Spread of the tiger: global risk of invasion by the mosquito Aedes albopictus

Abstract

Aedes albopictus, commonly known as the Asian tiger mosquito, is currently the most invasive mosquito in the world. It is of medical importance due to its aggressive daytime human-biting behavior and ability to vector many viruses, including dengue, LaCrosse, and West Nile. Invasions into new areas of its potential range are often initiated through the transportation of eggs via the international trade in used tires. We use a genetic algorithm, Genetic Algorithm for Rule Set Production (GARP), to determine the ecological niche of Ae. albopictus and predict a global ecological risk map for the continued spread of the species. We combine this analysis with risk due to importation of tires from infested countries and their proximity to countries that have already been invaded to develop a list of countries most at risk for future introductions and establishments. Methods used here have potential for predicting risks of future invasions of vectors or pathogens.

FIG. 1

Predicted Australasian range map of Ae. albopictus. Darker shades indicate pixels for which higher numbers of models predicted potential suitable niches with the darkest shades signifying 10 models. The legend bar shows the 10 colors used. White squares represent the known occurrence points used to create the models. Yellow squares are known introduction sites outside of the native range.

FIG. 2

Predicted non-Australasian potential distribution of Ae. albopictus. Darker shades indicate greater numbers of models in agreement for suitable habitat with the darkest shades signifying 10 models with the legend showing each. The predicted distribution in western North America is shown in Figure 3.

FIG. 3

Predicted distribution maps and actual spread of Ae. albopictus in the lower 48 states. The predicted distribution areas (red) and the documented spread (yellow) of Ae. albopictus through the year 2001 are shown. One of the two prediction maps for the US is shown. Differences between the two consisted largely of one of the ten models used to create the prediction map that predicted a broader Texas distribution. Counties colored green are those in which introduction has occurred but not establishment.

FIG. 4

Predicted distribution and actual spread of Ae. albopictus in Brazil as of 2004. Both the predicted distribution (shades of red) and the documented spread (yellow points) of Ae. albopictus are displayed.

FIG. 5

Relationship of average annual precipitation and temperature for a subset of global sites of Ae. albopictus establishments. Note that the data points fall into two clusters of temperature and precipitation (p < 0.0001). Those in the quadrant beneath approximately 18°C and 225 cm precipitation are located above 30 degrees north latitude (Δ). For this analysis, all worldwide points plus a subsample of 10 random U.S. counties and 67 early references to occurrence from Brazil were selected. These are the same points whose values are presented in Table 2.

FIG. 6

Comparison of tire imports from infested countries and extent of suitable habitat. Tire imports from infested countries compared to extent of niche in the 4–10 model agreement range. Not labeled individually within the cluster of points in the dotted shape are Germany, Russia, Nepal, Romania, United Kingdom, Benin, Senegal, Pakistan, Guinea, Switzerland, Slovenia, Croatia, Bulgaria, Uganda, Luxembourg, Austria, Macedonia, Hungary, Burkina Faso, Ireland, Zambia, and Malawi.