Several dengue epidemics recently occurred in La Reunion, an island harboring two dengue viruses (DVs) vectors: Aedes albopictus, and Ae. aegypti, the former being the main local DV vector. Aedes aegypti shows a peculiar ecology, compared to other tropical populations of the same species. This study aimed to provide researchers and public-health users with locally validated oviposition traps (ovitraps) to monitor Aedes populations. A field experiment was performed in Saint-Joseph to assess the effect of different settings on the detection probability and apparent density of Aedes mosquitoes. Black plastic ovitraps were identified as the best choice. Vacoa trees (Pandanus utilis) were the only observed breeding sites for Ae. aegypti, shared with Ae. albopictus. They were the experimental units in a Latin square design with three factors: trap position in the trees (ground vs canopy), oviposition surface in the trap (blotting paper vs. vacoa leaf), and addition of organic matter to the trap water. The latter factor was found unimportant. On the ground, Ae. aegypti eggs were only found with vacoa leaves as the oviposition surface. Their detection and apparent density increased when ovitraps were located in the tree canopy. The main factor for Ae. albopictus was the oviposition surface, with a preference for blotting paper. In all trap settings, their detection was close to 100%. Larval survival was lower for a high egg density, combined with blotting paper as the oviposition surface. When monitoring mixed Aedes populations in La Reunion, we recommend using black plastic ovitraps, placed at 1.50-to-2.00-m high in vacoa trees, with vacoa leaves as the oviposition surface.

Competent arbovirus vectors are found in the culicid mosquito fauna of south-west Indian Ocean (SWIO) islands. In La Réunion Island, Aedes albopictus and Aedes aegypti mosquitoes are known vectors of dengue and chikungunya viruses. Culex quinquefasciatus is a potential vector of Rift Valley fever and West Nile viruses. To prepare a vector-control field trial against Ae. aegypti, this study aimed at identifying the best baiting scheme to catch adult Ae. aegypti, using BG-Sentinel™ traps (Biogents). It was implemented in two sites in southern La Réunion Island. Catches of Ae. albopictus and Cx. quinquefasciatus mosquitoes were also recorded. A Latin square design was used to estimate the detection probability and the apparent daily density - according to the BG-sentinel trap baiting scheme: none, carbon dioxide (CO2), a commercial attractant - BG-Lure™ (Biogents), or both. The use of CO2 alone was associated with a higher detection probability for Ae. aegypti and Cx. quinquefasciatus mosquitoes, as well as a large increase in their apparent density. Traps with BG-Lure - alone or in combination with CO2, did not improve the detection probability of Ae. aegypti and Cx. quinquefasciatus mosquitoes. The same result was found for male Ae. albopictus. For females, baiting BG traps with CO2or BG-Lure had no significant effect. The same apparent densities were found for Ae. aegypti and Ae. albopictus mosquitoes in both study sites - where Ae. aegypti mosquitoes were found at very low densities during previous surveys.

Competent arbovirus vectors are found in the culicid mosquito fauna of south-west Indian Ocean (SWIO) islands. In La Reunion, Aedes albopictus and Aedes aegypti mosquitoes are known vectors of dengue and chikungunya viruses. Culex quinquefasciatus is a potential vector of Rift Valley fever and West Nile viruses. To prepare a vector-control field trial against Ae. aegypti, this study aimed at identifying the best trapping strategy to catch adult Ae. aegypti, using BG-Sentinel traps (Biogents, Germany). It was implemented in two sites in southern La Reunion. Catches of Ae. albopictus and Cx. quinquefasciatus mosquitoes were also recorded. A Latin square design was used to estimate the detection probability and the apparent daily density—according to the BG-Sentinel trapping strategy: none, carbon dioxide (CO2), a commercial attractant—BG-Lure (Biogents, Germany), or both. The use of CO2 alone was associated with a higher detection probability for Ae. aegypti and Cx. quinquefasciatus mosquitoes, as well as a large increase in their apparent density. Traps with BG-Lure—alone or in combination with CO2, did not improve the detection probability of Ae. aegypti and Cx. quinquefasciatus mosquitoes. The same result was found for male Ae. albopictus. For females, baiting BG-Sentinel traps with CO2 or BG-Lure had no significant effect. The same apparent densities were found for Ae. aegypti and Ae. albopictus mosquitoes in both study sites—where Ae. aegypti mosquitoes were found at very low densities during previous surveys.

Recently, several epidemics caused by mosquito-borne viruses - including dengue viruses (DV) have occurred in La Reunion and other Indian Ocean islands. Aedes albopictus and Ae. aegypti - two important DV vectors, co-occur in La Reunion. Aedes albopictus is the major DV vector, preponderant and widespread in the island. Aedes aegypti is localized in certain areas and shows a peculiar ecology, compared to other tropical populations of the same species. This study aimed at providing users (researchers, mosquito control operators, health managers) with a locally-validated oviposition traps (ovitraps) to monitor Aedes populations.A field experiment was achieved in Saint-Joseph - where both mosquito species occur in sympatry, to assess the effect of different ovitrap settings on their detection probability and apparent density. Preliminary surveys indicated black plastic ovitraps were the best traps. Vacoa trees (Pandanus utilis) were the only observed breeding sites for Ae. aegypti, shared with Ae. albopictus. They were the experimental units in a design considering three factors: trap position in the trees (ground vs canopy), the oviposition surface used in the trap (blotting paper vs. vacoa leaf), and addition of organic matter (fish food) to the trap water.The addition of organic matter to trap water was not an important factor in this study. On the ground, Ae. aegypti eggs were only found when vacoa leaves were used for oviposition. Their detection and apparent density increased greatly when ovitraps were located in the tree canopy. The main factor for Ae. albopictus was the oviposition surface, with a strong preference for blotting paper. However, with vacoa leaves, the detection was also close to 100%. Further laboratory studies indicated larvae survival was lower for a high egg density, combined with blotting paper as the oviposition surface.When monitoring mixed Aedes populations in La Reunion, we recommend the use of black plastic ovitraps, filled with tap water, placed at 1.50-to-2.00-m high in vacoa trees, with vacoa leaves as the oviposition surface.