The hitchhiker's guide to becoming invasive: exotic mosquitoes spread across a US state by human transport not autonomous flight

How far do forest container mosquitoes (Diptera: Culicidae) invade rural and urban areas in Japan? - Simple landscape ecology with comparison of the invasive Aedes ecology between native and invasive ranges

The distribution of container mosquitoes in relation to distances from forests was studied in temperate Japan. Mosquito larvae were collected between May and September in 4 years from tree holes, bamboo stumps, riverine rock pools, and artificial containers; sampling ranged spatially from the mountain forest across the deforested plain developed as agriculture and urban areas to the seacoast. Although tree holes, bamboo stumps, and artificial containers existed throughout the deforested plain area, 10 container species of 6 genera were found virtually only within 5 km from the nearest forest edge. Worldwide invasive Aedes albopictus (Skuse) and Aedes japonicus (Theobald) of Asian origin showed unique occurrence patterns different from other container species and from each other. Ae. japonicus was dominant in artificial containers in and near the forest but minor in forest natural containers and only occurred within 5 km from the forest. Ae. albopictus was minor in the forest irrespective of container types but not bound to the forest and dominant in natural and artificial containers throughout rural and urban areas. The 5-km range was designated as the circum-forest zone for container mosquitoes (except Ae. albopictus) in Japan, and an expanded concept, circum-boundary zone, is proposed. The widths of these zones primarily depend on the dispersal traits of mosquitoes. Whether the relation of Ae. albopictus and Ae. japonicus to forests we observed are common in the native and invasive ranges is discussed. The study of across-ecosystem dispersal is important for mosquito management under anthropogenically changing environments due to either deforestation or green restoration.

Aedes (Ochlerotatus) scapularis, Aedes japonicus japonicus, and Aedes (Fredwardsius) vittatus (Diptera: Culicidae): Three Neglected Mosquitoes with Potential Global Health Risks

More than 3550 species of mosquitoes are known worldwide, and only a fraction is involved in the transmission of arboviruses. Mosquitoes in sylvatic and semi-sylvatic habitats may rapidly adapt to urban parks and metropolitan environments, increasing human contact. Many of these mosquitoes have been found naturally infected with arboviruses from the Alphaviridae, Flaviviridae, and Bunyaviridae families, with many being the cause of medically important diseases. However, there is a gap in knowledge about the vector status of newly invasive species and their potential threat to human and domestic animal populations. Due to their rapid distribution, adaptation to urban environments, and anthropophilic habits, some neglected mosquito species may deserve more attention regarding their role as secondary vectors. Taking these factors into account, we focus here on Aedes (Ochlerotatus) scapularis (Rondani), Aedes japonicus japonicus (Theobald), and Aedes (Fredwardsius) vittatus (Bigot) as species that have the potential to become important disease vectors. We further discuss the importance of these neglected mosquitoes and how factors such as urbanization, climate change, and globalization profoundly alter the dynamics of disease transmission and may increase the participation of neglected species in propagating diseases.

Spatial Distribution Pattern and Risk Assessment of Invasive Alien Plants on Southern Side of the Daba Mountain Area

The southern side of the Daba Mountain area is a hotspot of global biodiversity and an essential barrier promoting ecological security. However, knowledge about the distribution status and transmission pathways of invasive alien species (IAS) in this area is limited. We counted the IAS on the southern side of the Daba Mountain area through sample transects and analyzed the factors affecting their spatial distribution. We also assessed IAS risk using the analytic hierarchy process (AHP), which found 64 IAS belonging to 23 families and 53 genera. Around rivers and roads, the results showed a vertical two-way dispersal pattern. Human and environmental factors, such as a very dense transportation network, can affect the distribution pattern of IAS. AHP assessed 43 IAS (67.19%), primarily distributed in villages and towns, as being of high or medium risk. High- and medium-risk IAS should be the focus of invasion prevention and control, and priority should be given to controlling the spread of IAS around rivers and roads.

Special Collection: Highlights of Medical, Urban and Veterinary Entomology. Highlights in Medical Entomology, 2021

Life remained far from normal as we completed the first year of the Covid-19 pandemic and entered a second year. Despite the challenges faced worldwide, together we continue to move the field of Medical Entomology forward. Here, I reflect on parallels between control of Covid-19 and vector-borne disease control, discuss the advantages and caveats of using new genotyping technologies for the study of invasive species, and proceed to highlight papers that were published between 2020 and 2021 with a focus on those related to mosquito surveillance and population genetics of mosquito vectors.

Genetic Diversity and Population Genetic Structure of Aedes albopictus in the Yangtze River Basin, China

Aedes albopictus is an indigenous primary vector of dengue and Zika viruses in China. Understanding the population spatial genetic structure, migration, and gene flow of vector species is critical to effectively preventing and controlling vector-borne diseases. The genetic variation and population structure of Ae. albopictus populations collected from 22 cities along the Yangtze River Basin were investigated with nine microsatellite loci and the mitochondrial CoxI gene. The polymorphic information content (PIC) values ranged from 0.534 to 0.871. The observed number of alleles (Na) values ranged from 5.455 to 11.455, and the effective number of alleles (Ne) values ranged from 3.106 to 4.041. The Shannon Index (I) ranged from 1.209 to 1.639. The observed heterozygosity (Ho) values ranged from 0.487 to 0.545. The FIS value ranged from 0.047 to 0.212. All Ae. albopictus populations were adequately allocated to three clades with significant genetic differences. Haplotype 2 is the most primitive molecular type and forms 26 other haplotypes after one or more site mutations. The rapid expansion of high-speed rail, aircraft routes and highways along the Yangtze River Basin have accelerated the dispersal and communication of mosquitoes, which appears to have contributed to inhibited population differentiation and promoted genetic diversity among Ae. albopictus populations.

The Invasive Mosquitoes of Canada: An Entomological, Medical, and Veterinary Review

Several invasive mosquitoes have become established in Canada, including important pathogen vectors such as Aedes albopictus, Ae. japonicus, and Culex pipiens. Some species have been present for decades, while others are recent arrivals. Several species present new health concerns and may result in autochthonous seasonal outbreaks of pathogens, particularly in southern Canada, that were previously restricted to imported cases. This review provides an overview of current knowledge of the biological, medical, and veterinary perspectives of these invasive species and highlights the need for increased monitoring efforts and information sharing.

Multiple introductions and overwintering shape the progressive invasion of Aedes albopictus beyond the Alps

Aedes albopictus originates from Southeast Asia and is considered one of the most invasive species globally. This mosquito is a nuisance and a disease vector of significant public health relevance. In Europe, Ae. albopictus is firmly established and widespread south of the Alps, a mountain range that forms a formidable biogeographic barrier to many organisms. Recent reports of Ae. albopictus north of the Alps raise questions of (1) the origins of its recent invasion, and (2) if this mosquito has established overwintering populations north of the Alps. To answer these questions, we analyzed population genomic data from >4000 genome-wide SNPs obtained through double-digest restriction site-associated DNA sequencing. We collected SNP data from specimens from six sites in Switzerland, north and south of the Alps, and analyzed them together with specimens from other 33 European sites, five from the Americas, and five from its Asian native range. At a global level, we detected four genetic clusters with specimens from Indonesia, Brazil, and Japan as the most differentiated, whereas specimens from Europe, Hong Kong, and USA largely overlapped. Across the Alps, we detected a weak genetic structure and high levels of genetic admixture, supporting a scenario of rapid and human-aided dispersal along transportation routes. While the genetic pattern suggests frequent re-introductions into Switzerland from Italian sources, the recovery of a pair of full siblings in two consecutive years in Strasbourg, France, suggests the presence of an overwintering population north of the Alps. The suggestion of overwintering populations of Ae. albopictus north of the Alps and the expansion patterns identified points to an increased risk of further northward expansion and the need for increased surveillance of mosquito populations in Northern Europe.

Population Genetic Analysis of Aedes aegypti Mosquitoes From Sudan Revealed Recent Independent Colonization Events by the Two Subspecies

Increases in arbovirus outbreaks in Sudan are vectored by Aedes aegypti, raising the medical importance of this mosquito. We genotyped 12 microsatellite loci in four populations of Ae. aegypti from Sudan, two from the East and two from the West, and analyzed them together with a previously published database of 31 worldwide populations to infer population structure and investigate the demographic history of this species in Sudan. Our results revealed the presence of two genetically distinct subspecies of Ae. aegypti in Sudan. These are Ae. aegypti aegypti in Eastern Sudan and Ae. aegypti formosus in Western Sudan. Clustering analysis showed that mosquitoes from East Sudan are genetically homogeneous, while we found population substructure in West Sudan. In the global context our results indicate that Eastern Sudan populations are genetically closer to Asian and American populations, while Western Sudan populations are related to East and West African populations. Approximate Bayesian Computation Analysis supports a scenario in which Ae. aegypti entered Sudan in at least two independent occasions nearly 70–80 years ago. This study provides a baseline database that can be used to determine the likely origin of new introductions for this invasive species into Sudan. The presence of the two subspecies in the country should be consider when designing interventions, since they display different behaviors regarding epidemiologically relevant parameters, such as blood feeding preferences and ability to transmit disease.

Spatiotemporal distribution, abundance, and host interactions of two invasive vectors of arboviruses, Aedes albopictus and Aedes japonicus, in Pennsylvania, USA

Background

Aedes albopictus and Aedes japonicus, two invasive mosquito species in the United States, are implicated in the transmission of arboviruses. Studies have shown interactions of these two mosquito species with a variety of vertebrate hosts; however, regional differences exist and may influence their contribution to arbovirus transmission.

Methods

We investigated the distribution, abundance, host interactions, and West Nile virus infection prevalence of Ae. albopictus and Ae. japonicus by examining Pennsylvania mosquito and arbovirus surveillance data for the period between 2010 and 2018. Mosquitoes were primarily collected using gravid traps and BG-Sentinel traps, and sources of blood meals were determined by analyzing mitochondrial cytochrome b gene sequences amplified in PCR assays.

Results

A total of 10,878,727 female mosquitoes representing 51 species were collected in Pennsylvania over the 9-year study period, with Ae. albopictus and Ae. japonicus representing 4.06% and 3.02% of all collected mosquitoes, respectively. Aedes albopictus was distributed in 39 counties and Ae. japonicus in all 67 counties, and the abundance of these species increased between 2010 and 2018. Models suggested an increase in the spatial extent of Ae. albopictus during the study period, while that of Ae. japonicus remained unchanged. We found a differential association between the abundance of the two mosquito species and environmental conditions, percent development, and median household income. Of 110 Ae. albopictus and 97 Ae. japonicus blood meals successfully identified to species level, 98% and 100% were derived from mammalian hosts, respectively. Among 12 mammalian species, domestic cats, humans, and white-tailed deer served as the most frequent hosts for the two mosquito species. A limited number of Ae. albopictus acquired blood meals from avian hosts solely or in mixed blood meals. West Nile virus was detected in 31 pools (n = 3582 total number of pools) of Ae. albopictus and 12 pools (n = 977 total pools) of Ae. japonicus.

Conclusions

Extensive distribution, high abundance, and frequent interactions with mammalian hosts suggest potential involvement of Ae. albopictus and Ae. japonicus in the transmission of human arboviruses including Cache Valley, Jamestown Canyon, La Crosse, dengue, chikungunya, and Zika should any of these viruses become prevalent in Pennsylvania. Limited interaction with avian hosts suggests that Ae. albopictus might occasionally be involved in transmission of arboviruses such as West Nile in the region.

Graphical Abstract

Supplementary Information

The online version contains supplementary material available at 10.1186/s13071-022-05151-8.

A machine-learning approach to map landscape connectivity in Aedes aegypti with genetic and environmental data

Aedes mosquitoes are projected to continue expanding their ranges, which could expose millions more humans to the diseases they carry. The implementation of vector control methods ranging from traditional (e.g., insecticides) to cutting edge (e.g., genetic modification) could be improved with landscape connectivity maps and increased understanding of the factors that affect mosquito dispersal. Here we present an iterative random forest method for integrating genetic and environmental data to map landscape connectivity. We achieve a correlation of 0.83 between the model’s predicted genetic distance and actual genetic distance. We produce a genetic connectivity map for the southern tier of the United States and discuss important factors to consider in mosquito control, e.g., the release of genetically modified mosquitoes.

Mapping landscape connectivity is important for controlling invasive species and disease vectors. Current landscape genetics methods are often constrained by the subjectivity of creating resistance surfaces and the difficulty of working with interacting and correlated environmental variables. To overcome these constraints, we combine the advantages of a machine-learning framework and an iterative optimization process to develop a method for integrating genetic and environmental (e.g., climate, land cover, human infrastructure) data. We validate and demonstrate this method for the Aedes aegypti mosquito, an invasive species and the primary vector of dengue, yellow fever, chikungunya, and Zika. We test two contrasting metrics to approximate genetic distance and find Cavalli-Sforza–Edwards distance (CSE) performs better than linearized F_ST. The correlation (R) between the model’s predicted genetic distance and actual distance is 0.83. We produce a map of genetic connectivity for Ae. aegypti’s range in North America and discuss which environmental and anthropogenic variables are most important for predicting gene flow, especially in the context of vector control.

How public reaction to disease information across scales and the impacts of vector control methods influence disease prevalence and control efficacy

With the development of social media, the information about vector-borne disease incidence over broad spatial scales can cause demand for local vector control before local risk exists. Anticipatory intervention may still benefit local disease control efforts; however, infection risks are not the only focal concerns governing public demand for vector control. Concern for environmental contamination from pesticides and economic limitations on the frequency and magnitude of control measures also play key roles. Further, public concern may be focused more on ecological factors (i.e., controlling mosquito populations) or on epidemiological factors (i.e., controlling infection-carrying mosquitoes), which may lead to very different control outcomes. Here we introduced a generic Ross-MacDonald model, incorporating these factors under three spatial scales of disease information: local, regional, and global. We tailored and parameterized the model for Zika virus transmitted by Aedes aegypti mosquito. We found that sensitive reactivity caused by larger-scale incidence information could decrease average human infections per patch breeding capacity, however, the associated increase in total control effort plays a larger role, which leads to an overall decrease in control efficacy. The shift of focal concerns from epidemiological to ecological risk could relax the negative effect of the sensitive reactivity on control efficacy when mosquito breeding capacity populations are expected to be large. This work demonstrates that, depending on expected total mosquito breeding capacity population size, and weights of different focal concerns, large-scale disease information can reduce disease infections without lowering control efficacy. Our findings provide guidance for vector-control strategies by considering public reaction through social media.

Field Observations of Invasive Species Aedes japonicus and Larval Contemporaries in Escambia County, Florida

The Asian bush mosquito, Aedes japonicus, is an invasive species that is well established in North America and Europe. Though it is considered a temperate species, we have observed an established population of Ae. japonicus in the subtropical climate of northwestern Florida. To evaluate the temporal patterns of Ae. japonicus abundance, mosquito larvae were collected from 15 artificial containers in Escambia County, FL, from August 2019 to July 2020, with the prediction that Ae. japonicus abundance would peak in the winter months and decline with increasing ambient temperatures. Aedes japonicus larvae were collected in low abundances during each month except for February (n = 51), with no clear temporal patterns of abundance. Larval contemporaries belonging to other species were considered in sampling of containers and were also cataloged. We demonstrate monthly observance of this temperate species at a single site in the Florida panhandle, exemplifying the persistence of Ae. japonicus through all seasons in a subtropical climate.

Molecular relationships of introduced Aedes japonicus (Diptera: Culicidae) populations in British Columbia, Canada using mitochondrial DNA

Aedes japonicus japonicus (Theobald) is a relatively recent immigrant to the Pacific Northwest, having been collected in Washington State in 2001 and in British Columbia (BC) since 2014. We applied a molecular barcoding approach to determine the phylogenetic relationship of Ae. j. japonicus populations in BC with those from around the world. We sequenced a 617 base-pair segment of the cytochrome c oxidase 1 gene and a 330 base-pair region of the NADH dehydrogenase 4 gene to find genetic variation and characterize phylogenetic and haplotypic relationships based on nucleotide divergences. Our results revealed low genetic diversity in the BC samples, suggesting that these populations arose from the same introduction event. However, our approach lacked the granularity to identify the exact country of origin of the Ae. j. japonicus collected in BC. Future efforts should focus on detecting and preventing new Ae. j. japonicus introductions, recognizing that current molecular techniques are unable to pin-point the precise source of an introduction.

Describing the current status of Plasmodium falciparum population structure and drug resistance within mainland Tanzania using molecular inversion probes

High-throughput Plasmodium genomic data is increasingly useful in assessing prevalence of clinically important mutations and malaria transmission patterns. Understanding parasite diversity is important for identification of specific human or parasite populations that can be targeted by control programmes, and to monitor the spread of mutations associated with drug resistance. An up-to-date understanding of regional parasite population dynamics is also critical to monitor the impact of control efforts. However, this data is largely absent from high-burden nations in Africa, and to date, no such analysis has been conducted for malaria parasites in Tanzania countrywide. To this end, over 1,000 P. falciparum clinical isolates were collected in 2017 from 13 sites in seven administrative regions across Tanzania, and parasites were genotyped at 1,800 variable positions genome-wide using molecular inversion probes. Population structure was detectable among Tanzanian P. falciparum parasites, approximately separating parasites from the northern and southern districts and identifying genetically admixed populations in the north. Isolates from nearby districts were more likely to be genetically related compared to parasites sampled from more distant districts. Known drug resistance mutations were seen at increased frequency in northern districts (including two infections carrying pfk13-R561H), and additional variants with undetermined significance for antimalarial resistance also varied by geography. Malaria Indicator Survey (2017) data corresponded with genetic findings, including average region-level complexity-of-infection and malaria prevalence estimates. The parasite populations identified here provide important information on extant spatial patterns of genetic diversity of Tanzanian parasites, to which future surveys of genetic relatedness can be compared.

Fine-scale population genetic structure of dengue mosquito vector, Aedes aegypti, in Metropolitan Manila, Philippines

Dengue is a highly endemic disease in Southeast Asia and is transmitted primarily by the mosquito, Aedes aegypti. The National Capital Region (NCR) of the Philippines, or Metropolitan Manila, is a highly urbanized area that is greatly affected by this arboviral disease. Urbanization has been shown to increase the dispersal of this mosquito vector. For this reason, we conducted a fine-scale population genetic study of Ae. aegypti in this region. We collected adult Ae. aegypti mosquitoes (n = 526 individuals) within the region (n = 21 study areas) and characterized the present population structure and the genetic relatedness among mosquito populations. We genotyped 11 microsatellite loci from all sampled mosquito individuals and analyzed their genetic diversity, differentiation and structure. The results revealed low genetic differentiation across mosquito populations which suggest high gene flow and/or weak genetic drift among mosquito populations. Bayesian analysis indicated multiple genetic structures (K = 3-6), with no clear genetically distinct population structures. This result implies the passive or long-distance dispersal capability nature Ae. aegypti possibly through human-mediated transportation. The constructed dendrogram in this study describes the potential passive dispersal patterns across Metropolitan Manila. Furthermore, spatial autocorrelation analysis showed the limited and active dispersal capability (<1km) of the mosquito vector. Our findings are consistent with previous studies that investigated the genetic structure and dual (active and passive) dispersal capability of Ae. aegypti in a fine-scale highly urbanized area.

Rift Valley Fever - epidemiological update and risk of introduction into Europe

Rift Valley fever (RVF) is a vector-borne disease transmitted by a broad spectrum of mosquito species, especially Aedes and Culex genus, to animals (domestic and wild ruminants and camels) and humans. Rift Valley fever is endemic in sub-Saharan Africa and in the Arabian Peninsula, with periodic epidemics characterised by 5-15 years of inter-epizootic periods. In the last two decades, RVF was notified in new African regions (e.g. Sahel), RVF epidemics occurred more frequently and low-level enzootic virus circulation has been demonstrated in livestock in various areas. Recent outbreaks in a French overseas department and some seropositive cases detected in Turkey, Tunisia and Libya raised the attention of the EU for a possible incursion into neighbouring countries. The movement of live animals is the most important pathway for RVF spread from the African endemic areas to North Africa and the Middle East. The movement of infected animals and infected vectors when shipped by flights, containers or road transport is considered as other plausible pathways of introduction into Europe. The overall risk of introduction of RVF into EU through the movement of infected animals is very low in all the EU regions and in all MSs (less than one epidemic every 500 years), given the strict EU animal import policy. The same level of risk of introduction in all the EU regions was estimated also considering the movement of infected vectors, with the highest level for Belgium, Greece, Malta, the Netherlands (one epidemic every 228-700 years), mainly linked to the number of connections by air and sea transports with African RVF infected countries. Although the EU territory does not seem to be directly exposed to an imminent risk of RVFV introduction, the risk of further spread into countries neighbouring the EU and the risks of possible introduction of infected vectors, suggest that EU authorities need to strengthen their surveillance and response capacities, as well as the collaboration with North African and Middle Eastern countries.

Gridlock and beltways: the genetic context of urban invasions

The rapid expansion of urban land across the globe presents new and numerous opportunities for invasive species to spread and flourish. Ecologists historically rejected urban ecosystems as important environments for ecology and evolution research but are beginning to recognize the importance of these systems in shaping the biology of invasion. Urbanization can aid the introduction, establishment, and spread of invaders, and these processes have substantial consequences on native species and ecosystems. Therefore, it is valuable to understand how urban areas influence populations at all stages in the invasion process. Population genetic tools are essential to explore the driving forces of invasive species dispersal, connectivity, and adaptation within cities. In this review, we synthesize current research about the influence of urban landscapes on invasion genetics dynamics. We conclude that urban areas are not only points of entry for many invasive species, they also facilitate population establishment, are pools for genetic diversity, and provide corridors for further spread both within and out of cities. We recommend the continued use of genetic studies to inform invasive species management and to understand the underlying ecological and evolutionary processes governing successful invasion.

High genetic diversity but no geographical structure of Aedes albopictus populations in Réunion Island

Background

In recent years, the Asian tiger mosquito Aedes albopictus has emerged as a species of major medical concern following its global expansion and involvement in many arbovirus outbreaks. On Réunion Island, Ae. albopictus was responsible for a large chikungunya outbreak in 2005–2006 and more recently an epidemic of dengue which began at the end of 2017 and is still ongoing at the time of writing. This dengue epidemic has seen a high number of human cases in south and west coastal regions, while few cases have been reported in the north and east of the island. To better understand the role of mosquito populations in such spatial patterns of dengue virus transmission in Réunion Island, we examined the genetic diversity and population structure of Ae. albopictus sampled across the island.

Results

Between November 2016 and March 2017, a total of 564 mosquitoes were collected from 19 locations in three main climatic regions (West, East and Center) of Réunion Island and were genotyped using 16 microsatellite loci. A high genetic diversity was observed with 2–15 alleles per locus and the average number of alleles per population varying between 4.70–5.90. Almost all F_IS values were significantly positive and correlated to individual relatedness within populations using a hierarchical clustering approach based on principal components analyses (HCPC). However, the largest part of genetic variance was among individuals within populations (97%) while only 3% of genetic variance was observed among populations within regions. Therefore, no distinguishable population structure or isolation by distance was evidenced, suggesting high rates of gene flow at the island scale.

Conclusions

Our results show high genetic diversity but no genetic structure of Ae. albopictus populations in Réunion Island thus reflecting frequent movements of mosquitoes between populations probably due to human activity. These data should help in the understanding of Ae. albopictus vector capacity and the design of effective mosquito control strategies.

Human-mediated dispersal in insects

Central to the problem of biological invasions, human activities introduce species beyond their native ranges and participate in their subsequent spread. Understanding human-mediated dispersal is therefore crucial for both predicting and preventing invasions. Here, we show that decomposing human-mediated dispersal into three temporal phases: departure, transport and arrival, allows to understand how the characteristics of human activities and the biological traits of species influence each phase of the dispersal process, and ultimately govern invasion pathways in insects. Integrating these precise mechanisms into future invasion models should increase their realism and generalization for any potential insect invader. Moreover, understanding these mechanisms can provide insight into why some invasive insects are more widely distributed than others, and to estimate risks posed by species that have not yet been introduced.

Risk assessment strategies for early detection and prediction of infectious disease outbreaks associated with climate change

A new generation of surveillance strategies is being developed to help detect emerging infections and to identify the increased risks of infectious disease outbreaks that are expected to occur with climate change. These surveillance strategies include event-based surveillance (EBS) systems and risk modelling. The EBS systems use open-source internet data, such as media reports, official reports, and social media (such as Twitter) to detect evidence of an emerging threat, and can be used in conjunction with conventional surveillance systems to enhance early warning of public health threats. More recently, EBS systems include artificial intelligence applications such machine learning and natural language processing to increase the speed, capacity and accuracy of filtering, classifying and analysing health-related internet data. Risk modelling uses statistical and mathematical methods to assess the severity of disease emergence and spread given factors about the host (e.g. number of reported cases), pathogen (e.g. pathogenicity) and environment (e.g. climate suitability for reservoir populations). The types of data in these models are expanding to include health-related information from open-source internet data and information on mobility patterns of humans and goods. This information is helping to identify susceptible populations and predict the pathways from which infections might spread into new areas and new countries. As a powerful addition to traditional surveillance strategies that identify what has already happened, it is anticipated that EBS systems and risk modelling will increasingly be used to inform public health actions to prevent, detect and mitigate the climate change increases in infectious diseases.

What makes the Asian bush mosquito Aedes japonicus japonicus feel comfortable in Germany? A fuzzy modelling approach

Background

The Asian bush mosquito Aedes japonicus japonicus is an invasive species native to East Asia and has become established in North America and Europe. On both continents, the species has spread over wide areas. Since it is a potential vector of human and livestock pathogens, distribution and dissemination maps are urgently needed to implement targeted surveillance and control in case of disease outbreaks. Previous distribution models for Europe and Germany in particular focused on climate data. Until now, effects of other environmental variables such as land use and wind remained unconsidered.

Results

In order to better explain the distribution pattern of Ae. j. japonicus in Germany at a regional level, we have developed a nested approach that allows for the combination of data derived from (i) a climate model based on a machine-learning approach; (ii) a landscape model developed by means of ecological expert knowledge; and (iii) wind speed data. The approach is based on the fuzzy modelling technique that enables to precisely define the interactions between the three factors and additionally considers uncertainties with regard to the acceptance of certain environmental conditions. The model combines different spatial resolutions of data for Germany and achieves a much higher degree of accuracy than previous published distribution models. Our results reveal that a well-suited landscape structure can even facilitate the occurrence of Ae. j. japonicus in a climatically unsuitable region. Vice versa, unsuitable land use types such as agricultural landscapes and coniferous forests reduce the occurrence probability in climatically suitable regions.

Conclusions

The approach has significantly improved existing distribution models of Ae. j. japonicus for the area of Germany. We generated distribution maps with a resolution of 100 × 100 m that can serve as a basis for the design of control measures. All model input data and scripts are open source and freely available, so that the model can easily be applied to other countries or, more generally, to other species.

The Asian bush mosquito Aedes japonicus japonicus (Diptera: Culicidae) in Europe, 17 years after its first detection, with a focus on monitoring methods

After the first detection of the Asian bush mosquito Aedes japonicus japonicus in the year 2000 in France, its invasive nature was revealed in 2008 in Switzerland and Germany. In the following years, accumulating reports have shown that Ae. j. japonicus succeeded in establishing in several European countries. Surveillance efforts suggest that there are currently four populations in Europe, with the largest one, formed by the recent fusion of several smaller populations, ranging from West Germany, with extensions to Luxembourg and French Alsace, southwards to Switzerland and continuing westwards through Liechtenstein to western Austria. This paper summarises the present distribution of Ae. j. japonicus in Europe, based on published literature and hitherto unpublished findings by the authors, and critically reviews the monitoring strategies applied. A proposal for a more standardised monitoring approach is provided, aiming at the harmonisation of future data collections for improving the comparability between studies and the suitability of collected data for further research purposes, e.g. predictive modelling approaches.

Diversity and Molecular Characterization of Mosquitoes (Diptera: Culicidae) in Selected Ecological Regions in Kenya

Mosquitoes play a predominant role as leading agents in the spread of vector-borne diseases and the consequent mortality in humans. Despite reports on increase of new and recurrent mosquito borne-disease outbreaks such as chikungunya, dengue fever and Rift Valley fever in Kenya, little is known about the genetic characteristics and diversity of the vector species that have been incriminated in transmission of disease pathogens. In this study,  mosquito species were collected from Kisumu city, Kilifi town and Nairobi city and we determined their genetic diversity and phylogenetic relationships. PCR was used to amplify the partial cytochrome oxidase subunit 1 (CO1) gene of mosquito samples. Molecular-genetic and phylogenetic analysis of the partial cytochrome oxidase subunit 1 (CO1) gene were employed to identify their relationship with known mosquito species. Fourteen (14) haplotypes belonging to genus Aedes, nine (9) haplotypes belonging to genus Anopheles and twelve (12) haplotypes belonging to genus Culex were identified in this study. Findings from this study revealed a potentially new haplotype belonging to Anopheles genus and reported the first molecular characterization of Aedes cumminsii in Kenya. Sequence results revealed variation in mosquito species from Kilifi, Kisumu and Nairobi. Since vector competence varies greatly across species as well as species-complexes and is strongly associated with specific behavioural adaptations, proper species identification is important for vector control programs.

Construction sites in Miami-Dade County, Florida are highly favorable environments for vector mosquitoes

Urbanization is increasing globally, and construction sites are an integral part of the urbanization process. It is unknown to what extent construction sites create favorable breeding conditions for mosquitoes. The main objectives of the present study were to identify what species of mosquitoes are present at construction sites and the respective physical features associated with their production. Eleven construction sites were cross-sectionally surveyed for the presence of mosquitoes in Miami-Dade County, Florida including in areas previously affected by the Zika virus outbreak in 2016. A total of 3.351 mosquitoes were collected; 2.680 adults and 671 immatures. Aedes aegypti and Culex quinquefasciatus comprised 95% of all collected mosquitoes and were the only species found in their immature forms breeding inside construction sites. Results for the Shannon and Simpson indices, considering both immature and adult specimens, yielded the highest values for Cx. quinquefasciatus and Ae. aegypti. The individual rarefaction curves indicated that sampling sufficiency was highly asymptotic for Cx. quinquefasciatus and Ae. aegypti, and the plots of cumulative species abundance (ln S), Shannon index (H) and log evenness (ln E) (SHE) revealed the lack of heterogeneity of species composition, diversity and evenness for the mosquitoes found breeding in construction sites. The most productive construction site breeding features were elevator shafts, Jersey plastic barriers, flooded floors and stair shafts. The findings of this study indicate that vector mosquitoes breed in high numbers at construction sites and display reduced biodiversity comprising almost exclusively Ae. aegypti and Cx. quinquefasciatus. Such findings suggest that early phase construction sites have suitable conditions for the proliferation of vector mosquitoes. More studies are needed to identify modifiable worker- and organizational-level factors to improve mosquito control practices and guide future mosquito control strategies in urban environments.

Evaluating the impact of Aedes japonicus invasion on the mosquito community in the Greater Golden Horseshoe region (Ontario, Canada)

Background

Aedes japonicus was first documented in Ontario, Canada, in 2001. The objective of this study was to determine the effect of Ae. japonicus establishment on the abundance of other mosquitoes in the Greater Golden Horseshoe (GGH) region of Ontario.

Methods

Adult mosquito data from the Ontario West Nile virus surveillance program were used. Descriptive analyses, linear trends and distribution maps of average trap count per month for six mosquito species of interest were produced. Multivariable negative binomial regression models were constructed to 1) test whether the invasion of Ae. japonicus affected the abundance of other mosquitoes by comparing the time period before Ae. japonicus was identified in an area (pre-detection), to after it was first identified (detection), and subsequently (establishment), and 2) identify the variables that explain the abundance of the various mosquito species.

Results

The monthly seasonal average (May–October) of Ae. japonicus per trap night increased from 2002 to 2016, peaking in September, when the average of most other mosquitoes decrease. There were increased numbers of Ae. triseriatus/hendersoni (Odds Ratio (OR): 1.40, 95% Confidence Interval (CI): 1.02–1.94) and decreased numbers of Coquillettidia perturbans (OR: 0.43, 95% CI: 0.26–0.73) in the detection period, compared to the pre-detection period. Additionally, there was a decrease in Cx. pipiens/restuans (OR: 0.87, 95% CI: 0.76–0.99) and Cq. perturbans (OR: 0.68, 95% CI: 0.49–0.94) in the establishment period, compared to the pre-detection period. None of the most parsimonious explanatory models included the period of the establishment of Ae. japonicus.

Conclusions

There is no evidence that the introduction of Ae. japonicus significantly reduced populations of Ae. triseriatus/hendersoni, Cx. pipiens/restuans or An. punctipennis in the GGH. While further research is needed to understand the impact of the Ae. japonicus invasion on other mosquito species, our work indicates that, on a regional scale, little impact has been noted.

Human movement, cooperation and the effectiveness of coordinated vector control strategies

Vector-borne disease transmission is often typified by highly focal transmission and influenced by movement of hosts and vectors across different scales. The ecological and environmental conditions (including those created by humans through vector control programmes) that result in metapopulation dynamics remain poorly understood. The development of control strategies that would most effectively limit outbreaks given such dynamics is particularly urgent given the recent epidemics of dengue, chikungunya and Zika viruses. We developed a stochastic, spatial model of vector-borne disease transmission, allowing for movement of hosts between patches. Our model is applicable to arbovirus transmission by Aedes aegypti in urban settings and was parametrized to capture Zika virus transmission in particular. Using simulations, we investigated the extent to which two aspects of vector control strategies are affected by human commuting patterns: the extent of coordination and cooperation between neighbouring communities. We find that transmission intensity is highest at intermediate levels of host movement. The extent to which coordination of control activities among neighbouring patches decreases the prevalence of infection is affected by both how frequently humans commute and the proportion of neighbouring patches that commits to vector surveillance and control activities. At high levels of host movement, patches that do not contribute to vector control may act as sources of infection in the landscape, yet have comparable levels of prevalence as patches that do cooperate. This result suggests that real cooperation among neighbours will be critical to the development of effective pro-active strategies for vector-borne disease control in today's commuter-linked communities.

Genetic diversity and distribution differ between long-established and recently introduced populations in the invasive mosquito Aedes albopictus

The Asian tiger mosquito Aedes albopictus, native to South-eastern Asia, is currently the most invasive mosquito in the world. The spatio-temporal dynamics of its expansion through the genetic characterization of invasive populations has been challenged so far by the limited number of genetic markers variable enough to infer the genetic structure in recently invaded areas. Here we applied the double-digest Restriction-site Associated DNA sequencing method (ddRADseq) to mosquitoes collected in two invaded areas, Reunion Island (12 localities) and Europe (18 localities). Analyses of genetic diversity, Bayesian clustering, Maximum Likelihood inference and isolation-by-distance tests based on 1561 genome-wide distributed Single Nucleotide Polymorphisms (SNPs) revealed that Reunion Island and Europe form two distinct genetic clusters, supporting no contemporary gene flow and suggesting two different and independent invasion histories. Long-established populations (Reunion Island) were more genetically diverse than recently introduced European populations. The largest part of genetic variance was found at the intra-individual level (>85%) and most F_IS values were positive, suggesting inbreeding at the local scale. The two invaded areas showed contrasting patterns of genetic structure. Significant isolation-by-distance was found among Reunion Island populations, suggesting that these populations are at the drift-migration equilibrium. In contrast, long-distance human-assisted transport is probably the main dispersal mechanism in Europe.

First Record of Aedes japonicus In Florida

The presence of Aedes j. japonicus in Florida is reported for the first time. Four adult females were collected by a Mosquito Magnet® X trap baited with pressurized CO₂ in Okaloosa County, FL, in August 2012 and later identified as Ae. japonicus in 2014. Additional adult and larval specimens were collected during 2014-17 from Bay, Leon, Okaloosa, Santa Rosa, or Walton counties, Florida. Notes are provided on the location, general habitats, and mosquito associates that may be found with Ae. japonicus in northwestern Florida. The role of Ae. japonicus in arbovirus transmission within Florida is currently unknown and should be further explored.

Population genomics of the Asian tiger mosquito, Aedes albopictus: insights into the recent worldwide invasion

Aedes albopictus, the "Asian tiger mosquito," is an aggressive biting mosquito native to Asia that has colonized all continents except Antarctica during the last ~30-40 years. The species is of great public health concern as it can transmit at least 26 arboviruses, including dengue, chikungunya, and Zika viruses. In this study, using double-digest Restriction site-Associated DNA (ddRAD) sequencing, we developed a panel of ~58,000 single nucleotide polymorphisms (SNPs) based on 20 worldwide Ae. albopictus populations representing both the invasive and the native range. We used this genomic-based approach to study the genetic structure and the differentiation of Ae. albopictus populations and to understand origin(s) and dynamics of the recent invasions. Our analyses indicated the existence of two major genetically differentiated population clusters, each one including both native and invasive populations. The detection of additional genetic structure within each major cluster supports that these SNPs can detect differentiation at a global and local scale, while the similar levels of genomic diversity between native and invasive range populations support the scenario of multiple invasions or colonization by a large number of propagules. Finally, our results revealed the possible source(s) of the recent invasion in Americas, Europe, and Africa, a finding with important implications for vector-control strategies.

Persistence of butterfly populations in fragmented habitats along urban density gradients: motility helps

In a simulation study of genotypes conducted over 100 generations for more than 1600 butterfly's individuals, we evaluate how the increase of anthropogenic fragmentation and reduction of habitat size along urbanisation gradients (from 7 to 59% of impervious land cover) influences genetic diversity and population persistence in butterfly species. We show that in areas characterised by a high urbanisation rate (>56% impervious land cover), a large decrease of both genetic diversity (loss of 60-80% of initial observed heterozygosity) and population size (loss of 70-90% of individuals) is observed over time. This is confirmed by empirical data available for the mobile butterfly species Pieris rapae in a subpart of the study area. Comparing simulated data for P. rapae with its normal dispersal ability and with a reduced dispersal ability, we also show that a higher dispersal ability can be an advantage to survive in an urban or highly fragmented environment. The results obtained here suggest that it is of high importance to account for population persistence, and confirm that it is crucial to maintain habitat size and connectivity in the context of land-use planning.

Direct Evidence of Adult Aedes albopictus Dispersal by Car

Whereas the Asian tiger mosquito (Aedes albopictus) has low active dispersal capabilities, its worldwide colonization has been rapid. Indirect evidence and informal reports have long implicated passive transportation in cars, but this has not previously been studied systematically given the difficulties of real-time roadside surveys. Here we report the first sampling study confirming that adult tiger mosquitoes travel with humans in cars and enabling us to estimate the frequency of these events. We combine the results with citizen science data to model the car-facilitated dispersal of Aedes albopictus at a nationwide level. During the summer of 2015, we sampled 770 cars in north-eastern Spain, discovering 4 adult female tiger mosquitoes that had entered cars prior to sampling. Our Bayesian model suggests that of the 6.5 million daily car trips in the Barcelona metropolitan area, between 13,000 and 71,500 facilitate tiger mosquito movement, and that Barcelona is the largest source of inter-province tiger mosquito transfers in Spain. Our results are supported by expert-validated citizen science data, and will contribute to better understanding the tiger mosquito's invasion process and ultimately lead to more effective vector control strategies.

City-Dwellers and Country Folks: Lack of Population Differentiation Along an Urban-Rural Gradient in the Mosquito Culex pipiens (Diptera: Culicidae)

Mosquitoes (Diptera, Culicidae) occur in natural, urban, and peri-urban areas throughout the globe. Although the characteristics of urban and peri-urban habitats differ from those of natural habitats in many ways (e.g., fragmentation, pollution, noise, and light), few studies have examined the population connectivity of mosquitoes in urban areas. To obtain an overview of the species composition, we sampled mosquitoes from 23 sites in and around the city of Berlin, Germany. Of 23 species, five occurred in urban, 10 in peri-urban, and 20 in rural areas. Culex pipiens Linnaeus (Diptera: Culicidae) was the most common species collected (75% of all individuals) and occurred in all habitats. Hence this species was selected to be analysed at 10 microsatellite markers. There was no significant differentiation (FST = 0.016, P = 0.9) or isolation by distance (P = 0.06) among Cx. pipiens populations along an urban-rural gradient. The only significant differences detected were between Cx. pipiens and a laboratory population of Cx. pipiens f. molestus (pairwise FST = 0.114-0.148, P ≤ 0.001 in all comparisons), suggesting that the markers chosen were suitable for the identification of population differentiation. Our results indicate that Cx. pipiens gene flow is widespread within and among urban, peri-urban, and rural areas and that urban habitat does not necessarily impede or enhance gene flow among these populations.

The genetic diversity and population structure of domestic Aedes aegypti (Diptera: Culicidae) in Yunnan Province, southwestern China

BACKGROUND

There was no record of Aedes aegypti in Yunnan Province, China, until 2002, but this species is now continuously found in nine cities (or counties). Until now, little was known about the genetic diversity and population structure of this invasive species. Thus, a detailed understanding of the invasion strategies, colonisation and dispersal of this mosquito from a population genetics perspective is urgently needed for controlling and eliminating this disease vector.

METHODS

The genetic diversity and population structure of Ae. aegypti communities were analysed by screening nine microsatellite loci from 833 Ae. aegypti mosquitoes sampled from 28 locations in Yunnan Province.

RESULTS

In total, 114 alleles were obtained, and the average polymorphic information content (PIC) value was 0.672. The value of the alleles per locus ranged from 2.90 to 5.18, with an average of 4.04. The value of He ranged from 0.353 to 0.681, and the value of Ho within populations ranged from 0.401 to 0.689. Of the 28 locations, two showed significant departures from the Hardy-Weinberg equilibrium (HWE) with P-values less than 0.05, and a bottleneck effect was detected among locations from Ruili and the border areas with the degree of 60% and 50%, respectively. Combined with the F-statistics (FIT = 0.222; FCT = 0.145), the analysis of molecular variance (AMOVA) revealed that there was substantial molecular variation among individuals, accounting for 77.76% of the sample, with a significant P-value (<0.0001). The results suggest that genetic differences in Ae. aegypti originated primarily among individuals rather than among populations. Furthermore, the STRUCTURE and UPGMA cluster analyses showed that Ae. aegypti from the border areas were genetically isolated compared to those from the cities Ruili and Jinghong, consistent with the results of the Mantel test (R 2 = 0.245, P < 0.0001).

CONCLUSIONS

Continuous invasion contributes to the maintenance of Ae. aegypti populations' genetic diversity and different invasion accidents result in the genetic difference among Ae. aegypti populations of Yunnan Province.

Genetic evidence for a worldwide chaotic dispersion pattern of the arbovirus vector, Aedes albopictus

BACKGROUND

Invasive species represent a global concern for their rapid spread and the possibility of infectious disease transmission. This is the case of the global invader Aedes albopictus, the Asian tiger mosquito. This species is a vector of medically important arboviruses, notably chikungunya (CHIKV), dengue (DENV) and Zika (ZIKV). The reconstruction of the complex colonization pattern of this mosquito has great potential for mitigating its spread and, consequently, disease risks.

METHODOLOGY/PRINCIPAL FINDINGS

Classical population genetics analyses and Approximate Bayesian Computation (ABC) approaches were combined to disentangle the demographic history of Aedes albopictus populations from representative countries in the Southeast Asian native range and in the recent and more recently colonized areas. In Southeast Asia, the low differentiation and the high co-ancestry values identified among China, Thailand and Japan indicate that, in the native range, these populations maintain high genetic connectivity, revealing their ancestral common origin. China appears to be the oldest population. Outside Southeast Asia, the invasion process in La Réunion, America and the Mediterranean Basin is primarily supported by a chaotic propagule distribution, which cooperates in maintaining a relatively high genetic diversity within the adventive populations.

CONCLUSIONS/SIGNIFICANCE

From our data, it appears that independent and also trans-continental introductions of Ae. albopictus may have facilitated the rapid establishment of adventive populations through admixture of unrelated genomes. As a consequence, a great amount of intra-population variability has been detected, and it is likely that this variability may extend to the genetic mechanisms controlling vector competence. Thus, in the context of the invasion process of this mosquito, it is possible that both population ancestry and admixture contribute to create the conditions for the efficient transmission of arboviruses and for outbreak establishment.