Four shades of red: optimizing the use of oviposition traps to monitor mosquito populations of arbovirus vectors in La Reunion

Abstract

Abstract 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.