Mosquito Diversity and Population Genetic Structure of Six Mosquito Species From Hainan Island

Population genetic structure of Culex tritaeniorhynchus in different types of climatic zones in China

BACKGROUND

Culex tritaeniorhynchus is widely distributed in China, from Hainan Island in the south to Heilongjiang in the north, covering tropical, subtropical, and temperate climate zones. Culex tritaeniorhynchus carries 19 types of arboviruses. It is the main vector of the Japanese encephalitis virus (JEV), posing a serious threat to human health. Understanding the effects of environmental factors on Culex tritaeniorhynchus can provide important insights into its population structure or isolation patterns, which is currently unclear.

RESULTS

In total, 138 COI haplotypes were detected in the 552 amplified sequences, and the haplotype diversity (Hd) value increased from temperate (0.534) to tropical (0.979) regions. The haplotype phylogeny analysis revealed that the haplotypes were divided into two high-support evolutionary branches. Temperate populations were predominantly distributed in evolutionary branch II, showing some genetic isolation from tropical/subtropical populations and less gene flow between groups. The neutral test results of HNQH (Qionghai) and HNHK(Haikou) populations were negative (P < 0.05), indicating many low-frequency mutations in the populations and that the populations might be in the process of expansion. Moreover, Wolbachia infection was detected only in SDJN (Jining) (2.24%), and all Wolbachia genotypes belonged to supergroup B. To understand the influence of environmental factors on mosquito-borne viruses, we examined the prevalence of Culex tritaeniorhynchus infection in three ecological environments in Shandong Province. We discovered that the incidence of JEV infection was notably greater in Culex tritaeniorhynchus from lotus ponds compared to those from irrigation canal regions. In this study, the overall JEV infection rate was 15.27 per 1000, suggesting the current risk of Japanese encephalitis outbreaks in Shandong Province.

CONCLUSIONS

Tropical and subtropical populations of Culex tritaeniorhynchus showed higher genetic diversity and those climatic conditions provide great advantages for the establishment and expansion of Culex tritaeniorhynchus. There are differences in JEV infection rates in wild populations of Culex tritaeniorhynchus under different ecological conditions. Our results suggest a complex interplay of genetic differentiation, population structure, and environmental factors in shaping the dynamics of Culex tritaeniorhynchus. The low prevalence of Wolbachia in wild populations may reflect the recent presence of Wolbachia invasion in Culex tritaeniorhynchus.

Population Genetics of Culex tritaeniorhynchus (Diptera: Culicidae) in Türkiye

PURPOSE

Mosquitoes are important vectors of pathogens that can affect humans and animals. Culex tritaeniorhynchus is an important vector of arboviruses such as Japanese encephalitis virus, West Nile virus among various human and animal communities. These diseases are of major public health concern and can have huge economic and health burdens in prevalent countries. Although populations of this important mosquito species have been detected in the Mediterranean and Aegean regions of Türkiye; little is known about its population structure. Our study is to examine the population genetics and genetic composition of Cx. tritaeniorhynchus mosquitoes collected from several localities using cytochrome oxidase subunit I (COI) and the NADH dehydrogenase subunit 5 genes (ND5). This is the first extensive study of Cx. tritaeniorhynchus in the mainland Türkiye with sampling spanning many of provinces.

METHODS

In this study, DNA extraction, amplification of mitochondrial COI and ND5 genes and population genetic analyses were performed on ten geographic populations of Culex tritaeniorhynchus in the Aegean and Mediterranean region of Türkiye.

RESULTS

Between 2019 and 2020, 96 samples were collected from 10 geographic populations in the Aegean and Mediterranean regions; they were molecularly analyzed and 139 sequences (50 sequence for COI and 89 sequence for ND5) were used to determine the population structure and genetic diversity. For ND5 gene region, the samples produced 24 haplotypes derived from 15 variable sites and for COI gene region, 43 haplotypes were derived from 17 variable sites. The haplotype for both gene regions was higher than nucleotide diversity. Haplotype phylogeny revealed two groups present in all populations. AMOVA test results show that the geographical populations were the same for all gene regions. Results suggest that Cx. tritaeniorhynchus is a native population in Türkiye, the species is progressing towards speciation and there is no genetic differentiation between provinces and regions.

CONCLUSION

This study provides useful information on the molecular identifcation and genetic diversity of Cx. tritaeniorhynchus; these results are important to improve mosquito control programs.

Population genetic structure and wing geometric morphometrics of the filarial vector Armigeres subalbatus (Diptera: Culicidae) in Thailand

Armigeres subalbatus (Diptera: Culicidae) is a mosquito species of significant medical and veterinary importance. It is widely distributed across Southeast and East Asia and is commonly found throughout Thailand. This study assessed the genetic diversity and population structure of Ar. subalbatus in Thailand using the cytochrome c oxidase subunit I (COI) gene sequences. Additionally, wing shape variations among these populations were examined using geometric morphometrics (GM). Our results demonstrated that the overall haplotype diversity (Hd) was 0.634, and the nucleotide diversity (π) was 0.0019. Significant negative values in neutrality tests (p < 0.05) indicate that the Ar. subalbatus populations in Thailand are undergoing a phase of expansion following a bottleneck event. The mismatch distribution test suggests that the populations may have started expanding approximately 16,678 years ago. Pairwise genetic differentiation among the 12 populations based on Fst revealed significant differences in 32 pairs (p < 0.05), with the degree of differentiation ranging from 0.000 to 0.419. The GM analysis of wing shape also indicated significant differences in nearly all pairs (p < 0.05), except for between populations from Nakhon Pathom and Samut Songkhram, and between those from Chiang Mai and Mae Hong Son, suggesting no significant difference due to their similar environmental settings. These findings enhance our understanding of the population structure and phenotypic adaptations of mosquito vectors, providing vital insights for the formulation of more efficacious vector control strategies.

Insights into the mitochondrial cytochrome oxidase I (mt-COI) gene and wing morphometrics of Anopheles baimaii (Diptera: Culicidae) in malaria-endemic islands of Thailand

Anopheles baimaii (Diptera: Culicidae) significantly contributes to the transmission of parasites causing malaria in Southeast Asia and South Asia. This study examined the morphological (wing shape) and molecular (mitochondrial gene) variations of An. baimaii in four of Thailand's border islands, and also investigated the presence of Plasmodium parasites in these mosquitoes. No Plasmodium infections were detected in the samples. Significant differences in wing shape were observed in most island populations (p < 0.05). A single-linkage tree, constructed using Mahalanobis distances, clustered the populations into two groups based on geographical locations. Genetic variation in An. baimaii was also analyzed through cytochrome c oxidase subunit I (COI) gene sequences. This analysis identified 22 segregating sites and a low nucleotide diversity of 0.004. Furthermore, 18 distinct haplotypes were identified, indicating a high haplotype diversity of 0.825. Neutrality tests for the overall population revealed a significantly negative Fu's Fs value (-5.029), indicating a population expansion. In contrast, Tajima's D yielded a negative value (-1.028) that did not reach statistical significance. The mismatch distribution analysis exhibited a bimodal pattern, and the raggedness index was 0.068, showing no significant discrepancy (p = 0.485) between observed and expected distributions. Pairwise genetic differentiation assessments demonstrated significant differences between all populations (p < 0.05). These findings provide valuable insights into the COI gene and wing morphometric variations in An. baimaii across Thailand's islands, offering critical information for understanding the adaptations of this malaria vector and guiding future comprehensive research.

Mitochondrial and microbial diversity of the invasive mosquito vector species Culex tritaeniorhynchus across its extensive inter-continental geographic range

Background

Culex (Cx.) tritaeniorhynchus is an invasive mosquito species with an extensive and expanding inter-continental distribution, currently reported across Asia, Africa, the Middle East, Europe and now Australia. It is an important vector of medical and veterinary pathogens which cause significant morbidity and mortality in human and animal populations. Across regions endemic for Japanese encephalitis virus (JEV), Cx. tritaeniorhynchus is considered the major vector and has also been shown to contribute to the transmission of several other zoonotic arboviruses including Rift Valley fever virus (RVFV) and West Nile virus (WNV).

Methods

In this study, we used laboratory vector competence experiments to determine if Cx. tritaeniorhynchus from a Southern European population were competent JEV vectors. We also obtained samples from multiple geographically dispersed Cx. tritaeniorhynchus populations from countries within Europe, Africa, Eurasia and Asia to perform phylogenetic analysis to measure the level of mitochondrial divergence using the cytochrome oxidase subunit 1 ( CO1) gene. We also undertook bacterial 16S rRNA gene amplicon sequencing to determine microbial diversity and used multi-locus sequence typing (MLST) to determine any evidence for the presence of strains of the naturally occurring endosymbiotic bacterium Wolbachia.

Results

Cx. tritaeniorhynchus from a Greek population were shown be be competent vectors of JEV with high levels of virus present in saliva. We found a signficant level of mitochondrial genetic diversity using the mosquito CO1 gene between geographically dispersed populations. Furthermore, we report diverse microbiomes identified by 16S rRNA gene amplicon sequencing within and between geographical populations. Evidence for the detection of the endosymbiotic bacteria Wolbachia was confirmed using Wolbachia-specific PCR and MLST.

Conclusions

This study enhances our understanding of the diversity of Cx. tritaeniorhynchus and the associated microbiome across its inter-continental range and highlights the need for greater surveillance of this invasive vector species in Europe.

Association of virome dynamics with mosquito species and environmental factors

BACKGROUND

The pathogenic viruses transmitted by mosquitoes cause a variety of animal and human diseases and public health concerns. Virome surveillance is important for the discovery, and control of mosquito-borne pathogenic viruses, as well as early warning systems. Virome composition in mosquitoes is affected by mosquito species, food source, and geographic region. However, the complex associations of virome composition remain largely unknown.

RESULTS

Here, we profiled the high-depth RNA viromes of 15 species of field-caught adult mosquitoes, especially from Culex, Aedes, Anopheles, and Armigeres in Hainan Island from 2018 to 2020. We detected 57 known and 39 novel viruses belonging to 15 families. We established the associations of the RNA viruses with mosquito species and their foods, indicating the importance of feeding acquisition of RNA viruses in determining virome composition. A large fraction of RNA viruses were persistent in the same mosquito species across the 3 years and different locations, showing the species-specific stability of viromes in Hainan Island. In contrast, the virome compositions of single mosquito species in different geographic regions worldwide are visibly distinct. This is consistent with the differences in food sources of mosquitoes distributed broadly across continents.

CONCLUSIONS

Thus, species-specific viromes in a relatively small area are limited by viral interspecific competition and food sources, whereas the viromes of mosquito species in large geographic regions may be governed by ecological interactions between mosquitoes and local environmental factors. Video Abstract.

Characterizing the Wolbachia infection in field-collected Culicidae mosquitoes from Hainan Province, China

BACKGROUND

Mosquitoes are vectors of many pathogens, such as malaria, dengue virus, yellow fever virus, filaria and Japanese encephalitis virus. Wolbachia are capable of inducing a wide range of reproductive abnormalities in their hosts, such as cytoplasmic incompatibility. Wolbachia has been proposed as a tool to modify mosquitoes that are resistant to pathogen infection as an alternative vector control strategy. This study aimed to determine natural Wolbachia infections in different mosquito species across Hainan Province, China.

METHODS

Adult mosquitoes were collected using light traps, human landing catches and aspirators in five areas in Hainan Province from May 2020 to November 2021. Species were identified based on morphological characteristics, species-specific PCR and DNA barcoding of cox1 assays. Molecular classification of species and phylogenetic analyses of Wolbachia infections were conducted based on the sequences from PCR products of cox1, wsp, 16S rRNA and FtsZ gene segments.

RESULTS

A total of 413 female adult mosquitoes representing 15 species were identified molecularly and analyzed. Four mosquito species (Aedes albopictus, Culex quinquefasciatus, Armigeres subalbatus and Culex gelidus) were positive for Wolbachia infection. The overall Wolbachia infection rate for all mosquitoes tested in this study was 36.1% but varied among species. Wolbachia types A, B and mixed infections of A × B were detected in Ae. albopictus mosquitoes. A total of five wsp haplotypes, six FtsZ haplotypes and six 16S rRNA haplotypes were detected from Wolbachia infections. Phylogenetic tree analysis of wsp sequences classified them into three groups (type A, B and C) of Wolbachia strains compared to two groups each for FtsZ and 16S rRNA sequences. A novel type C Wolbachia strain was detected in Cx. gelidus by both single locus wsp gene and the combination of three genes.

CONCLUSION

Our study revealed the prevalence and distribution of Wolbachia in mosquitoes from Hainan Province, China. Knowledge of the prevalence and diversity of Wolbachia strains in local mosquito populations will provide part of the baseline information required for current and future Wolbachia-based vector control approaches to be conducted in Hainan Province.

Emergence of zoonotic Brugia pahangi parasite in Thailand

Zoonotic Brugia pahangi parasite infections in humans have emerged over two decades in Southeast Asia (SEA), including Malaysia and Thailand. The species is commonly found in domestic cats and dogs as the natural reservoir hosts. The sporadic transmission pattern of B. pahangi zoonosis causes childhood infections in Thailand and adulthood infections in Malaysia. It is crucial to understand the vulnerability in how zoonotic B. pahangi parasite is transmitted to susceptible persons in receptive settings and the exposure to the infection under impoverished environment to which the human-vector-animal interactions are related. This acquisition of knowledge will help multiple health science professions to apply One Health approach to strengthening the capacity in diagnosis and surveillance, and hence detecting and monitoring the "lingering" zoonotic B. pahangi infections present in vulnerable populations in Thailand and elsewhere in SEA. In this review article, the authors focused on articulating the concepts of plantation-related zoonotic B. pahangi filariasis by updating current knowledge of B. pahangi life cycle, vector's life cycle and current state of research on the epidemiology and ecology of B. pahangi zoonosis.

Global Distribution of Culex tritaeniorhynchus and Impact Factors

Culex tritaeniorhynchus is the primary vector of Japanese encephalitis (JE) and has a wide global distribution. However, the current and future geographic distribution maps of Cx. tritaeniorhynchus in global are still incomplete. Our study aims to predict the potential distribution of Cx. tritaeniorhynchus in current and future conditions to provide a guideline for the formation and implementation of vector control strategies all over the world. We collected and screened the information on the occurrence of Cx. tritaeniorhynchus by searching the literature and online databases and used ten algorithms to investigate its global distribution and impact factors. Cx. tritaeniorhynchus had been detected in 41 countries from 5 continents. The final ensemble model (TSS = 0.864 and AUC = 0.982) indicated that human footprint was the most important factor for the occurrence of Cx. tritaeniorhynchus. The tropics and subtropics, including southeastern Asia, Central Africa, southeastern North America and eastern South America, showed high habitat suitability for Cx. tritaeniorhynchus. Cx. tritaeniorhynchus is predicted to have a wider distribution in all the continents, especially in Western Europe and South America in the future under two extreme emission scenarios (SSP5-8.5 and SSP1-2.6). Targeted strategies for the control and prevention of Cx. tritaeniorhynchus should be further strengthened.

Genetic Diversity, Haplotype Relationships, and kdr Mutation of Malaria Anopheles Vectors in the Most Plasmodium knowlesi-Endemic Area of Thailand

Plasmodium knowlesi, a malaria parasite that occurs naturally in long-tailed macaques, pig-tailed macaques, and banded leaf monkeys, is currently regarded as the fifth of the human malaria parasites. We aimed to investigate genetic diversity based on the cytochrome c oxidase subunit I (COI) gene, detect Plasmodium parasites, and screen for the voltage-gated sodium channel (VGSC)-mutation-mediated knockdown resistance (kdr) of Anopheles mosquitoes in Ranong province, which is the most P. knowlesi-endemic area in Thailand. One hundred and fourteen Anopheles females belonging to eight species, including An. baimaii (21.05%), An. minimus s.s. (20.17%), An. epiroticus (19.30%), An. jamesii (19.30%), An. maculatus s.s. (13.16%), An. barbirostris A3 (5.26%), An. sawadwongporni (0.88%), and An. aconitus (0.88%), were caught in three geographical regions of Ranong province. None of the Anopheles mosquitoes sampled in this study were infected with Plasmodium parasites. Based on the sequence analysis of COI sequences, An. epiroticus had the highest level of nucleotide diversity (0.012), followed by An. minimus (0.011). In contrast, An. maculatus (0.002) had the lowest level of nucleotide diversity. The Fu's Fs and Tajima's D values of the Anopheles species in Ranong were all negative, except the Tajima's D values of An. minimus (0.077). Screening of VGSC sequences showed no presence of the kdr mutation of Anopheles mosquitoes. Our results could be used to further select effective techniques for controlling Anopheles populations in Thailand's most P. knowlesi-endemic area.

Modification of the Folmer primers for the cytochrome c oxidase gene facilitates identification of mosquitoes

BACKGROUND

Accurate identification of mosquito species is essential for the development and optimization of strategies to control mosquitoes and mosquito-borne diseases. Problems with the morphological identification of mosquito species have led to the use of molecular identification techniques, in particular the Folmer cytochrome c oxidase subunit I (COI) PCR system (FCOS), originally designed to identify a range of other invertebrates.

METHODS

As there can be difficulties identifying mosquitoes using FCOS, we re-evaluated the FCOS primers and developed a new COI-based SYBR PCR (the Auburn COI system-AUCOS) to improve the molecular identification of mosquitoes. Sequence data in GenBank for 33 species from 10 genera of mosquitoes were used to develop our AUCOS primers. Two molecular assays (AUCOS, FCOS) and morphological identification were carried out on mosquitoes collected from the field in Auburn, Alabama (USA) and on Saint Kitts.

RESULTS

With a convenience sample of individual mosquitoes comprising 19 species from six genera in Saint Kitts (n = 77) and Auburn (n = 48), our AUCOS provided higher-quality sequence data than FCOS. It also proved more sensitive than FCOS, successfully amplifying 67.5% (85/126) as opposed to 16.7% (21/126) of the samples. The species determined by morphology, or genus with damaged samples, matched that as determined by AUCOS for 84.9% (62/73) of the samples. Morphological classification was confirmed by FCOS with 81.0% (17/21) of samples producing utilizable sequences. While both FCOS and AUCOS correctly identified all the Aedes, Anopheles, Deinocerites, and Uranotaenia species in the study, identification of Culex species was less successful with both methods: 50.0% (3/6) by FCOS and 35.7% (5/14) by AUCOS.

CONCLUSIONS

The AUCOS DNA barcoding system for mosquito species described in this study is superior to the existing FCOS for the identification of mosquito species. As AUCOS and FCOS amplify the same variable region of the COI, the large amount of existing data on GenBank can be used to identify mosquito species with sequences produced by either PCR.

Arbovirus Epidemiology: The Mystery of Unnoticed Epidemics in Ghana, West Africa

It is evident that all the countries surrounding Ghana have experienced epidemics of key arboviruses of medical importance, such as the recent dengue fever epidemic in Burkina Faso. Therefore, Ghana is considered a ripe zone for epidemics of arboviruses, mainly dengue. Surprisingly, Ghana never experienced the propounded deadly dengue epidemic. Indeed, it is mysterious because the mosquito vectors capable of transmitting the dengue virus, such as Aedes aegypti, were identified in Ghana through entomological investigations. Additionally, cases may be missed, as the diagnostic and surveillance capacities of the country are weak. Therefore, we review the arbovirus situation and outline probable reasons for the epidemic mystery in the country. Most of the recorded cases of arbovirus infections were usually investigated via serology by detecting IgM and IgG immunoglobulins in clinical samples, which is indicative of prior exposure but not an active case. This led to the identification of yellow fever virus and dengue virus as the main circulating arboviruses among the Ghanaian population. However, major yellow fever epidemics were reported for over a decade. It is important to note that the reviewed arboviruses were not frequently detected in the vectors. The data highlight the necessity of strengthening the diagnostics and the need for continuous arbovirus and vector surveillance to provide an early warning system for future arbovirus epidemics.

Mosquito (Diptera: Culicidae) Diversity and Community Structure in Doi Inthanon National Park, Northern Thailand

Urbanization and human activities create new suitable aquatic habitats for the immature stages of mosquitoes in many countries. This also applies to Doi Inthanon National Park in northern Thailand, which is named for the highest mountain in the country. Despite its popularity, there is no information regarding mosquito diversity and community structure in the different ecosystems of the park. Monthly collections of immature stages from various habitats were conducted from August 2004 to December 2005 using dipping and sucking methods. The specimens collected from each habitat were reared to adults and identified based on their morphology. Diversity parameters and community structure were statistically analyzed. A total of 140 species (3795 specimens) belonging to 15 genera were identified. Among these, four genera (Culex, Aedes, Anopheles, and Uranotaenia) had high species richness, each represented by 48, 27, 19, and 15 species, respectively. Aedes albopictus was the most relatively abundant species, representing 6.7% of the total number of captured specimens, followed by Tripteroides aranoides (5.6%) and Cx. mimulus (5%). Species richness in natural habitats was significantly higher than in artificial containers. Species richness and abundance were highest in the rainy season. In comparison to agricultural areas and villages, mosquito diversity was found to be higher in forest areas. Ground pools, stream pools, rock pools, bamboo stumps, bamboo internode, and rice fields were the most preferred natural habitats. The results indicate that Doi Inthanon National Park has a high mosquito diversity. Each species exhibits differences in abundance and distribution in different habitats, which is useful information for planning conservation measures and vector control in the park.

Mansonia spp. population genetics based on mitochondrion whole-genome sequencing alongside the Madeira River near Porto Velho, Rondonia, Brazil

In high abundance, females of the genus Mansonia (Blanchard) can be a nuisance to humans and animals because they are voraciously hematophagous and feed on the blood of a myriad of vertebrates. The spatial-temporal distribution pattern of Mansonia species is associated with the presence of their host plants, usually Eichhornia crassipes, E. azurea, Ceratopteris pteridoides, Limnobium laevigatum, Pistia stratiotes, and Salvinia sp. Despite their importance, there is a lack of investigation on the dispersion and population genetics of Mansonia species. Such studies are pivotal to evaluating the genetic structuring, which ultimately reflects populational expansion-retraction patterns and dispersal dynamics of the mosquito, particularly in areas with a history of recent introduction and establishment. The knowledge obtained could lead to better understanding of how anthropogenic changes to the environment can modulate the population structure of Mansonia species, which in turn impacts mosquito population density, disturbance to humans and domestic animals, and putative vector-borne disease transmission patterns. In this study, we present an Illumina NGS sequencing protocol to obtain whole-mitogenome sequences of Mansonia spp. to assess the microgeographic genetic diversity and dispersion of field-collected adults. The specimens were collected in rural environments in the vicinities of the Santo Antônio Energia (SAE) hydroelectric reservoir on the Madeira River.

Genetic structure of Culex tritaeniorhynchus (Diptera: Culicidae) based on COI DNA barcodes

Culex tritaeniorhynchus Gile is a major vector of Japanese encephalitis in China. The population genetics study is crucial as it helps understanding the epidemiological aspects of mosquito-brone diseases and improving vector control measures. Here, the genetic population structure of C. tritaeniorhynchus in the mainland China were estimated using the cytochrome c oxidase subunit 1 (COI) DNA barcodes region. 485 individuals of C. tritaeniorhynchus were collected from 38 sampling sites in 21 geographic populations in the mainland China. In total, 485 sequences were used to explore the population structure and genetic diversity. The results showed that the populations of C. tritaeniorhynchus had high haplotype diversity (Hd = 0.98, with 303 haplotypes), low nucleotide diversity (p = 0.02245) and high gene flow (Nm = 47.11) with two maternal lineages and four groups. An AMOVA indicated that 98.8% of the total variation originated from variation within populations. In addition, the population genetic structure exhibited by C. tritaeniorhynchus filling the vacant of the genetic structure in the mainland China. Human activities may also assist mosquito movement and migration. Gene flow among the populations of C. tritaeniorhynchus can facilitate the spread of insecticide resistance genes over geographical areas, and it will be a challenging for controlling the populations.