Understanding Anopheles Diversity in Southeast Asia and Its Applications for Malaria Control

The need to understand diversity in Anopheles mosquitoes to win the fight against malaria first became apparent with the paradox of ‘anophelism without malaria’, as it became evident that there is a vast diversity of Anopheles species and that not all species transmit malaria [1]. For example, in Europe it was eventually deduced that the mosquito Anopheles maculipennis existed as a species complex comprising several species that differed in their breeding, feeding and resting habitats, which resulted not only in differences in malaria epidemiology but also the success or failure of malaria control efforts [2]. This realisation resulted in countless studies around the world to distinguish and characterise Anopheles species, often using molecular or chromosomal characters in the absence of reliable morphological characters [3-4]. Such studies have played an invaluable role in improving malaria control and have, in turn, revealed another layer of complexity. This is exemplified most clearly in the Anopheles gambiae Complex, which includes several important African malaria vectors. Taxa within the An. gambiae Complex can exist as recently diverged species such as An. gambiae and An. arabiensis, which still have the potential to exchange genes [5]; as incipient species such as the S and M molecular forms, or as genetically divergent locally adapted forms, e.g. adapted to forest or savannah [6]. Recent genomic studies of the An. gambiae Complex are revealing patterns of differential divergence and introgression across the genome between species [7-8]; such phenomena are likely to further complicate the definition of species boundaries within Anopheles complexes. Differences in characteristics relevant to malaria control may be present at even the subspecific level (e.g. larval habitat and insecticide resistance both within and between the S and M