Spatial and temporal characterization of Aedes albopictus oviposition activity in candidate urban settings for sterile insect technique testing in La Reunion Island

Abstract

Background: Understanding of mosquito spatiotemporal dynamics is central to characterize candidate field sites for the sterile insect technique (SIT) testing, and is critical to the effective implementation and evaluation of pilot sterile male release programs. Here, we present a detailed description of Aedes albopictus (Skuse) egg-laying activity over a 6-year period in urban areas identified as potential SIT testing sites on Reunion Island.

Method: Weekly entomological collections using ovitraps were carried out in residential and adjacent uninhabited habitats in two urban areas, Duparc and Bois Rouge, in the municipality of Sainte Marie, Reunion Island. Time-series data incorporating the frequency of positive ovitraps and the total number of eggs/ovitrap recorded each time at each locality during the study period from May 2013 to December 2018 were analyzed with multifaceted statistical approaches including descriptive statistics and spatiotemporal analyses incorporating the role of climatic factors on overall ovitrap productivity.

Results: During the ovitrap survey, the proportion of egg-positive ovitraps differed among study sites (χ² = 50.21, df = 2, P < 0.001), being relatively lower in Duparc (89.5%) than in Bois-Rouges (95.3%) and the adjacent buffer zone (91.2%). Within each neighborhood, Ae. albopictus egg abundance varied by month in a roughly seasonal pattern marked by a single peak occurring more regularly February each year, a decline at the onset of the austral winter in July, followed by a period of lower ovitrap productivity in August and September. Fluctuation in both positivity rate and eggs densities per ovitraps were related to annual and seasonal variations in local temperature and rainfall (P < 0.001 in all cases). The spatial analysis also captured substantial between- and within-habitats heterogeneity, whereby the overall ovitrap productivity was higher in residential areas than in the buffer zone.

Conclusions: Collectively, these results reveal that the distribution of Ae. albopictus oviposition activity is shaped by local habitat heterogeneity and seasonal climatic factors. Overall, this study provides baseline insights into the reproductive dynamics of Ae. albopictus, which would assist in planning locally tailored SIT interventions, while addressing concerns related to focal areas of high egg-laying intensity and potential immigration of females from natural areas.

Keywords: Aedes albopictus; Egg abundance; Ovitrap; Spatiotemporal variability; Urban environment.

Fig. 1

Sampling sites. Map showing the location of the study sites. Background layer: OpenStreetMap, Bing Aerial. Reunion Island (bottom left map) lies in the southern Indian Ocean, to the southeast of the African continent at a distance of 679 km east-southeast of Madagascar (upper left map). Each dot in the main map corresponds to the ovitrap positions and is colour-coded according to specific habitats defined by Duparc (yellow dots) and Bois Rouge (grey dots) and the buffer zone (blue dots)

Fig. 2

Time series of monthly records of ovitrap positivity rates (%) and average numbers of Ae. albopictus eggs per ovitrap through the study period (May 2013 to December 2018). Dots represent average proportions of egg-positive ovitraps, and bars represent a time series of the average number of eggs recorded per ovitrap at each sampling month. The dry winter season (May–October) is shaded light grey

Fig. 3

Mean proportion of egg-positive ovitraps (top panel) and mean numbers of Ae. albopictus eggs per ovitrap—week (low panel) at residences in study neighborhoods over the entire sampling period, split by season. The numbers on the bars indicate the mean values in different locations over the sampling period. The numbers of ovitraps used and in each study site are provided in Supplementary Table S2

Fig. 4

Spatiotemporal variation of the relative abundance of Aedes albopictus eggs in ovitraps in Bois-Rouge (A) and Duparc (B). The spatial representation shows the variability of ovitrap productivity defined as monthly total egg abundance in all ovitraps for each year and season at the three study sites: low suitability areas were defined with egg density < 100 eggs/ovitrap, intermediate suitability with 100–200 eggs/ovitrap, and high suitability when egg density is > 200 eggs/ovitrap

Fig. 5

Comparison of temporal dynamics of recorded Ae. albopictus egg densities in residential (Bois-Rouge and Duparc) and non-residential buffer zones.The first panel shows the distribution of the yearly total (A) and yearly average (B) egg density per ovitraps in the different years, whereas the second panel show the monthly total (A) and monthly average (B) egg density per ovitraps at the surveyed study areas