The spread of Aedes albopictus (Diptera: Culicidae) in the islands of São Tomé and Príncipe

Abstract

The mosquito Aedes albopictus (Diptera: Culicidae) is a vector species of the causal agents of Dengue, yellow fever, and Zika among other diseases pathogens. The species originated in Southeast Asia and has spread widely and rapidly in the last century. The species has been reported in localities from the Gulf of Guinea since the early 2000s, but systematic sampling has been scant. We sampled Ae. albopictus twice, in 2013 and 2023 across the altitudinal gradient in São Tomé and found that the species was present in all sampled years at altitudes up to 680 m. We also found some evidence of increases in proportional representation compared to Ae. aegypti over time. We report the presence of the species in Príncipe for the first time, suggesting that the range of Ae. albopictus is larger than previously thought. Finally, we use bioclimatic niche modeling to infer the potential range of Ae. albopictus and infer that the species has the potential to spread across a large portion of São Tomé and Príncipe. Our results suggest that Ae. albopictus has established itself as a resident species of the islands of the Gulf of Guinea and should be incorporated into the list of potential vectors that need to be surveyed and controlled.

Keywords: Aedes; Invasive species; Islands.

Fig. 1.

Mosquito collection scheme. A. Example of a location that yielded Ae. albopictus in the midlands of São Tomé. B. Map of the Gulf of Guinea, depicting the islands of the Cameroon Volcanic Line and highlighting São Tomé and Príncipe. C. Map showing the location of the traps on Príncipe and on São Tomé (D).

Fig. 2.

Abundance of two different species of Aedes along the altitudinal gradient in São Tomé island in two different years. A. Immature stages in 2013. B. Adults in 2013. C. Immature stages in 2023. D. Adults in 2023. Red: Ae. aegypti. Blue: Ae. albopictus. Lines represent the best fitting linear regression for each dataset.

Fig. 3.

Change of Ae. albopictus over the 2013–2023 The y axis represents the difference in the proportional representation of Ae. albopictus individuals vs a second species, Ae. aegypti between 2023 and 2013. Positive values indicate an increase in 2023. A. Larval collections (n = 14). B. Adult collections (n = 15). The dashed line represents no change in the Ae. albopictus proportion.

Fig. 4.

Maximum likelihood phylogenetic tree based on a COI barcode. Numbers above the nodes represent the ultrafast bootstrap branch support (1000 replicates). Branches with bootstrap support higher than 50 % are labeled with blue circles; labels with bootstrap support lower than 50 % are labeled with red circles. GenBank accession numbers are listed in Table S1. ST: São Tomé, Rep. Congo: Republic of Congo, DRC: Democratic Republic of Congo.

Fig. 5.

Map depicting the results of a maximum entropy (MaxEnt) model for the Gulf of Guinea (A) and the islands of Príncipe (B) and São Tomé (C). Heatmap coloration shows predicted habitat suitability for Aedes albopictus mosquitoes based on bioclimatic data from the WorldClim database, with bluer colors representing relatively poor habitat and the yellow end of the gradient depicting more suitable habitat. Data points in panes B and C show presence (black data points) or absence (white crosses) of Ae. albopictus from our sampling efforts. The contribution of each WorldClim variable to predicting favorable Ae. albopictus habitat is shown in pane D.

Fig. 6.

Bioclimatic niche axes for Aedes albopictus on São Tomé and Príncipe. MaxEnt modeling identified five bioclimatic niche axes that are associated with global suitability of habitat for Ae. albopictus (see Fig. 5). The pale blue boxes depict the central 95 % quantile range (discarding the upper and lower 2.5 %) of the global distribution of Ae. albopictus on each bioclimatic axis. The extent of each of the axes is represented with a green box for São Tomé and with a blue box for Príncipe. Vertical hash marks within each island box show the values at each of our sampling localities.