Spread of invasive Aedes albopictus and decline of resident Aedes aegypti in urban areas of Mayotte 2007-2010

The invasive Asian tiger mosquito, Aedes albopictus, has been established on the French overseas island of Mayotte in the Indian Ocean since 2007. Despite the presence of a resident population of Aedes aegypti, Ae. albopictus has expanded its presence in urban areas, in contrast to the pattern of invasion by this mosquito elsewhere in the world. We undertook a comparative study of the distribution and abundance of Ae. albopictus and Ae. aegypti populations between 2007 and 2010 in different types of urban landscapes to document the invasion process. Urban and suburban areas at five localities on Mayotte were selected and ten houses with mosquito-infested larval habitats on the property were located in each area. To calculate variables that might explain mosquito infestation, the areas around the houses selected were overlaid on maps with grid cells (each 25 x 25 m) and the areas inside grid cells were analyzed to define landscape characteristics (percentage of built on land and human density) that might be predictive of Ae. albopictus presence and abundance. The proportion of sites occupied by only Ae. albopictus and the relative abundance of this species relative to total Aedes larvae and pupae significantly increased between 2007 and 2010, in both urban and in rural areas. In the 2010 survey, the number of larval habitats occupied by Ae. aegypti in the sampled area decreased sharply compared to 2007. The proportion of land with paved or hard surfaces (roads, buildings, hereafter built-up area), the increase of urbanized areas between 2003 and 2008, and the density of human residents were all correlated with higher relative abundance of Ae. albopictus. The urban areas of Mayotte have significant amounts of vegetation even in the more densely populated areas, and this factor may have facilitated the invasion of Ae. albopictus by providing abundant adult resting sites. These findings are relevant for vector control strategies and forecasting the success of invasions of Ae. albopictus in urban areas in other countries.