Anopheles prachongae, a new species of the Gigas Complex of subgenus Anopheles (Diptera: Culicidae) in Thailand, contrasted with known forms of the complex

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Study of mosquito fauna in rice ecosystems around Hanoi, Northern Vietnam

Species of the Culex vishnui subgroup, Cx. fuscocephala and Cx. gelidus, which are known Japanese encephalitis (JE) vectors, are distributed in rice agroecosystems in Asian countries. Hence, although ecological studies of rice agroecosystems in northern Vietnam are necessary, very few integrated studies of breeding habitats of mosquitoes, including JE vectors, have been conducted. We carried out a field study and investigated the mosquito fauna in six rice production areas in northern Vietnam during the rainy and dry seasons of 2009. Mosquitoes and potential mosquito predators were collected from aquatic habitats by using larval dippers. We collected 1780 Culex individuals (including 254 Cx. tritaeniorhynchus; 113 Cx. vishnui, 58 Cx. vishnui complex, consisting of Cx. vishnui and Cx. pseudovishnui; 12 Cx. gelidus; 1 Cx. bitaeniorhynchus; and 1 Cx. fuscocephala), 148 Anopheles individuals (including 5 An. vagus), 1 Mansonia annulifera, and 1 Mimomyia chamberlaini during the rainy season. During the dry season, we collected 176 Culex individuals (including 33 Cx. vishnui, 24 Cx. tritaeniorhynchus, 8 Cx. vishnui complex, and 1 Cx. gelidus) and 186 Anopheles individuals (including 9 An. tessellatus, 2 An. kochi, and 2 An. barbumbrosus). We found mosquitoes in all aquatic habitats, namely, rice fields, ditches, ponds, wetlands, irrigation canals, and rice nurseries, and Cx. tritaeniorhynchus and Cx. vishnui complex were found in all the above six areas. Heteroptera such as Micronecta, Veliidae, and Pleidae were abundant and widely distributed in both the seasons. The abundance of mosquito larvae was higher in the rice fields, ditches, and ponds during the rainy season than during the dry season. Cx. tritaeniorhynchus, Cx. vishnui complex, Cx. fuscocephala, and Cx. gelidus were abundant in rice agroecosystems (rice fields, ditches, ponds, and wetlands) in northern Vietnam, and their abundance was high during the rainy season. These findings deepen our understanding of mosquito ecology and strengthen mosquito control strategies to be applied in rice ecosystems Vietnam in the future

Evidence to Support Karyotypic Variation of the Mosquito, Anopheles peditaeniatus in Thailand

Eight isoline colonies of Anopheles peditaeniatus Leicester (Diptera: Culicidae) were established from wild-caught females collected from buffalo-baited traps at 8 localities in Thailand. They showed 2 types of X (X2, X3) and 4 types of Y (Y2, Y3, Y4, Y5) chromosomes based on the number and amount of major block(s) of heterochromatin present in the heterochromatic arm, and were tentatively designated as Forms B (X2, X3, Y2), C (X3, Y3), D (X3, Y4) and E (X2, X3, Y5). Form B was found in Nan, Ratchaburi, and Chumphon provinces; Form C was obtained in Chon Buri province; Form D was recovered in Kamphaeng Phet province; and Form E was acquired in Chiang Mai, Udon Thani, and Ubon Ratchathani provinces. Crossing studies among the 8 isoline colonies, which were representative of 4 karyotypic forms of An. peditaeniatus, revealed genetic compatibility in providing viable progenies and synaptic salivary gland polytene chromosomes through F2-generations, thus suggesting the conspecific nature of these karyotypic forms. These results were supported by the very low intraspecific sequence variations (0.0 – 1.1%) of the nucleotide sequences in ribosomal DNA (ITS2) and mitochondrial DNA (COI and COII) of the 4 forms

Malaria vectors of Timor-Leste

Background: The island of Timor lies at the south-eastern edge of Indonesia on the boundary of the Oriental and Australian faunal regions. The country of Timor-Leste, which occupies the eastern part of the island, is malarious but anopheline faunal surveys and malaria vector incrimination date back to the 1960 s. Over the last decade the malaria vectors of south-east Asia and the south-west Pacific have been intensely studied using molecular techniques that can confirm identification within complexes of isomorphic species. The aim of this study is to accurately identify the Anopheles fauna of Timor-Leste using these techniques

An effective method for the identification and separation of Anopheles minimus, the primary malaria vector in Thailand, and its sister species Anopheles harrisoni, with a comparison of their mating behaviors

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Estimating the Magnitude and Direction of Altered Arbovirus Transmission Due to Viral Phenotype

Vectorial capacity is a measure of the transmission potential of a vector borne pathogen within a susceptible population. Vector competence, a component of the vectorial capacity equation, is the ability of an arthropod to transmit an infectious agent following exposure to that agent. Comparisons of arbovirus strain-specific vector competence estimates have been used to support observed or hypothesized differences in transmission capability. Typically, such comparisons are made at a single time point during the extrinsic incubation period, the time in days it takes for the virus to replicate and disseminate to the salivary glands. However, vectorial capacity includes crucial parameters needed to effectively evaluate transmission capability, though often this is based on the discrete vector competence values. Utilization of the rate of change of vector competence over a range of days gives a more accurate measurement of the transmission potential. Accordingly, we investigated the rate of change in vector competence of dengue virus in Aedes aegypti mosquitoes and the resulting vectorial capacity curves. The areas under the curves represent the effective vector competence and the cumulative transmission potentials of arboviruses within a population of mosquitoes. We used the calculated area under the curve for each virus strain and the corresponding variance estimates to test for differences in cumulative transmission potentials between strains of dengue virus based on our dynamic model. To further characterize differences between dengue strains, we devised a displacement index interpreted as the capability of a newly introduced strain to displace the established, dominant circulating strain. The displacement index can be used to better understand the transmission dynamics in systems where multiple strains/serotypes circulate or even multiple arbovirus species. The use of a rate of a rate of change based model of vectorial capacity and the informative calculations of the displacement index will lead to better measurements of the differences in transmission potential of arboviruses

Susceptibility of Anopheles campestris-like and Anopheles barbirostris species complexes to Plasmodium falciparum and Plasmodium vivax in Thailand

Nine colonies of five sibling species members of Anopheles barbirostris complexes were experimentally infected with Plasmodium falciparum and Plasmodium vivax. They were then dissected eight and 14 days after feeding for oocyst and sporozoite rates, respectively, and compared with Anopheles cracens. The results revealed that Anopheles campestris-like Forms E (Chiang Mai) and F (Udon Thani) as well as An. barbirostris species A3 and A4 were non-potential vectors for P. falciparum because 0% oocyst rates were obtained, in comparison to the 86.67-100% oocyst rates recovered from An. cracens. Likewise, An. campestris-like Forms E (Sa Kaeo) and F (Ayuttaya), as well as An. barbirostris species A4, were non-potential vectors for P. vivax because 0% sporozoite rates were obtained, in comparison to the 85.71-92.31% sporozoite rates recovered from An. cracens. An. barbirostris species A1, A2 and A3 were low potential vectors for P. vivax because 9.09%, 6.67% and 11.76% sporozoite rates were obtained, respectively, in comparison to the 85.71-92.31% sporozoite rates recovered from An. cracens. An. campestris-like Forms B and E (Chiang Mai) were high-potential vectors for P. vivax because 66.67% and 64.29% sporozoite rates were obtained, respectively, in comparison to 90% sporozoite rates recovered from An. cracens

The dominant Anopheles vectors of human malaria in the Asia-Pacific region: occurrence data, distribution maps and bionomic précis

<p>Abstract</p> <p>Background</p> <p>The final article in a series of three publications examining the global distribution of 41 dominant vector species (DVS) of malaria is presented here. The first publication examined the DVS from the Americas, with the second covering those species present in Africa, Europe and the Middle East. Here we discuss the 19 DVS of the Asian-Pacific region. This region experiences a high diversity of vector species, many occurring sympatrically, which, combined with the occurrence of a high number of species complexes and suspected species complexes, and behavioural plasticity of many of these major vectors, adds a level of entomological complexity not comparable elsewhere globally. To try and untangle the intricacy of the vectors of this region and to increase the effectiveness of vector control interventions, an understanding of the contemporary distribution of each species, combined with a synthesis of the current knowledge of their behaviour and ecology is needed.</p> <p>Results</p> <p>Expert opinion (EO) range maps, created with the most up-to-date expert knowledge of each DVS distribution, were combined with a contemporary database of occurrence data and a suite of open access, environmental and climatic variables. Using the Boosted Regression Tree (BRT) modelling method, distribution maps of each DVS were produced. The occurrence data were abstracted from the formal, published literature, plus other relevant sources, resulting in the collation of DVS occurrence at 10116 locations across 31 countries, of which 8853 were successfully geo-referenced and 7430 were resolved to spatial areas that could be included in the BRT model. A detailed summary of the information on the bionomics of each species and species complex is also presented.</p> <p>Conclusions</p> <p>This article concludes a project aimed to establish the contemporary global distribution of the DVS of malaria. The three articles produced are intended as a detailed reference for scientists continuing research into the aspects of taxonomy, biology and ecology relevant to species-specific vector control. This research is particularly relevant to help unravel the complicated taxonomic status, ecology and epidemiology of the vectors of the Asia-Pacific region. All the occurrence data, predictive maps and EO-shape files generated during the production of these publications will be made available in the public domain. We hope that this will encourage data sharing to improve future iterations of the distribution maps.</p

Co-occurrence of Point Mutations in the Voltage-Gated Sodium Channel of Pyrethroid-Resistant Aedes aegypti Populations in Myanmar

Background:Single amino acid substitutions in the voltage-gated sodium channel associated with pyrethroid resistance constitute one of the main causative factors of knockdown resistance in insects. The kdr gene has been observed in several mosquito species; however, point mutations in the para gene of Aedes aegypti populations in Myanmar have not been fully characterized. The aim of the present study was to determine the types and frequencies of mutations in the para gene of Aedes aegypti collected from used tires in Yangon City, Myanmar.Methodology/Principal Findings:We determined high pyrethroid resistance in Aedes aegypti larvae at all collection sites in Yangon City, by using a simplified knockdown bioassay. We showed that V1016G and S989P mutations were widely distributed, with high frequencies (84.4% and 78.8%, respectively). By contrast, we were unable to detect I1011M (or I1011V) or L1014F mutations. F1534C mutations were also widely distributed, but with a lower frequency than the V1016G mutation (21.2%). High percentage of co-occurrence of the homozygous V1016G/S989P mutations was detected (65.7%). Additionally, co-occurrence of homozygous V1016G/F1534C mutations (2.9%) and homozygous V1016G/F1534C/S989P mutations (0.98%) were detected in the present study.Conclusions/Significance:Pyrethroid insecticides were first used for malaria control in 1992, and have since been constantly used in Myanmar. This intensive use may explain the strong selection pressure toward Aedes aegypti, because this mosquito is generally a domestic and endophagic species with a preference for indoor breeding. Extensive use of DDT for malaria control before the use of this chemical was banned may also explain the development of pyrethroid resistance in Aedes aegypti