Population genetic structure of the Asian bush mosquito, Aedes japonicus (Diptera, Culicidae), in Belgium suggests multiple introductions

Clash of mosquito wings: Larval interspecific competition among the mosquitoes, Culex pipiens, Aedes albopictus and Aedes aegypti reveals complex population dynamics in shared habitats

Globalisation, climate change and international trade are the factors contributing to the spread of Aedes albopictus (Diptera: Culicidae) and Ae. aegypti into new areas. In newly invaded habitats, these non-native species can serve as arbovirus disease vectors or increase the risk of disease spill over. These mosquitoes continue to emerge in new areas where they have or will have overlapping ranges with other resident mosquito species. The study investigates how invasive Aedes mosquitoes compete with the native Culex pipiens in Türkiye, which might affect the overall mosquito population dynamics and disease transmission risks. Both Aedes species exhibited contrasting responses to interspecific competition with Cx. pipiens. While Ae. albopictus suffers reduced emergence primarily in larger containers with abundant food, Ae. aegypti surprisingly thrives in mixed cultures under all food conditions. Adult Cx. pipiens emergence drops by half against Ae. albopictus and under specific conditions with Ae. aegypti. Competition influences mosquito size differently across species and life stages. Culex pipiens females grow larger when competing with Ae. aegypti, potentially indicating resource advantage or compensatory strategies. However, Ae. albopictus size shows more nuanced responses, suggesting complex interactions at play. Understanding how invasive and native mosquitoes interact with each other can provide insights into how they adapt and coexist in shared habitats. This knowledge can inform effective control strategies. The study highlights the differential responses of invasive Aedes species and the potential for managing populations based on their competitive interactions with the native Cx. pipiens. It can contribute to improved monitoring and prediction systems for the spread of invasive mosquitoes and the associated disease risks.

Shallow Whole-Genome Sequencing of Aedes japonicus and Aedes koreicus from Italy and an Updated Picture of Their Evolution Based on Mitogenomics and Barcoding

Aedes japonicus and Aedes koreicus are two invasive mosquitoes native to East Asia that are quickly establishing in temperate regions of Europe. Both species are vectors of arboviruses, but we currently lack a clear understanding of their evolution. Here, we present new short-read, shallow genome sequencing of A. japonicus and A. koreicus individuals from northern Italy, which we used for downstream phylogenetic and barcode analyses. We explored associated microbial DNA and found high occurrences of Delftia bacteria in both samples, but neither Asaia nor Wolbachia. We then assembled complete mitogenomes and used these data to infer divergence times estimating the split of A. japonicus from A. koreicus in the Oligocene, which was more recent than that previously reported using mitochondrial markers. We recover a younger age for most other nodes within Aedini and other Culicidae. COI barcoding and phylogenetic analyses indicate that A. japonicus yaeyamensis, A. japonicus amamiensis, and the two A. koreicus sampled from Europe should be considered as separate species within a monophyletic species complex. Our studies further clarify the evolution of A. japonicus and A. koreicus, and indicate the need to obtain whole-genome data from putative species in order to disentangle their complex patterns of evolution.

Development of microsatellite markers for the invasive mosquito Aedes koreicus

BACKGROUND

Aedes koreicus is a mosquito species native to East Asia which has recently invaded several countries in Europe. In Italy, this mosquito was first detected in the North-East in 2011 and is now widely distributed in the entire northern part of the country. The development of specific genetic markers, such as microsatellites, is necessary to uncover the dispersal routes of this mosquito from its native areas and, eventually, to plan future control interventions.

METHODS

Available raw sequences of genomic DNA of Ae. koreicus were screened in silico using BLASTn to identify possible microsatellite-containing sequences. Specific primer pairs were then designed, and their efficiency was determined through polymerase chain reaction (PCR) on 32 individuals of Ae. koreicus collected in Italy. PCR conditions were optimised in three multiplex reactions. Genotyping of individual mosquitoes was performed on both single and multiplex PCR reactions. Finally, analysis of intra-population variation was performed to assess the level of polymorphism of the markers.

RESULTS

Mosquito genotyping provided consistent results in both single and multiplex reactions. Out of the 31 microsatellite markers identified in the Ae. koreicus genome raw sequences, 11 were polymorphic in the examined mosquito samples.

CONCLUSIONS

The results show that the 11 microsatellite markers developed here hold potential for investigating the genetic structure of Ae. koreicus populations. These markers could thus represent a novel and useful tool to infer the routes of invasion of this mosquito species into Europe and other non-native areas.

Aedes koreicus, a vector on the rise: Pan-European genetic patterns, mitochondrial and draft genome sequencing

Background

The mosquito Aedes koreicus (Edwards, 1917) is a recent invader on the European continent that was introduced to several new places since its first detection in 2008. Compared to other exotic Aedes mosquitoes with public health significance that invaded Europe during the last decades, this species’ biology, behavior, and dispersal patterns were poorly investigated to date.

Methodology/Principal findings

To understand the species’ population relationships and dispersal patterns within Europe, a fragment of the cytochrome oxidase I (COI or COX1) gene was sequenced from 130 mosquitoes, collected from five countries where the species has been introduced and/or established. Oxford Nanopore and Illumina sequencing techniques were combined to generate the first complete nuclear and mitochondrial genomic sequences of Ae. koreicus from the European region. The complete genome of Ae. koreicus is 879 Mb. COI haplotype analyses identified five major groups (altogether 31 different haplotypes) and revealed a large-scale dispersal pattern between European Ae. koreicus populations. Continuous admixture of populations from Belgium, Italy, and Hungary was highlighted, additionally, haplotype diversity and clustering indicate a separation of German sequences from other populations, pointing to an independent introduction of Ae. koreicus to Europe. Finally, a genetic expansion signal was identified, suggesting the species might be present in more locations than currently detected.

Conclusions/Significance

Our results highlight the importance of genetic research of invasive mosquitoes to understand general dispersal patterns, reveal main dispersal routes and form the baseline of future mitigation actions. The first complete genomic sequence also provides a significant leap in the general understanding of this species, opening the possibility for future genome-related studies, such as the detection of ‘Single Nucleotide Polymorphism’ markers. Considering its public health importance, it is crucial to further investigate the species’ population genetic dynamic, including a larger sampling and additional genomic markers.

Assessing the distribution of invasive Asian mosquitoes in Northern Italy and modelling the potential spread of Aedes koreicus in Europe

In the last decade, Aedes koreicus and Aedes japonicus japonicus mosquitoes, which are competent vectors for various arboviruses of public health relevance, colonised Italy and other European countries. Nevertheless, information about their current and potential distribution is partial. Accordingly, in this study four regions of Northern Italy (Lombardy, Liguria, Piedmont and Aosta Valley) were surveyed during 2021 for the presence of eggs, larvae and pupae of these two invasive species. We found evidence for a widespread presence of Ae. koreicus in pre-Alpine territories of Lombardy and Piedmont. Larvae from the invasive subspecies of Ae. j. japonicus were also collected in the same geographic areas, though they were less frequent. Occurrence data from this study and results from previous monitoring campaigns were used to generate a Maxent model for the prediction of habitat suitability for Ae. koreicus mosquitoes in Northern Italy and the rest of Europe. Peri-urban areas located in proximity to forests, pastures and vineyards were revealed as highly suitable environments for colonisation by this invasive species. Maps of the potential distribution also suggest the presence of further suitable areas in currently uncolonized countries. We conclude that this invasive mosquito species has the potential for a broad expansion at the European level in the coming decades.

Emergence of the invasive Asian bush mosquito Aedes (Hulecoeteomyia) japonicus (Theobald, 1901) in the Czech Republic

BACKGROUND

Aedes japonicus is a mosquito species native to North-East Asia that was first found established outside its original geographic distribution range in 1998 and has since spread massively through North America and Europe. In the Czech Republic, the species was not reported before 2021.

METHODS

Aedes invasive mosquitoes (AIM) are routinely surveyed in the Czech Republic by ovitrapping at potential entry ports. This surveillance is supported by appeals to the population to report uncommon mosquitoes. The submission of an Ae. japonicus specimen by a citizen in 2021 was followed by local search for aquatic mosquito stages in the submitter's garden and short-term adult monitoring with encephalitis virus surveillance (EVS) traps in its surroundings. Collected Ae. japonicus specimens were subjected to nad4 haplotype and microsatellite analyses.

RESULTS

Aedes japonicus was detected for the first time in the Czech Republic in 2021. Aquatic stages and adults were collected in Prachatice, close to the Czech-German border, and eggs in Mikulov, on the Czech-Austrian border. Morphological identification was confirmed by molecular taxonomy. Genetic analysis of specimens and comparison of genetic data with those of other European populations, particularly from Germany, showed the Prachatice specimens to be most closely related to a German population. The Mikulov specimens were more distantly related to those, with no close relatives identifiable.

CONCLUSIONS

Aedes japonicus is already widely distributed in Germany and Austria, two countries neighbouring the Czech Republic, and continues to spread rapidly in Central Europe. It must therefore be assumed that the species is already present at more than the two described localities in the Czech Republic and will further spread in this country. These findings highlight the need for more comprehensive AIM surveillance in the Czech Republic.

From a long-distance threat to the invasion front: a review of the invasive Aedes mosquito species in Belgium between 2007 and 2020

Invasive mosquito species (IMS) and their associated mosquito-borne diseases are emerging in Europe. In Belgium, the first detection of Aedes albopictus (Skuse 1894) occurred in 2000 and of Aedes japonicus japonicus (Theobald 1901) in 2002. Early detection and control of these IMS at points of entry (PoEs) are of paramount importance to slow down any possible establishment. This article reviews the introductions and establishments recorded of three IMS in Belgium based on published (2007-2014) and unpublished (2015-2020) data collected during several surveillance projects. In total, 52 PoEs were monitored at least once for the presence of IMS between 2007 and 2020. These included used tyre and lucky bamboo import companies, airports, ports, parking lots along highways, shelters for imported cutting plants, wholesale markets, industrial areas, recycling areas, cemeteries and an allotment garden at the country border with colonised areas. In general, monitoring was performed between April and November. Mosquitoes were captured with adult and oviposition traps as well as by larval sampling. Aedes albopictus was detected at ten PoEs, Ae. japonicus at three PoEs and Aedes koreicus (Edwards 1917) at two PoEs. The latter two species have established overwintering populations. The percentage of PoEs positive for Ae. albopictus increased significantly over years. Aedes albopictus is currently entering Belgium through lucky bamboo and used tyre trade and passive ground transport, while Ae. japonicus through used tyre trade and probably passive ground transport. In Belgium, the import through passive ground transport was first recorded in 2018 and its importance seems to be growing. Belgium is currently at the invasion front of Ae. albopictus and Ae. japonicus. The surveillance and control management actions at well-known PoEs associated to long-distance introductions are more straightforward than at less-defined PoEs associated with short-distance introductions from colonised areas. These latter PoEs represent a new challenge for IMS management in Belgium in the coming years. Aedes albopictus is expected to become established in Belgium in the coming years, hence increasing the likelihood of local arbovirus transmission. The implementation of a sustainable, structured and long-term IMS management programme, integrating active and passive entomological surveillance, vector control and Public Health surveillance is therefore pivotal.

MEMO: Monitoring of exotic mosquitoes in Belgium

'MEMO

Monitoring of Exotic MOsquitoes in Belgium' is a sampling event dataset published by the Institute of Tropical Medicine (ITM) in Antwerp, Belgium. It forms part of the early detection of exotic mosquito species (EMS) along high-risk introduction routes in Belgium, where data are collected at defined points of entry (PoEs) using a standardised protocol. The MEMO dataset contains mosquito sampling counts performed between 2017 and 2020. MEMO+2020, an extension of the MEMO dataset, contains only Aedes albopictus mosquito trap counts performed in 2020. Here, we present these data published as a standardised Darwin Core archive, which includes, for each sampling event, an eventID, date, location and sampling protocol (in the event core); and an occurrenceID for each occurrence (tube), the number of collected individuals per tube, species status (present/absent), information on the identification and scientific name (in the occurrence extension).

Japanese Encephalitis Virus Interaction with Mosquitoes: A Review of Vector Competence, Vector Capacity and Mosquito Immunity

Japanese encephalitis virus (JEV) is a mosquito-borne zoonotic flavivirus and a major cause of human viral encephalitis in Asia. We provide an overview of the knowledge on vector competence, vector capacity, and immunity of mosquitoes in relation to JEV. JEV has so far been detected in more than 30 mosquito species. This does not necessarily mean that these species contribute to JEV transmission under field conditions. Therefore, vector capacity, which considers vector competence, as well as environmental, behavioral, cellular, and biochemical variables, needs to be taken into account. Currently, 17 species can be considered as confirmed vectors for JEV and 10 other species as potential vectors. Culex tritaeniorhynchus and Culex annulirostris are considered primary JEV vectors in endemic regions. Culex pipiens and Aedes japonicus could be considered as potentially important vectors in the case of JEV introduction in new regions. Vector competence is determined by various factors, including vector immunity. The available knowledge on physical and physiological barriers, molecular pathways, antimicrobial peptides, and microbiome is discussed in detail. This review highlights that much remains to be studied about vector immunity against JEV in order to identify novel strategies to reduce JEV transmission by mosquitoes.

First Detections of Culiseta longiareolata (Diptera: Culicidae) in Belgium and the Netherlands

Culiseta (Allotheobaldia) longiareolata (Macquart) (Diptera: Culicidae) is an ornithophilic mosquito species that occurs in the southern Palaearctic Region from the Azores to Central Asia, the Ethiopian Region, India, and Pakistan. Although it has a widespread distribution range, the species was only recently reported in Western and Central Europe. Between 2017 and 2020, larvae, pupae, and adults of Cs. longiareolata (n = 161) were found at 13 distinct locations in Belgium (n = 4) and The Netherlands (n = 9). Collected mosquitoes were morphologically identified and the identification was then validated by COI DNA barcoding. These are the first records of the species in the above-mentioned countries. The present results suggest that Cs. longiareolata could be increasing its distribution range in temperate regions, indicating a warming climate. As the species might be a potential vector of bird pathogens (e.g., West Nile virus), its spread in Western Europe is noteworthy.