Understanding the processes by which species colonize and adapt to human habitats is particularly important in the case of disease-vectoring arthropods. The mosquito species Aedes aegypti, a major vector of dengue and yellow fever viruses, probably originated as a wild, zoophilic species in sub-Saharan Africa, where some populations still breed in tree holes in forested habitats. Many populations of the species, however, have evolved to thrive in human habitats and to bite humans. This includes some populations within Africa as well as almost all those outside Africa. It is not clear whether all domestic populations are genetically related and represent a single 'domestication' event, or whether association with human habitats has developed multiple times independently within the species. To test the hypotheses above, we screened 24 worldwide population samples of Ae. aegypti at 12 polymorphic microsatellite loci. We identified two distinct genetic clusters: one included all domestic populations outside of Africa and the other included both domestic and forest populations within Africa. This suggests that human association in Africa occurred independently from that in domestic populations across the rest of the world. Additionally, measures of genetic diversity support Ae. aegypti in Africa as the ancestral form of the species. Individuals from domestic populations outside Africa can reliably be assigned back to their population of origin, which will help determine the origins of new introductions of Ae. aegypti.

Mosquitoes, especially Aedes aegypti, are becoming important models for studying invasion biology. We characterized genetic variation at 12 microsatellite loci in 79 populations of Ae. aegypti, from 30 countries in six continents and used them to infer historical and modern patterns of invasion. Our results support the two subspecies Ae. aegypti formosus and Ae. aegypti aegypti as genetically distinct units. Ae. aegypti aegypti populations outside Africa are derived from ancestral African populations and are monophyletic. The two subspecies co-occur in both East Africa (Kenya) and West Africa (Senegal). In rural/forest settings (Rabai District of Kenya) the two subspecies remain genetically distinct whereas in urban settings they introgress freely. Populations outside Africa are highly genetically structured likely due to a combination of recent founder effects, discrete discontinuous habitats, and low migration rates. Ancestral populations in sub-Saharan Africa are less genetically structured, as are the populations in Asia. Introduction of Ae. aegypti to the New World coinciding with trans-Atlantic shipping in the 16th to 18th Centuries was followed by its introduction to Asia in the late 19th Century from the New World or from now extinct populations in the Mediterranean Basin. Aedes mascarensis is a genetically distinct sister species to Ae. aegypti s.l.. This study provides a reference database of genetic diversity that can be used to determine the likely origin of new introductions that occur regularly for this invasive species. The genetic uniqueness of many populations and regions has important implications for attempts to control Ae. aegypti, especially for methods using genetic modification of populations.

Aedes aegypti (L.) and Aedes albopictus (Skuse) were collected with aspirators from Mae Sot, Nakhon Sawan, Nakhon Ratchasima, Surat Thani, and Phatthalung study sites in Thailand from July 2003 though April 2004. The sandwich-B enzyme-linked immunosorbent assay was used to analyze 1,021 blood-fed specimens. Ae. aegypti almost exclusively fed on humans (99%, 658/664) in single host species, and 97% (86/88) of multiple-host bloodmeals included at least one human host. A low frequency of other hosts, including bovine, swine, cat, rat, and chicken were detected, but they represented <1% of bloodmeals. An even higher percentage of human feeding was detected in Ae. albopictus. Hosts of Ae. albopictus collected from sites in southern Thailand were entirely human (100%, n = 105) from both single and mixed meals. In the small number of double-host meals from Ae. albopictus, we detected 3.8% as swine-human and <1% from dog-human and cat-human. Forage ratios for Ae. aegypti indicated that human, dog, and swine were preferred hosts in order of preference. In contrast, bovine and chicken were avoided hosts for this species in Thailand.

We studied the effects of male Aedes aegypti age, body size, and density on mating success under laboratory and field conditions. Older males under field conditions transferred the greatest number of sperm to females (1,152 by 1-day-old males to 1,892 sperm by 10-day-old males). Larger males inseminated females with more sperm than smaller ones. Male age, female body size, and density also influenced male mating success. Larger females successfully mated with males more often than smaller females, especially with older males (> 25 days old). Female insemination rates in small high-density laboratory cages (0.009 m(3)) were artificially high (81.6-98.7%) compared with rates (65.4-84.6%) in large low-density field cages (9 m(3)). This is the first study to systematically evaluate the effect of Ae. aegypti male body size and age on sperm transfer to females and the first one to evaluate the mating performance of males in a field setting.

Dengue viruses (DENV) are characterized by extensive genetic diversity and can be organized in multiple, genetically distinct lineages that arise and die out on a regular basis in regions where dengue is endemic. A fundamental question for understanding DENV evolution is the relative extent to which stochastic processes (genetic drift) and natural selection acting on fitness differences among lineages contribute to lineage diversity and turnover. Here, we used a set of recently collected and archived lowpassage DENV-1 isolates from Thailand to examine the role of mosquito vector-virus interactions in DENV evolution. By comparing the ability of 23 viruses isolated on different dates between 1985 and 2009 to be transmitted by a present-day Aedes aegypti population from Thailand, we found that a major clade replacement event in the mid-1990s was associated with virus isolates exhibiting increased titers in the vector's hemocoel, which is predicted to result in a higher probability of transmission. This finding is consistent with the hypothesis that selection for enhanced transmission by mosquitoes is a possible mechanism underlying major DENV clade replacement events. There was significant variation in transmission potential among isolates within each clade, indicating that in addition to vector-driven selection, other evolutionary forces act to maintain viral genetic diversity. We conclude that occasional adaptive processes involving the mosquito vector can drive major DENV lineage replacement events. W orldwide, dengue viruses (DENV) are the most important mosquito-borne viral pathogens of humans. The four antigenically distinct DENV serotypes (DENV-1 to -4) cause a broad spectrum of clinical manifestations. An estimated 50 million people experience dengue illness each year, approximately 500,000 of which are associated with severe, life-threatening disease (18). In addition, a significant portion of infections can be inapparent and thus go undetected by surveillance programs (15). Despite the large disease burden imposed by dengue on the human population, there is currently no commercially available DENV vaccine or antiviral therapy (46). In regions where dengue is endemic and multiple serotypes cocirculate, DENV epidemiological dynamics are characterized by complex oscillations in incidence and serotype prevalence (6,32,43). A variety of ecological (10, 24) and immunological factors (1, 36) are thought to govern these complex spatiotemporal dynamics. There is also compelling evidence for the influence of virological factors in disease incidence and severity (reviewed in reference 37). DENV are single-stranded, positive-sense RNA viruses of the genus Flavivirus (family Flaviviridae) with extensive genetic diversity (21). Each serotype can be divided into large, genetically diverse phylogenetic clusters, which, in turn, consist of multiple, distinct lineages (22). Here, we use the terms clade and lineage interchangeably. In the last 2 decades, in-depth phylogenetic analyses have significantly improved understandi...