Mitochondrial DNA barcoding of mosquito species (Diptera: Culicidae) in Thailand

Demographic inference from the mt-DNA COI gene and wing geometry of Culex gelidus (Diptera: Culicidae), an important vector of Japanese encephalitis in Thailand

Culex gelidus (Diptera: Culicidae), an important vector of the Japanese encephalitis virus (JEV), contributes to human viral encephalitis in many Asian countries, including Thailand. This study represents the first investigation of the demographic patterns of Cx. gelidus populations in Thailand using cytochrome c oxidase subunit I (COI) gene analysis and wing geometric morphometrics (GM). Mosquitoes were collected from 10 provinces across six regions of Thailand in 2022. Analysis of the COI sequences (n = 182) indicated high haplotype diversity (0.882) and low nucleotide diversity (0.006), with 72 haplotypes identified. The haplotype network demonstrated no profound splits among the geographic populations. Neutral tests, including Tajima's D and Fu's Fs, displayed negative values, with a significant result observed for Fu's Fs (-33.048, p < 0.05). The mismatch distribution analysis indicated that the population does not statistically deviate from a model of sudden population expansion (SSD = 0.010, p > 0.05; Rg = 0.022, p > 0.05). The estimations suggest that the Cx. gelidus population in Thailand began its expansion approximately between 459,243 and 707,011 years ago. The Mantel test showed no significant relationship between genetic and geographic distances (r = 0.048, p > 0.05). Significant phenotypic differences (based on wing shape) were observed among most populations. Additionally, in this study, we found no significant relationships between phenotypic and genetic distances (r = 0.250, p > 0.05). Understanding the genetic and morphological dynamics of Cx. gelidus is vital for developing targeted surveillance and vector control measures. This knowledge will also help to predict how future environmental changes might affect these populations, thereby informing long-term vector management strategies.

Island mosquitoes of Thailand: an update on species diversity and DNA barcoding

Mosquitoes (Diptera: Culicidae) are among the most medically significant insects, with several species acting as vectors for human pathogens. Although there are frequent reports of mosquito-borne diseases in the border island areas of Thailand, comprehensive data on the diversity and DNA barcoding of these mosquito species remain limited. This study investigated mosquito diversity in two main archipelagos in Thailand-the Trat archipelago (comprising Chang Island and Kood Island) and the Ranong archipelago (comprising Chang Island and Phayam Island)-and generated DNA barcode data from the mosquitoes found there. The survey across these islands discovered a total of 41 species, highlighting the presence of several species known to be vectors for human diseases. Thirty-seven mosquito species from the island areas were documented to provide reference DNA barcode sequences for mosquitoes in Thailand's island regions. Two species, Aedes fumidus and Finlaya flavipennis, have been added as new COI sequence records in the database. DNA barcoding was highly effective in classifying almost all species by identifying barcoding gaps, except for Anopheles baimaii and Anopheles dirus, which could not be distinguished. Additionally, the study noted that geographical variations might influence certain mosquito species, such as Anopheles barbirostris A3 and Mansonia dives, causing them to be split into two distinct subgroups. The findings of this study are crucial, as they aid in classifying mosquito species using molecular techniques and expand our knowledge of disease vectors in these biodiverse regions.

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.

First report on the molecular phylogenetics and population genetics of Aedes aegypti in Iran

BACKGROUND

Aedes aegypti, the primary vector of various human arboviral diseases, is a significant public health threat. Aedes aegypti was detected in Iran in 2018, in Hormozgan province, but comprehensive information regarding its genetic diversity and origin within the country remains scarce. This study aimed to determine the origin and genetic diversity of Ae. aegypti in southern Iran.

METHODS

Aedes aegypti mosquitoes were collected from Bandar Abbas City, Hormozgan Province, southern Iran, between May and July 2022. Specimens were morphologically identified. Origin and assess genetic diversity were assessed based on the mitochondrial DNA-encoded cytochrome c oxidase subunit I (mtDNA-COI) gene.

RESULTS

BLAST (basic local alignment search tool) analysis confirmed the accuracy of the morphological identification of all specimens as Ae. aegypti, with 100% similarity to GenBank sequences. Calculated variance and haplotype diversity were 0.502 and 0.00157, respectively. Among the 604 examined nucleotide sequences, only a single site was non-synonymous. Total nucleotide diversity and average pairwise nucleotides were determined as 0.00083 and 0.502, respectively. Fu and Li's D test values were not statistically significant. Strobeck's S statistic value was 0.487, and Tajima's D value was 1.53395; both were not statistically significant (P > 0.10).

CONCLUSIONS

Phylogenetic analysis revealed two distinct clades with minimal nucleotide differences and low haplotype diversity, suggesting the recent establishment of Ae. Aegypti in the southern region of Iran. The phylogenetic analysis also indicated an association between Ae. aegypti populations and mosquitoes from Saudi Arabia and Pakistan.

Outline-based geometric morphometrics: Wing cell differences for mosquito vector classification in the Tanaosri mountain range, Thailand

Recent studies have revealed taxonomic signals within the wing cells of certain mosquito species. In our study, wing cell differentiation among mosquito vectors from the Tanaosri mountain range in Thailand was evaluated using the outline-based geometric morphometric (GM) approach. Our focus was on four specific wing cells for GM analysis: the wing contour (external cell), the second submarginal cell (internal cell 1), the first posterior cell (internal cell 2), and the third posterior cell (internal cell 3). Before proceeding with the GM approach, the identity of seven mosquito genera and 21 species was confirmed using molecular techniques. Our validated classification tests demonstrated that the performance of mosquito species classification varies according to genus. Notably, three Aedes species exhibited the highest accuracy for both internal cell 2 and internal cell 3, each registering a score of 93.20 %. In the case of two Mansonia species, the wing contour displayed a remarkable accuracy of 98.57 %. Consequently, we suggest the use of the outline-based GM approach, particularly focusing on the wing contour, for differentiating Mansonia annulifera and Mansonia uniformis. In contrast, the highest accuracy for classifying Culex species was found in internal cell 1, at 75.51 %, highlighting the challenges due to similarities in wing cells within this genus. These findings provide a guideline for future applications of the outline-based GM approach, focusing on wing cells, as an alternative method to classify mosquito vector species.

Wing geometric morphometrics and DNA barcoding to distinguish three closely related species of Armigeres mosquitoes (Diptera: Culicidae) in Thailand

Armigeres subalbatus, a mosquito species widely found in Thailand and other Asian countries, serves as a vector for filarial parasites, affecting both humans and animals. However, the surveillance of this vector is complicated because of its morphological similarity to two other species, Armigeres dohami and Armigeres kesseli. To differentiate these morphologically similar species, our study employed both wing geometric morphometrics (GM) and DNA barcoding, offering a comprehensive approach to accurately identify these closely related Armigeres species in Thailand. Our GM analyses based on shape demonstrated significant accuracy in differentiating Armigeres species. Specifically, the outline-based GM method focusing on the 3rd posterior cell exhibited an accuracy rate of 82.61%, closely followed by the landmark-based GM method with 81.54%. Both these GM techniques effectively distinguished Ar. subalbatus from Ar. dohami and Ar. kesseli. Regarding DNA barcoding, our investigation of pairwise intra- and interspecific divergences revealed a "barcoding gap". Furthermore, the results of species confirmation using both species delimitation methods including the automatic barcode gap discovery method (ABGD) and the Multi-rate Poisson tree process (mPTP) were consistent with those of morphological identification, sequence comparisons with the GenBank and Barcode of Life Data System (BOLD) databases, and the neighbor-joining tree construction. These consistent results emphasize the efficacy of DNA barcoding in the precise identification of Armigeres species.

Molecular characterization and genetic diversity of three Stomoxys flies S. bengalensis, S. calcitrans, and S. sitiens (Diptera: Muscidae) in Central Thailand

Stomoxys flies (Diptera: Muscidae) are hematophagous ectoparasites of medical and veterinary importance. In this study, three Stomoxys species, i.e. S. bengalensis, S. calcitrans, and S. sitiens, were collected from three provinces in Central Thailand with the aim of estimating the genetic divergence between species, for species identification, as well as within species, for a genetic diversity study based on the cytochrome c oxidase subunit I (COI) gene. Our results showed that the average intraspecific genetic divergences of Stomoxys flies ranged from 0.11% in S. sitiens to 0.98% in S. calcitrans, whereas the average interspecific genetic divergences ranged from 5.24% between S. sitiens and S. bengalensis to 6.69% between S. calcitrans and S. bengalensis. In addition, there was no overlap between the intraspecific and interspecific genetic divergences. The COI sequence analysis revealed a high haplotype diversity and low nucleotide diversity, reflecting a rapid population expansion after past bottlenecks. Moreover, there was no significant difference (P > 0.05) in the pairwise population differentiation (Fst) among Stomoxys flies in Central Thailand, because of the lack of natural barriers, thus allowing genetic exchange between them. The monitoring of the haplotype network revealed that two lineages of S. calcitrans in Central Thailand were distributed in all study areas, including the Nakhon Pathom, Pathum Thani, and Saraburi Provinces. These findings may improve our understanding of the genetic patterns of these three Stomoxys flies, as well as the underlying biological mechanisms, which is knowledge that can be used for further effective control of these flies.

Molecular and morphometric differentiation of secondary filariasis vector Coquillettidia mosquitoes (Diptera: Culicidae) in Thailand

Coquillettidia mosquitoes are important nuisance-biting pests and a vector of brugian filariasis in Thailand. However, comprehensive information about these mosquitoes remains unavailable such as molecular and morphometric differences among species. The lack of vector knowledge on Coquillettidia species could affect future disease control. This study aims to investigate differences in molecular variations based on mitochondrial cytochrome oxidase subunit I (COI) gene and wing geometric traits of three Coquillettidia species, namely Cq. crassipes, Cq. nigrosignata, and Cq. ochracea in Thailand. The results of molecular analyses revealed the differences among three Coquillettidia species. The genetic difference measure based on the Kimura two-parameter model among three Coquillettidia species showed low intraspecific distances (0%-3.05%) and large interspecific distances (10.10%-12.41%). The values of intra- and inter-genetic differences of three Coquillettidia species did not overlap which showed the existence of a barcoding gap indicating the efficiency of the identification based on the COI gene. As with molecular analysis, the landmark-based geometric morphometrics approach based on wing shape analysis indicated three distinct species groups which were supported by the high total performance score of cross-validated classification (97.16%). These results provide the first evidence of taxonomic signal based on molecular and wing geometric differences to support species identification and biological variations of Coquillettidia mosquitoes in Thailand for understanding these rare vector mosquitoes in depth and leading to effective further mosquito control.

Species Identification of the Major Japanese Encephalitis Vectors within the Culex vishnui Subgroup (Diptera: Culicidae) in Thailand Using Geometric Morphometrics and DNA Barcoding

Japanese encephalitis (JE) is a viral infection of the brain caused by the Japanese encephalitis virus, which spreads globally, particularly in 24 countries of Southeast Asia and the Western Pacific region. In Thailand, the primary vectors of JE are Cx. pseudovishnui, Cx. tritaeniorhynchus, and Cx. vishnui of the Cx. vishnui subgroup. The morphologies of three mosquito species are extremely similar, making identification challenging. Thus, geometric morphometrics (GM) and DNA barcoding were applied for species identification. The results of cross-validation reclassification revealed that the GM technique based on wing shape analysis had relatively high potential for distinguishing Cx. pseudovishnui, Cx. tritaeniorhynchus, and Cx. vishnui (total performance = 88.34% of correctly assigned individuals). While the DNA barcoding yielded excellent results in identifying these Culex species based on the DNA barcode gap (average intraspecific genetic distance = 0.78% ± 0.39% and average interspecific genetic distance = 6.14% ± 0.79%). However, in the absence of the required facilities for DNA barcoding, GM techniques can be employed in conjunction with morphological methods to enhance the reliability of species identification. Based on the results of this study, our approach can help guide efforts to identify members of the Cx. vishnui subgroup, which will be useful for the effective vector control of JE in Thailand.

Evaluation of Modern Techniques for Species Identification of Lutzia Mosquitoes (Diptera: Culicidae) in Thailand: Geometric Morphometrics and DNA Barcoding

There are four species of Lutzia mosquitoes in Thailand, including Lutzia chiangmaiensis, Lt. fuscana, Lt. halifaxii, and Lt. vorax. The accurate species identification of adult Lutzia mosquitoes based on morphological features requires many body parts, including the abdominal terga and wing. However, species identification is difficult in the case of damaged specimens when some of their morphological character is missing due to transit or gathering in the field. Thus, we evaluated the efficacy of the landmark-based geometric morphometric (GM) approach for the discrimination of Lutzia species in Thailand. In addition, DNA barcoding was also used in parallel with the GM approach to identify the species. Larvae of Lutzia were collected, raised into adults, and identified based on their morphological characteristics. The validated reclassification test results clearly demonstrated that wing shape resulted in a high level of success in identification (correct identifications ranged from 92.50% to 100%); however, based on the DNA barcoding analyses, our results showed that it was poorly effective in identifying Lt. fuscana and Lt. halifaxii based on an overlap between the intraspecific and interspecific divergence. Moreover, our survey results provide updates on the distribution of Lt. chiangmaiensis and Lt. vorax in Thailand. This research will help medical entomologists more efficiently identify mosquitoes in the genus Lutzia, resulting in more effective mosquito control and surveillance.

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.

Geometric morphometric and molecular techniques for discriminating among three cryptic species of the Anopheles barbirostris complex (Diptera: Culicidae) in Thailand

Anopheles members of the Barbirostris complex are important vectors of malaria in Thailand. However, they are morphologically indistinguishable because they are closely related species. In this study, wing geometric morphometrics (GM) and DNA barcoding based on the cytochrome c oxidase subunit 1 (COI) gene were applied to differentiate cryptic species of the Barbirostris complex in Thailand. Three cryptic species of the Barbirostris complex, Anopheles dissidens (19.44%), Anopheles saeungae (24.54%), and Anopheles wejchoochotei (56.02%) were initially identified using the multiplex polymerase chain reaction assay. DNA barcoding analyses showed low intraspecific distances (range, 0.27%–0.63%) and high interspecific distances (range, 1.92%–3.68%), consistent with the phylogenetic analyses that showed clear species groups. While wing size and shape analyses based on landmark-based GM indicated differences between three species (p < 0.05). The cross-validated reclassification revealed that the overall efficacy of wing size analysis for species identification of the Barbirostris complex was less than the wing shape analysis (56.43% vs. 74.29% total performance). Therefore, this study's results are guidelines for applying modern techniques to identify members within the Barbirostris complex, which are still difficult to distinguish by morphology-based identification and contribute to further appropriate malaria control.

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DNA barcoding based on the cytochrome c oxidase subunit 1 (COI) gene is the most reliable identification tool for the Anopheles barbirostris complex.

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Analysis of wing size and shape of Anopheles dissidens, An. saeungae and An. wejchoochotei based on geometric morphometrics revealed differences between species (p < 0.05).

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The efficacy of wing shape analysis for species identification of the Barbirostris complex was moderate levels of performance (74.29% accuracy score).