Dating the origin and spread of specialization on human hosts in Aedes aegypti mosquitoes

Environmental heterogeneity across an urban gradient influences detritus and nutrients within artificial containers and their associated vector Aedes sp. larvae in San Juan, Puerto Rico

Detrital inputs from the surrounding terrestrial environment provide essential nutrients that sustain mosquito populations in aquatic containers. The larvae of Aedes aegypti (L.), an anthropophilic invasive vector species, often develop in artificial habitats in urban areas but little is known about how that environment shapes their life history or phenotypic traits. We hypothesized that container detritus, nutrients, and larval interspecific competition with the endemic mosquito, Aedes mediovittatus (Coquillett), would vary along an urban gradient in the San Juan Metropolitan Area in Puerto Rico. We also hypothesized that fine-scale variations within a 200 m buffer of the container environment would alter Ae. aegypti larval nutrients, density, and biomass. We sampled mosquito larvae, container detritus, and suspended particulate organic matter in 44 locations and characterized the surrounding environment in terms of land cover, land use, and vegetation α diversity. We show that container detritus and nutrients are influenced by fine-scale environmental variations environment, affecting Ae. aegypti and Ae. mediovittatus larvae phenotypic traits and nutrient composition. Aedes aegypti was the dominant species in all samples across the urban gradient. We found a negative relationship between Ae. mediovittatus larval % carbon and vegetation cover in the surrounding environment, and a negative correlation between this species' larval C:N and suspended particulate organic matter C:N. These findings suggest a potential disadvantage in nutrient allocation that could affect its competitive ability in urban areas. We found smaller and less nitrogen enriched (δ¹⁵N) Ae. aegypti in containers surrounded by higher impervious cover. The implications of these findings on potential vector disease risk across urban gradients are discussed.

Genomics of urban adaptation and exaptation in mosquitoes and consequences for vectorial capacity

As urbanization accelerates around the world, mosquitoes that are capable of surviving and thriving in urban habitats increasingly spread mosquito-borne diseases. Across the >3500 known species of mosquitoes, only a few rapidly adapted to the novel (on an evolutionary timescale) urban environments. In this review, we highlight several emerging themes and testable hypotheses from recent literature. First, apparent urban adaptations can be roughly divided into newer adaptations arising in an urban context and exaptations - traits that evolved in a different context, before modern urbanization. Second, variants involved in urban adaptation are often partitioned among species complexes and cryptic lineages, and the history of gene flow-selection balance may be related to the evolution of compact genomic architectures that could facilitate rapid urban adaptation. Third, urban adaptation often has consequences for vectorial capacity - the ability of mosquitoes to serve as effective vectors of a particular pathogen - though the selective drivers and genetic mechanisms underlying these differences are incompletely understood. To fully understand urban adaptation in mosquitoes, we advocate for a coordinated effort to increase linkages between evolutionary ecology, population genomics, and medical entomology research. We discuss the two traits for which all three perspectives are the most developed - host preference and insecticide resistance - before reviewing several other less studied traits.

Exploring 97 Years of Aedes aegypti as the Vector for Dengue, Yellow Fever, Zika, and Chikungunya (Diptera: Culicidae): Scientometric Analysis

BACKGROUND

Aedes aegypti is an important vector that transmits dengue, Zika, chikungunya, and yellow fever viruses. Although research on Aedes aegypti has been conducted for decades, scientometric studies on Aedes aegypti are scarce, are limited to regions, and cover short periods. Thus, there is still a knowledge gap in the current trend, research focuses and directions, leading authors and collaboration, journal and citation impacts, countries, and worldwide collaborations.

OBJECTIVE

The objectives of the study are to investigate the research trend, focus and directions, citation impact, leading authors and collaboration, journals, and countries of the published works on Aedes aegypti to inform the current knowledge gaps and future direction of the control of the vector.

METHODS

In this study, we searched the Scopus database for articles on Aedes aegypti published from the year 1927 until April 5th, 2024, and included articles, reviews, books, and book chapters that were written in English. A total of 16,247 articles in 160 journals with 481,479 citations were included. Inconsistencies in authors' names were checked and cleaned using OpenRefine. The data were grouped into 4 periods; years 1927-1999, 2000-2009, 2010-2019, and 2020-2023. The relative growth rate and doubling time of publications were calculated. The analysis was conducted using VOSviewer, R bibliometrics, and citeSpace.

RESULTS

The overall RGR was 0.1. Doubling time increased from 9.3 in 1978-1998 to 12.1 in 2000-2009. The main research clusters were "using Wolbachia," "Dengue Zika," "worldwide diversity," "community support," "larvicidal activity," "mosquito genotype-dependent," and "sterile insect technique." Journal of Medical Entomology was the leading journal (758/16,247, 4.7%). The most cited articles were authored by Halstead SB and team in Science (N=1355) and Kraemer MU and team in eLife (N=1324). The United States (5806/23,538, 24.7%) and Brazil (2035/23,538, 8.6%) were the top countries. Gubler DJ was the top co-cited author (n=2892) from 2000 to 2019. The co-cited author cluster patterns informed the significant specialty research on Aedes aegypti across time. Authors from various specialized research fields tended to collaborate across countries, especially neighboring countries. Countries with more research funding on the study of Aedes aegypti published more papers.

CONCLUSIONS

Researchers or entomologists could understand the current knowledge gap on Aedes aegypti and plan for future research pathways. This study contributed to the public health stakeholders in improving the vector control interventions and elucidated the extent of research subject areas.

Demographic History, Genetic Load, and the Efficacy of Selection in the Globally Invasive Mosquito Aedes aegypti

Aedes aegypti is the main vector species of yellow fever, dengue, Zika, and chikungunya. The species is originally from Africa but has experienced a spectacular expansion in its geographic range to a large swath of the world, and the demographic effects of which have remained largely understudied. In this report, we examine whole-genome sequences from six countries in Africa, North America, and South America to investigate the demographic history of the spread of A. aegypti into the Americas and its impact on genomic diversity and deleterious genetic load. In the Americas, we observe patterns of strong population structure consistent with relatively low (but probably nonzero) levels of gene flow but occasional long-range dispersal and/or recolonization events. We also find evidence that the colonization of the Americas has resulted in introduction bottlenecks. However, while each sampling location shows evidence of a past population contraction and subsequent recovery, our results suggest that the bottlenecks in America have led to a reduction in genetic diversity of only ∼35% relative to African populations, and the American samples have retained high levels of genetic diversity (expected heterozygosity of ∼0.02 at synonymous sites). We additionally find that American populations of aegypti have experienced only a minor reduction in the efficacy of selection, with evidence for both an accumulation of deleterious alleles and some purging of strongly deleterious alleles. These results exemplify how an invasive species can expand its range with remarkable genetic resilience in the face of strong eradication pressure.

Adaptive genomic signatures of globally invasive populations of the yellow fever mosquito Aedes aegypti

In the arboviral vector Aedes aegypti, adaptation to anthropogenic environments has led to a major evolutionary shift separating the domestic Aedes aegypti aegypti (Aaa) ecotype from the wild Aedes aegypti formosus (Aaf) ecotype. Aaa mosquitoes are distributed globally and have higher vectorial capacity than Aaf, which remained in Africa. Despite the evolutionary and epidemiological relevance of this separation, inconsistent morphological data and a complex population structure have hindered the identification of genomic signals distinguishing the two ecotypes. Here we assessed the correspondence between the geographic distribution, population structure and genome-wide selection of 511 Aaf and 123 Aaa specimens and report adaptive signals in 186 genes that we call Aaa molecular signatures. Our results indicate that Aaa molecular signatures arose from standing variation associated with extensive ancestral polymorphisms in Aaf populations and have been co-opted for self-domestication through genomic and functional redundancy and local adaptation. Overall, we show that the behavioural shift of Ae. aegypti mosquitoes to live in association with humans relied on the fine regulation of chemosensory, neuronal and metabolic functions, as seen in the domestication processes of rabbits and silkworms. Our results also provide a foundation for the investigation of new genic targets for the control of Ae. aegypti populations.

Evolutionary consequences of long-distance dispersal in mosquitoes

Long-distance dispersal (LDD) provides a means for mosquitoes to invade new regions and spread adaptive alleles, including those conferring insecticide resistance. Most LDD takes place on human transport vessels and will typically be rarer and more directionally constrained than active flight but can connect populations and regions that are otherwise mutually inaccessible. These features make LDD worthy of specific consideration in mosquito research. This paper reviews recent evolutionary research on LDD and its consequences for mosquito populations and mosquito control. LDD is the main source of mosquito range expansions, and genomic methods can now trace the origins of new invasions to specific towns or cities. Genomic methods can also give a rough indication of the number of invaders, which if very small may lead to the stochastic loss of advantageous alleles during invasion bottlenecks. Once invasions are established, LDD spreads adaptive alleles between populations. Emerging insights into insecticide resistance evolution indicate that LDD has repeatedly spread resistance mutations across global species ranges, but these broad patterns are convoluted by two other evolutionary processes: parallel adaptation at the same gene or gene cluster and polygenic adaptation at different genes in different populations. Together, these processes have produced patterns of similarity and dissimilarity at resistance genes that are decoupled from geographical distance. LDD within cities is less well studied but is important for planning and evaluating local control efforts. Urban investigations of LDD may help identify areas experiencing weaker selection pressures from insecticides and isolated areas to target for control.

Multiple blood feeding bouts in mosquitoes allow for prolonged survival and are predicted to increase viral transmission during dry periods

Dry conditions increase blood feeding in mosquitoes, but it is unknown if dehydration-induced bloodmeals are increased beyond what is necessary for reproduction. In this study, we investigated the role of dehydration in secondary blood feeding behaviors of mosquitoes. Following an initial bloodmeal, prolonged exposure to dry conditions increased secondary blood feeding in mosquitoes by nearly two-fold, and chronic blood feeding allowed mosquitoes to survive up to 20 days without access to water. Exposure to desiccating conditions following a bloodmeal resulted in increased activity, decreased sleep levels, and prompted a return of CO2 sensing before egg deposition. Increased blood feeding and higher survival during dry periods are predicted to increase pathogen transmission, allowing for a rapid rebound in mosquito populations when favorable conditions return. Overall, these results solidify our understanding of how dry periods impact mosquito blood feeding and the role that mosquito dehydration contributes to pathogen transmission dynamics.

Ancient origin of an urban underground mosquito

Understanding how life is adapting to urban environments represents an important challenge in evolutionary biology. Here we investigate a widely cited example of urban adaptation, Culex pipiens form molestus, also known as the London Underground Mosquito. Population genomic analysis of ~350 contemporary and historical samples counter the popular hypothesis that molestus originated belowground in London less than 200 years ago. Instead, we show that molestus first adapted to human environments aboveground in the Middle East over the course of >1000 years, likely in concert with the rise of agricultural civilizations. Our results highlight the role of early human society in priming taxa for contemporary urban evolution and have important implications for understanding arbovirus transmission.

Intra-species quantification reveals differences in activity and sleep levels in the yellow fever mosquito, Aedes aegypti

Aedes aegypti is an important mosquito vector of human disease with a wide distribution across the globe. Climatic conditions and ecological pressure drive differences in the biology of several populations of this mosquito species, including blood-feeding behaviour and vector competence. However, no study has compared activity and/or sleep among different populations/lineages of Ae. aegypti. Having recently established sleep-like states in three mosquito species with observable differences in timing and amount of sleep among species, we investigated differences in activity and sleep levels among 17 Ae. aegypti lines drawn from both its native range in Africa and its invasive range across the global tropics. Activity monitoring indicates that all the lines show consistent diurnal activity, but significant differences in activity level, sleep amount, number of sleep bouts and bout duration were observed among the lines. The variation in day activity was associated with differences in host preference and ancestry for the lineages collected in Africa. This study provides evidence that the diurnal sleep and activity profiles for Ae. aegypti are consistent, but there are significant population differences for Ae. aegypti sleep and activity levels and interactions with host species may significantly impact mosquito activity.

Livestock-vector interaction using volatile organic metabolites

Biological interaction between two organisms living together in a given habitat is essential for healthy ecosystem functionality, got complexity, and exerts an arms race between the interacting organisms. Some vectors are exclusively blood feeders, and others supplement their diet with plant nectar. The feeding dynamics may determine their olfactory system complexity. Arthropod vectors that interact with livestock rely mainly on olfaction. Livestock odor profile is a complex trait and depends on host genetics, microbes, diet, and health status, which highlights its dynamic nature. Furthermore, volatile metabolites are shared between host animals, which exert its own challenge for vectors to find their preferred host. Elucidating the underlying host chemodiversity, especially signature scents, neuroethological mechanism of discrimination of preferred/unpreferred host from plethora of coexisting host is crucial to understand evolution and adaptation in vector-livestock interaction.

The role of vector population variation and climate in Zika virus transmission patterns in Africa: a modelling study

BACKGROUND

Zika virus (ZIKV) outbreaks have raised major global health concerns recently, yet reported outbreaks are rare in Africa, where ZIKV was first discovered. Recent studies on Aedes aegypti, the mosquito that transmits ZIKV, might explain this phenomenon. The Ae aegypti subspecies present in Africa shows lower preference for biting humans and reduced susceptibility to ZIKV infection compared with the subspecies distributed outside Africa. Alternatively, climate might strongly limit transmission as it affects multiple traits of ZIKV and the mosquito vector.

METHODS

We used a modelling approach informed by empirical data to assess ZIKV transmission risk across Africa. We fitted the model using data from laboratory experiments, and validated the model by comparing predicted transmission suitability with seroprevalence surveys conducted across Africa. Additionally, we used mosquito genetic and climate-based projections to map future ZIKV outbreak risk at 59 urban centres in Africa.

FINDINGS

The model predictions partially and significantly explain historical patterns of ZIKV circulation in Africa (accounting for 46% of the variation in seroprevalence surveys). Mosquito population genetics influence transmission more strongly than climate through two mechanisms: vector-host contact and vector competence. If climate and mosquito genetic population projections are accurate and there are no other changes to drivers of Zika virus transmission in Africa, we predict that approximately three-quarters of the most populous African cities will be suitable for ZIKV outbreaks by the end of the century.

INTERPRETATION

Both population-level genomic variation in mosquitoes and climate contribute to the lack of ZIKV outbreaks in Africa. Given the importance of mosquito genetics in driving this pattern, local genomic surveillance of mosquito populations would help predict outbreaks in vulnerable communities. This will become increasingly important with population growth, urbanisation, and climate change.

FUNDING

Princeton University, French Government's Investissement d'Avenir and France 2030 programmes, MSDAVENIR, and US National Institutes of Health.

Assessing the ecological patterns of Aedes aegypti in areas with high arboviral risks in the large city of Abidjan, Côte d'Ivoire

BACKGROUND

The city of Abidjan, Côte d'Ivoire has increasingly faced multiple outbreaks of Aedes mosquito-borne arboviral diseases (e.g., dengue (DEN) and yellow fever (YF)) during the recent years, 2017-2023. Thus, we assessed and compared Aedes aegypti larval and adult population dynamics and Stegomyia indices in four urbanized areas with differential arboviral incidences in Abidjan, Côte d'Ivoire.

METHODS

From August 2019 to July 2020, we sampled Aedes mosquito immatures (larvae and pupae), adults and breeding habitats in Anono and Gbagba with high arboviral incidences and Ayakro and Entente with low arboviral incidences in the Abidjan city, using standardized methods. Sampling was conducted in the peridomestic and domestic (indoors and outdoors) premises during short dry season (SDS), short rainy season (SRS), long dry season (LDS) and long rainy season (LRS). The abdomens and ovaries of Ae. aegypti females were examined to determine their blood-meal and parity statuses. Stegomyia indices (container index: CI, house index: HI and Breteau index: BI), blood-meal status and parity rates were compared by study sites and seasons and with the World Health Organization (WHO)-established epidemic thresholds.

RESULTS

Overall, Aedes and arboviral risk indices were high and similar between the four study areas. In total, 86,796 mosquitoes were identified and dominated by Ae. aegypti species (97.14%, 84,317/86,796). The most productive larval breeding habitats were tires, discarded containers and water storage containers. CI, HI, and BI in Anono (22.4%, 33.5% and 89.5), Ayakro (23.1%, 43.8% and 91.0), Entente (15.9%, 24.8% and 48.5) and Gbagba (23.3%, 43.0% and 102.0) were high in the respective study sites. Stegomyia indices were higher than the WHO-established epidemic thresholds during any seasons for DEN, and LRS and SRS for YF. The numbers of Ae. aegypti-positive breeding sites were higher in the domestic premises (68.0%, 900/1,324) than in the peridomestic premises (32.0%, 424/1,324). In the domestic premises, Ae. aegypti-positive breeding sites (94.6%, 851/4,360) and adult individuals (93.4%, 856/916) were mostly found outdoors of houses. Aedes aegypti adult females were mostly unfed (51.3%, 203/396), followed by blood-fed (22.2%, 88/396), gravid (13.9%, 55/396) and half-gravid (12.6%, 50/396), and had parity rate of 49.7% (197/396) that was comparable between the study sites.

CONCLUSIONS

The city of Abidjan, Côte d'Ivoire is highly infested with Ae. aegypti which showed comparable ecological patterns across study sites and seasons. Thus, the local communities are exposed to high and permanent risks of transmission of DEN and YF viruses that were above the WHO-established epidemic thresholds throughout. The results provide a baseline for future vector studies needed to further characterize the observed patterns of local Ae. aegypti abundances and behaviors, and risks of transmission of these arboviruses. Community-based larval source management of identified productive containers might reduce Ae. aegypti numbers and risks of transmission of Aedes-borne arboviruses in Abidjan, and other sub-Saharan African cities.

Dengue is a product of the environment: an approach to the impacts of the environment on the Aedes aegypti mosquito and disease cases

Dengue is an arbovirus infection whose etiologic agent is transmitted by the Aedes aegypti mosquito. Since the early 1980s, when the circulation of the dengue virus (DENV) was confirmed in Brazil, the disease has become a growing multifactorial public health problem. This article presented the main factors that have contributed to the frequent dengue epidemics in recent years, such as the behavior of the vector, climate change, and social, political, and economic aspects. The intersection between these different factors in the dynamics of the disease is highlighted, including the increase in the mosquito population due to higher temperatures and rainy periods, as well as the influence of socioeconomic conditions on the incidence of dengue. Some mosquito control strategies are also addressed, including the use of innovative technologies such as drones and the Wolbachia bacterium, as well as the hope represented by the dengue vaccine. Nevertheless, the need for integrated and effective public policies to reduce social inequalities and the impacts of climate change on the spread of dengue is emphasized.

The Risk of Virus Emergence in South America: A Subtle Balance Between Increasingly Favorable Conditions and a Protective Environment

South American ecosystems host astonishing biodiversity, with potentially great richness in viruses. However, these ecosystems have not yet been the source of any widespread, epidemic viruses. Here we explore a set of putative causes that may explain this apparent paradox. We discuss that human presence in South America is recent, beginning around 14,000 years ago; that few domestications of native species have occurred; and that successive immigration events associated with Old World virus introductions reduced the likelihood of spillovers and adaptation of local viruses into humans. Also, the diversity and ecological characteristics of vertebrate hosts might serve as protective factors. Moreover, although forest areas remained well preserved until recently, current brutal, sudden, and large-scale clear cuts through the forest have resulted in nearly no ecotones, which are essential for creating an adaptive gradient of microbes, hosts, and vectors. This may be temporarily preventing virus emergence. Nevertheless, the mid-term effect of such drastic changes in habitats and landscapes, coupled with explosive urbanization and climate changes, must not be overlooked by health authorities.

Effects of climate change and human activities on vector-borne diseases

Vector-borne diseases are transmitted by haematophagous arthropods (for example, mosquitoes, ticks and sandflies) to humans and wild and domestic animals, with the largest burden on global public health disproportionately affecting people in tropical and subtropical areas. Because vectors are ectothermic, climate and weather alterations (for example, temperature, rainfall and humidity) can affect their reproduction, survival, geographic distribution and, consequently, ability to transmit pathogens. However, the effects of climate change on vector-borne diseases can be multifaceted and complex, sometimes with ambiguous consequences. In this Review, we discuss the potential effects of climate change, weather and other anthropogenic factors, including land use, human mobility and behaviour, as possible contributors to the redistribution of vectors and spread of vector-borne diseases worldwide.

Multiple bouts of blood feeding in mosquitoes allow prolonged survival and are predicted to increase viral transmission during drought

Survival through periods of drought is critical for mosquitoes to reside in semi-arid regions with humans, but water sources may be limited. Previous studies have shown that dehydrated mosquitoes will increase blood feeding propensity, but how this would occur over extended dry periods is unknown. Following a bloodmeal, prolonged exposure to dry conditions increased secondary blood feeding in mosquitoes by nearly two-fold, and chronic blood feeding allowed mosquitoes to survive twenty days without access to water sources. This refeeding did not alter the number of eggs generated, suggesting this refeeding is for hydration and nutrient replenishment. Exposure to desiccating conditions following a bloodmeal resulted in increased activity, decreased sleep levels, and prompted a return of CO2 sensing before egg deposition. The increased blood feeding during the vitellogenic stage and higher survival during dry periods are predicted to increase pathogen transmission and explain the elevated levels of specific arbovirus cases during dry conditions. These results solidify our understanding of the role of dry periods on mosquito blood feeding and how mosquito dehydration contributes to vectorial capacity and disease transmission dynamics.

Robustness in population-structure and demographic-inference results derived from the Aedes aegypti genotyping chip and whole-genome sequencing data

The mosquito Aedes aegypti is the primary vector of many human arboviruses such as dengue, yellow fever, chikungunya, and Zika, which affect millions of people worldwide. Population genetic studies on this mosquito have been important in understanding its invasion pathways and success as a vector of human disease. The Axiom aegypti1 SNP chip was developed from a sample of geographically diverse A. aegypti populations to facilitate genomic studies on this species. We evaluate the utility of the Axiom aegypti1 SNP chip for population genetics and compare it with a low-depth shotgun sequencing approach using mosquitoes from the native (Africa) and invasive ranges (outside Africa). These analyses indicate that results from the SNP chip are highly reproducible and have a higher sensitivity to capture alternative alleles than a low-coverage whole-genome sequencing approach. Although the SNP chip suffers from ascertainment bias, results from population structure, ancestry, demographic, and phylogenetic analyses using the SNP chip were congruent with those derived from low-coverage whole-genome sequencing, and consistent with previous reports on Africa and outside Africa populations using microsatellites. More importantly, we identified a subset of SNPs that can be reliably used to generate merged databases, opening the door to combined analyses. We conclude that the Axiom aegypti1 SNP chip is a convenient, more accurate, low-cost alternative to low-depth whole-genome sequencing for population genetic studies of A. aegypti that do not rely on full allelic frequency spectra. Whole-genome sequencing and SNP chip data can be easily merged, extending the usefulness of both approaches.

Humidity and temperature preference in two Neotropical species of sand flies

BACKGROUND

Arthropods vector a multitude of human disease-causing organisms, and their geographic ranges are shifting rapidly in response to changing climatic conditions. This is, in turn, altering the landscape of disease risk for human populations that are brought into novel contact with the vectors and the diseases they carry. Sand flies in the genera Lutzomyia and Pintomyia are vectors of serious disease-causing agents such as Leishmania (the etiological agent of leishmaniasis) and may be expanding their range in the face of climate change. Understanding the climatic conditions that vector species both tolerate physiologically and prefer behaviorally is critical to predicting the direction and magnitude of range expansions and the resulting impacts on human health. Temperature and humidity are key factors that determine the geographic extent of many arthropods, including vector species.

METHODS

We characterized the habitat of two species of sand flies, Lutzomyia longipalpis and Pintomyia evansi. Additionally, we studied two behavioral factors of thermal fitness-thermal and humidity preference in two species of sand flies alongside a key aspect of physiological tolerance-desiccation resistance.

RESULTS

We found that Lu. longipalpis is found at cooler and drier conditions than Pi. evansi. Our results also show significant interspecific differences in both behavioral traits, with Pi. evansi preferring warmer, more humid conditions than Lu. longipalpis. Finally, we found that Lu. longipalpis shows greater tolerance to extreme low humidity, and that this is especially pronounced in males of the species.

CONCLUSIONS

Taken together, our results suggest that temperature and humidity conditions are key aspects of the climatic niche of Lutzomyia and Pintomyia sand flies and underscore the value of integrative studies of climatic tolerance and preference in vector biology.

Host preference patterns in domestic and wild settings: Insights into Anopheles feeding behavior

The adaptation of Anopheles malaria vectors to domestic settings is directly linked to their ability to feed on humans. The strength of this species-habitat association is unequal across the species within the genus, with the major vectors being particularly dependent on humans. However, our understanding of how blood-feeding behavior interacts with and adapts to environmental settings, including the presence of humans, remains limited. Using a field-based approach, we first investigated Anopheles community structure and feeding behavior patterns in domestic and sylvatic settings in La Lopé National Park in Gabon, Central Africa. We characterized the preference indices using a dual-host choice sampling approach across mosquito species, habitats, and seasons. We then quantified the plastic biting behavior of mosquito species in each habitat. We collected individuals from 16 Anopheles species that exhibited significant differences in species composition and abundance between sylvatic and domestic settings. The host-seeking behavior also varied among the seven most abundant species. The general attractiveness to each host, human or animal, remained relatively constant for each species, but with significant variations between habitats across species. These variations, to more generalist and to more anthropophilic behavior, were related to seasonal changes and distance from the village, respectively. Finally, we pointed out that the host choice of major malaria vectors changed in the absence of humans, revealing a plastic feeding behavior of these species. This study highlights the effect of humans on Anopheles distribution and feeding evolution. The characterization of feeding behavior in wild and domestic settings provides opportunities to better understand the interplay between genetic determinants of host preference and ecological factors. Our findings suggest that protected areas may offer alternative thriving conditions to major malaria vectors.

Thermal tolerance of mosquito eggs is associated with urban adaptation and human interactions

Climate change is expected to profoundly affect mosquito distributions and their ability to serve as vectors for disease, specifically with the anticipated increase in heat waves. The rising temperature and frequent heat waves can accelerate mosquito life cycles, facilitating higher disease transmission. Conversely, higher temperatures could increase mosquito mortality as a negative consequence. Warmer temperatures are associated with increased human density, suggesting a need for anthropophilic mosquitoes to adapt to be more hardy to heat stress. Mosquito eggs provide an opportunity to study the biological impact of climate warming as this stage is stationary and must tolerate temperatures at the site of female oviposition. As such, egg thermotolerance is critical for survival in a specific habitat. In nature, Aedes mosquitoes exhibit different behavioral phenotypes, where specific populations prefer depositing eggs in tree holes and prefer feeding non-human vertebrates. In contrast, others, particularly human-biting specialists, favor laying eggs in artificial containers near human dwellings. This study examined the thermotolerance of eggs, along with adult stages, for Aedes aegypti and Ae. albopictus lineages associated with known ancestry and shifts in their relationship with humans. Mosquitoes collected from areas with higher human population density, displaying increased human preference, and having a human-associated ancestry profile have increased egg viability following high-temperature stress. Unlike eggs, thermal tolerance among adults showed no significant correlation based on the area of collection or human-associated ancestry. This study highlights that the egg stage is likely critical to mosquito survival when associated with humans and needs to be accounted when predicting future mosquito distribution.

Finding divergent sequences of homomorphic sex chromosomes via diploidized nanopore-based assembly from a single male

Although homomorphic sex chromosomes can have non-recombining regions with elevated sequence divergence between its complements, such divergence signals can be difficult to detect bioinformatically. If found in genomes of e.g. insect pests, these sequences could be targeted by the engineered genetic sexing and control systems. Here, we report an approach that can leverage long-read nanopore sequencing of a single XY male to identify divergent regions of homomorphic sex chromosomes. Long-read data are used for de novo genome assembly that is diploidized in a way that maximizes sex-specific differences between its haploid complements. We show that the correct assembly phasing is supported by the mapping of nanopore reads from the male's haploid Y-bearing sperm cells. The approach revealed a highly divergent region (HDR) near the centromere of the homomorphic sex chromosome of Aedes aegypti, the most important arboviral vector, for which there is a great interest in creating new genetic control tools. HDR is located ~5Mb downstream of the known male-determining locus on chromosome 1 and is significantly enriched for ovary-biased genes. While recombination in HDR ceased relatively recently (~1.4 MYA), HDR gametologs have divergent exons and introns of protein coding genes, and most lncRNA genes became X-specific. Megabases of previously invisible sex-linked sequences provide new putative targets for engineering the genetic systems to control this deadly mosquito. Broadly, our approach expands the toolbox for studying cryptic structure of sex chromosomes.

Aedes albopictus is present in the lowlands of southern Zambia

Identifying the current geographic range of disease vectors is a critical first step towards determining effective mechanisms for controlling and potentially eradicating them. This is particularly true given that historical vector ranges may expand due to changing climates and human activity. The Aedes subgenus Stegomyia contains over 100 species, and among them, Ae. aegypti and Ae. albopictus mosquitoes represent the largest concern for public health, spreading dengue, chikungunya, and zika viruses. While Ae. aegypti has been observed in the country of Zambia for decades, Ae. albopictus has not. In 2015 we sampled four urban and three rural areas in Zambia for Aedes species. Using DNA barcoding, we confirmed the presence of immature and adult Ae. albopictus at two sites: Siavonga and Livingstone. These genotypes seem most closely related to specimens previously collected in Mozambique based on mtDNA barcoding. We resampled Siavonga and Livingstone sites in 2019, again observing immature and adult Ae. albopictus at both sites. Relative Ae. albopictus frequencies were similar between sites, with the exception of immature life stages, which were higher in Siavonga than in Livingstone in 2019. While Ae. albopictus frequencies did not vary through time in Livingstone, both immature and adult frequencies increased through time in Siavonga. This report serves to document the presence of Ae. albopictus in Zambia, which will contribute to understanding the potential public health implications of this disease vector in southern Africa.

The spread of Aedes albopictus (Diptera: Culicidae) in the islands of São Tomé and Príncipe

The mosquito Aedes albopictus (Diptera: Culicidae) is a vector species of the causal agents of Dengue, yellow fever, and Zika among other diseases pathogens. The species originated in Southeast Asia and has spread widely and rapidly in the last century. The species has been reported in localities from the Gulf of Guinea since the early 2000s, but systematic sampling has been scant. We sampled Ae. albopictus twice, in 2013 and 2023 across the altitudinal gradient in São Tomé and found that the species was present in all sampled years at altitudes up to 680 m. We also found some evidence of increases in proportional representation compared to Ae. aegypti over time. We report the presence of the species in Príncipe for the first time, suggesting that the range of Ae. albopictus is larger than previously thought. Finally, we use bioclimatic niche modeling to infer the potential range of Ae. albopictus and infer that the species has the potential to spread across a large portion of São Tomé and Príncipe. Our results suggest that Ae. albopictus has established itself as a resident species of the islands of the Gulf of Guinea and should be incorporated into the list of potential vectors that need to be surveyed and controlled.

Microsatellite-based analysis reveals Aedes aegypti populations in the Kingdom of Saudi Arabia result from colonization by both the ancestral African and the global domestic forms

The Aedes aegypti (Linnaeus, 1762) mosquito is the main vector of dengue, chikungunya and Zika and is well established today all over the world. The species comprises two forms: the ancestral form found throughout Africa and a global domestic form that spread to the rest of the tropics and subtropics. In Saudi Arabia, A. aegypti has been known in the southwest since 1956, and previous genetic studies clustered A. aegypti from Saudi Arabia with the global domestic form. The purpose of this study was to assess the genetic structure of A. aegypti in Saudi Arabia and determine their geographic origin. Genetic data for 17 microsatellites were collected for A. aegypti ranging from the southwestern highlands of Saudi Arabia on the border of Yemen to the north-west in Madinah region as well as from Thailand and Uganda populations (as representatives of the ancestral African and global domestic forms, respectively). The low but significant level of genetic structuring in Saudi Arabia was consistent with long-distance dispersal capability possibly through road connectivity and human activities, that is, passive dispersal. There are two main genetic groupings in Saudi Arabia, one of which clusters with the Ugandan population and the other with the Thailand population with many Saudi Arabian individuals having mixed ancestry. The hypothesis of genetic admixture of the ancestral African and global domestic forms in Saudi Arabia was supported by approximate Bayesian computational analyses. The extent of admixture varied across Saudi Arabia. African ancestry was highest in the highland area of the Jazan region followed by the lowland Jazan and Sahil regions. Conversely, the western (Makkah, Jeddah and Madinah) and Najran populations corresponded to the global domesticated form. Given potential differences between the forms in transmission capability, ecology and behaviour, the findings here should be taken into account in vector control efforts in Saudi Arabia.

Urbanization and Water Containers Influence the Mosquito Community with Consequences for Aedes aegypti

We aimed to determine how the degree of urbanization in a Neotropical city influences Aedes aegypti (L.), a pantropical vector of urban yellow fever, dengue, Zika and Chikungunia, via other mosquito species, whether they are competitors or predators, native to the area or invasive. We conducted experiments twice a month during one year in the city of Kourou, French Guiana, on three sites characterized by increasing percentages of imperviousness (i.e., 0.65%, 33.80% and 86.60%). These sites were located in a ≈5 ha forest fragment, a residential area with gardens, and in the older part of the city, respectively, and correspond to slightly, moderately and highly urbanized sites. There, we monitored twice a month during one year a total of 108 mosquito communities inhabiting four types of containers (i.e., a tank bromeliad, dry stumps of bamboo, ovitraps and car tires) installed in a random block design. In the tanks of the bromeliad, likely due to the acidity of the water, the immatures of native mosquito species prevailed, particularly Wyeomyia pertinans (Williston) in the slightly urbanized site. The general pattern was very similar in the three other types of containers where Limatus durhamii Théobald dominated in the slightly urbanized site, so that the abundance of Ae. aegypti immatures was low compared to those of native species. Yet, Ae. aegypti strongly dominated in the two more urbanized sites. These findings open up perspectives for vector management, including the conservation and/or the augmentation of natural enemies through modifications to landscape features.

Metagenomic Analysis of Viromes of Aedes Mosquitoes across India

Metagenomic analysis of Aedes aegypti and Ae. albopictus mosquitoes from diverse geographical regions of India revealed the presence of several insect viruses of human interest. Most abundant reads found in Ae. aegypti mosquitoes were of Phasi Charoen-like virus (PCLV), Choristoneura fumiferana granulovirus (CfGV), Cell fusing agent virus (CFAV), and Wenzhou sobemo-like virus 4 (WSLV4), whereas WSLV4 and CfGV constituted the highest percentage of reads in Ae. albopictus viromes. Other reads that were of low percentage included Hubei mosquito virus 2 (HMV2), Porcine astrovirus 4 (PAstV4), and Wild Boar astrovirus (WBAstV). PCLV and CFAV, which were found to be abundant in Ae. aegypti viromes were absent in Ae. albopictus viromes. Among the viromes analyzed, Ae. aegypti sampled from Pune showed the highest percentage (79.82%) of viral reads, while Ae. aegypti mosquitoes sampled from Dibrugarh showed the lowest percentage (3.47%). Shamonda orthobunyavirus (SHAV), African swine fever virus (ASFV), Aroa virus (AROAV), and Ilheus virus (ILHV), having the potential to infect vertebrates, including humans, were also detected in both mosquito species, albeit with low read numbers. Reads of gemykibivirus, avian retrovirus, bacteriophages, herpesviruses, and viruses infecting protozoans, algae, etc., were also detected in the mosquitoes. A high percentage of reads in the Ae. albopictus mosquito samples belonged to unclassified viruses and warrant further investigation. The data generated in the present work may not only lead to studies to explain the influence of these viruses on the replication and transmission of viruses of clinical importance but also to find applications as biocontrol agents against pathogenic viruses.

Mechanisms of Yellow Fever Transmission: Gleaning the Overlooked Records of Importance and Identifying Problems, Puzzles, Serious Issues, Surprises and Research Questions

In viral disease research, few diseases can compete with yellow fever for the volume of literature, historical significance, richness of the topics and the amount of strong interest among both scientists and laypersons. While the major foci of viral disease research shifted to other more pressing new diseases in recent decades, many critically important basic tasks still remain unfinished for yellow fever. Some of the examples include the mechanisms of transmission, the process leading to outbreak occurrence, environmental factors, dispersal, and viral persistence in nature. In this review, these subjects are analyzed in depth, based on information not only in old but in modern literatures, to fill in blanks and to update the current understanding on these topics. As a result, many valuable facts, ideas, and other types of information that complement the present knowledge were discovered. Very serious questions about the validity of the arbovirus concept and some research practices were also identified. The characteristics of YFV and its pattern of transmission that make this virus unique among viruses transmitted by Ae. aegypti were also explored. Another emphasis was identification of research questions. The discovery of a few historical surprises was an unexpected benefit.

Arbovirus surveillance in mosquitoes: Historical methods, emerging technologies, and challenges ahead

Arboviruses cause millions of infections each year; however, only limited options are available for treatment and pharmacological prevention. Mosquitoes are among the most important vectors for the transmission of several pathogens to humans. Despite advances, the sampling, viral detection, and control methods for these insects remain ineffective. Challenges arise with the increase in mosquito populations due to climate change, insecticide resistance, and human interference affecting natural habitats, which contribute to the increasing difficulty in controlling the spread of arboviruses. Therefore, prioritizing arbovirus surveillance is essential for effective epidemic preparedness. In this review, we offer a concise historical account of the discovery and monitoring of arboviruses in mosquitoes, from mosquito capture to viral detection. We then analyzed the advantages and limitations of these traditional methods. Furthermore, we investigated the potential of emerging technologies to address these limitations, including the implementation of next-generation sequencing, paper-based devices, spectroscopic detectors, and synthetic biosensors. We also provide perspectives on recurring issues and areas of interest such as insect-specific viruses.

Aedes albopictus is present in the lowlands of southern Zambia

Identifying the current geographic range of disease vectors is a critical first step towards determining effective mechanisms for controlling and potentially eradicating them. This is particularly true given that historical vector ranges may expand due to changing climates and human activity. The Aedes subgenus Stegomyia contains over 100 species, and among them, Ae. aegypti and Ae. albopictus mosquitoes represent the largest concern for public health, spreading dengue, chikungunya, and Zika viruses. While Ae. aegypti has been observed in the country of Zambia for decades, Ae. albopictus has not. In 2015 we sampled four urban and two rural areas in Zambia for Aedes species. Using DNA barcoding, we confirmed the presence of immature and adult Ae. albopictus at two rural sites: Siavonga and Livingstone. These genotypes seem most closely related to specimens previously collected in Mozambique based on CO1 sequence from mtDNA. We resampled Siavonga and Livingstone sites in 2019, again observing immature and adult Ae. albopictus at both sites. Relative Ae. albopictus frequencies were similar between sites, with the exception of immature life stages, which were higher in Siavonga than in Livingstone in 2019. While Ae. albopictus frequencies did not vary through time in Livingstone, both immature and adult frequencies increased through time in Siavonga. This report serves to document the presence of Ae. albopictus in Zambia, which will contribute to the process of determining the potential public health implications of this disease vector in Central Africa.

Exploring natural odour landscapes: A case study with implications for human-biting insects

The natural world is full of odours-blends of volatile chemicals emitted by potential sources of food, social partners, predators, and pathogens. Animals rely heavily on these signals for survival and reproduction. Yet we remain remarkably ignorant of the composition of the chemical world. How many compounds do natural odours typically contain? How often are those compounds shared across stimuli? What are the best statistical strategies for discrimination? Answering these questions will deliver crucial insight into how brains can most efficiently encode olfactory information. Here, we undertake the first large-scale survey of vertebrate body odours, a set of stimuli relevant to blood-feeding arthropods. We quantitatively characterize the odour of 64 vertebrate species (mostly mammals), representing 29 families and 13 orders. We confirm that these stimuli are complex blends of relatively common, shared compounds and show that they are much less likely to contain unique components than are floral odours-a finding with implications for olfactory coding in blood feeders and floral visitors. We also find that vertebrate body odours carry little phylogenetic information, yet show consistency within a species. Human odour is especially unique, even compared to the odour of other great apes. Finally, we use our newfound understanding of odour-space statistics to make specific predictions about olfactory coding, which align with known features of mosquito olfactory systems. Our work provides one of the first quantitative descriptions of a natural odour space and demonstrates how understanding the statistics of sensory environments can provide novel insight into sensory coding and evolution.

Dating the origin and spread of specialization on human hosts in Aedes aegypti mosquitoes

The globally invasive mosquito subspecies Aedes aegypti aegypti is an effective vector of human arboviruses, in part because it specializes in biting humans and breeding in human habitats. Recent work suggests that specialization first arose as an adaptation to long, hot dry seasons in the West African Sahel, where Ae. aegypti relies on human-stored water for breeding. Here, we use whole-genome cross-coalescent analysis to date the emergence of human-specialist populationsand thus further probe the climate hypothesis. Importantly, we take advantage of the known migration of specialists out of Africa during the Atlantic Slave Trade to calibrate the coalescent clock and thus obtain a more precise estimate of the older evolutionary event than would otherwise be possible. We find that human-specialist mosquitoes diverged rapidly from ecological generalists approximately 5000 years ago, at the end of the African Humid Period-a time when the Sahara dried and water stored by humans became a uniquely stable, aquatic niche in the Sahel. We also use population genomic analyses to date a previously observed influx of human-specialist alleles into major West African cities. The characteristic length of tracts of human-specialist ancestry present on a generalist genetic background in Kumasi and Ouagadougou suggests the change in behavior occurred during rapid urbanization over the last 20-40 years. Taken together, we show that the timing and ecological context of two previously observed shifts towards human biting in Ae. aegypti differ; climate was likely the original driver, but urbanization has become increasingly important in recent decades.