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.

The salivary gland transcriptome of the eastern tree hole mosquito, Ochlerotatus triseriatus.

Saliva of blood-sucking arthropods contains a complex mixture of peptides that affect their host's hemostasis, inflammation, and immunity. These activities can also modify the site of pathogen delivery and increase disease transmission. Saliva also induces hosts to mount an antisaliva immune response that can lead to skin allergies or even anaphylaxis. Accordingly, knowledge of the salivary repertoire, or sialome, of a mosquito is useful to provide a knowledge platform to mine for novel pharmacological activities, to develop novel vaccine targets for vector-borne diseases, and to develop epidemiological markers of vector exposure and candidate desensitization vaccines. The mosquito Ochlerotatus triseriatus is a vector of La Crosse virus and produces allergy in humans. In this work, a total of 1,575 clones randomly selected from an adult female O. triseriatus salivary gland cDNA library was sequenced and used to assemble a database that yielded 731 clusters of related sequences, 560 of which were singletons. Primer extension experiments were performed in selected clones to further extend sequence coverage, allowing for the identification of 159 protein sequences, 66 of which code for putative secreted proteins. Supplemental spreadsheets containing these data are available at http://exon.niaid.nih.gov/transcriptome/Ochlerotatus_triseriatus/S1/Ot-S1.xls and http://exon.niaid. nih.gov/transcriptome/Ochlerotatus_triseriatus/S2/Ot-S2.xls.

An analysis of gene flow among midwestern populations of the mosquito Ochlerotatus triseriatus.

A population genetics study of the mosquito Ochlerotatus triseriatus was performed on 36 collections from adjoining regions of Iowa, Minnesota, and Wisconsin covering approximately 120 km(2). Single nucleotide polymorphism analysis was used to estimate variation in the mitochondrial NADH dehydrogenase subunit 4 (ND4) gene. The heated oligonucleotide ligation assay was used to identify the ND4 haplotype of each mosquito. No evidence of genetic isolation by distance was found, nor did Interstate 90 or the Mississippi River serve as barriers to gene flow. The effective migration rate varied from 18 to 45 reproductive migrants/generation, which is similar to estimates from an earlier study. The collections belong to a single, large, panmictic population. However, within this panmictic population, local genetic drift arises, possibly due to one or a few females ovipositing in larval breeding containers. From generation to generation, there is sufficient gene flow to mix families arising from individual breeding sites and eliminate founder effects due to drift.

Characterization of apyrase-like activity in Ochlerotatus triseriatus, Ochlerotatus hendersoni, and Aedes aegypti.

The saliva of a blood-feeding insect can facilitate the intake of blood and effect the transmission of a pathogen. Apyrase is a salivary enzyme that inhibits the aggregation of platelets by hydrolyzing the activating molecule ADP. Apyrase also hydrolyzes ATP, which is a signal for neutrophil activation. Investigators have reported that malaria vector species in the Anopheles gambiae species complex and the genus Simulium had more apyrase activity than sibling species that were non-vectors. In this study, salivary gland extracta from sibling species Ochlerotatus triseriatus (Say), vector of LaCrosse virus, and the non-vector Oc. hendersoni Cockerell were examined. Apyrase activity was characterized from both species, but no difference in activities was observed. Differences in days to maximal apyrase activity after eclosion and apyrase levels after a blood meal were detected between Oc. triseriatus and Aedes aegypti L. (Rockefeller strain). These differences indicate that Ae. aegypti may be able to feed sooner and more often than Oc. triseriatus.

Population structure of the peridomestic mosquito Ochlerotatus notoscriptus in Australia.

Ochlerotatus notoscriptus (Skuse) (Diptera: Culicidae) is the predominant peridomestic mosquito in Australia where it is the primary vector of dog heartworm, Dirofilaria immitis (Leidy), and a potentially important vector of arboviruses (Barmah Forest, Ross River) with geographical variation of vector competence. Although widespread, Oc. notoscriptus has low dispersal ability, so it may have isolated subpopulations. The identification of gene flow barriers may assist in understanding arbovirus epidemiology and disease risk, and for developing control strategies for this species. We investigated the population structure of Oc. notoscriptus from 17 sites around Australia, using up to 31 putative allozyme loci, 11 of which were polymorphic. We investigated the effect of larval environment and adult morphology on genetic variation. At least five subpopulations were found, four in New South Wales (NSW) and one unique to Darwin. Perth samples appear to be a product of recent colonization from the Australian east coast. For NSW sites, a Mantel test revealed an isolation by distance effect and spatial autocorrelation analysis revealed an area of effective gene flow of 67 km, which is high given the limited dispersal ability of this species. No consistent difference was observed between 'urban' and 'sylvan' habitats, which suggests frequent movement between these sites. However, a finer-scaled habitat study at Darwin revealed small but significant allele frequency differences, including for Gpi. No fixed allozyme differences were detected for sex, size, integument colour or the colour of species-diagnostic pale scales on the scutum. The domestic habit of Oc. notoscriptus and assisted dispersal have helped to homogenize this species geographically but population structure is still detectable on several levels associated with geographical variation of vector competence.