Climatic factors driving invasion of the tiger mosquito (Aedes albopictus) into new areas of Trentino, northern Italy

Abstract

Background: The tiger mosquito (Aedes albopictus), vector of several emerging diseases, is expanding into more northerly latitudes as well as into higher altitudes in northern Italy. Changes in the pattern of distribution of the tiger mosquito may affect the potential spread of infectious diseases transmitted by this species in Europe. Therefore, predicting suitable areas of future establishment and spread is essential for planning early prevention and control strategies.

Methodology/principal findings: To identify the areas currently most suitable for the occurrence of the tiger mosquito in the Province of Trento, we combined field entomological observations with analyses of satellite temperature data (MODIS Land Surface Temperature: LST) and human population data. We determine threshold conditions for the survival of overwintering eggs and for adult survival using both January mean temperatures and annual mean temperatures. We show that the 0°C LST threshold for January mean temperatures and the 11°C threshold for annual mean temperatures provide the best predictors for identifying the areas that could potentially support populations of this mosquito. In fact, human population density and distance to human settlements appear to be less important variables affecting mosquito distribution in this area. Finally, we evaluated the future establishment and spread of this species in relation to predicted climate warming by considering the A2 scenario for 2050 statistically downscaled at regional level in which winter and annual temperatures increase by 1.5 and 1°C, respectively.

Conclusions/significance: MODIS satellite LST data are useful for accurately predicting potential areas of tiger mosquito distribution and for revealing the range limits of this species in mountainous areas, predictions which could be extended to an European scale. We show that the observed trend of increasing temperatures due to climate change could facilitate further invasion of Ae. albopictus into new areas.

Figure 1. Differences between the areas with/without Ae. albopictus presence and the four explanatory variables: JanT^mean LST (top left), AnnT^mean LST (top right), human population density (log) (bottom left) and distance to human population centers (bottom right).

Figure 2. Relationship between the JanT^mean LST (left) and the AnnT^mean LST (right) and elevation.

All the pixels with a JanT^mean LST > = 0°C and with an AnnT^mean LST > = 11°C were included and compared with elevation.

Figure 3. Potential and current distributional areas of Ae. albopictus.

Overlap of both indicators (JanT^mean LST> = 0°C and AnnT^mean LST > = 11°C) were plotted for the period 2001–09 and integrated in a final map with 3 categories (see methods). Red spots represent the presence and green spots the absence of Ae. albopictus.

Figure 4. Potential distribution of Ae. albopictus in an A2 scenario for 2050 (see text).

Overlap of both indicators (JanT^mean LST +1.5°C and AnnT^mean LST +1°C) were plotted for the study period and integrated in a final map with 3 categories (see methods).