Simple indices provide insight to climate attributes delineating the geographic range of Aedes albopictus (Diptera: Culicidae) prior to worldwide invasion

Abstract

Aedes albopictus (Skuse) has expanded its distribution worldwide during the past decades. Despite attempts to explain and predict its geographic occurrence, analyses of the distribution of Ae. albopictus in the context of broad climatic regions (biomes) has not been performed. We analyzed climate conditions at its distribution sites in the range before the worldwide invasions (from the easternmost Hawaii through westernmost Madagascar) by using thermal and aridity-humidity indices descriptive of major biomes. A significant advantage of this approach is that it uses simple indices that are clearly related to the population dynamics of Ae. albopictus. Although it has been regarded as a forest species preferring humid climate, in areas with significant human habitation, the distribution sites extended from the per-humid, rain-forest zone to the semi-arid, steppe zone. This pattern was common from the tropics through the temperate zone. There was no seasonal discordance between temperature and precipitation; at sites where winter (monthly means <10°C) prevents Ae. albopictus reproduction, precipitation was concentrated in warm months (>10°C) under the Asian summer monsoon. Absence of the species in northern and eastern coastal Australia and eastern coastal Africa was not attributable solely to climate conditions. However, Asia west of the summer monsoon range was climatically unsuitable due to low precipitation throughout the year or in warm months favorable to reproduction (concentration of precipitation in winter). We hypothesized that Ae. albopictus originated in continental Asia under the monsoon climate with distinct dry seasons and hot, wet summer enabling rapid population growth.