Aedes albopictus oviposition activity in Sainte Marie, Réunion Island, 2013-2018

Study Extent

Sainte Marie (Latitude: 20° 52' 60'' South, Longitude: 55° 33' East) is a coastal municipality covering 87.2 km² with a population of 34,061 since the last census. With a population density of 390.6 inhabitants per km², Sainte-Marie is located at an altitude of 5 meters, 9 km southeast of Saint-Denis. Priority was given to urbanized settlements where Ae. albopictus is the only Stegomiya species present. Other considerations taken into account for selecting the study sites were (a) areas with manageable sizes (range: 20-40 hectares) and well-delimited residential areas geographically isolated by natural barriers, (b) proximity to laboratory facilities and accessibility by car. Accordingly, “Duparc” and “Bois Rouge”, two urban areas are within the municipality of Sainte Marie located in the the south-west of Saint-Denis, the capital of Reunion island, were given preference over other cities because they were representative of most urban agglomerations on the island of Reunion, being relatively isolated, and accessible in around fifteen minutes by car from the laboratories.
Duparc covers an area of ​​ca. 42 ha at the altitude between 5 and 8 meters asl. With approximately 1,885 inhabitants, its urban habitat is quite densely and homogeneous built with more than more than 94% of the land area almost exclusively made up of individual properties (about 300-500 households) with private gardens. The surrounding area features a variety of amenities and infrastructures for transport, education, healthcare services, and businesses and shopping centers. The site is isolated by expressway linking Saint Denis to Saint Benoit to the north, by the rain-fed Ravine La Mare and to the east, west and south by sugar cane fields. This rain-fed ravine is semi-natural wooded area made up of difficult to access landscape with rocks. The residential area is perfectly well demarcated with sugarcane fields all around, with the exception of the grassland located to the north (towards the sea). Bois Rouge, an urban area of about ​​24 ha extending over an elevation of approximately 5-9 meters asl with an estimated population of 3,877 inhabitants. The residential area made up of slightly more heterogeneous individual housing spread over 21% of its total surface area (63% of the properties are individual houses and 37% are apartments) and interspersed with uninhabited land with few small poultry or goat farms. The neighborhood's most common socio-professional category is working-class people and farmers. The western and southern periphery of Bois-Rouge is mainly agricultural. A small, shallow ravine runs through the residential area, which is entirely surrounded market gardening fields, while the southwest part is bordered with sugarcane field up to the Duparc.
The sampling period using oviposition traps (Ovitrap) covered 6 years, May 2013 and continued until 2018. Every weeks during the survey from 2013 to 2018, the ovitraps were repeatedly placed in the same position in each defined zone.

Sampling

The survey consisted of placing 29, 27 and 20 ovitraps in previously selected location dispatched in Bois Rouge, Duparc, and buffer zone separating the two urban areas, respectively. Trapping sites represented the mix of dominant residential and wild habitat types within each of the study sites. Indeed, the surveys took place mainly from inhabited houses, although in some cases traps were also placed in a numbers of in the public domains and natural areas within and outside (buffer zone) of the residential neighborhoods. Each ovitrap consisted of a 1.2 liter black plastic pots filled with 650 ml of water collected from a river. The oviposition substrate (ovistrip) was made of a brown germination paper (400HPT Sedburo Equipment, Des Plaines, USA) (measuring 15x10 cm) attached with a paper clip on a 15x10 cm smooth and rigid PVC sheet, which was placed slightly obliquely inside the ovitrap pot. The papers were labelled on the back with unique number number, followed by the number of the week of installation. In each sampling zone, the ovitraps were usually placed placed at ground level in a shaded location or in low vegetation and preferably sheltered from the wind and the sun, most frequently in the garden within volunteered private properties and more rarely in the public domain for the Duparc and Bois Rouge sites. Each ovitrap was numerated and GPS coordinates was recorded for each trap. Every weeks during the survey from 2013 to 2018, the ovitraps were repeatedly placed in the same position in each defined zone. The egg laying papers were collected weekly and annotated with the trap number and collection date before being taken to the lab for egg counting. Any larvae observed in the traps was counted and identified by stage of development. The pots were completely emptied of their residual water and cleaned in order to remove any eggs that may have been deposited. They were filled with water before being set again with new substrate. At the laboratory, each egg paper was separated from its PVC sheet and checked to remove any debris or dirt. The presence of eggs (positivity) was noted and the number of eggs counted either immediately after cleaning, or deferred after drying and maturation of the embryos, when field collected egg samples were used to evaluate the hatching rate. In the first case, the number of eggs from each each weekly sampling was recorded, based on three scores: i) the overall number of eggs observed on each ovitrap substrate, ii) the number of opened eggs when the opercula is clearly separated from the rest of the egg shell (corresponding to viable eggs); (iii) and the number of eggs that have a completely flattened appearance (corresponding either to non-embryonated eggs or to non-viable embryos). Weekly, monthly and annual average number of eggs/trap were calculated, and used as a proxy of Ae. albopictus abundance in each study site. In the latter case, the assessment of the viability of field collected eggs took place every 2-weeks for Duparc and every month for Bois rouge. In brief, a minimum of six positive papers (with Ae. albopictus eggs) per study site were randomly picked from the field-collected egg laying papers to assess the hatching rate. These egg papers were placed in the dark inside plastic tray covered by a Plexiglas for five days allowing gentle drying and egg maturation under laboratory conditions. After this period, each dried egg paper was completely immersed in plastic containers previously filled with 250 ml of “rested” water (i.e. tap water stored overnight in a jerrycan) and a small amount of rabbit pellet powder was added to each container. After 24 hrs hours of egg immersion, all eggs present were examined under stereomicroscope and the hatching rate was estimated by dividing the number of opened eggs (or newly eclosed L1 larvae) by total egg counts.

Method steps

1. Several study sites were selected, and data were collected in these sites, as detailed in the Sampling Method section
2. The data were collected as detailed in the Sampling Method section
3. The collected data were digitized
4. A custom R script was created to map the original data to Darwin Core as an event core with the relevant extension (occurrence)
5. The Darwin Core files were connected to the French IPT and documented with metadata.
6. The data was published and registered with GBIF
7. Several villages were selected as detailed in the Sampling Method section.

1. Aedes (Stegomyia) albopictus (Skuse, 1895)
   common name: Aedes albopictus rank: species

The sampling took place in the municipality of Sainte Marie, Réunion Island. Sainte Marie (Latitude: 20° 52' 60'' South, Longitude: 55° 33' East) is a coastal municipality covering 87.2 km² with a population of 34,061 since the last census. Three study sites within the municipality were selected to collect the entomological data : Duparc, Bois Rouge, and a buffer area between these two study sites.