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.

Updated distribution of anopheline mosquitoes in Hokkaido, Japan, and the first evidence of Anopheles belenrae in Japan

Background

In Hokkaido, northern island of Japan, at least seven cases of falciparum malaria were reported by 1951. A survey conducted at that time was unsuccessful in implicating any mosquito species as the possible vector. Although active anopheline mosquito surveillance continued until the middle of the 1980s, there is very limited information on their current status and distribution in Japan. Therefore, this study is an update on the current status and distribution of anopheline mosquitoes in Hokkaido based on a 15-year entomological surveillance between 2001 and 2015.

Methods

A survey of mosquitoes was conducted at 22 sites in Hokkaido, Japan, from 2001 to 2015. Adult mosquitoes were collected from cowsheds, lakesides, shrubs, and habitats ranging from open grassland to coniferous forest using a Centers for Disease Control and Prevention (CDC) miniature light trap enhanced with dry ice, aspirators, and sweeping nets. Larvae were collected from lakes, ponds, swamps, stagnant and flowing rivers, and paddy fields. All specimens were morphologically identified and subjected to polymerase chain reaction (PCR)-based sequence analysis of the internal transcribed spacer 2 ( ITS2) region of rDNA. Phylogenetic trees were reconstructed using the neighbor-joining method with the Kimura 2-parameter model on MEGA X version 10.2.2.

Results

A total of 46 anopheline specimens were used for the phylogenetic analysis. During the survey, a new member of the Anopheles hyrcanus group, An. belenrae, was discovered in eastern Hokkaido in 2004. Anopheles belenrae has since then been consistently found and confirmed to inhabit only this area of Japan. Four members of the An. hyrcanus group, namely An. belenrae, An. engarensis, An. lesteri, and An. sineroides, have been found in Hokkaido. The results also suggest that An. sinensis, formerly a dominant species throughout Japan, has become a rarely found species, at least currently in Hokkaido.

Conclusion

The updated distribution of anopheline mosquitoes in Hokkaido, Japan, showed considerable differences from that observed in previous surveys conducted from 1969 to 1984. In particular, areas where An. sinensis was previously distributed may have been greatly reduced in Hokkaido. The phylogenetic analysis revealed a novel An. hyrcanus group member identified as An. belenrae, described in South Korea in 2005. It is interesting that An. belenrae was confirmed to inhabit only eastern Hokkaido, Japan.

Graphical abstract

Comparative Phylogeography and Integrative Taxonomy of Ochlerotatus caspius (Dipera: Culicidae) and Ochlerotatus dorsalis

Given that accurately identifying pathogen vectors is vital for designing efficient mosquito control programs based on the proper surveillance of the epidemiologically important species, it has been suggested the complementary use of independently evolving genes and morphometric traits as a reliable approach for the characterization and delimitation of related species. Hence, we examined the spatial distribution of COI mtDNA and ITS2 rDNA variation from the historical perspective of Ochlerotatus caspius (Pallas, 1771) and O. dorsalis (Meigen, 1830), while simultaneously testing the utility of the two markers in integrative species delimitation when combined with phenotypic character analyses of larvae and adults. Despite the striking difference in haplotype diversity (high in COI mtDNA, low in ITS2 rDNA), no evident phylogeographic structure was apparent in the Palearctic O. caspius. The Holarctic O. dorsalis species was subdivided into two highly distinctive COI mtDNA phylogroups which corresponded to the Nearctic and Palearctic regions. Strong support for the independence of the two allopatric evolutionary lineages suggested that geographical barrier and climatic changes during Pleistocene caused vicariance of the ancestral range. COI mtDNA reliably distinguished O. caspius and O. dorsalis, while ITS2 rDNA yet again lacked the proper resolution for solving this problem. An integrative approach based on the larval and adult morphological traits have varying taxonomic applications due to their differential diagnostic values. Thus, by the implementation of an integrative taxonomic approach, we successfully detected species borders between the two epidemiologically relevant species and uncovered the presence of cryptic diversity within O. dorsalis.

DNA barcoding of mosquitoes collected through a nationwide survey in 2011 and 2012 in Malawi, Southeast Africa

We conducted a nationwide survey of mosquito distribution in Malawi from November 2011 to April 2012, and from July to September 2012. Using dried specimens of mosquito adults collected during the survey, we analyzed their cytochrome c oxidase subunit I (COI) gene sequences, prepared specimens, and registered the genetic information (658 bp) of 144 individuals belonging to 51 species of 10 genera in GenBank. Using the obtained genetic information, we analyzed the degree of intraspecific variation and investigated the various species from morphological and genetic perspectives. Moreover, we conducted phylogenetic analysis of the medically important species distributed from Africa to Asia and explored their geographical differentiation. Results showed that individuals morphologically classified as Culex univittatus complex included a individual of Cx. perexiguus which, to date, have not been reported in southern Africa. Furthermore, Mansonia uniformis, distributed in Africa and Asia, was revealed to belong to genetically distinct populations, with observed morphological differences of the samples suggesting that they are separate species. The results of genetic analysis further suggested that Cx. ethiopicus is not a synonym of Cx. bitaeniorhynchus, but that it is an independent species; although, in this study, the only definite morphological difference observed was in the shape of the wing scales. Further morphological and genetic investigation of individuals of these species, including larvae, is highly recommended.

Aedes albopictus and Aedes flavopictus (Diptera: Culicidae) pre-imaginal abundance patterns are associated with different environmental factors along an altitudinal gradient

Aedes (Stegomyia) albopictus (Skuse) is a major global invasive mosquito species that, in Japan, co-occurs with Aedes (Stegomyia) flavopictus Yamada, a closely related species recently intercepted in Europe. Here, we present results of a detailed 25-month long study where we biweekly sampled pupae and fourth instar larvae of these two species from ovitraps set along Mt. Konpira, Nagasaki, Japan. This setting allowed us to ask whether these species had different responses to changes in environmental variables along the altitudinal gradient of an urban hill. We found that spatially Ae. albopictus abundance decreased, while Ae. flavopictus abundance increased, the further away from urban land. Ae. flavopictus also was more abundant than Ae. albopictus in locations with homogenous vegetation growth with a high mean Enhanced Vegetation Index (EVI), platykurtic EVI, and low SD in canopy cover, while Ae. albopictus was more abundant than Ae. flavopictus in areas with more variable (high SD) canopy cover. Moreover, Ae. flavopictus abundance negatively impacted the spatial abundance of Ae. albopictus. Temporally we found that Ae. flavopictus was more likely to be present in Mt. Konpira at lower temperatures than Ae. albopictus. Our results suggest that spatial and temporal abundance patterns of these two mosquito species are partially driven by their different response to environmental factors.

Detection of Aedes flavopictus (Yamada, 1921), Netherlands, June 2019

In June 2019, a single specimen collected at a used tyre company was identified as Aedes flavopictus (Yamada, 1921), a sibling species of Ae. albopictus. Ae. flavopictus has not been recorded outside Japan and South Korea. Although it has only shown dengue virus vector competence under laboratory conditions, its detection demonstrates the value of active surveillance at risk locations and molecular tools for timely intervention against exotic mosquitoes with potential future public health impact.

Identification of Three Distinct Groups of Anopheles lindesayi in Japan by Morphological and Genetic Analyses

Anopheles (Anopheles) lindesayi Giles consists of 5 subspecies. In Japan, only one subspecies, An. l. japonicus Yamada, has been reported. Its geographical populations are morphologically diverse; however, they are regarded as a single subspecies. In this study, we re-evaluated the taxonomic status of An. l. japonicus in Japan, and that of another subspecies, An. l. pleccau, distributed in Taiwan, by comparative morphological and molecular analyses based on the gene sequences of mitochondrial DNA cytochrome c oxidase I (COI) and ribosomal DNA internal transcribed spacer 2 (ITS2). Nucleotide sequence divergence was calculated using the Kimura-two-parameter (K2P) distance model. Phylogenetic trees based on COI and ITS2 sequences showed 3 distinct clades: Eastern Japan, Western Japan, and the Ryukyus. The sequences of the Ryukyu specimens were located within the same clade as that of the sequences of the Taiwanese specimens. Regarding the COI sequences, the 3 geographical groups in Japan were genetically distinct. The following morphological characteristics distinguished the groups: larval seta 1-S, pupal setae 5 through segments IV-VII, and pupal setae 6 on segments IV-VII. Based on these results, it was revealed that An. l. japonicus included 3 genetically and morphologically distinct groups: 2 groups of An. l. japonicus and a group in the Ryukyus, which was a synonym of An. l. pleccau.

Culex (Culiciomyia) sasai (Diptera: Culicidae), senior synonym of Cx. spiculothorax and a new country record for Bhutan

Culex (Culiciomyia) spiculothorax was described from Thailand based on the presence of spiculation on the thorax of larvae. Adult females are characterized but are indistinguishable from those of related species, such as Cx. pallidothorax. Phylogenetic analysis of mitochondrial oxidase subunit I (COI) sequences revealed that specimens identified as Cx. spiculothorax from Thailand, Japan and Bhutan form a single clade with Cx. sasai from Japan (Kimura 2-parameter genetic distances 0-0.9%) that is clearly distinct from clades comprised of other species of subgenus Culiciomyia. Attempts to collect Cx. sasai from several locations in Japan were unsuccessful - only larvae with thoracic vesicular-like spicules identified as Cx. spiculothorax were collected. Careful examination of specimens collected near the type locality of Cx. sasai revealed the presence of spicules on the thorax. Based on these findings, Cx. spiculothorax is formally synonymized with Cx. sasai, which replaces the former as the species present in Thailand and is a new country record for Bhutan.