the risk of emergence to a low level.

La Reunion Island has been the scene of unusually large epidemics of dengue and chikungunya viruses with Aedes albopictus as the sole vector. After experimental oral infection, Ae. albopictus from La Reunion Island can disseminate both dengue and chikungunya viruses but not the Asian genotype of Zika virus, suggesting a strong midgut barrier to dissemination. Autochthonous transmission of the Asian genotype of Zika virus is improbable on La Reunion Island.

International audience; Simple Summary: Aedes albopictus is a well-established competent arbovirus vector in Reunion Island, a French overseas territory in the Indian Ocean, occurring in a range of natural to urban environments where it represents a major threat to public health. Following the 2006 Chikungunya outbreak and periodic occurrence of dengue epidemics, the sterile insect technique (SIT) emerged as the most environment-friendly option for integration with the current vector control strategy that relies mainly on the elimination of breeding sites and insecticide applications. This paper describes the trajectory that has been followed in assessing the feasibility of SIT against Ae. albopictus in Reunion Island, and reviews some of the main achievements since 2009. These include essential scientific information so far obtained on the biology and ecology of Ae. albopictus, and the development of the requisite technological capabilities for the production and release of sexually competitive sterile males. Furthermore, it also draws attention to the strategies established to streamline the decision-making process, including an awareness campaign to enhance public understanding, efforts to secure public acceptance and regulatory validation of SIT pilot testing for small-scale suppression of wild Ae. albopictus in selected urban sites on the island. Abstract: The global expansion of Aedes albopictus, together with the absence of specific treatment and vaccines for most of the arboviruses it transmits, has stimulated the development of more sustainable and ecologically acceptable methods for control of disease transmission through the suppression of natural vector populations. The sterile insect technique (SIT) is rapidly evolving as an additional tool for mosquito control, offering an efficient and more environment-friendly alternative to the use of insecticides. Following the devastating chikungunya outbreak, which affected 38% of the population on Reunion Island (a French overseas territory in the southwest of the Indian Ocean), there has been strong interest and political will to develop effective alternatives to the existing vector control strategies. Over the past 10 years, the French Research and Development Institute (IRD) has established an SIT feasibility program against Ae. albopictus on Reunion Island in collaboration with national and international partners. This program aimed to Insects 2020, 11, 770 2 of 25 determine whether the SIT based on the release of radiation-sterilized males is scientifically and technically feasible, and socially acceptable as part of a control strategy targeting the local Ae. albopictus population. This paper provides a review of a multi-year and a particularly broad scoping process of establishing the scientific and technological feasibility of the SIT against Ae. albopictus on Reunion Island. It also draws attention to some prerequisites of the decision-making process, through awareness campaigns to enhance public understanding and support, social adoption, and regulatory validation of the SIT pilot tests.

First isolated from a forest in East Africa in the mid-20th century, Zika virus (ZIKV) has now emerged worldwide in urbanized areas where its mosquito vectors, mainly Aedes aegypti and Ae. albopictus, are present. Europe and French overseas territories in the Indian Ocean have been so far spared despite the presence of Ae. albopictus, the Asian tiger mosquito. However, because they have strong economic and touristic links with regions affected by ZIKV, French territories in the Indian Ocean have a high risk of introduction. Here, we assess the susceptibility of two Ae. albopictus populations from Metropolitan France and the Reunion island (a French oversea territory in the Indian Ocean) for a ZIKV isolate from the Asian genotype at a titer ranging from 3 to 7.5 × 106 focus-forming units per milliliter. High infection rates and unpreceded levels of systemic infection rates were observed in both Metropolitan France and the Reunion island populations, without differences in infection rates or intra-mosquito systemic infection dynamics between the two mosquito populations. Ten and 20-days were needed by the virus to disseminate in 50% and 100% of the exposed mosquitoes respectively. Such slow intra-mosquito viral dynamics, in addition to repeatedly reported high transmission barrier in the literature, can impact ZIKV transmission when potentially vectored by Ae. albopictus. However, because mosquito-borne virus intra-host transmission dynamics can be influenced by numerous factors, including virus dose dynamics inside infectious humans or viral evolution towards shorter extrinsic incubation periods (EIP), our results highlight that Ae. albopictus populations present in Metropolitan France and the French territoires in the Indian Ocean might become potential vector for autochthonous ZIKV transmissions.

International audience; Since 1953, leptospirosis has been recognized as a public health problem on Reunion Island. In 2004, was implemented a specific surveillance system that included systematic reporting and the realization of environmental investigations around hospitalized cases. Here, we present the synthesis of historical data and the assessment of 9 years of leptospirosis surveillance. From 2004 to 2012, 414 hospitalized cases were reported. Cases of leptospirosis occurred mostly during the rainy season from December to May. Approximately 41% of infections occurred at home, 12% of infections occurred during aquatic leisure and 5% of cases were linked to professional activities. Furthermore, for 41% of cases, the place of infection could not be determined due to the accumulation of residential and non-residential exposure. Most of the cases of leptospirosis were linked to rural areas or traditional, rural occupations. We did not observe a shift to recreational leptospirosis as described in some developed countries. According to the new surveillance system, the number of reported cases has regularly increased since 2004. This situation is in part due to the improvement of the system in the first years but also to a real increase in the number of detected cases due to the introduction of molecular methods and to increased biological investigation into the Dengue-like syndrome by medical practitioners on the island since the Chikungunya crisis in 2006. This increase is probably due to surveillance and diagnosis biases but need to be carefully monitored. Nevertheless, the possibility of an outbreak is always present due to climatic events, such as after the "hyacinth" hurricane in 1980.

Study of the human antibody (Ab) response to Aedes salivary proteins can provide new biomarkers to evaluate human exposure to vector bites. The identification of genus- and/or species-specific proteins is necessary to improve the accuracy of biomarkers. We analysed Aedes albopictus immunogenic salivary proteins by 2D immunoproteomic technology and compared the profiles according to human individual exposure to Ae. albopictus or Ae. aegypti bites. Strong antigenicity to Ae. albopictus salivary proteins was detected in all individuals whatever the nature of Aedes exposure. Amongst these antigenic proteins, 68% are involved in blood feeding, including D7 protein family, adenosine deaminase, serpin and apyrase. This study provides an insight into the repertoire of Ae. albopictus immunogenic salivary proteins for the first time.

A literature analysis coupled with new entomological surveys conducted between 2009 and 2012 led to changes in the list of mosquito species present on the island of La Reunion. Using morphological criteria, Orthopodomyia arboricollis is replaced by Or. reunionensis. On the basis of morphometrical and genetic criteria, Culex univittatus is replaced by Cx. neavei. Cx. poicilipes, which was already reported missing 40 years ago, has not been found again. Anopheles arabiensis is confirmed as the only species of the Gambiae complex present on the island. Thus, twelve species are currently known. For each of them, elements of taxonomic, biological and medical interest are listed. An. arabiensis is a major vector of human Plasmodium (last case of indigenous malaria in 1967). In the Indian Ocean, Aedes albopictus and Ae. aegypti both are competent for transmitting dengue and chikungunya viruses. In Africa, Cx. quinquefasciatus transmits Wuchereria bancrofti and Cx. neavei transmits the Sindbis virus; both species also transmit the West Nile virus. Cx. tritaeniorhynchus is the major vector of Japanese Encephalitis virus in Asia. Two species are endemic (Ae. dufouri and Or. reunionensis), the ten other ones are also found in Madagascar and on the African continent (An. coustani, An. arabiensis, Ae. fowleri, Cx. tritaeniorhynchus, Cx. neavei, Cx. insignis, Lutzia tigripes), with three of them having also a cosmopolitan distribution (Ae. aegypti, Ae. albopictus and Cx. quinquefasciatus). Among the twelve recorded taxa, eight species are anthropophilic, three are supposedly zoophilic and one is a predatory species. No new invasive anthropophilic species did settle on the island. Updated identification keys of larval and adult stages are proposed.

International audience; Chikungunya virus (CHIKV) and dengue virus (DENV) are mosquito-borne viruses transmitted by the Aedes genus. Dengue is considered as the most important arbovirus disease throughout the World. Chikungunya, known from epidemics in continental Africa and Asia, has up to now been poorly studied. It has been recently responsible for the severe 2004-2007 epidemic reported in the Indian Ocean (IO), which has caused several serious health and economic problems. This unprecedented epidemic of the IO has shown severe health troubles with morbidity and death associated, which had never been observed before. The two major vectors of those arboviruses in the IO area are Aedes aegypti and Aedes albopictus. The latest is considered as the main vector in most of the islands of the area, especially in Reunion Island. Ae. albopictus showed strong ecological plasticity. Small disposable containers were the principal urban breeding sites, and preferred natural developmental sites were bamboo stumps and rock holes in peri-urban and gully areas. The virus has been isolated from field collected Ae. albopictus females, and in two out of 500 pools of larvae, demonstrating vertical transmission. Experimental works showed that both Ae. albopictus and Ae. aegypti from west IO islands are efficient vectors of dengue and chikungunya viruses. Since 2006 and all along the epidemic of CHIKV, measures for the control of larvae (temephos then Bacillus thuringiensis) and adults (fenitrothion, then deltamethrine) of Ae. albopictus where applied along with individual and collective actions (by the use of repellents, and removal of breeding sites around houses) in Reunion Island. In order to prevent such epidemics, a preventive plan for arboviruses upsurge is ongoing processed. This plan would allow a quicker response to the threat and adapt it according to the virus and its specific vector.; Résumé : Les virus du chikungunya (CHIKV) et de la dengue (DENV) sont transmis par des moustiques du genre Aedes. La dengue est considérée comme l'arbovirose la plus importante dans le monde. Le chikungunya, connu d'Afrique continentale et d'Asie, et jusqu'à présent peu étudié, a été de 2004 à 2007 à l'origine de graves épidémies dans l'Océan Indien (OI), en Inde et en Afrique centrale, générant d'importants problèmes de santé publique et économiques. La récente épidémie dans le sud-ouest de l'Océan Indien (SOOI) a mis en exergue le caractère explosif de son émergence ainsi que la morbidité et la mortalité qui lui ont été associées, jusque-là sans précédent. Les deux vecteurs majeurs impliqués dans la transmission de ces arbovirus dans la zone OI sont Aedes aegypti et Aedes albopictus, ce dernier étant considéré comme le vecteur principal dans la majorité des îles de la zone. Dans l'île de la Réunion, où Ae. albopictus est le vecteur du CHIKV, la lutte anti-larvaire (téméphos puis Bacillus thuringiensis), anti-adulte (fénitrothion, puis deltaméthrine), ainsi qu'une protection individuelle et communautaire (utilisation de répulsifs, destruction des gîtes larvaires autour des habitations) ont été réalisées depuis 2006 et tout au long de la crise sanitaire. Afin de prévenir de telles épidémies, un plan de prévention des arboviroses est en cours de réalisation. Il devra permettre d'intervenir plus rapidement dès la réception des premiers signaux d'alerte, et d'adapter la réponse en fonction du virus et de son vecteur.

Aedes albopictus is generally considered to have a low vectorial capacity because of its lack of host specificity. Nevertheless, it has been the sole vector of the Chikungunya virus in recent explosive epidemics on the islands of La Réunion and Mauritius. We report on investigations of the seasonal prevalence, container preferences, and geographic distribution of the species on La Réunion. Ae. albopictus showed strong ecological plasticity. In the warm wet season, small disposable containers were the principal urban breeding site, with 1939 positive containers in 750 houses. In the dry winter season, the species remained abundant throughout the island up to 800 m and was present to a maximum altitude of 1200 m. Natural containers were clearly important in this season, although productive sources were hard to find. The preferred natural developmental sites were bamboo stumps and rock holes, over 357 developmental sites observed in peri-urban and gully areas. Generalized logistic models indicated that the optimum sites contained clear water with high organic content and were situated in sites with moderate shade. Our data will provide input into the models of the epidemiology of the disease and design of vector control programs.

Background Arboviral diseases are an important public health concerns. Vector control remains the sole strategy to fight against these diseases. Because of the important limits of methods currently used to assess human exposure to Aedes mosquito bites, much effort is being devoted to develop new indicators. Recent studies have reported that human antibody (Ab) responses to Aedes aegypti Nterm-34kDa salivary peptide represent a promising biomarker tool to evaluate the human-Aedes contact. The present study aims investigate whether such biomarker could be used for assessing the efficacy of vector control against Aedes. Methodology/Principal findings Specific human IgG response to the Nterm-34kDa peptide was assessed from 102 individuals living in urban area of Saint-Denis at La Reunion Island, Indian Ocean, before and after the implementation of vector control against Aedes mosquitoes. IgG response decreased after 2 weeks (P < 0.0001), and remained low for 4 weeks post-intervention (P = 0.0002). The specific IgG decrease was associated with the decline of Aedes mosquito density, as estimated by entomological parameters and closely correlated to vector control implementation and was not associated with the use of individual protection, daily commuting outside of the house, sex and age. Our findings indicate a probable short-term decrease of human exposure to Aedes bites just after vector control implementation. Conclusion/Significance Results provided in the present study indicate that IgG Ab response to Aedes aegypti Nterm-34kDa salivary peptide could be a relevant short-time indicator for evaluating the efficacy of vector control interventions against Aedes species., Author Summary In absence of effective treatment and vaccine, vector control is the main strategy against arboviral diseases such as dengue, Zika and chikungunya. Given the limitation of entomologic tool currently used, news tools are urgently needed to assess the efficacy of vector control against arboviral diseases. The present study aimed to investigate whether human IgG antibody specific response to only one Aedes salivary peptide could be useful for assessing the efficacy of vector control against arboviral diseases. For this purpose, IgG response to Nterm-34kDa peptide was assessed from 102 individuals living in urban area at La Reunion Island, Indian Ocean, before and after the implementation of vector control against Aedes albopictus mosquito species. A significant decrease of this specific IgG level was noticed after vector control implementation. The decrease was associated to the decline in Aedes mosquito density estimated by entomological parameters, such as adult mosquito density, House and Breteau indices. The results of the present study indicated that human IgG response to the Aedes Nterm-34kDa salivary peptide could be a useful tool to evaluate the efficacy of vector control strategies against arboviruses.

In mosquitoes, the maternally inherited bacterial Wolbachia induce a form of embryonic lethality called cytoplasmic incompatibility (CI). This property can be used to reduce the density of mosquito field populations through inundative releases of incompatible males in order to sterilize females (Incompatible Insect Technique, or IIT, strategy). We have previously constructed the LR[wPip(Is)] line representing a good candidate for controlling field populations of the Culex quinquefasciatus mosquito in the islands of the south-western Indian Ocean. The main purpose of the present study was to fill the gap between laboratory experiments and field implementation, i.e. assessing mating competitiveness of these incompatible males under semi-field conditions. In a first set of experiments, we analyzed crossing relationships between LR[wPip(Is)] males and La Reunion field females collected as larvae in 19 distinct localities throughout the island. This investigation revealed total embryonic mortality, confirming the strong sterilizing capacity of LR[wPip(Is)] males. Subsequently, mating competitiveness of LR[wPip(Is)] males was assessed under semi-field conditions in the presence of field males and females from La Reunion. Confrontations were carried out in April and December using different ratios of LR[wPip(Is)] to field males. The results indicated that the LR[wPip(Is)] males successfully compete with field males in mating with field females, displaying even higher competitiveness than field males in April. Our results support the implementation of small-scale field tests in order to assess the feasibility of IIT against Cx. quinquefasciatus in the islands of southwestern Indian Ocean where this mosquito species is a proven competent vector for human pathogens.

International audience; The implementation of the sterile insect technique for area-wide vector control requires that natural population density be accurately estimated to determine both the appropriate time to treat and the adequate number of sterile males for release. Herein, we used mark-release-recapture (MRR) to derive seasonal abundance estimates of Aedes albopictus population sizes within a delimited geographical area in Reunion Island. Population size of Ae. albopictus was estimated through four mark-release-recapture experiments carried out separately in different seasons. Marked males and females were released each time, and recaptured using BG sentinel traps for six consecutive days. Data were used to estimate the population size using a conceptual model that incorporates the variation in daily mortality rates. The likely influence of environmental factors on the magnitude of catches and on population fluctuation was analyzed. A total of 2827 mosquitoes (1914 males and 913 females) were marked and released on four occasions during dry and wet seasons. After release, 138 males (7.21%) and 86 females (9.41%) of the marked specimens were recaptured in subsequent samplings. The effectiveness of the daily captures of wild and released mosquitoes was significantly influenced by meteorological conditions such as temperature, rainfall, wind speed and light intensity. The estimates of Ae. albopictus population size obtained with our model estimator ranged from 298 to 1238 males and 604 to 2208 females per ha, with seasonal variability - higher population size in the humid season. The presented results will be essential in designing more effective sterile male release strategies for long-term suppression of wild Ae. albopictus populations.

International audience; Following the 2006 Chikungunya disease in La Reunion, questions were raised concerning the monitoring survey of Aedes albopictus populations and the entomological indexes used to evaluate population abundance. The objectives of the present study were to determine reliable productivity indexes using a quantitative method to improve entomological surveys and mosquito control measures on Aedes albopictus. Between 2007 and 2011, 4 intervention districts, 24 cities, 990 areas and over 850,000 houses were used to fulfil those objectives. Four indexes including the classical Stegomyia index (House Index, Container Index, Breteau Index) plus an Infested Receptacle Index were studied in order to determine whether temporal (year, month, week) and/or spatial (districts, cities, areas) heterogeneities existed. Temporal variations have been observed with an increase of Ae. albopictus population density over the years, and a seasonality effect with a highest population during the hot and wet season. Spatial clustering was observed at several scales with an important autocorrelation at the area scale. Moreover, the combination among these results and the breeding site productivity obtained during these 5 years allowed us to propose recommendations to monitor Aedes albopictus by eliminating not the most finding sites but the most productive ones. As the other strategies failed in La Reunion, this new approach should should work better.

Aedesborne viruses represent public health problems in southern countries and threat to emerge in the developed world. Their control is currently based on vector population control. Much effort is being devoted to develop new tools to control such arbovirus. Recent findings suggest that the evaluation of human antibody (Ab) response to arthropod salivary proteins is relevant to measuring the level of human exposure to mosquito bites. Using an immunoepidemiological approach, the present study aimed to assess the usefulness of the salivary biomarker for measuring the efficacy ofAe. albopictuscontrol strategies in La Reunion urban area. The antisaliva Ab response of adult humans exposed toAe. albopictuswas evaluatedbefore and after vector control measures. Our results showed a significant correlation between antisaliva Ab response and the level of exposure to vectors bites. The decrease ofAe.albopictusdensity has been detected by this biomarker two weeks after the implementation of control measures, suggesting its potential usefulness for evaluating control strategies in a short time period. The identification of species specific salivary proteins/peptides should improve the use of this biomarker.

International audience; Several mosquito-borne diseases affect the Western Indian Ocean islands. Culex pipiens quinquefasciatus is one of these vectors and transmits filariasis, Rift Valley and West Nile viruses and the Japanese encephalitis. To limit the impact of these diseases on public health, considerable vector control efforts have been implemented since the 50s, mainly through the use of neurotoxic insecticides belonging to Organochlorines (OC), Organophosphates (OP) and pyrethroids (PYR) families. However, mosquito control failures have been reported on site, and they were probably due to the selection of resistant individuals in response to insecticide exposure. In this study, we used different approaches to establish a first regional assessment of the levels and mechanisms of resistance to various insecticides. Bioassays were used to evaluate resistance to various insecticides, enzyme activity was measured to assess the presence of metabolic resistances through elevated detoxification, and molecular identification of known resistance alleles was investigated to determine the frequency of target-site mutations. These complementary approaches showed that resistance to the most used insecticides families (OC, OP and PYR) is widespread at a regional scale. However, the distribution of the different resistance genes is quite heterogeneous among the islands, some being found at high frequencies everywhere, others being frequent in some islands and absent in others. Moreover, two resistance alleles displayed clinal distributions in Mayotte and La Réunion, probably as a result of a heterogeneous selection due to local treatment practices. These widespread and diverse resistance mechanisms reduce the capacity of resistance management through classical strategies (e.g. insecticide rotation). In case of a disease outbreak, it could undermine the efforts of the vector control services, as only few compounds could be used. It thus becomes urgent to find alternatives to control populations of Cx. p. quinquefasciatus in the Indian Ocean.

Background The identification of mosquito vectors is typically based on morphological characteristics using morphological keys of determination, which requires entomological expertise and training. The use of protein profiling by matrix-assisted laser desorption/ionization time-of-flight mass spectrometry (MALDI-TOF-MS), which is increasingly being used for the routine identification of bacteria, has recently emerged for arthropod identification. Methods To investigate the usefulness of MALDI-TOF-MS as a mosquito identification tool, we tested protein extracts made from mosquito legs to create a database of reference spectra. The database included a total of 129 laboratory-reared and field-caught mosquito specimens consisting of 20 species, including 4 Aedes spp., 9 Anopheles spp., 4 Culex spp., Lutzia tigripes, Orthopodomyia reunionensis and Mansonia uniformis. For the validation study, blind tests were performed with 76 specimens consisting of 1 to 4 individuals per species. A cluster analysis was carried out using the MALDI-Biotyper and some spectra from all mosquito species tested. Results Biomarker mass sets containing 22 and 43 masses have been detected from 100 specimens of the Anopheles, Aedes and Culex species. By carrying out 3 blind tests, we achieved the identification of mosquito vectors at the species level, including the differentiation of An. gambiae complex, which is possible using MALDI-TOF-MS with 1.8 as the cut-off identification score. A cluster analysis performed with all available mosquito species showed that MALDI-Biotyper can distinguish between specimens at the subspecies level, as demonstrated for An gambiae M and S, but this method cannot yet be considered a reliable tool for the phylogenetic study of mosquito species. Conclusions We confirmed that even without any specific expertise, MALDI-TOF-MS profiling of mosquito leg protein extracts can be used for the rapid identification of mosquito vectors. Therefore, MALDI-TOF-MS is an alternative, efficient and inexpensive tool that can accurately identify mosquitoes collected in the field during entomological surveys.

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.